LTC4013 60V Synchronous Buck Multi

LTC4013 60V Synchronous Buck Multi
LTC4013
60V Synchronous Buck
Multi-Chemistry Battery Charger
FEATURES
DESCRIPTION
Wide Input Voltage Range: 4.5V to 60V
nn Wide Battery Voltage Range: 0V to 60V
nn Built-In Charge Algorithms for Lead-Acid and Li-Ion
nn ±0.5% Float Voltage Accuracy
nn ±5% Charge Current Accuracy
nn Maximum Power Point Tracking Input Control
nn NTC Temperature Compensated Float Voltage
nn Two Open Drain Status Pins
nn Thermally Enhanced 28-Lead 4mm × 5mm QFN
Package
The LTC®4013 is a high voltage battery charger controller
that supports float, absorption and equalization lead-acid
and constant-current/constant-voltage Li-Ion charging
algorithms. It is particularly well suited for charging a wide
range of lead-acid batteries, including both vented and
sealed type. The LTC4013 also supports Li-Ion/Polymer,
LiFePO4, NiMH, NiCd and other battery types.
nn
APPLICATIONS
Battery Backup for Lighting, UPS Systems, Security
Cameras, Computer Control Panels
nn Portable Medical Equipment
nn Solar-Powered Systems
nn Industrial Battery Charging
nn
L, LT, LTC, LTM, Burst Mode. Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners. Protected by U.S. Patents, including 9246383.
Charging is performed with a high efficiency synchronous
buck (step-down) converter that uses external N-channel
MOSFETs. Switching frequency is programmed with a
resistor or synchronized with an external clock for use
in multiphase applications. Charge current is set with an
external sense resistor.
The device includes maximum power point tracking input voltage regulation for limited power inputs such as
solar panels. Other features include user-programmable
absorption and equalization times, temperature-adjusted
regulation voltages and an external NFET isolation diode.
TYPICAL APPLICATION
15V-34V to 6 Cell Lead-Acid (12.6V) 5A Step-Down Battery Charger
Efficiency and Power Loss vs Charge Current
15V-34V
2.5
97
EFFICIENCY
96
VIN_S
VIN
SW
BG
MPPT
FBOC
LTC4013
INTVCC
MODE2
1.5
93
92
1.0
91
90
INTVCC
89
PGND
88
SENSE
87
0.5
VIN = 24V
VBAT = 13.8V
0
1
2
3
4
CHARGE CURRENT (A)
5
0
4013 TA01a
BAT
MODE1
POWER LOSS
94
POWER LOSS (W)
TG
ENAB
2.0
95
BST
EFFICIENCY (%)
INFET
DCIN
BASED ON APPLICATION ON BACK PAGE
FB
INTVCC
SYNC
NTC
PINS NOT USED
IN THIS CIRCUIT
STAT0
STAT1
ISMON
CLKOUT
RT
TMR
LB
RNTC
SGND
ITH
4013 TA01
4013f
For more information www.linear.com/LTC4013
1
LTC4013
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
SW
BG
INTVCC
PGND
VIN
VIN_S
TOP VIEW
28 27 26 25 24 23
INFET 1
22 TG
DCIN 2
21 BST
MPPT 3
20 SENSE
FBOC 4
19 BAT
29
SGND
ENAB 5
18 FB
ISMON 6
17 NTC
STAT0 7
16 ITH
STAT1 8
15 RT
SYNC
CLKOUT
MODE2
MODE1
LB
9 10 11 12 13 14
TMR
DCIN, VIN, VIN_S, ENAB, STAT0, STAT1..... –0.3V to 60V
INFET.......................................................... –0.3V to 73V
BST ............................................................ –0.3V to 66V
STAT0, STAT1...........................................................5mA
SENSE, BAT................................................ –0.3V to 60V
SENSE-BAT................................................ –0.3V to 0.3V
FBOC, MPPT, FB, MODE1, MODE2, SYNC,
INTVCC, NTC............................................. –0.3V to 6V
TMR, LB, ITH................................................ –0.3V to 3V
Operating Junction Temperature Range
(Note 2).............................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
UFD PACKAGE
28-LEAD (4mm × 5mm) PLASTIC QFN
TJMAX = 125°C, θJA = 43°C/W, θJC = 3.4°C/W
EXPOSED PAD (PIN 29) IS SGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
http://www.linear.com/product/LTC4013#orderinfo
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4013EUFD#PBF
LTC4013EUFD#TRPBF
4013
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LTC4013IUFD#PBF
LTC4013IUFD#TRPBF
4013
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
4013f
For more information www.linear.com/LTC4013
LTC4013
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). DCIN, VIN, VIN_S = 18V, ENAB = 1.4V, SYNC = 0V
unless otherwise noted.
PARAMETER
CONDITIONS
MIN
Input Voltage Range (DCIN, VIN)
l
Battery Voltage Range (BAT)
l
ENAB Pin Threshold (Rising)
Threshold Hysteresis
l
1.175
ENAB Pin Bias Current
VIN Rising, Power Enabled
VIN Rising, Power Disabled
VIN UVLO
TYP
4.5
1.220
170
MAX
UNITS
60
V
60
V
1.275
V
mV
10
nA
3.45
3.08
V
V
DCIN Pin
Operating Current
Shutdown Current
Not Switching
ENAB = 0V
l
480
4
625
7.9
µA
µA
VIN Pin
Operating Current
Shutdown Current
Not Switching (Notes 3 and 4)
ENAB = 0V, RT = 40.2k
l
2.1
32
2.8
80
mA
µA
BAT Pin
Operating Current
Shutdown Current
Not Switching
ENAB = 0V
l
6.2
0.5
9.3
1.5
µA
µA
SENSE Pin
Operating Current
Shutdown Current
Not Switching
ENAB = 0V
l
5.3
0.4
8.1
2.5
µA
µA
SW Pin Current in Shutdown
ENAB = 0V, SW = 60V, BST = 66V
0.25
STAT0, STAT1 Enabled Voltage
STAT0, STAT1 Pin Current =1mA
STAT0, STAT1 Pin Current = 5mA
0.14
0.77
STAT0, STAT1 Leakage Current
STAT0, STAT1 Pin Voltage = 60V
l
µA
0.2
1.0
V
V
1
µA
FB Regulation Voltage (See Tables 2-5)
Battery Float Voltage VFB(FL)
MODE1 = L, H MODE2 = L, H
l
2.256
2.244
2.267
2.267
2.278
2.291
V
V
l
2.189
2.178
2.200
2.200
2.211
2.223
V
V
l
2.320
2.309
2.332
2.332
2.344
2.356
V
V
l
2.355
2.343
2.367
2.3670
2.380
2.392
V
V
l
2.388
2.376
2.400
2.400
2.412
2.425
V
V
l
2.487
2.475
2.500
2.500
2.513
2.526
V
V
l
2.587
2.574
2.600
2.600
2.613
2.627
V
V
l
2.355
2.343
2.367
2.367
2.38
2.392
V
V
l
2.388
2.376
2.400
2.400
2.412
2.425
V
V
l
2.284
2.272
2.295
2.295
2.306
2.319
V
V
MODE1 = M, MODE2 = L, H
MODE1 = L, MODE2 = M
Battery Absorption Voltage VFB(ABS)
MODE1 = H, MODE2 = L, H
MODE1 = L, MODE2 = H
MODE1 = M, MODE2 = L, H
Battery Equalization Voltage VFB(EQ)
MODE1 = L, H, MODE2 = H, TMR = Cap
MODE1 = M, MODE2 = H, TMR = Cap
Battery Charge Voltage VFB(CHG)
MODE1 = H, MODE2 = M
MODE1 = M, MODE2 = M
Battery Recharge Voltage VFB(RECHG)
MODE1 = M, H MODE2 = M
NTC Amplifier Gain
∆VFB(FL)/∆VNTC
NTC Amplifier Offset
∆VFB(FL) with VNTC = INTVCC/2
FB Pin Current
VFB = 3V
LB Pin Current
VLB = 2V
0.21
–15
0
V/V
15
10
19.6
20
mV
nA
20.4
μA
4013f
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3
LTC4013
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). DCIN, VIN, VIN_S = 18V, ENAB = 1.4V, SYNC = 0V
unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ΔIITH/Δ(VSENSE–VBAT) VITH = 1.8V
1300
1800
2300
µmho
Error Amp Current Source
VITH =1.8V, VFB = 2.0V, (Float) MODE1 = H, MODE2 = L
–6.5
–10
–13.5
µA
Error Amp Current Sink
VITH =1.8V, VFB = 2.4V, (Float) MODE1 = H, MODE2 = L
18
27
35
µA
Error Amp
Error Amp Transconductance
Current Sense (all measured as VSENSE – VBAT unless otherwise noted)
Maximum Charging Sense Resistor Voltage
In Absorption, Float, Li-Ion Charge, BAT = 14V
l
48
50
52
mV
Equalization and Low Battery Charging Sense
Resistor Voltage
BAT = 14V
l
8
10
12.5
mV
Current Sense C/10 Threshold
Termination when TMR = 0
l
2.0
Constant Voltage (CV) Threshold
VFB(ABS,EQ) – VFB, Timeout Initiation with Cap on TMR
l
Overcurrent Charging Turnoff
l
ISMON Fullscale Output Voltage
VSENSE – VBAT = 50mV
SENSE Input UVLO
VSENSE Rising (Charging Enabled)
SENSE Input UVLO Hysteresis
VSENSE Rising to Falling (Charging Disabled)
4.6
7.0
mV
15.6
24.5
mV
100
106
mV
1.00
l
1.86
1.97
V
2.07
100
V
mV
Configuration Pins
MODE1, MODE2 Pin, Low Threshold
l
MODE1, MODE2 Pin, Mid Threshold
l
1.3
MODE1, MODE2 Pin, High Threshold
l
2.5
0.8
V
1.8
V
V
Timer
TMR Oscillator High Threshold
TMR Oscillator Low Threshold
Safety Timer Turn on Voltage
TMR Voltage Rising
l
0.45
Safety Timer Turn on Hysteresis Voltage
1.5
V
0.97
V
0.5
0.65
250
8.5
10.0
V
mV
TMR Source/Sink Current
TMR = 1.25V
TMR Pin Period
CTMR = 0.2µF
20.8
11.5
ms
μA
End of Charge Termination Time, tEOC
CTMR = 0.2µF
3.03
hr
Equalization Charge Termination Time
CTMR = 0.2µF, MODE1 = M, H
CTMR = 0.2µF, MODE1 = L
0.379
0.758
hr
hr
5.00
V
INTVCC Dropout Voltage
DCIN = 4.5V, INTVCC = 5mA
4.46
V
INTVCC Supply Short-Circuit Current
INTVCC = 0V
175
mA
Non-Overlap Time TG to BG
40
ns
Non-Overlap Time BG to TG
74
ns
Minimum On-Time BG
38
ns
Minimum On-Time TG
37
ns
INTVCC Regulator (INTVCC Pin)
INTVCC Regulation Voltage
100
NMOS FET Drivers
Minimum Off-Time BG
65
ns
Top Gate Driver Switch On Resistance
BST – SW = 5V, Pull Up
BST – SW = 5V, Pull Down
2.3
1.3
Ω
Ω
Bottom Gate Driver Switch On Resistance
INTVCC = 5V, Pull Up
INTVCC = 5V, Pull Down
2.3
1
Ω
Ω
4
4013f
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LTC4013
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). DCIN, VIN, VIN_S = 18V, ENAB = 1.4V, SYNC = 0V,
unless otherwise noted.
