LTC4010 FEATURES DESCRIPTIO U

LTC4010 FEATURES DESCRIPTIO U
LTC4010
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FEATURES
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DESCRIPTIO
The LTC®4010 provides a complete, cost-effective nickel
battery fast charge solution in a small package using few
external components. A 550kHz PWM current source
controller and all necessary charge initiation, monitoring
and termination control circuitry are included.
Complete NiMH/NiCd Charger for 1 to 16 Cells
No Microcontroller or Firmware Required
550kHz PWM Current Source Controller
No Audible Noise with Ceramic Capacitors
Wide Input Voltage Range: 5.5V to 34V
Programmable Charge Current: 5% Accuracy
Automatic Trickle Precharge
–∆V Fast Charge Termination
Optional ∆T/∆t Fast Charge Termination
Optional Temperature Qualification
Automatic NiMH Top-Off Charge
Programmable Timer
Automatic Recharge
Multiple Status Outputs
Micropower Shutdown
16-Lead Thermally Enhanced TSSOP Package
The LTC4010 automatically senses the presence of a DC
adapter and battery insertion or removal. When an external DC source is not present, the LTC4010 enters shutdown and supply current drawn from an installed battery
drops to the lowest possible level. Heavily discharged
batteries are precharged with a trickle current. The LTC4010
can simultaneously use both –∆V and ∆T/∆t fast charge
termination techniques and can detect various battery
faults. If necessary, a top-off charge is automatically
applied to NiMH batteries after fast charging is completed.
The IC will also resume charging if the battery selfdischarges after a full charge cycle.
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APPLICATIO S
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All LTC4010 charging operations are qualified by actual
charge time and maximum average cell voltage. Charging
may also be gated by minimum and maximum temperature limits. NiMH or NiCd fast charge termination parameters are pin selectable.
Integrated or Standalone Battery Charger
Portable Instruments or Consumer Products
Battery-Powered Diagnostics and Control
Back-Up Battery Management
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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TYPICAL APPLICATIO
2A NiMH Battery Charger
3k
10µF
R
TO
SYSTEM
LOAD
LTC4010
TIMER
49.9k
VCC
TGATE
BGATE
10µH
PGND
SENSE
GND
CHEM
0.05Ω
BAT
10k
10µF
10k
VCDIV
VCELL
33nF
1.60
42
1.55
40
1.50
38
SINGLE CELL
VOLTAGE
1.45
1.40
1.35
CHARGE
CURRRENT
1.30
2-CELL
NiMH PACK
WITH 10k NTC
INTVDD VTEMP
36
BATTERY
TEMPERATURE
34
2A
32
1A
TOP OFF
30
1.25
0
20
60
40
TIME (MINUTES)
80
BATTERY TEMPERATURE (°C)
FAULT
CHRG
READY
0.1µF
2A NiMH Charge Cycle at 1C
SINGLE CELL VOLTAGE (V)
FROM
ADAPTER
5.5V TO 34V
28
100
4010 TA01b
68nF
4010 TA01a
4010fa
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LTC4010
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ABSOLUTE MAXIMUM RATINGS
PACKAGE/ORDER INFORMATION
(Note 1)
VCC (Input Supply) to GND ....................... –0.3V to 36V
FAULT, CHRG, VCELL, VCDIV, SENSE,
BAT or READY to GND ................... –0.3V to VCC + 0.3V
SENSE to BAT ...................................................... ±0.3V
CHEM, VTEMP or TIMER to GND .............. –0.3V to 3.5V
PGND to GND ...................................................... ±0.3V
Operating Ambient Temperature Range
(Note 2) ....................................................... 0°C to 85°C
Operating Junction Temperature (Note 3) ........... 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
TOP VIEW
FAULT
1
16 READY
CHRG
2
15 VCC
CHEM
3
14 TGATE
GND
4
VTEMP
5
12 BGATE
VCELL
6
11 INTVDD
VCDIV
7
10 BAT
TIMER
8
9
LTC4010CFE
13 PGND
17
FE PART
MARKING
SENSE
4010CFE
FE PACKAGE
16-LEAD PLASTIC TSSOP
TJMAX = 125°C, θJA = 38°C/W
EXPOSED PAD (PIN 17) IS GND. MUST BE SOLDERED TO
PCB TO OBTAIN SPECIFIED THERMAL RESISTANCE
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
(Note 4) The ● indicates specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 12V, BAT = 4.8V, GND = PGND = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
34
V
5
10
µA
3
5
mA
5
9
mA
4.2
4.45
VCC Supply
●
VCC
Input Voltage Range
ISHDN
Shutdown Quiescent Current (Note 8)
VCC = BAT = 4.8V
4.5
IQ
Quiescent Current
Waiting to Charge (Pause)
●
ICC
Operating Current
Fast Charge State, No Gate Load
●
VUVLO
Undervoltage Threshold Voltage
VCC Increasing
●
VUV(HYST)
Undervoltage Hysteresis Voltage
VSHDNI
Shutdown Threshold Voltage
VCC – BAT, VCC Increasing
●
45
65
90
mV
VSHDND
Shutdown Threshold Voltage
VCC – BAT, VCC Decreasing
●
15
25
45
mV
VCE
Charge Enable Threshold Voltage
VCC – BAT, VCC Increasing
●
400
510
600
mV
VDD
Output Voltage
No Load
●
4.5
5
5.5
V
IDD
Short-Circuit Current (Note 5)
INTVDD = 0V
●
–100
–50
–10
mA
INTVDD(MIN)
Output Voltage
VCC = 4.5V, IDD = –10mA
●
3.85
3.85
170
V
mV
INTVDD Regulator
V
PWM Current Source
VFS
BAT – SENSE Full-Scale Regulation
Voltage (Fast Charge)
0.3V < BAT < VCC – 0.3V (Note 8)
BAT = 4.8V
●
95
95
100
100
105
105
mV
mV
VPC
BAT – SENSE Precharge Regulation
Voltage
0.3V < BAT < VCC – 0.3V (Note 8)
BAT = 4.8V
●
16
16
20
20
24
24
mV
mV
VTC
BAT – SENSE Top-Off Charge
Regulation Voltage
0.3V < BAT < VCC – 0.3V (Note 8)
BAT = 4.8V
●
6.5
6.5
10
10
13.5
13.5
mV
mV
4010fa
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LTC4010
ELECTRICAL CHARACTERISTICS
The ● indicates specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 12V, BAT = 4.8V, GND = PGND = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
∆VLI
BAT – SENSE Line Regulation
5.5V < VCC < 25V, Fast Charge
IBAT
BAT Input Bias Current
0.3V < BAT < VCC – 0.1V
ISENSE
SENSE Input Bias Current
SENSE = BAT
IOFF
Input Bias Current, (VCELL = 0V)
SENSE
BAT
fTYP
MIN
TYP
MAX
±0.3
–2
UNITS
mV
2
mA
50
150
µA
●
●
–1
0
0
2
1
6
µA
µA
Typical Switching Frequency
●
460
550
615
kHz
fMIN
Minimum Switching Frequency
●
DCMAX
Maximum Duty Cycle
VOL(TG)
TGATE Output Voltage Low
(VCC – TGATE) (Note 6)
VCC > 9V, No Load
VCC < 7.5V, No Load
●
5
● VCC – 0.5
VOH(TG)
TGATE Output Voltage High
VCC – TGATE, No Load
●
tR(TG)
TGATE Rise Time
tF(TG)
TGATE Fall Time
VOL(BG)
BGATE Output Voltage Low
No Load
●
VOH(BG)
BGATE Output Voltage High
No Load
●
tR(BG)
BGATE Rise Time
CLOAD = 1.6nF, 10% to 90%
30
65
ns
tF(BG)
BGATE Fall Time
CLOAD = 1.6nF, 10% to 90%
15
65
ns
Analog Channel Leakage
0V < VCELL < 2V
20
30
98
99
kHz
%
5.6
VCC
8.75
0
50
mV
CLOAD = 3nF, 10% to 90%
35
100
ns
CLOAD = 3nF, 10% to 90%
45
100
ns
0
50
mV
INTVDD
– 0.075
INTVDD
V
V
V
ADC Inputs
ILEAK
±100
nA
Charger Thresholds
VBP
Battery Present Threshold Voltage
●
320
350
370
VBOV
Battery Overvoltage
●
1.85
1.95
2.05
V
VMFC
Minimum Fast Charge Voltage
●
850
900
950
mV
VFCBF
Fast Charge Battery Fault Voltage
●
1.17
1.22
1.27
V
∆VTERM
–∆V Termination
CHEM OPEN (NiCd)
CHEM = 0V (NiMH)
●
●
16
6
20
10
25
14
VAR
Automatic Recharge Voltage
VCELL Decreasing
●
1.275
1.325
1.375
∆TTERM
∆T Termination (Note 7)
CHEM = 3.3V (NiCd)
CHEM = 0V (NiMH)
●
●
1.3
0.5
2
1
2.7
1.5
TMIN
Minimum Charging Temperature
(Note 7)
VTEMP Increasing
●
0
5
9
°C
TMAXI
Maximum Charge Initiation
Temperature (Note 7)
VTEMP Decreasing, Not Charging
●
41.5
45
47
°C
TMAXC
Maximum Charging Temperature
(Note 7)