PARAMETER
CONDITIONS
BST UVLO
TG Enabled (Rising)
TG Disabled (Falling)
MIN
TYP
MAX
4.25
3.81
UNITS
V
V
OSC
Switching Frequency
RT = 40.2kΩ
RT = 232kΩ
l
SYNC Pin Threshold (Falling Edge)
950
1.3
SYNC Pin Hysteresis
CLK Output Logic Level
1000
200
1050
1.4
1.5
190
High
Low
4.5
kHz
kHz
V
mV
0.5
V
V
Input PowerPath Control
Reverse Turn-Off Threshold Voltage
DCIN – VIN
l
–7.3
–4.4
–1.3
mV
Forward Turn-On Threshold Voltage
DCIN – VIN
l
–7.1
–4.2
–1.1
mV
Forward Turn-On Hysteresis Voltage
DCIN – VIN
0.2
mV
INFET Turn-Off Current
INFET = VIN + 1.5V
–9.0
mA
INFET Turn-On Current
INFET = VIN + 1.5V
INFET Clamp Voltage
IINFET = 2μA , DCIN = 12V to 60V
VIN = DCIN – 0.1V
Measure VINFET – DCIN
l
11.0
12.5
V
INFET Off Voltage
IINFET = –2μA , DCIN = 12V to 59.9V
VIN = DCIN +0.1V
Measure VINFET – DCIN
l
–2.2
–1.6
V
DCIN to BAT UVLO
60
µA
Switching Regulator Turn Off (VDCIN – VBAT Falling)
69
mV
Switching Regulator Turn On (VDCIN – VBAT Rising)
99
mV
MPPT Regulation
FBOC Voltage Range
l
1.0
MPPT Sample Period
3.0
10.2
MPPT Sample Pulse Width
s
271
Regulation Input Offset
Set FBOC Look at MPPT Regulation
MPPT Input Burst Mode Turn On Threshold
VMPPT – VFBOC (Converted) , VFBOC = 1.5
VSENSE – VBAT < C/10 Part Enter Burst Mode
l
–45
MPPT Input Burst Mode Hysteresis
FBOC = 1.5, VSENSE – VBAT < C/10
MPPT Turn Off – Turn On
l
35
Note 1. Stresses beyond those listed under Absolute Maximum Ratings may
cause permanent damage to the device. Exposure to any Absolute Maximum
Rating condition for extended periods may affect device reliability and lifetime.
Note 2. The LTC4013 is tested under pulse loaded conditions such that
TJ ≈ TA. The LTC4013E is guaranteed to meet performance specifications
from 0°C to 85°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC4013I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The junction temperature (TJ in °C) is calculated
from the ambient temperature (TA in °C) and power dissipation (PD in
Watts) according to the formula: TJ = TA + PD • θJA where θJA (in °C/W)
is the package thermal impedance. Note that the maximum ambient
–40
V
µs
40
mV
–32
–15
mV
62
85
mV
temperature consistent with these specifications is determined by specific
operating conditions in conjunction with board layout, the rated package
thermal resistance and other environmental factors. This IC includes
over temperature protection that is intended to protect the device during
momentary overload. Junction temperature will exceed 125°C when over
temperature protection is active. Continuous operation above the specified
maximum operating junction temperature may impair device reliability.
Note 3. VIN does not include switching currents. VBST = INTVCC and
VSW = 0V for testing.
Note 4. IVIN current also includes current that charges capacitance on
CLKOUT. This current is approximately CCLKOUT • 5V • fSW. For this test
CCLKOUT was 100pF, fSW was 1MHz (RT = 40.2k) so the current included is
0.5mA. In normal operation the CLKOUT capacitance is much less.
4013f
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5
LTC4013
TYPICAL PERFORMANCE CHARACTERISTICS
Change in Absorption,
Equalization, Float and Li-Ion
Charge Voltages vs Temperature
Li-Ion Recharge% vs
Temperature
1.00
Low Battery (LB) Current
vs Temperature
98.0
0.75
10 PIECE SAMPLE
0.2
0.1
MODE1 = H
97.5
0.50
0
–0.25
–0.50
–0.75
–1.00
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
0.0
97.0
∆ ILB (%)
0.25
VFB(RECHG) / VFB(CHG) (%)
∆VFB(ABS,EQ,FL,CHG) (%)
TA = 25°C, unless otherwise noted.
96.5
96.0
MODE1 = M
–0.2
–0.3
95.5
–0.4
95.0
–50
125
–0.1
–25
0
25
50
75
TEMPERATURE (°C)
4013 G01
100
–0.5
–50
125
–25
0
25
50
75
TEMPERATURE (°C)
100
4013 G03
4013 G02
Maximum Sense Voltage
vs Temperature
Change in ENAB Voltage
vs Temperature
C/10 Thresholds vs Temperature
50.2
125
10
0.3
9
50.0
49.9
7
RISING
0.1
6
5
∆VENAB (%)
VSENSE–VBAT (mV)
VSENSE-VBAT (mV)
0.2
8
50.1
FALLING
4
0.0
–0.1
3
2
FALLING
–0.2
1
49.8
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
0
–50
125
–25
0
25
50
75
TEMPERATURE (°C)
4013 G04
4.2
RISING
100
125
105
100
RISING
3.1
FALLING
3.0
4.1
VDCIN-VBAT (V)
VBST-VSW (V)
VVIN (V)
3.2
4.0
3.9
RISING
25
50
75
TEMPERATURE (°C)
100
125
4013 G07
3.7
–50
90
85
80
75
FALLING
3.8
2.9
6
25
50
75
TEMPERATURE (°C)
95
3.3
0
0
DCIN to BAT UVLO Voltage
vs Temperature
4.3
–25
–25
4013 G06
BST UVLO vs Temperature
3.5
2.8
–50
–0.3
–50
125
4013 G05
VIN UVLO vs Temperature
3.4
100
FALLING
70
–25
0
25
50
75
TEMPERATURE (°C)
100
125
4013 G08
65
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
4013 G09
4013f
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LTC4013
TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Charge Current
vs ΔV from VCHARGE
0.230
1.00
0.225
0.80
0.60
0.220
40
0.40
0.215
∆FSW (%)
60
∆VFB /∆VNTC
0.210
0.205
CV
–40
–0.60
0.195
–30
–20
–10
VFB – VFB(CHG)(mV)
–0.80
0.190
–50
0
0.00
–0.20
–0.40
0.200
20
–25
0
25
50
75
TEMPERATURE (°C)
4013 G10
100
–1.00
–50
125
2.8
2.6
2.4
∆VINTVCC (%)
1.8
1.6
1.4
1.0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
0.30
520
0.20
500
0.00
–0.10
–25
0
25
50
75
TEMPERATURE (°C)
100
380
–50
125
4.6
25
50
75
TEMPERATURE (°C)
100
125
2.1
4013 G16
1.9
–50
125
60
IVIN (µA)
IVIN (mA)
0
100
70
NOT SWITCHING
2.0
3.4
25
50
75
TEMPERATURE (°C)
VIN Current in Shutdown
vs Temperature
2.2
3.8
0
4013 G15
VIN Operating Current
vs Temperature (Note 4)
4.2
–25
4013 G14
2.3
–25
440
400
4013 G13
3.0
–50
460
420
–0.30
–50
5.0
125
480
0.10
DCIN Current in Shutdown
vs Temperature (Note 3)
100
DCIN Operating Current
vs Temperature
–0.20
1.2
0
25
50
75
TEMPERATURE (°C)
4013 G12
Change in VINTVCC
vs Temperature
2.0
–25
4013 G11
Error Amp Transconductance
vs Temperature
2.2
200kHz
1MHz
0.20
IDCIN (µA)
MAXIMUM CHARGE CURRENT (%)
80
0
–50
∆IITH/∆VSENSE (mmho)
Change in Switching Regulator
Frequency vs Temperature
NTC Amplifier Gain
vs Temperature
100
IDCIN (µA)
TA = 25°C, unless otherwise noted.
50
40
30
–25
0
25
50
75
TEMPERATURE (°C)
100
125
4013 G17
20
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
4013 G18
4013f
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7
LTC4013
PIN FUNCTIONS
INFET (Pin 1): Input PowerPath MOSFET Gate Drive. An
internal charge pump provides turn on drive for this pin.
This pin is connected to the gate of an external N-channel
MOSFET(s) used to prevent the battery discharge in the
event that DCIN is less than the battery voltage.
DCIN (Pin 2): Input Supply Pin. This pin is used to sense
the input voltage and determines whether the external input
MOSFET (INFET) is turned on. It also supplies power to
the internal charge pump that drives INFET.
MPPT, FBOC (Pins 3, 4): These pins are the inputs for the
Maximum Peak Power Tracking (MPPT) regulation loop.
This loop regulates charge current in order to maintain
maximum power charging in the presence of a power
limited source such as a solar panel. A three resistor
divider is placed from the input supply to MPPT to FBOC
and then to ground. These pins are used to program an
input voltage regulation loop as a percentage of the input
open circuit voltage. During normal operation, if the input
voltage falls below the programmed percentage of the
open-circuit voltage, the MPPT loop will reduce charge
current to maintain the target voltage at DCIN. If the voltage
regulation feature is not used, connect FBOC to INTVCC.
See the Applications section for more details.
ENAB (Pin 5): Precision Threshold Enable Pin. Enable
threshold is 1.22V (rising), with 170mV of input hysteresis.
When in shutdown, all charging functions are disabled and
input supply current is reduced. Typical ENAB pin input
bias current is 10nA.
ISMON (Pin 6): Output of Current Sense Amplifier. The
voltage on this pin is twenty times the differential voltage
between SENSE and BAT.
STAT0, STAT1 (Pins 7, 8): Open drain outputs indicate
the charger status. They are capable of sinking 5mA of
current when on, enabling them to drive an LED. Specific
states are detailed in Table 6.
8
LB (Pin 9): A resistor on this pin to ground is used to set
the detection voltage for a “discharged” battery. If the
battery stays below this voltage for 1/8 of the absorption
timeout period, charging is stopped. Charging is reinitiated
through an ENAB toggle or swapping out the battery. A
20µA current sourced from the pin through an external
resistor from ground sets the voltage on the pin. This
voltage is then compared to the FB pin voltage to ascertain
the battery condition.
TMR (Pin 10): Battery End of Charge Time Set. A capacitor
on this pin to ground sets the time the charger spends
during various charging stages. Absorption and Li-Ion
charge time is set as three hours per 0.2µF. The equalization timeout is a ratio of this time, either one fourth or
one eight of the absorption time, depending on the MODE
pins settings.
MODE1 (Pin 11) MODE2 (Pin 12): These pins set the
charging algorithm used. See Tables 2 to 5 for a complete
listing. The part supports 2, 3, 4-stage lead-acid and Li-Ion
charging algorithms with and without time termination.
CLKOUT (Pin 13): This output pin has a signal that can be
used to synchronize the oscillator on another LTC4013 or
other circuitry. See the applications section for more detail.
SYNC (Pin 14): Frequency Synchronization Pin. This pin is
used for paralleling multiple LTC4013 for higher currents.
This pin allows the switching frequency to be synchronized to an external clock. The RT resistor is chosen to
operate the internal clock at 20% slower than the SYNC
pulse frequency. Ground this pin when not in use. When
laying out the PC board, avoid noise coupling to or from
SYNC trace.
RT (Pin 15): A resistor to ground sets the switching frequency between 200kHz and 1MHz. This pin is current
limited to 60μA. Do not leave this pin open.
ITH (Pin 16): This pin provides loop compensation for the
switching regulator control loops. See the applications
section for further information.
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LTC4013
PIN FUNCTIONS
NTC (Pin 17): This pin connects to an external resistor
divider string that contains an NTC resistor. The voltage
difference between VNTC and INTVCC/2 is converted to an
offset in the switching regulator charge voltages. Place
the NTC resistor as close to the battery as possible, with
good Kelvin ground connection. See the Applications
section for more details.
FB (Pin 18): This pin provides feedback for regulating
battery voltage during charging. A resistor divider from
the battery to this pin sets the input to the charger voltage error amp. Use care in connections to provide a good
Kelvin connection and to insure accurate measurement.
See applications section for more details.
BAT, SENSE (Pins 19, 20): Battery charge current is
monitored and regulated via a resistor connected between
SENSE and BAT. Maximum voltage across these pins
during charge current regulation is 50mV. The switching
regulator inductor is connected between SW and SENSE.
Take care to insure that the signal between these pins is
not corrupted with noise. Overcurrent shutdown occurs
when the voltage across SENSE and BAT exceeds 100mV.
BST (Pin 21): The BST pin provides a floating 5V regulated
supply for the high-side MOSFET driver. Connect a 0.22μF
capacitor from this pin to SW. Connect a 1A Schottky diode
cathode to this pin, anode to INTVCC pin.
BG (Pin 24): This pin drives the gate of the external bottom
side N-channel MOSFET.
INTVCC (Pin 25): This pin is the output of a regulated 5V
output and is current limited to 100mA. Connect a ceramic
capacitor from this pin to PGND. The BST pin refresh diode
anode is connected to this pin.
PGND (Pin 26): This pin is the ground return for high
current paths for the part. This is primarily the low side
gate drive.
VIN (Pin 27): High current input supply pin that provides
power to the IC. This pin provides power to the INTVCC
internal 5V regulator. It is usually tied to the switching
regulator high side MOSFET. This pin must be bypassed
with a low ESR capacitor to ground. See the applications
section for sizing information.
VIN_S (Pin 28): This pin provides a Kelvin input for the
VIN connection of the input PowerPath circuitry.
SGND (Exposed Pad Pin 29): Signal Ground Reference.
This pin is the “quiet” ground used as a reference point
for critical resistor dividers such as battery feedback,
MPPT dividers and NTC resistor. Connect to the output
decoupling capacitor negative terminal and battery negative
terminal. Solder the exposed pad to PCB ground (SGND)
for electrical connection and rated thermal performance.
TG (Pin 22): This pin drives the gate of the top side external
N-channel MOSFET.
SW (Pin 23): This pin connects to the switch mode power
supply switch node. It connects to one side of the switching regulator inductor, the source of the top side MOSFET
and the drain of the bottom side MOSFET as well as the
boost capacitor. This pin has high current associated with
the turn off of the high side MOSFET.
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9
LTC4013
BLOCK DIAGRAM
SENSE
DCIN
BAT
INFET CONTROL
–
+
CHARGE
PUMP
INFET
20
SWOFF
SENSE
AMPLIFIER
–
+
OC
ISMON
VIN_S
INFET
CONTROL
DCIN
BAT
C/10
17mV
INTVCC
CHARGE REGULATION
VOLTAGE
1.5V
A5
VCH
D-A
INTVCC
ENAB
+
–
CV
MPPT
ERROR AMP
–
+
+
–
NTC
VIN
VSEN
20X
FB
CURRENT
ERROR AMP
VOLTAGE
ERROR AMP
–
A1
+
–
A3
+
ITH
SWOFF
PWM
BURST
MODE
SET MAX
CURRENT
MPPT
VIN
5V LDO
INTVCC
VDAC
SAMPLE AND HOLD
FBOC
+
–
150°C
OVER TEMP
BST
SYNC
CLK
OSCILLATOR
1V
BST
PWM
C/10
SWITCH
CONTROL
BURST
–
+
RT
TG
BG
TG
SW
NOL
DRIVERS
INTVCC
OC
BG
SWOFF
CLKOUT
PGND
3.3V
CHARGE VOLTAGE
STATE
MODE2
MODE1
3.3V
SGND
C/10
MODE STATE
MODE
DECODE
CV
±10µA
TIMER
OSCILLATOR
TERMINATION AND
CHARGE CONTROL
LOGIC
LOW BATTERY
RESTART
20µA
–
+
LB
FB
TMR
ACTIVE
TMR
STAT0
0.5V
STAT1
4013 BD
10
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LTC4013
OPERATION
OVERVIEW
The LTC4013 is a high voltage multi-chemistry battery
charger with specific focus on lead-acid batteries. It
incorporates a step-down (buck) DC/DC synchronous
converter controller using external N channel mosfets
for high efficiency. The LTC4013 accommodates a wide
range of battery voltages from 2.4V to 60V. The device is
aimed for high current charging applications. The upper
limit is determined from efficiency (power loss) which is
mostly limited by strength of gate drives, switch losses
and current sense voltages. Major features include:
Current control is maintained throughout the charge cycle
by using an average current control scheme. The charger
has an input voltage range of 4.5V to 60V. A resistor divider
from the battery to FB adjusts the charge voltage with a
practical range of 2.4V to 58V.
The LTC4013 also provides three monitor pins. STAT0
and STAT1 are open drain outputs that can drive an LED
to provide visual indication of charge status and fault
conditions. The ISMON pin provides analog information
about charge current.
• Selectable charger profiles:
DC/DC OPERATION
• 2-stage charging: constant current to constant
voltage with and without timeout.
• 3-stage lead-acid charging: absorption, float with
low battery restart and either charge current (C/10)
or safety time termination.
• 4-stage lead-acid charging: absorption, equalization, float with low battery restart and safety time
termination.
• Li-Ion constant current to constant voltage charging with either charge current (C/10) or safety time
termination.
• User adjustable maximum power point tracking (MPPT)
circuitry that allows simple power optimization for power
limited sources such as solar panels. Includes improved
high efficiency operation during MPPT operation.
(See Block Diagram)
• Continuous temperature adjustment of charge voltages
(programmable).
• External input MOSFET (INFET) to prevent battery
discharge with a shorted input.
• Maximum battery charge current programmable using
an external sense resistor.
• DC/DC switching regulator frequency adjustable using
external resistor and externally synchronizable.
• A precision ENAB pin that controls turn on with an
external resistor divider.
The LTC4013 uses a fixed frequency, average current mode
DC/DC converter architecture to regulate inductor current
(and thus charge current) independent of battery voltage.
The control loop will regulate current to an accuracy of
±5%. When the battery reaches the charge voltage, current is reduced by a voltage regulation loop. The charge
voltage accuracy is ±0.5%.
Note a general switching regulator overview is found in
Linear Technology application notes, AN-19 and AN-140.
The inductor current is sensed via the sense resistor
placed between SENSE and BAT. The amplified signal
is compared to a voltage that represents the maximum
allowable charge current. The error amp regulates the
average inductor current by controlling duty cycle on the
output switches. A single frequency compensation point
(ITH pin) is used to provide stability of the loop.
When the battery voltage is below the programmed charge
voltage, the control loop servos the differential voltage
between SENSE and BAT to 50mV. The charge current at
50mV is referred to as ICHGMAX. When the battery voltage
reaches the programmed charge voltage, error amplifier
A3 continuously adjusts the average inductor current to
servo the battery voltage to the programmed charge voltage. This error amplifier can reduce the battery current to
zero, if necessary.
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11
LTC4013
OPERATION
This control loop has additional features. At startup the
maximum current is ramped over approximately 1.6ms to
provide a soft start function. There is an additional burst
mode feature used for maximum power point transfer as
described below.
The charge voltage is determined by amplifier A5 and the
charge algorithm. The voltage is made a continuous function of temperature by use of the NTC pin. The NTC pin
controls a transconductance amp that linearly adjusts the
charge regulation voltage. In normal operation a resistor
divider with a bottom NTC resistor sets the temperature
coefficient of the voltage. See the Temperature Compensation section for more details.
The switching regulator oscillator frequency is set by a
resistor from the RT pin to ground. There is an option to
synchronize the clock frequency to an external oscillator
by using the SYNC pin.
The switching regulator uses external low RDS(ON) MOSFETs
for both high and low side switches. It operates in synchronous step-down (Buck) mode at high currents. When the
current level falls below ICHGMAX/10 the bottom MOSFET
is disabled and switching operation is discontinuous with
the bottom side MOSFET body diode used for low side
conduction. This insures the battery is not discharged.
Drive voltage for the top gate drive is generated by a boost
circuit that uses an external diode and boost cap that
is charged via the diode from INTVCC. The bottom side
MOSFET is disabled when current is below ICHGMAX/10. If
BST – SW is below 3.8V (e.g. at startup), the bottom side
MOSFET is enabled to charge the BST cap.
Maximum Power Point Tracking
If the MPPT function is enabled (FBOC pin voltage < 3V)
the LTC4013 employs a MPPT circuit that compares a
stored open-circuit input voltage measurement against the
instantaneous DCIN voltage while charging. The LTC4013
12
automatically reduces the charge current if the DCIN voltage
falls below the user defined percentage of the open-circuit
voltage. This algorithm lets the LTC4013 optimize power
transfer for a variety of different input sources.
When MPPT is enabled the LTC4013 periodically measures the open-circuit input voltage. About once every
10.2s the LTC4013 pauses charging, samples the input
voltage as measured through a resistor divider at the
FBOC pin, and outputs this value via a digital to analog
converter (DAC). When charging resumes, the DAC voltage, (VDAC) is compared against the MPPT pin voltage
that is programmed with a resistor divider. If the MPPT
voltage falls below VDAC, the charge current is reduced
to regulate the input voltage at that level. This regulation
loop maintains the input voltage at or above a user defined
level that corresponds to the peak power available from
the applied source. Input sampling is useful, for instance,
for first order temperature compensation of a solar panel.
When charging resumes after the sampling period, the input
voltage drops if the source cannot support the demanded
charge current. When the input voltage drops to VDAC,
the charge current is reduced to maintain DCIN at VDAC.
The sampling timing is fixed internally. Switching stops for
approximately 1ms every 10.2s. There is an initial 720µs
delay allowing the DCIN node to rise to its open circuit
voltage. During the next 300µs, the FBOC pin voltage is
sampled and stored. The ITH pin is high impedance during
the sample period. The sampling of DCIN is done at an
extremely low duty cycle so as to have minimum impact
on the average charge current. Figure 1 shows a picture
of MPPT timing.
Keep capacitance low on DCIN to ensure that DCIN achieves
open circuit voltage during the initial MPPT delay. The
time constant is set by the capacitor and the impedance
of the input source.
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LTC4013
OPERATION
VINFET
5V/DIV
BATTERY CHARGER OPERATION
VIN
OPEN CIRUIT
VVIN
5V/DIV
VIN MPPT
REGULATED
INFET TURN OFF
VSW
10V/DIV
400µs/DIV
4013 F01
Fig 1. MPPT Timing
MPPT Burst Mode Operation
If input power levels drop during MPPT operation it is
desirable to improve switching regulator efficiency in
order to deliver the most power. The LTC4013 contains
proprietary circuitry that improves overall switching
regulator efficiency during these conditions. Efficiency is
improved by reducing the maximum switching regulator
current and disabling the switching regulator for part of
the operation, producing a burst mode operation. Entrance
to burst mode occurs when MPPT is below the sampled
FBOC voltage by approximately 32mV and the current is
below ICHGMAX/10 (SENSE-BAT <5mV). The part stays in
burst mode operation until the next sampling period when
it is reevaluated. If, when resampled, MPPT is above the
sampled FBOC voltage by approximately 31mv then burst
mode is exited. The net result is that in burst mode the
DCIN voltage has approximately a 63mV hysteretic ripple
at the FBOC pin. During burst mode maximum current is
set to approximately ICHGMAX/5 (SENSE-BAT = 10mV).
ISMON Current Monitor
Sense resistor current is monitored via the ISMON pin.
The ISMON voltage is 20 • (VSENSE – VBAT).
(See Block Diagram)
The battery charge voltage is regulated via the FB pin. The
FB voltage regulation levels are appropriate for a single
cell lead-acid battery. For instance a 2.267V single cell
float voltage corresponds to a 6 cell battery voltage of
6 • 2.267V = 13.6V
The battery charge current is determined by the battery
voltage. When the battery voltage is below the charge
voltage, battery current is limited to the programmed
charge current. As the battery voltage approaches the
charge voltage current falls off to maintain the battery at
the charge voltage.
In addition the LTC4013 contains a charge cycle timer
that is used for time based control of a charge cycle.
The timer is activated by connecting a capacitor from the
TMR pin to ground. Grounding TMR disables all timer
functions. This timer is used for absorption timeout in
3- and 4-stage lead-acid charging, equalization timeout
in 4-stage lead-acid charging, and timeout in Li-Ion or
constant current charging.
The LB pin provides a user adjustable voltage that is used
to set the restart voltage in some modes and low battery
fault in others.
Lead-Acid Battery Charger Basics
Lead-acid batteries can be charged in a number of ways.
The simplest is a 2-stage method where a constant current
is applied until the battery voltage reaches the float voltage.
Float voltage is the electrochemical voltage generated by
the cell under no charging or load. The disadvantages of
this scheme is that it doesn't fully charge the battery and
battery capacity drops over time. The battery capacity loss
is because of the increase of deposits on the electrodes. In
this mode maximum charge current is limited for safety and
falls as the battery voltage approaches the charge voltage.
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13
LTC4013
OPERATION
A 4-stage charging algorithm adds an additional stage to
the 3-stage method after absorption called equalization.
Equalization voltage is significantly higher than the absorption voltage and works in two ways. One is to purposely
introducing gassing which stirs the battery electrolyte
and reduces electrolyte stratification. Equalization also
electrochemically eliminates sulfates on the electrodes
which is the main cause of battery performance degradation
(sulfates form in heavily discharged batteries). Equalization
is not done with sealed batteries because of the gassing.
If loss of water is significant it degrades the battery if not
replaced. In equalization the maximum current is reduced
to approximately ICHGMAX/5.
ICHGMAX
VABSORPTION
CURRENT
VOLTAGE
1
2
3
BULK
ABSORPTION
FLOAT
4013 F02
Figure 2. 3-Stage Charge Cycle
VEQUALIZATION
ICHGMAX
VABSORPTION
VFLOAT
CURRENT
VOLTAGE
1
2
Equalization Cycle
Equalization should not be performed frequently and is
always done with a timer to limit excessive battery stress.