VTEMP Decreasing, Charging
●
57
60
63
°C
VTEMP(D)
VTEMP Disable Threshold Voltage
●
2.8
3.3
V
VTEMP(P)
Pause Threshold Voltage
●
130
280
mV
●
–10
10
%
●
–20
20
%
mV
mV
mV
V
°C/min
°C/min
Charger Timing
∆tTIMER
Internal Time Base Error
∆tMAX
Programmable Timer Error
RTIMER = 49.9k
4010fa
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LTC4010
ELECTRICAL CHARACTERISTICS
The ● indicates specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 12V, BAT = 4.8V, GND = PGND = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
435
300
700
600
mV
mV
10
µA
Status and Chemistry Select
VOL
Output Voltage Low (ILOAD = 10mA)
VCDIV
All Other Status Outputs
●
●
ILKG
Output Leakage Current
All Status Outputs Inactive, VOUT = VCC
●
–10
IIH(VCDIV)
Input Current High
VCDIV = VBAT (Shutdown)
●
–1
VIL
Input Voltage Low
CHEM (NiMH)
●
VIH
Input Voltage High
CHEM (NiCd)
●
2.85
IIL
Input Current Low
CHEM = GND
●
IIH
Input Current High
CHEM = 3.3V
●
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 LTC4010E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the 0°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Operating junction temperature TJ (in °C) is calculated from the
ambient temperature TA and the total continuous package power
dissipation PD (in watts) by the formula:
TJ = TA + θJA • PD
Refer to the Applications Information section for details. This IC includes
overtemperature protection that is intended to protect the device during
momentary overload conditions. Junction temperature will exceed 125°C
1
µA
900
mV
–20
–5
µA
–20
20
µA
V
when overtemperature protection is active. Continuous operation above
the specified maximum operating junction temperature may result in
device degradation or failure.
Note 4: All current into device pins are positive. All current out of device
pins are negative. All voltages are referenced to GND, unless otherwise
specified.
Note 5: Output current may be limited by internal power dissipation. Refer
to the Applications Information section for details.
Note 6: Either TGATE VOH may apply for 7.5V < VCC < 9V.
Note 7: These limits apply specifically to the thermistor network shown in
Figure 5 in the Applications Information section with a β of 3750 and are
guaranteed by specific VTEMP voltage measurements during test.
Note 8: These limits are guaranteed by correlation to wafer level
measurements.
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TYPICAL PERFOR A CE CHARACTERISTICS
NiCd Charge Cycle at 2C
NiCd Charge Cycle at 1C
36
1.65
1.45
28
BATTERY
TEMPERATURE
1.40
26
1A
1.35
0
20
40
60
1.65
BATTERY
TEMPERATURE
1.50
1.45
35
3A
30
2A
25
1A
20
CHARGE CURRENT
22
80
1.35
4010 G01
40
1.55
1.40
TIME (MINUTES)
45
1.60
24
CHARGE CURRENT
1.30
SINGLE CELL VOLTAGE (V)
SINGLE CELL VOLTAGE (V)
30
1.50
50
SINGLE CELL
VOLTAGE
BATTERY TEMPERATURE (°C)
32
SINGLE CELL
VOLTAGE
BATTERY TEMPERATURE (°C)
1.55
4 SERIES NiCd 1300mAhr
SC CELLS CHARGED AT 2C
1.70
34
1.60
55
1.75
15
0
10
20
30
TIME (MINUTES)
40
4010 G02
4010fa
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LTC4010
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TYPICAL PERFOR A CE CHARACTERISTICS
Battery Present Threshold Voltage
(per Cell)
NiMH Charge Cycle at 0.5C
40
35
30
BATTERY
TEMPERATURE
1A
1.40
25
CHARGE CURRENT
1.45
350
340
890
860
15
20 40 60 80 100 120 140 160 180 200
TIME (MINUTES)
0
900
870
TOP OFF
1.30
910
880
330
20
0.5A
930
920
VOLTAGE (mV)
1.50
360
BATTERY TEMPEATURE (°C)
SINGLE CELL
VOLTAGE
1.45
950
940
1.55
SINGLE CELL VOLTAGE (V)
370
45
4 SERIES NiMH 2100mAhr
AA CELLS CHARGED AT 0.5C
VOLTAGE (mV)
1.60
Minimum Fast Charge Threshold