If MODE2 is high, then only one equalization cycle is
initiated per power up without further user intervention.
BULK
Table 1 summarizes the various charging methods.
14
VFLOAT
ABSORPTION
3
4
EQUALIZATION
The most popular charging method is called 3-stage
charging cycle (see Figure 2). In this method the battery
is initially charged with a constant current (CC) until the
battery voltage achieves the absorption voltage. This helps
to increase the amount of stored charge in the battery.
Because the voltage is above the electrochemical float
level, the time that the battery stays in this condition
is usually limited, either by a timer (the safest method)
or just waiting for the charge current to diminish. After
absorption is complete the charger voltage drops back
to the float voltage. Minor gassing of water from the battery can occur from charging the battery above the float
voltage, so choosing an appropriate absorption voltage is
important for best battery life. Always consult the battery
manufacturer for their recommendations.
FLOAT
4013 F02
Figure 3. 4-Stage Charge Cycle
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LTC4013
OPERATION
Table 1. Battery Charging Stages
Mode
Charge Algorithm
Duration and Additional Details
2-Stage Charging
Charge current is set to ICHGMAX. Charge voltage is set to the If no TMR cap, charger continual charges at float voltage.
float voltage
With the cap charging terminates after timeout. The timer
starts after float voltage is reached
3-Stage Charging
Charge current is initially set to ICHGMAX. Charge voltage is
set to the absorption voltage
Terminates by either current reducing to ICHGMAX/10 or
timeout set by timer (TMR). Charge voltage is then changed to
the float voltage
4-Stage Charging
Similar to 3-stage but at the end of the absorption cycle the
charge voltage is increased to the equalization voltage and
the maximum current is set at ICHGMAX/5
Terminates by timeout set by timer (TMR). Charge voltage is
then changed to the float voltage
Li-Ion
Charge at ICHGMAX to the charge voltage. Charger turns off
when either the charge current reduces to ICHGMAX/10 or
timeout set by TMR.
When charger turns off, charge voltage is then changed to the
recharge voltage. When the battery voltage drops below this
voltage, charging is reinitiated.
Low Battery Restart
(all modes)
If FB voltage drops to recharge threshold the charge cycle is
reinitiated. Maximum charge current is set to ICHGMAX/5.
If the timer is active on 3,4-stage and Li-Ion then charging is
terminated if below the low battery threshold for longer than
tEOC/8
16.5
The LTC4013 allows for several different options for setting float, absorption and equalization voltages. In normal
mode, single cell absorption is approximately 100mV
above float (600mV for 6 cells), equalization is then approximately 133mV above absorption (800mV for 6 cells).
Another option uses a wider voltage spread where single
cell absorption voltage is 200mV above float (1.2V for 6
cells) and equalization is 200mV above absorption (1.2V
for 6 cells). Absolute voltages are adjusted through the FB
resistor divider to shift voltages up proportionately. It is
important that you consult your battery manufacture for
what they suggest for the charging voltages. There is no
industry consensus and it depends heavily on the type of
battery and anticipated usage.
16.0
Figure 4 shows how the FB resistor divider allows for the
range of charge settings for the normal and wide spread
voltage modes.
Restart, Low Battery Pin
For lead-acid a normal charge cycle completes with the
battery at the float voltage. A new cycle is initiated if the
FB referred battery voltage drops below the voltage on the
programmable LB pin. The user defines this voltage by
setting the resistor from LB to ground. The LB pin sources
20µA. For instance 100k to ground sets the LB pin to 2.0V.
CHARGE VOLTAGE (V)
Battery Charge Voltages
15.5
15.0
EQUALIZATION
WIDE SPREAD
ABSORPTION
WIDE SPREAD
14.5
14.0
13.5
EQUALIZATION
13.0
12.5
12.0
12.0
ABSORPTION
FLOAT
12.5
13.0
13.5
14.0
VFLOAT(V)
4013 F04
Figure 4. 6 Cell Lead-Acid Charge
Voltages with RFB1/RFB2 Change
Note a commonly used low battery voltage for 6 cell leadacid is 10.4V which represents the voltage with one of 6
cells shorted. This LB voltage is set with an 88.6k resistor
for 1.73V, (10.4V/6) if you are using a 6-to-1 FB divider.
Restart is disabled when using 2-stage charging with
timeout (TMR pin active). When the FB voltage is below
the LB voltage then maximum charge current is set to
20% of the programmed maximum current.
When the charge timer is active a low battery fault is
signaled if the battery remains below the LB referred low
battery voltage for 1/8 of the normal absorption end of
charge time (tEOC). The fault is indicated by STAT0 turning off and STAT1 turning on. Charging is also stopped.
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15
LTC4013
OPERATION
Lead-Acid Battery Types
There is a wide variety of lead-acid batteries available for
use. It is beyond the scope of this data sheet to detail all
of them. There are numerous online resources and books
available for further education. A good starting point is
found at www.batteryuniversity.com. Many of the battery
manufacturers also provide detailed information. The following sections outline the various charge modes in detail.
2-Stage Charging
Table 2. 2-Stage Charging Settings
2-Stage
When the TMR pin is used the charge cycle terminates
after a fixed time period determined by the LTC4013 timer,
so there is only a single charge cycle.
In 2-stage charging without the timer, the STAT1 pin indicates a change from constant current (CC) to constant
voltage (CV). When the FB voltage rises to 16mV below
VFB(FL), STAT1 pulls down indicating the CC to CV transition.
The battery charger continues to provide current during the
float charge phase and responds to any changes in load
while maintaining the battery voltage at the programmed
float charge voltage.
There are two different voltage settings for 2-stage charging as noted in Table 2.
If the timer is enabled (cap on TMR pin), the constantcurrent/constant-voltage algorithm is unchanged, but the
timer starts counting when the battery voltage reaches the
float voltage. At the end of the timeout period, tEOC, charging stops. Charging is reinitiated only after the FB referred
battery voltage drops below the restart voltage (set by the
LB pin) or the part is powered off and back on (ENAB).
Low battery protection is enabled if the timer is activated.
The charge cycle terminates if the battery voltage remains
below the low battery voltage (set by the LB voltage) longer
than 1/8 of the normal timeout period (tEOC).
Settings
VFLOAT
Termination
MODE1
MODE2
TMR
WRT VFB
No Termination
L
L
0V
2.267V
L
M
0V
2.332V
Timeout
2-stage charging is useful for lead-acid charging with
no absorption preconditioning. It is also useful for other
battery types (NiCd, NiMH) or supercapacitor charging.
In this mode the LTC4013 charges with constant current
(CC) (ICHGMAX) until the battery reaches the programmed
charge voltage. The charge current is reduced to maintain
the battery at the charge float voltage.
16
Table 2 shows the MODE pin settings and float voltage in
this mode. L means the pin is grounded, H means the pin
voltage is above 2.5V (tie to INTVCC), M means the pin is
midrange (leave unconnected).
L
L
Cap
2.267V
L
M
Cap
2.332V
Note: For nickel-chemistry batteries (e.g. NiCd or NiMH),
the possibility of overcharging must be considered. A
typical method is to charge with low currents for a long
period of time. NiCd and NiMH batteries can absorb a
C/300 charge rate indefinitely. Shorter duration charging
is possible using a timed current source charge algorithm.
It is recommended to ensure a depleted battery before
charging, and then subsequently charge the battery to
no more than 125% capacity. For example, a depleted
2000mAh NiMH battery is charged with 2.5A for one hour.
3- and 4-Stage Charging
A more common lead-acid battery charging method is
3-stage (absorption) or 4-stage (absorption and equalization) charging as discussed above. Equalization always
uses a timer and there is an option to have the equalization
timeout be 1/8 or 1/4 of the normal absorption timeout
period.
For the 3-stage cycle, charging is initiated on power up
or when the battery drops below the LB restart voltage.
The battery then charges toward the absorption voltage.
As the battery voltage approaches absorption the current
falls. When it reaches ICHGMAX/10, STAT1 turns on. When
the battery voltage reaches CV (approximately 16mV
from the FB referred absorption voltage) the internal
charge voltage changes to the float voltage. The charging
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LTC4013
OPERATION
remains active at the float voltage. If the battery voltage
(FB referred) subsequently drops below the LB pin or the
part is powered off and back on (ENAB) a new 3-stage
charge cycle is initiated.
equalization voltage is limited. If the TMR pin is grounded
inadvertently the charge cycle will revert to 3-stage. Not
all batteries can be charged with a 4-stage cycle so you
must consult with your battery manufacturer as to its use
and recommended charge voltage.
Timeout is added to the 3-stage cycle by placing a capacitor
on TMR. With timeout, when the voltage then reaches CV
(16mV from the absorption voltage) the timer starts and
the charge voltage remains at absorption for the set timer
period. At the end of that time period the charge voltage
changes to the float voltage. The charging remains active
at the float voltage.
Charging is initiated when the part is enabled. The battery then starts charging toward the absorption voltage.
As the battery voltage approaches the absorption voltage the current falls. When the voltage then reaches CV
(16mV from the absorption voltage) the timer starts and
the charge voltage remains at absorption for the set timer
period. At the end of the timer period the internal charge
voltage changes to the equalization voltage. The timer is
immediately restarted and charging at ICHGMAX/5 occurs
with the equalization voltage until the end of equalization
timeout, either 1/4 or 1/8 of the absorption timeout period, tEOC. After equalization timeout the charge voltage
is reduced to the float voltage. At the end of equalization
STAT1 turns on (STAT0 is already on).
There are options for different absorption and float voltages.
Table 3 details the MODE pins settings and FB voltages.
Figure 4 shows a graph that indicates the relationship
between float and absorption voltages for a 6 cell battery.
Table 3. 3-Stage Mode Settings
3-Stage
Settings
Absorption to
Float
MODE1 MODE2
TMR
100mV
H
L
0V
100mV + Timeout
H
L
Cap
200mV
M
L
0V
200mV + Timeout
M
L
Cap
VFLOAT
VABS
WRT VFB
WRT VFB
2.267V
2.367V
2.200V
2.400V
The charging remains active at the float voltage and charging responds to battery load. If the battery voltage (FB
referred) subsequently drops below the LB pin or the part
is powered off and back on (ENAB) a new charge cycle is
initiated. Only one equalization cycle is allowed per power
on cycle. A full 4-stage cycle can be restarted by cycling
the part with the ENAB pin.
4-Stage Cycle
The 4-stage cycle is similar to the 3-stage cycle. However
at the end of absorption charging the charge voltage is
increased to the equalization voltage. The 4-stage cycle
always requires the use of the timer (cap on TMR) as a
safety precaution to insure that charging time at the high
Figure 4 shows a graph that indicates the relationship
between float, absorption and equalization voltages for a
6 cell battery as the FB resistor divider is changed.
Table 4. 4-Stage Mode Settings
4-Stage
(Requires Timer)
Settings
Absorption to Float
Timeout
MODE1
MODE2
TMR
100mV
1/4 tEOC
L
H
Cap
1/8 tEOC
H
H
Cap
1/8 tEOC
M
H
Cap
200mV
VFLOAT
VABS
VEQ
WRT VFB
WRT VFB
WRT VFB
2.267V
2.367V
2.500V
2.200V
2.400V
2.600V
4013f
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17
LTC4013
OPERATION
Charging with a Battery Load
Typically, maintaining a battery at float voltage requires
little charge current. However, when the LTC4013 is in a
float charging state it maintains the capability to increase
current to the full charge current in the event there is
load on the battery. If the load on the battery does not
exceed this current then battery voltage is maintained. If
the battery load exceeds the constant current, the battery
supplies the difference and is discharged. At the low battery threshold a new charge cycle is initiated but still only
at the full charge current so reducing the load is required
for charging to occur.
Li-Ion Charging
The LTC4013 can charge higher capacity Li-Ion batteries
(including Li-Polymer, and LiFePO4). A resistor divider
from the battery to FB sets the desired charge voltage. The
Li-Ion charge algorithm charges the battery at ICHGMAX
to the charge voltage. When the charge current drops
to ICHGMAX/10 or the timer times out (timer active), the
charger turns off and the charge voltage drops to the lower
recharge voltage. When the battery voltage drops below
this recharge level, charging is reinitiated. Table 5 shows
MODE pin settings for Li-Ion charging.
In this mode, after charge termination a new charge cycle
occurs at the recharge voltage. The recharge voltage is
97.0% or 95.6% of the charge voltage depending on MODE
state. The wider difference is useful for LiFePO4 batteries
to avoid constant recharge events. The shift to recharge
can occur with and without timeout.
STAT1 turns on sinking current at charge termination.
Without a timer (TMR = 0V) this happens when the charge
current drops to ICHGMAX/10. If the timer is active (capacitor on TMR) timeout starts when the FB voltage reaches
approximately 16mV from VFB(CHG). Termination is then
indicated after the end of charge termination time (tEOC).
Status Pins
As previously mentioned there are 2 status pins that
indicate charger status. Table 6 details that information.
On implies that the STAT0/1 pin is actively pulled down.
Off implies the STAT0/1 pins are open circuit.
INFET Behavior
The LTC4013 supports an input MOSFET that provides a
blocking path to prevent discharging the battery if the input
voltage is below the battery voltage. Secondly it allows the
input to be disconnected from the charger so that measurement of the input voltage is done with no load. This
measurement is used in conjunction with the Maximum
Power Point Tracking (MPPT) function to determine the
optimal set point for that function.
Table 5. Li-Ion Charge Settings
Settings
VCHG
VRECHRG
% Recharge
MODE1
MODE2
WRT VFB
WRT VFB
3.6V VCHG
3.8V VCHG
4.1V VCHG
4.2V VCHG
97.0%
H
M
2.367V
2.295V
3.490V
3.684V
3.975V
4.072V
95.6%
M
M
2.400V
2.295V
3.443V
3.634V
3.921V
4.016V
18
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LTC4013
OPERATION
Table 6. Status Pin Indications
STAT0
STAT1
CHARGING MODE
Off
Off
Not Charging in
Standby or Shutdown
On
Off
Battery Charge Cycle Active
Termination Not Achieved
On
On
Charge Cycle Complete
Charge Voltage Set to VFB(FL) or for Li-Ion
VFB(RECHG)
Off
On
Bad Battery or Over Temp Fault
The input MOSFET(s) are controlled via the INFET pin which
is connected to the MOSFET gate. The input MOSFETs are
turned on with an on chip charge pump sourced through
INFET. The charge pump is activated when the part is
enabled via the ENAB pin.
below BAT. Specifically the comparators check that DCIN
is approximately 99mV above BAT and that DCIN is larger
than 4mV below VIN. The slight negative voltage on the
later helps to reduce ringing when INFET is turned off.
When ENAB and the comparators allow, both the PowerPath and the switching regulator are enabled. If any
condition is not met then the input MOSFETs are turned
off and the switching regulator disabled. Turn off occurs
by INFET sinking current and pulling the INFET voltage to
approximately 1.8V below the lower voltage of DCIN or VIN.
The input PowerPath MOSFETs are also turned off when
measuring the no load open circuit input voltage when
using the MPPT function.
The INFET MOSFETs are not allowed to turn on unless
DCIN can support charging of the battery. This is accomplished by two comparators, one looks to ensure
that DCIN is larger than BAT and the other looks to see if
DCIN is greater than VIN. The DCIN to BAT comparator also
ensures that the battery is not discharged when DCIN is
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19
LTC4013
BATTERY CHARGER FLOW CHART
VCHG=VFLOAT
ICHG=ICHGMAX
Power On Reset
VCHG<VLOWBAT
No
3-Stage
Yes
2-Stage
VCHG<VLOWBAT
VCHG=VABSORB
STAT0 on
STAT1 off
3/4-Stage
Li-Ion
ICHG=ICHGMAX/5
3-Stage Charging
Algorithm
TMR Pin Active
TMR Pin Active
Yes
Yes
Counting
No
Yes
No
Yes
No
Yes
Charging
Complete
STAT0 on
STAT1 on
Yes
Counting
Charging Complete
for This Stage
Timeout
Enable
Equalization
Yes
Yes
Timeout
No
No
Is Equalization
Enabled
TMR Pin Active
Equalization
State
Stop
Charging
Pause
Counting
Start Timer
No
VCHG within
16mV of VABSORB
MODE2 High
No
ICHG<C/10
No
L-H Transition
on MODE2
after Power Up
FAULT
Temp>150
OVLO
STAT0/1 on
Start Timer
VCHG<VLOWBAT
No
TMR Pin Active
Charge Mode
Yes
No
STAT0 on
STAT1 off
Yes
2-Stage Charging?
Disable
Equalization
Yes
VCHG=VEQUAL
ICHG=ICHGMAX/5
Li-Ion
Charging
Algorithm
4-Step Charging
Algorithm
Start Timer
Reset Counter
VCHG=VCHARGE
Turn on STAT0
Counting
Yes
VCHG
TMR
Pin17mv
Active
from VCHARGE
No
ICHG<C/10
VCHG Within
16mV of VCHRG
No
Yes
No
Equalization
Timeout
No
Start Timer
Yes
Counting
Charge Complete
VCHG=VRECHARGE
Switcher Off
STAT0,1 On
Yes
20
VBAT<VRECHARGE
Yes
Timeout
No
No
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LTC4013
APPLICATIONS INFORMATION
SWITCHING REGULATOR
Setting Maximum Charge Current
Maximum charge current, ICHGMAX, is determined by the
sense resistor. The maximum SENSE – BAT voltage for
normal operation is 50mV. The maximum charge current is 50mV/RSENSE. So for instance if you want a 10A
maximum then RSENSE is set to 5mΩ. Accuracy requires
the use of 4 terminal sense resistors or careful attention
to insure a solid Kelvin connection to the sense resistor.
Fig 17 shows examples. Remember to size the resistor
for power dissipation with PRSENSE = ICHGMAX • 50mV. As
an example for the above 10A charger the sense resistor
needs to be rated greater than 0.5W. Susumu, Panasonic
and Vishay offer a wide variety of accurate sense resistors.
Resistance associated with board traces can add up quickly
(2oz copper is approximately 0.24mΩ /square). Review
trace width for all high current paths.
Inductor Selection
Size the inductor so that the peak-to-peak ripple current is
approximately 30% of the maximum charging current. This
is a reasonable tradeoff between inductor size and ripple.
Inductance can be computed with the following equation:
VIN • VBAT – VBAT 2
L=
0.3 • fSW •ICHGMAX • VIN
where VBAT is the battery voltage, VIN is the input voltage,
ICHGMAX is the maximum charge current in the inductor
and fSW is the switching frequency. Choose the saturation
current for the inductor to be at least 20% higher than the
maximum charge current.
There is an overcurrent comparator which terminates
switching when the voltage between the SENSE and BAT
pins exceeds 100mV to protect against faults. When tripped
switching is stopped for 4 switch cycles.
Switching Regulator MOSFET Selection
MOSFET selection is done with the goal of giving the best
efficiency and lowest cost. The key parameters are: total
gate charge (QG), on-resistance (RDS(ON)), gate to drain
charge (QGD), gate-to-source charge (QGS), gate resistance
(RG), breakdown voltages (maximum VGS and VDS) and
drain current (maximum ID). The following guidelines
provide information to make the selection process easier,
and Table 7 lists some recommended manufacturers.
The rated drain current for both MOSFETs must be greater
than the maximum inductor current. Peak inductor current
is approximately:
V •V –V 2
ILMAX =ICHGMAX + IN BAT BAT
2 • fSW •L • VIN
The rated drain current is temperature dependent, and
most data sheets include a table or graph of the rated
drain current versus temperature.
The rated VDS must be higher than the maximum input
voltage (including transients) for both MOSFETs. As for
the rated VGS, the signals driving the gates of the switching MOSFETs have a maximum voltage of 5V (INTVCC)
with respect to the source. However, during start-up and
recovery conditions, the gate drive signals may be as low
as 3V. Therefore, to ensure that the LTC4013 recovers
properly, use logic level threshold MOSFETs with VT less
than 2V. For a robust design, ensure that the rated VGS
is greater than 7V.
Power losses in the switching MOSFETs are related to the
on-resistance, RDS(ON) ; gate resistance, RG; gate-to-drain
charge, QGD and gate-to-source charge, QGS. Power lost to
the on-resistance is an Ohmic loss, I2RDS(ON), and usually
dominates for input voltages less than 15V. Power lost
while charging the gate capacitance typically dominates
for voltages greater than 15V. When operating at higher
input voltages, efficiency is optimized by selecting a high
side MOSFET with higher RDS(ON) and lower QG. The total
power loss in the high side MOSFET is approximated by
the sum of Ohmic losses and transition losses:
V
PHIGH_LOSS = BAT •IL 2•RDS(ON) •ρ T +
VIN
VIN •IL •(Q +Q )•(2•R +R +R )• f
PU
PD SW
GD
GS
G
5V
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21
LTC4013
APPLICATIONS INFORMATION
IL is the current in the inductor. ρT is a dimensionless
temperature dependent factor in the MOSFET’s on-resistance. Using 70°C as the maximum ambient operating
temperature, ρT is roughly equal to 1.3. RPD and RPU are
the LTC4013 high side gate driver output impedances:
2.3Ω and 1.3Ω, respectively.
A good approach to MOSFET sizing is to select a high side
MOSFET, then select the low side MOSFET. The trade-off
between RDS(ON), QG, and QGS for the high side MOSFET is
evident in the following example. As an example, charging
a 6 cell lead-acid from a 30V source at 20A. VBAT is equal
to 14V, fSW = 200kHz.
For the low side MOSFET the power loss is approximated by.
Starting with two N-channel MOSFETs rated for a VDS of
40V. We start with a BSC018N04LS on the top side with
a RDS(ON) of 2.5mΩ at 4.5V, QG = 60nC, QGS = 25nC,
QGD =10nC, RG = 1.3Ω. The bottom side is a BSC093N04LS
has a RDS(ON) of 11.0mΩ at 4.5V, QG = 8.6nC, QGS = 4.9nC,
QGD = 2nC, RG = 1.0Ω. Power loss for the MOSFETs is
shown in Figures 5 and 6. Observe that the total power
loss at 30V is just over 5W for the top side and about
3.5W for the bottom side.
Where Vf is the voltage drop of the lower MOSFET bulk
diode, typically 0.7V; tnol is the non-overlap time when
neither top or bottom gate is on, approximately 50ns. This
last term represents the loss due to the bulk diode that is
active during the non-overlap time.
In addition to the above, it is desirable that the bottom
MOSFET has reduced G-D capacitance as it minimizes
problems when the top side switch turns on. Coupling
through this capacitance during top side turn on creates
a capacitor divider with the bottom MOSFET G-S capacitance. It is possible to momentarily turn on the bottom
side MOSFET creating a possible shoot through condition,
that at best reduces efficiency, and at worse can destroy
the MOSFET.
Consideration must also be given for power dissipation
in each MOSFET. While it is possible to get high and low
side MOSFETs bonded in a common package, power dissipation concerns may suggest that two separate packages
or even multiple high or low side MOSFETS be used to
spread the heat over a larger PCB area to improve overall
board temperature and efficiency. This is more important
at the high power levels associated with higher current
and higher voltages.
At lower VIN, the top side is on longer and low RDS(ON) helps
lower dissipation but as you go up in voltage the transient
losses increase and in fact can dominate. For the bottom
side MOSFET the opposite is true. Optimization for best
efficiency suggests different top and bottom MOSFETs.
22
8
7
6
POWER LOSS (W)
VIN •I L
• (QGD +QGS ) •(2 •RG +RPU +RPD )• fSW
5V
+Vf •2•fSW •I L • tnol
5
TOTAL
4
OHMIC
3
2
TRANSIENT
1
0
15
20
25
30
DIODE
Diode
35
40
VIN (V)
4013 F05
Figure 5. Top MOSFET Power Loss Example
8
7
6
POWER LOSS (W)
⎛ V ⎞
PLOW _LOSS = ⎜1– BAT ⎟•I L 2•RDS(ON) •ρ T +
VIN ⎠
⎝
TOTAL
5
TRANSIENT
4
3
2
OHMIC
1
0
15
20
25
30
35
40
VIN (V)
4013 F06
Figure 6. Bottom MOSFET Power Loss Example
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LTC4013
APPLICATIONS INFORMATION
Of course MOSFET choices need to be examined. Normally
RDS(ON) and QG are inversely related so perhaps finding a
top side MOSFET with higher RDS(ON) and lower QG might
lower top side losses. Conversely the bottom side MOSFET
is dominated by ohmic losses so perhaps a larger MOSFET
would be better. But of course we also need to watch total
QGD on the bottom side so that presents a limit.
Supplying gate charge current has its own loss most of
which is dissipated from the internal LDO and represents a
potential limitation at higher voltages. The power dissipated
in the IC is: PLDO = (VIN-5) × (QGL+QGH) × fSW where QGL
is the low side gate charge and QGH is the high side gate
charge.