Voltage (per Cell)
320
–50
–30
30
–10 10
50
TEMPERATURE (°C)
4010 G03
850
–50
90
70
–30
30
–10 10
50
TEMPERATURE (°C)
4010 G04
Automatic Recharge Threshold
Voltage (per Cell)
4010 G05
–∆V Termination Voltage
(per Cell)
Battery Overvoltage Threshold
Voltage (per Cell)
2.05
1.375
90
70
0
2.03
2.01
1.355
–5
1.335
1.315
VOLTAGE (mV)
VOLTAGE (V)
VOLTAGE (V)
1.99
1.97
1.95
1.93
–10
NiMH
–15
1.91
1.89
1.295
–20
NiCd
1.87
1.275
–50
–30
30
–10 10
50
TEMPERATURE (°C)
70
1.85
–50
90
–30
30
–10 10
50
TEMPERATURE (°C)
30
–10 10
50
TEMPERATURE (°C)
90
70
4010 G08
Charge Current Accuracy
Programmable Timer Accuracy
PWM Switching Frequency
5
1000
RTIMER = 49.9k
BAT = 4.8V
15
3
5
0
–5
–10
TOP-OFF CHARGE
FREQUENCY (kHz)
10
CURRENT ERROR(%)
TIMING ERROR (%, ±30s)
–30
4010 G07
4010 G06
20
–25
–50
90
70
1
FAST CHARGE
–1
PRECHARGE
100
MINIMUM (LOW DROPOUT)
–3
–15
–20
–50
–30
–10
30
50
10
TEMPERATURE (°C)
70
90
4010 G09
–5
–50
–30
–10 10
30
50
TEMPERATURE (°C)
70
90
4010 G10
VCC = 12V
10
–50 –30 –10 10
30
50
TEMPERATURE (°C)
70
90
4010 G11
4010fa
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LTC4010
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TYPICAL PERFOR A CE CHARACTERISTICS
Charger Efficiency
Charger Efficiency
90
Charger Soft-Start
100
DCIN = 20V
IOUT = 2A
10
VOLTAGE (V)
DCIN = 5.5V
IOUT = 2A
85
EFFICIENCY (%)
80
75
SWITCHING
5
TGATE
5
BGATE
0
80
2
FAST CHARGE CURRENT
1
70
70
0
PRECHARGE
CURRENT
60
65
1
1.5
3
2.5
2
3.5
BATTERY VOLTAGE (V)
4.5
4
0
2
4
4010 G12
Fast Charge Current Output
Regulation
3
BAT = 4.8V
VCC = 20V
25°C
–1
0°C
–2
8
1
CURRENT (µA)
CURRENT ERROR (%)
CURRENT ERROR (%)
50°C
0
–3
Shutdown Quiescent Current
10
2
2
1
50°C
0
25°C
–1
10
14
18
VCC (V)
22
26
4
2
0
–50 –30
–3
30
6
0°C
–2
6
0
4
12
8
BATTERY VOLTAGE (V)
4010 G15
16
6
5
Shutdown Threshold Voltage
(VCC – BAT)
4.45
100
4.35
80
VOLTAGE (mV)
VOLTAGE (V)
CURRENT (µA)
4
BAT
4.25
4.15
VCC INCREASING
60
40
1
0
–1
–50
–30
–10 10
30
50
TEMPERATURE (°C)
VCC DECREASING
4.05
SENSE
70
90
4010 G18
3.95
–50
90
70
4010 G17
Undervoltage Lockout Threshold
Voltage
2
30
–10 10
50
TEMPERATURE (°C)
4010 G16
PWM Input Bias (OFF)
3
4010 G14
4010 G13
Fast Charge Current Line
Regulation
3
200µs/DIV
6 8 10 12 14 16 18 20
BATTERY VOLTAGE (V)
AMPS (A)
EFFICIENCY (%)
90
20
–30
30
–10 10
50
TEMPERATURE (°C)
70
90
4010 G19
0
–50
–30
30
–10 10
50
TEMPERATURE (°C)
70
90
4010 G20
4010fa
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LTC4010
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TYPICAL PERFOR A CE CHARACTERISTICS
Charge Enable Threshold
Voltage (VCC – BAT)
Thermistor Disable Threshold
Voltage
Pause Threshold Voltage
3.3
600
270
250
3.2
500
VOLTAGE (mV)
230
VOLTAGE (V)
VOLTAGE (mV)
550
3.1
3.0
210
190
170
450
2.9
150
400
–50
50
–10 10
30
TEMPERATURE (°C)
–30
70
90
2.8
–50
–30
30
–10 10
50
TEMPERATURE (°C)
4010 G21
30
50
–10 10
TEMPERATURE (°C)
–30
70
90
4010 G23
INTVDD Short-Circuit Current
–35
CURRENT (mA)
5.3
VOLTAGE (V)
130
–50
–30
NO LOAD
5.1
4.9
4.7
4.5
–50
90
4010 G22
INTVDD Voltage
5.5
70
–40
–45
–50
–55
–30
30
–10 10
50
TEMPERATURE (°C)
70
90
4010 G24
–60
–50 –30
30
50
–10 10
TEMPERATURE (°C)
70
90
4010 G25
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PI FU CTIO S
FAULT (Pin 1): Active-Low Fault Indicator Output. The
LTC4010 indicates various battery and internal fault conditions by connecting this pin to GND. Refer to the Operation and Applications Information sections for further
details. This output is capable of driving an LED and should
be left floating if not used. FAULT is an open-drain output
to GND with an operating voltage range of GND to VCC.