The INTVCC supply has limitations on the maximum current
as well. Figure 7 shows the curve of maximum gate charge
current vs VIN for a power loss of 0.5W. This power level
would add 22°C of temperature to the die at 43°C/W thermal
resistance. Dividing the Y axis value (mA) by fSW(MHz)
gives the maximum QG (nC) that can be charged (the sum
of top and bottom gates.) For instance at 30V and 500kHz
QG is under 20(mA)/0.5(MHz) = 40(nC).
100
INTVCC CURRENT (mA)
90
TOTAL QG(nC) = I(mA)/fsw(MHz)
80
70
60
INTVCC CURRENT BASED
ON 0.5W DISSIPATION
30
20
Manufacturer
Web Site
Infineon
www.infineon.com
Renesas
www.renesas.com
Fairchild
www.fairchildsemi.com
Vishay
www.vishay.com
NXP/Philips
www.nxp.com
Input Supply Capacitor Selection
DCIN provides power to the charge pump and is used
for input voltage sensing so high quality capacitance is
required on this node. Since most of the switching regulator transients are handled by the VIN capacitor, a smaller
capacitor on DCIN is adequate. It primarily needs to handle
filtering input voltage when the INFET is off. We recommend starting with a 4.7µF high quality ceramic capacitor.
The LTC4013 receives power from DCIN through the input
MOSFET to VIN. VIN then provides power to the switching
regulator. This supply provides large currents with fast
switching edges, so a high quality, low ESR, low ESL
decoupling capacitors are required to minimize voltage
glitches on the VIN supply.
RMS ripple current (IVIN(RMS)) follows the relation:
10
0
Table 7. Suggested MOSFET Suppliers
The VIN supply decoupling capacitor (CVIN) is intended to
absorb the input switching ripple current in the charger,
so it must have an adequate ripple current rating.
50
40
There are many power MOSFET manufacturers that make
devices appropriate for this application. Some are listed
in Table 7.
0
10
20
30
40
50
60
VIN (V)
4013 G24
Figure 7. Maximum INTVCC current
If desired operation places the internal 5V regulator out of
the allowable region, deriving gate drive power externally
is required. This could be done by carefully driving the
INTVCC with tight regulation (do not exceed the 6V absmax)
or by supplying 5V power for the BST drive (top gate QG).
IVIN(RMS) ≈ICHGMAX •DC •
1
–1
DC
which has a maximum at DC = 0.5, or VIN = 2 • VOUT, where:
IVIN(RMS) ≈
ICHGMAX
2
where ICHGMAX is the maximum charge current is set by
RSENSE. The simple worst-case equation is commonly
used for design.
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23
LTC4013
APPLICATIONS INFORMATION
The input capacitance CIN is determined by the desired
input ripple voltage (ΔVIN). For step-down operation:
CIN ≥
ICHGMAX VBAT(MAX)
•
ΔVIN • fSW VIN(MIN)
where fSW is the operating frequency, VBAT(MAX) is the
DC/DC converter maximum output voltage and VIN(MIN)
is the minimum input operating voltage. Keeping ΔVIN
below 100mV is a good starting point. As an example say
ICHGMAX = 10A, ΔVIN = 0.1V, fSW = 500k, VBAT(MAX)=15V,
VIN(MIN) = 18V then CIN is greater than 167µF
is made to have ripple current equal or below 30% of
ICHGMAX rating, the BAT capacitors for 40% • ICHGMAX is
adequate. The capacitors also need to be surge rated to
the maximum output current.
Sizing for output ripple voltage is similar to input decoupling:
CBAT ≥
0.4 •ICHGMAX
ΔVBAT • fSW
For example if ICHGMAX = 10A, ΔVBAT = 0.1V, fSW = 500k
then choose CBAT greater than 80µF.
At higher voltages meeting all of these requirements probably requires multiple capacitors and perhaps a mixture
of cap types. Because of the fast switching edges it is
important that the total decoupling capacitance has low
ESR and ESL components because they generate sharp
voltage spikes. Best practice is to use several low ESR
ceramic capacitors as part of the capacitance, with higher
density capacitors utilized for bulk requirements. X5R or
X7R capacitors maintain their capacitance over a wide
range of operating voltages and temperatures. Minimize
the loop created by the input capacitor, high side MOSFET, low side MOSFET to reduce radiation components.
See Linear application notes AN139 and AN144 for more
information on EMI.
INTVCC LDO Output, and BST Supply
Battery Capacitor Selection
The output of the charger is the battery, which represents
a large effective capacitance. Because the battery often has
significant wiring connecting it to the charger additional
decoupling output capacitors at the charger are needed.
The BAT node is also used for voltage sensing so better
performance is obtained with lower voltage ripple at the
BAT and FB pins. The capacitors need to have low ESR to
reduce output ripple. To achieve the lowest possible ESR,
use several low ESR ceramic capacitors in parallel. Lower
output voltage applications may benefit from the use of high
density POSCAP capacitors, which are easily destroyed
when exposed to overvoltage conditions. To prevent this,
select POSCAP capacitors that have a voltage rating that
are at least 50% higher than the regulated voltage.
where QGH is the top side MOSFET QG at 5V.
The ripple current on these capacitors is the same as
the inductor ripple. Since in general inductor selection
24
INTVCC provides power to the IC but also serves to provide charge to the gate drives. The boosted supply pin
allows the use of N channel top MOSFET switches for
increased conversion efficiency and lower cost. The BST
cap is connected from the SW to BST with a low leakage
1A Schottky diode connected from INTVCC and BST. The
diode must be rated for a reverse voltage greater than the
input supply voltage maximum.
CBST is sized to hold the BST rail reasonably constant
when delivering gate charge to the to MOSFET. A good
rule of thumb is:
CBST > 50 •
QGH
=10 •QGH
VGS
So as an example say that the top gate charge is 20nC,
being charged to the INTVCC voltage of 5V then keep the
CBST capacitance larger than 0.2µF.
The CBST is charged during the bottom switch on time.
The LTC4013 maintains a minimum top gate off time to
provide this charge. If the LTC4013 is in discontinuous
mode with the bottom switch off and boost voltage drops,
the bottom side switch is enabled to provide BST charging.
Since BST cap charge current is drawn from the INTVCC
capacitor, that cap needs to be sized to have minimal drop
during recharge. A good starting point for high current
switching MOSFETs with high gate charge is to set CINTVCC
larger than 4.7µF. Connect it as close as possible to the
exposed pad underneath the package. Because of the fast
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LTC4013
APPLICATIONS INFORMATION
high current edges use low ESR ceramic, with ESR typically lower than 20mΩ. For driving MOSFETs with gate
charges larger than 44nC, size INTVCC with 0.5µF/nC of
total gate charge (top and bottom MOSFETs).
approximate formula is:
Enable
Table 8: RT Resistor Value
The part has an ENAB pin that allows the part to be enabled when the input voltage reaches a certain threshold.
Normally a resistor divider is used from DCIN to ENAB
(see Figure 8). The turn on threshold at ENAB is approximately 1.22V (rising), with 170mV of hysteresis. When in
shutdown, all charging functions are disabled and input
supply current is reduced to around 40μA.
Typical ENAB pin input bias current is 10nA which needs
to be accounted for when using high value resistors. So
choose REN1 and then:
⎞
⎛V
REN2 =REN1 • ⎜ ENAB – 1⎟
⎝ 1.22 ⎠
DCIN
REN2
DCIN
LTC4013
ENAB
REN1
SGND
4013 F07
Figure 8. ENAB Resistor Divider
R T (kΩ)=
40.2
fSW
1.088
(MHz)
Switching Frequency
RT (Ω)
1MHz
40.2k
750kHz
54.9k
500kHz
86.6k
300kHz
150k
200kHz
232k
Switching Frequency Synchronization
As detailed above the switching frequency of the LTC4013 is
set from 200kHz to 1MHz using an RT resistor. The internal
oscillator may also be synchronized to an external clock
through the SYNC pin. An external clock applied to the
SYNC pin must have a logic low below 1.3V and a logic high
above 1.7V. The input sync frequency must be 20% higher
than the frequency that would otherwise be determined by
the resistor at the RT pin. Input signals outside of these
specified parameters cause erratic switching behavior
and sub harmonic oscillations. When synchronizing to an
external clock, please be aware that there is a fixed delay
from the input clock edge to the edge of the signal at the
SW pin. Ground the SYNC pin if synchronization to an
external clock is not required. When SYNC is grounded,
the switching frequency is determined by the resistor RT.
CLKOUT
Starting the charger requires that the LTC4013 is enabled,
and the DCIN voltage is greater than VIN by about 4mV.
DCIN also needs to be greater than VBAT by about 100mV.
Programming Switching Frequency
The LTC4013 has an operational switching frequency range
between 200kHz and 1MHz. This frequency is programmed
with an external resistor from the RT pin to ground. Do
not leave this pin open under any condition. The RT pin
is also current-limited to 60μA. See Table 8 for resistor
values and the corresponding switching frequencies. An
Often synchronization is done with an externally generated
clock signal. As part of the synchronization capability, a
pulse stream is generated on CLKOUT that can be used as
the SYNC input to another LTC4013 and produce switching that is approximately 180° out of phase. This allows
two LTC4013s to be operated in parallel in a manner that
would reduce input current ripple (and thus capacitance).
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LTC4013
APPLICATIONS INFORMATION
Output Current Monitoring
The LTC4013 ISMON pin allows users the capability to
monitor the output current as a voltage. The voltage
increases linearly from 0V to 1V as the voltage between
SENSE and BAT increases from 0mV to 50mV (voltage gain
of about 20). The bandwidth on the amplifier is sufficient
so that if you want average current you need to filter the
ISMON output with a simple RC filter. A 100k resistor from
ISMON to a 200pF capacitor to ground is usually sufficient.
Average Current Mode Control Compensation
The LTC4013 uses average current mode control for precise
regulation of the inductor/charge current. Figure 9 shows
an overview of the control loop. The current is measured
via the sense amp and compared against the target value.
The error amp with compensation components RC and
CC sets the duty cycle that controls the inductor current.
A separate voltage amp modulates the maximum current
as the battery voltage approaches the charge voltage level,
reducing the maximum current.
COMPARATOR
+
–
SENSE
AMP
ERROR AMP
ITH
RC
gm
20x
–
+
VIMAX
L
SENSE
+
BAT
–
CC
gm
VOLTAGE
AMP
–
+
RSENSE
FB
VCH
RFB1
RFB2
4013 F09
Figure 9. Switching Regulator Control Loop
To design the compensation network, the maximum compensation resistor needs to be calculated. In current mode
controllers, the ratio of the sensed inductor current ramp
to the slope compensation ramp determines the stability
of the current regulation loop above 50% duty cycle. In
the same way, average current mode controllers require
the slope of the error voltage to not exceed the PWM ramp
slope during the switch off time. Since the closed loop
gain at the switching frequency produces the error signal
26
RC (kΩ) =
CC(nF)=
L(µH)• fSW (kHz)
VBAT (V)•RSENSE (mΩ)
2000
fSW (kHz)
where fSW is the switching frequency, L is the inductance
value, VBAT is the battery voltage and RSENSE is the sense
resistor. CC is inversely proportion to fSW so lower switching
frequencies will need higher CC. RC is linearly dependent
to inductance, for higher inductance RC is higher.
An example: DCIN = 24V, VBAT = 14V ICHGMAX = 10A,
RSENSE = 5mΩ, fSW = 500kHz, L = 3.6µH then CC = 4nF,
RC = 25.7kΩ. Of course check stability on the actual
physical circuit.
In some circumstances an additional capacitor from ITH
to ground is helpful. The capacitance is usually 0.01 to
0.1 times CC.
Thermal Shutdown
SW
MODULATOR
slope, the output impedance of the error amplifier is the
compensation resistor, RC. Use the following equation as
a good starting point for compensation component sizing:
The internal thermal shutdown within the LTC4013 engages
at approximately 160°C and disables switching. When the
part has cooled to 150°C, the part resumes charging. This
feature is not tested but guaranteed by design. Thermal
shutdown protects the device from excessive gate drive
power and excess internal LDO dissipation but does not
protect from excess power dissipation in the external
MOSFETS or other external components. Battery over
temperature is handled via the use of the external NTC
resistor and the NTC function as described below, but
does not shutdown the part.
BATTERY CHARGER SECTION
Battery Charge Voltage Programming
The Battery Charger Operation section details how to set
the mode switches for the desired charging algorithm.
Further tweaking of voltages is done through the resistor
divider between the BAT and FB pins as shown in Figure 10.
4013f
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LTC4013
APPLICATIONS INFORMATION
the absorption voltage to be 14.4 then you would use:
BAT
BATTERY
LTC4013
⎛V
⎞
⎛ 14.4 ⎞
RFB2 =RFB1 • ⎜ ABS –1⎟ =RFB1 • ⎜
–1⎟
⎝ 2.367 ⎠
⎝ 2.367 ⎠
RFB2
FB
=RFB1 •(6.084–1)
RFB1
SGND
The associated voltages are shown in the 4th row of Table 9.
4013 F10
Figure 10. Battery FB Resistor Divider
By way of example consider a 4-stage cycle with MODE1
low and MODE2 high. The associated voltages are shown
in Table 9. The first row shows the FB referred voltages.
Table 9. Charge Voltage Examples
VFLOAT
VABSORPTION
VEQUALIZATION
FB
2.267
2.367
2.500
6x
13.6
14.2
15.0
6.043x
13.7
14.3
15.1
6.084x
13.8
14.4
15.2
Generating the divider requires finding resistors that give
as close to correct ratio as possible. If we use standard
value 1% resistors this may require a bit of searching. For
instance, RFB1 = 46.4k and RFB2 = 232k programs the 6x
case with less than 0.015% error for the charge votages
shown in Table 9. If more than two resistors are used
series and parallel combinations can make it easier. A
tool that might help is found at http://reaylabs.com/tools/
VoltageRegulator.html
But lets say we want a slightly different float voltage, say
13.7V. Then the divider would be set with:
⎛V
⎞
⎛ 13.7 ⎞
RFB2 = RFB1 • ⎜ FLOAT – 1⎟ = RFB1 • ⎜
–1
⎝ 2.267 ⎟⎠
⎝ 2.267 ⎠
The MODE pins provide additional options for different
charge voltage spreads which may better fit the battery
recommendations.
Low Battery Voltage Setting
As described earlier the LB pin provides the user a way
to set when low battery conditions occur. The LB pin
sources approximately 20µA so placing a resistor from
LB to ground generates the LB voltage. Low battery is
determined relative to the FB voltage pin. So for instance
say we are charging a 6 cell lead acid battery and we
want to set the low battery voltage to 10.6V (1.77 V, FB
referred). Set the LB resistor to 1.77V/20µA = 88.5k (88.7k
is closest 1% value).
Charge Voltage Temperature Compensation
As mentioned the LTC4013 uses a charge voltage method
that can be used to shift the charge voltage as a function
of temperature. In the simplest view the voltage (VNTCVINTVCC/2) is multiplied by 0.21 and added to the charge
voltage. Figure 11 shows how to configure the pin and
Table 10 shows some common temperature coefficient
(TC) and associated resistor settings using 10k, B = 3380
NTC resistor. Note TC is with respect to the charge voltage
at FB which is roughly 1 cell of a lead acid battery.
= RFB1 • ( 6.043 – 1)
INTVCC
If you are more concerned about obtaining a certain absorption or equalization voltage then the resistor divider
would be set based on that ratio. If for instance you want
RN1
LTC4013
Absorption and equalization voltages would scale accordingly as shown in the 3rd row of Table 9.
NTC
SGND
OPTIONAL
RNTC
RN2
4013 F11
Figure 11. NTC Configuration for Temperature Compensation
4013f
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27
LTC4013
APPLICATIONS INFORMATION
Table 10. Charge Voltage TC Examples Using B=3380 RNTC
TC (WRT VFB)
RN1
RN2
–2.5mV/°C
2.49k
3.32k
–5.0mV/°C
4.99k
10.0k
–10mV/°C
10.0k
Open
Since the NTC resistor is used to adjust for changes in
battery temperature it is ideally placed in thermal contact
with the battery. This is not always practical so the next
best thing is to position the resistor for an accurate reading
of the battery ambient temperature. Take care to reduce
noise pickup on wires and make sure that good Kelvin
connections are used.
node. Battery ESR, however, can produce significant AC
voltages due to ripple currents, causing unstable operation.
This ESR effect can be reduced by adding a capacitor to
the FB input, producing a low-frequency pole as shown
in Figure 12. If ripple suppression proves necessary, the
filter frequency is typically set to ~1/1000 of the switching frequency.
1000 • (RFB1+ RFB2 )
CFB =
2π • fSW • (RFB1 • RFB2 )
BAT
Charge Termination Timer
FB
The LTC4013 supports timer-based functions, where battery charge cycle control occurs after a specific amount
of time. Timer termination is engaged when a capacitor
(CTMR) is connected from the TMR pin to ground. CTMR
for a desired end-of-cycle time (tEOC) follows the relation:
CTMR (µF) = tEOC (Hr) • 0.066
Table 11 represents some typical capacitors and associated times.
Table 11. Representative Timer Capacitor Values
Capacitor
CTMR
BATTERY
RFB2
LTC4013
Absorption
Time
Equalization Time
(MODE1 L/M, H)
Bad Battery
Timeout
68nF
1.03 Hrs
15.5, 7.7 Min
7.7 Min
0.22µF
3.33 Hrs
50, 25 Min
25 Min
0.47µF
7.12 Hrs
1.78, 0.89 Hrs
0.89 Hrs
The absorption and Li-Ion timer cycle starts when the
charger transitions from constant-current to constantvoltage charging (when VFB is 16mV away from final value).
Equalization timing starts immediately upon transition to
the equalization charge state. Bad battery timing commences with FB falling below LB.
CFB
SGND
RFB1
4013 F12
Figure 12. FB Voltage Filtering
Maximum Power Point Tracking (MPPT)
MPPT is used to regulate the input voltage to maximize
power transfer from a power limited source. The first
step is to determine the maximum power voltage. For a
solar panel this can be determined from the data sheet. A
resistor divider between the input source and the FBOC
and MPPT pins is used to program the LTC4013 to regulate the input source at its maximum power voltage. The
FBOC pin is used to sample the input source open circuit
voltage when charging is paused while the MPPT pin is
used to regulate the maximum power voltage when the
charger is running. The MPPT resistor divider should be
configured as shown in Figure 13.
DCIN
DCIN
RMP3
LTC4013
MPPT
BATTERY CHARGER FUNCTIONS: FILTERING
COMPONENTS
RMP2
FBOC
RMP1
Voltage Regulation Loop (FB)
SGND
4013 F13
The charger voltage regulation loop monitors battery
voltage, and as such, is controlled by a very slow moving
28
Figure 13. Resistor Divider for MPPT
4013f
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LTC4013
APPLICATIONS INFORMATION
Choose the attenuation ratio of FBOC to DCIN voltages (KF)
so VFBOC is between 1.0V and 3.0V when the input voltage
is at its highest (i.e. open circuit, VDCIN(OC)). The attenuation ratio of MPPT to DCIN voltages is set so that VMPPT
equals the chosen VFBOC when DCIN is at the maximum
power voltage, VDCIN(MP). The following equations define
those conditions:
VFBOC
=
VMPPT
=
VDCIN(OC)
VDCIN(MP)
RMP1
=KF
RMP1 + RMP2 + RMP3
⎛ 1
1 ⎞
–
RMP3 = 50k • ⎜
⎟ = 729k
⎝ 0.0625 0.708 ⎠
RMP1 +RMP2
RMP1 + RMP2 + RMP3
When the MPPT loop is in regulation, the MPPT voltage
equals the FBOC voltage as measured during the open
circuit interval. Reworking the above equations to define
the ratio of the DCIN voltages at regulation and open
circuit as KR gives:
VDCIN(MP)
VDCIN(OC)
=
1.5V
= 0.0625
24V
K = 17V = 0.708
R
24V
1.5V
RMP1 =
= 50k (Choose 30µA in Divider)
30µA
⎛ 1
⎞
– 1⎟ = 20.6k
RMP2 = 50k • ⎜
⎝ 0.708 ⎠
KF =
RMP1
=KR
RMP1 +RMP2
We can rewrite this equation to solve for RMP2 as a function of RMP1 and the DCIN ratio KR:
⎛ 1 ⎞
RMP2 =RMP1 • ⎜ – 1⎟
⎝ KR ⎠
Substitute that for RMP2 in the equation for KF and solve
for RMP3:
⎛ 1 1⎞
RMP3 =RMP1 • ⎜ – ⎟
⎝ KF KR ⎠
This sets up the design procedure:
1. Choose RMP1 such that VFBOC = 1.0V to 3.0V. We recommended a current in the resistor string of 5 to 50µA.
2. Calculate RMP2 based on RMP1 and the ratio, KR, between
the maximum power voltage and the open circuit voltage.
3. Calculate RMP3 based on RMP1, and the KR and KF ratios.
As an example, consider a solar panel with an open circuit
voltage VDCIN(OC) = 24V and a maximum power voltage
VDCIN(MP) = 17V. Choose VFBOC = 1.5V. Then calculate:
Note these are ideal values and adjustments to use actual
physical resistor values. The absolute value of VFBOC is
not critical so set it to help match ideal values to actual
resistor values.
As another example consider charging a battery from a
source with an open-circuit voltage of 30V and a source
impedance of 5Ω. This resistive supply has a short circuit
current of 6A, and the peak available power of 45W occurs
with a load of 3A at 50% of VOC. MPPT settings would
have VDCIN(OC) = 30V, VFBOC = 1.5V,
V
1.5V
KF = FBOC =
= 0.05
V
30V
DCIN(OC)
KR =
VDCIN(MP)
VDCIN(OC)
=
15V
= 0.5
30V
Again with 30µA in RMP1, RMP1 = 50k then
⎛ 1 ⎞
RMP2 = 50k • ⎜
– 1 = 50k and
⎝ 0.5 ⎟⎠
1 ⎞
⎛ 1
–
= 900k
RMP3 = 50k • ⎜
⎝ 0.05 0.5 ⎟⎠
Additional MPPT Considerations
MPPT operation requires the use of back-to-back MOSFETs for the input PowerPath to allow accurate open
circuit DCIN voltage measurement. When using back to
back MOSFETs the sources are tied together, drains on
the outside. If a single MOSFET is used the body diode
effectively clamps DCIN to VIN when the input MOSFET
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29
LTC4013
APPLICATIONS INFORMATION
is off. This could result in inaccurate measurement of the
DCIN open circuit voltage.
Because MPPT operation involves large changes of input
voltage, it is important to ensure that the programmed
maximum power voltage does not violate minimum input
operating conditions: 4.5V or 100mV above the battery
voltage, whichever is higher.
In general MPPT operation produces no control loop stability issues. If input oscillation is detected a lead capacitor
(CMPPT) from DCIN to MPPT can help mitigate problems.
If MPPT is not used the function is disabled by tying FBOC
to INTVCC.
Battery Stacks
Batteries are stacked serially to increase voltage and reduce
load currents. The LTC4013 does allow for charging of
higher voltage stacks, up to 60V. However the user needs
to carefully consider the need for balancing individual
cells of the stack. Cell balancing improves battery life
at the expense of additional circuitry. Linear Technology
provides ICs that facilitate this task. Some are mentioned
in the Related Parts section at the end of this data sheet.
Plugging in a Battery
Care must be taken when hot plugging a battery into the
charging circuit. Discharged capacitors on the charger side
can cause very high battery discharge current as the battery
voltage and the capacitor voltage equalize. Figure 14 shows
the current path which has very little series impedance
between the battery and capacitor.
As with other Hot Swap issues, the first step is to try
and reduce capacitance. It is also possible to partially
precharge the capacitors using power from VIN. However,
this must be done carefully to avoid a direct current path
from the battery back to the input supply. Any application
circuit must be bidirectional to support both battery charging through a low impedance path while controlling the
reverse current during a hot plug event. See ideal diode
application circuit, Figure 18.
VIN
CIN
M1
L1
RSENSE
BAT
+
M2
CBAT
PGND
HIGH
FREQUENCY
CIRCULATING
PATH
4013 F14
Figure 14. Current Flow During Hot Plugging of Battery
System Load During Charging
If there is a system load on the battery when charging, it
can interfere with the charging algorithms. For instance if
the load is greater than ICHGMAX/10 the charger might not
detect an end of charge condition. Careful management
of the load can assist. Current is monitored through the
sense resistor (and reported on ISMON) so it may be possible to use this signal to help detect this kind of problem.
Starting Without a Battery
The LTC4013 requires the SENSE voltage to be above
1.97V (typ) to run the charger and VIN above VIN UVLO.
This insures that the SENSE amp has sufficient headroom
to operate. Normally this requirement is met if a battery
is present. There are conditions where this may not be
met, such as testing without a battery. In order to have
the switching regulator start, the voltage on SENSE needs
to be pulled up. There is no built in trickle current in the
part to do this method. A simple method is in Figure 15. In
this case a few mA’s of current is taken from INTVCC and
used to charge the capacitance on BAT. The time required
will depend on the current and size of the capacitor. Once
above the UVLO threshold the switching regulator turns on
and will charge the node at higher currents, typically C/5
if you are below LB. Once above 4.3V there is not further
drain on INTVCC.
INFET MOSFETS
The input N channel MOSFETs are used for blocking battery discharge when the input is below battery as well as
disconnecting DCIN to VIN for open circuit measurement
30
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LTC4013
APPLICATIONS INFORMATION
avoid corrupting the signal ground reference (SGND)
used by the IC. Isolate SGND from high current paths
and transients from the input supply and any local drive
supplies because sensitive circuits such as the error amp
reference are referred there. As a general rule keep the
high frequency circulation path area as shown in Figure
16 minimized.
D1
1N914
INTVCC
C1
LTC4013
SENSE
R1
430Ω
RSENSE
BAT
CBAT
4013 F15
Figure 15. SENSE Precharge
VIN
M1
CIN
L1
HIGH
FREQUENCY
CIRCULATING
PATH
RSENSE
+
M2
PGND
BAT
CBAT
4013 F16
Figure 16. High Frequency Radiation Path
of DCIN in MPPT. This is done with back-to-back MOSFETs
but if reverse discharge, or MPPT is not an issue, then a
single MOSFET can be used with the source on the DCIN
side. If a single MOSFET is used then VIN is charged up
initially though the bulk diode of the MOSFET. Take care
when using back-to-back MOSFETs as INFET charging of
gate turn on is controlled by DCIN to VIN voltage, DCIN
to VBAT voltage, the part ENAB voltage and absolute VIN
voltage. Pick MOSFETs with low RDS on as they conduct
all charger current. Select breakdown voltage to stand off
supply voltages.
LAYOUT CONSIDERATIONS
Note a general switching regulator layout overview is
found in Linear Technology application notes, AN-136,
AN-139 and AN-144.
For high current applications, current path traces need to
meet current density guidelines as well as having minimal
IR drops. There will also be substantial switching transients.
The switch drivers on the IC are designed to drive large
capacitances and generate significant transient currents.
Carefully consider supply bypass capacitor locations to
Effective grounding is achieved by considering switch current in the ground plane, and the return current paths of
each respective bypass capacitor. The VIN bypass return,
INTVCC bypass return, and the sources of the groundreferred switch FETs carry PGND currents. SGND originates
at the negative terminal of the BAT bypass capacitor, and
is the small signal reference for the LTC4013. Do not run
small traces to separate ground paths. A good ground
plane is important. Orient PGND referred bypass elements
such that transient currents in these return paths do not
corrupt the SGND reference.
During the dead-time between the synchronous bottom
switch and top switch conduction, the body diode of the
synchronous FET conducts inductor current. Commutating
the body diode requires a significant charge contribution
from the top switch during initiation, creating a current spike
in the top switch. At the instant the body diode commutates,
a current discontinuity is created between the inductor and
top switch, with parasitic inductance causing the switch
node to transition in response to this discontinuity. High
currents and excessive parasitic inductance can generate
extremely fast δV/δt times during this transition. These
fast δV/δt transitions can sometimes cause avalanche
breakdown in the synchronous MOSFET body diode,
generating shoot-through currents via parasitic turn-on
of the synchronous MOSFET. Layout practices and component orientations that minimize parasitic inductance on
the switched nodes are critical for reducing these effects.
Orient power path components such that current paths in
the ground plane do not cross through signal ground areas.
Power ground currents are controlled on the LTC4013 via
the PGND pin, and this ground references the high current
synchronous switch drive components, as well as the local
INTVCC supply. It is important to keep PGND and SGND
voltages consistent with each other, do not separate these
grounds with thin traces.
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LTC4013
APPLICATIONS INFORMATION
When the bottom side MOSFET is turned off, gate drive
currents return to the LTC4013 PGND pin from the MOSFET
source. The BST supply refresh surge currents also return
through this same path. Orient the MOSFET such that these
PGND return currents do not corrupt the SGND reference.
The high δi/δt loop formed by the switch MOSFETs and
the input capacitor (CVIN) should have short wide traces
to minimize high frequency noise and voltage stress
from inductive ringing. Surface mount components are
preferred to reduce parasitic inductances from component
leads. Switch path currents can be controlled by orienting
switch FETs, the switched inductor, and input and output
decoupling capacitors in close proximity to each other.
Locate the INTVCC, and BST capacitors in close proximity
to the IC. These capacitors carry the MOSFET gate drive
currents. Locate the small-signal components away from
high frequency switching nodes (TG, BG, SW, BST and
INTVCC). High current switching nodes are oriented across
the top of the LTC4013 package to simplify layout and
prevent corruption of the SGND reference.
Locate the battery charger feedback resistors, and MPPT
resistors in close proximity to the LTC4013 and minimize
the length of the high impedance feedback nodes.
Route the SENSE and BAT traces together, keeping them
as short as possible, and avoid corruption of these lines
by high current switching nodes.
The LTC4013 packaging has been designed to efficiently
remove heat from the IC via the exposed backside pad.
Solder the pad to a copper footprint on the PCB that
contains a large number of vias to the ground plane. This
reduces both the electrical ground resistance, as well as
the thermal resistance to ambient.
Accurate sensing of charge current is dependent on good
printed circuit board layout as shown in Figure 17. 4 terminal sense resistors are the best option but it is possible
to get good results with 2 terminal devices.
RSENSE
RSENSE
TO SENSE
TO BAT
TO SENSE
TO BAT
4013 F17
Figure 17. Sense Resistor PCB Layout
32
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LTC4013
APPLICATIONS INFORMATION
Figure 18. Ideal Diode to Block Current Surge When Hot Plugging Battery
VIN
CIN
VIN
TG
M1
SW
BG
M2
L1
LTC4013
SENSE
1k
M5
BSC060N10NS3
RSENSE
BAT
CBAT
IN
SOURCE
SHDN
GATE
BATTERY
OUT
C1
1.5µ
LTC4359
RFB2
FB
OPTIONAL RESITIVE BLEED
FOR VIN CHARGE UP
R2
VSS
RFB1
R1
1k
4013 TA02
Figure 19. 6 Cell, 5A Lead Acid Charger with 24V Solar Panel Input and MPPT Optimization
DCIN
M1
M2
C2/10
10µF×2
C1
4.7µF
INFET
R1
475k
R19
7.5k
D2
RED
RMP2
10k
R18
7.5k
D3
GREEN
BST
C15
0.15µF
TG
CMP4
100pF
BG
MPPT
M3
C13
D1
4.7µF
B0540W
M4
L1
6.8µH
INTVCC
PGND
LTC4013
SENSE
STAT0
STAT1
ISMON
INTVCC
3 STAGE CHARGING WITH
13.6V FLOAT, 14.2V ABSORPTION
3.3 HR TIMEOUT
SW
FBOC
RMP1
49.9k
MPPT REGULATION SET AT
83% OF OPEN CIRCUIT VOLTAGE
FOR 22V OC, 18.3V
VIN
ENAB
RMP4
100k
R2
40.2k
VIN_S
DCIN
C3
CMP3
33pF 0.1µF
RMP3
665k
C9
68µF
BAT
FB
MODE1
MODE2
NTC
RSENSE
10m
RFB2
499k
RFB1
100k
C19
0.1µF
C16-18
22µF×3
C23
220µF
CLKOUT
RT
R23
86.6k
SGND
TMR
LB
C31
0.22µF
ITH
R24
86.6k
R22
23.2k
C29
4.7nF
RN2
3.32k
INTVCC
RN1
2.49k
SYNC
M1, M2, M3, M4 VISHAY SiS434DN
L1 WURTH 7443340680
C1 4.7µF 50V
C2, C10 10µF, 50V
C16-18 22µF 25V
C23 220µF 25V
C9 PANASONIC 68µF 50V EEHZA1H680P
BAT
T
BATTERY
RNTC
10k B=3380
CHARGE VOLTAGE SHIFTED
–2.5mV/°C
4013 TA03
4013f
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33
LTC4013
APPLICATIONS INFORMATION
Figure 20. 18V-60V 6.25A LiFePO4 15V SLA Replacement Battery Charger
18V-60V
DCIN
M1
M2
C2-C5
4.7µF ×4
C1
4.7µF
R1
549k
C3
0.1µF
D2
RED
R17
12k
D3
GREEN
VIN_S
VIN
BST
C15
0.15µF
TG
ENAB
R3
40.2k
R18
12k
INFET
DCIN
C9-C12
56µF ×4
MPPT
ISMON
MODE1
MODE2
M4-M5
C13
4.7µF
L1
22µH
D2
DFLS1100
PGND
LTC4013
STAT1
D1
DFLS160
INTVCC
FBOC
STAT0
M3
SW
BG
INTVCC
LI-Ion CHARGING WITH 15V FLOAT,
14.35V RECHARGE, 3.3HR TIMEOUT
SENSE
RSENSE
8m
BAT
RFB2
536k
FB
NTC
RFB1
102k
INTVCC
BAT
C16-18
22µF×3
C19
0.1µF
C23
330µF
BATTERY
SYNC
CLKOUT
SGND
M1, M2, M3, M4, M5 VISHAY SiS468DN
L1 WURTH 7443632200
RT TMR
LB
ITH
C1 4.7µF 100V
C2-C5 4.7µF, 100V
C31
R24
R23
R22
C16-C18 22µF 25V
0.22µF
86.6k
232k
36.5k
C23 330µF 25V
C29
C9-C12 56µF 63V PANASONIC EEHZA1J560P
10nF
4013 TA04
34
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LTC4013
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/product/LTC4013#packaging for the most recent package drawings.
UFD Package
28-Lead Plastic QFN (4mm × 5mm)
(Reference LTC DWG # 05-08-1712 Rev B)
0.70 ±0.05
4.50 ±0.05
3.10 ±0.05
2.50 REF
2.65 ±0.05
3.65 ±0.05
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
3.50 REF
4.10 ±0.05
5.50 ±0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ±0.10
(2 SIDES)
0.75 ±0.05
R = 0.05
TYP
PIN 1 NOTCH
R = 0.20 OR 0.35
× 45° CHAMFER
2.50 REF
R = 0.115
TYP
27
28
0.40 ±0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
5.00 ±0.10
(2 SIDES)
3.50 REF
3.65 ±0.10
2.65 ±0.10
(UFD28) QFN 0506 REV B
0.25 ±0.05
0.200 REF
0.50 BSC
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X).
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
4013f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representaFor more
information
www.linear.com/LTC4013
tion that the interconnection
of its circuits
as described
herein will not infringe on existing patent rights.
35
LTC4013
TYPICAL APPLICATION
Figure 21. 24V 5A 6 Cell Lead Acid Charger with Absorption and Equalization Charging
24V
DCIN
M1
M2
C2/10
10µF×2
C1
4.7µF
R1
665k
INFET
DCIN
C3
0.1µF
D2
RED
R17
7.5k
D3
GREEN
VIN
BST
BG
M4
C13
D1
4.7µF
B0540W
L1
6.8µH
INTVCC
FBOC
PGND
LTC4013
STAT0
STAT1
ISMON
MODE1
INTVCC
M3
SW
MPPT
INTVCC
4 STAGE CHARGING WITH
13.6V FLOAT, 14.2V ABSORPTION
AND 15.0V EQUALIZATION
3.3 HR TIMEOUT
C15
0.15µF
TG
ENAB
R3
40.2k
R18
7.5k
VIN_S
C9
68µF
MODE2
SENSE
RSENSE
10m
BAT
RFB2
499k
FB
NTC
RFB1
100k
INTVCC
BAT
C16-18
22µF×3
C23
220µF
C19
0.1µF
BATTERY
SYNC
CLKOUT
SGND
M1, M2, M3, M4 VISHAY SiS434DN
L1 WURTH 7443340680
RT TMR
LB
ITH
C1 4.7µF 50V
C2, C10 10µF, 50V
C31
R24
R23
R22
C16-C18 22µF 25V
0.22µF
86.6k
86.6k
23.2k
C23 220µF 25V
C29
C9 PANASONIC 68µF 50V EEHZA1H680P
4.7nF
4013 TA05
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36 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTC4013
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LTC4013
4013f
LT 0816 • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 2016
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