CHRG (Pin 2): Active-Low Charge Indicator Output. The
LTC4010 indicates it is providing charge to the battery by
connecting this pin to GND. Refer to the Operation and
Applications Information sections for further details. This
output is capable of driving an LED and should be left
floating if not used. CHRG is an open-drain output to GND
with an operating voltage range of GND to VCC.
CHEM (Pin 3): Battery Chemistry Selection Input. This pin
should be wired to GND to select NiMH fast charge
termination parameters. If a voltage greater than 2.85V is
applied to this pin, or it is left floating, NiCd parameters are
used. Refer to the Applications Information section for
further details. Operating voltage range is GND to 3.3V.
GND (Pin 4): Ground. This pin provides a single-point
ground for internal references and other critical analog
circuits.
4010fa
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LTC4010
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PI FU CTIO S
VTEMP (Pin 5): Battery Temperature Input. An external 10k
NTC thermistor may be connected between VTEMP and GND
to provide temperature-based charge qualification and
additional fast charge termination control. Charging may
also be paused by connecting the VTEMP pin to GND. Refer
to the Operation and Applications Information sections for
complete details on external thermistor networks and
charge control. If this pin is not used it should be wired to
INTVDD through 56k. Operating voltage range is GND to
3.3V.
VCELL (Pin 6): Average Single-Cell Voltage Input. An
external voltage divider between BAT and VCDIV is attached
to this pin to monitor the average single-cell voltage of the
battery pack. The LTC4010 uses this information to protect against catastrophic battery overvoltage and to control the charging state. Refer to the Applications Information
section for further details on the external divider network.
Operating voltage range is GND to BAT.
VCDIV (Pin 7): Average Cell Voltage Resistor Divider Termination. The LTC4010 connects this pin to GND provided the
charger is not in shutdown. VCDIV is an open-drain output
to GND with an operating voltage range of GND to BAT.
TIMER (Pin 8): Charge Timer Input. A resistor connected
between TIMER and GND programs charge cycle timing
limits. Refer to the Applications Information section for
complete details. Operating voltage range is GND to 1V.
SENSE (Pin 9): Charge Current Sense Input. An external
resistor between this input and BAT is used to program
charge current. Refer to the Applications Information
section for complete details on programming charge
current. Operating voltage ranges from (BAT – 50mV) to
(BAT + 200mV).
BAT (Pin 10): Battery Pack Connection. The LTC4010 uses
the voltage on this pin to control current sourced from VCC
to the battery during charging. Allowable operating voltage range is GND to VCC.
INTVDD (Pin 11): Internal 5V Regulator Output. This pin
provides a means of bypassing the internal 5V regulator
used to power the BGATE output driver. Typically, power
should not be drawn from this pin by the application circuit. Refer to the Application Information section for additional details.
BGATE (Pin 12): External Synchronous N-channel MOSFET Gate Control Output. This output provides gate drive
to an optional external NMOS power transistor switch
used for synchronous rectification to increase efficiency in
the step-down DC/DC converter. Operating voltage is GND
to INTVDD. BGATE should be left floating if not used.
PGND (Pin 13): Power Ground. This pin provides a return
for switching currents generated by internal LTC4010
circuits. Externally, PGND and GND should be wired
together using a very low impedance connection. Refer to
PCB Layout Considerations in the Applications Information section for additional grounding details.
TGATE (Pin 14): External P-channel MOSFET Gate Control
Output. This output provides gate drive to an external PMOS
power transistor switch used in the DC/DC converter. Operating voltage range varies as a function of VCC. Refer to
the Electrical Characteristics table for specific voltages.
VCC (Pin 15): Power Input. External diodes normally connect either the DC input power supply or the battery to this
pin. Refer to the Applications Information section for further details. Suggested applied voltage range is GND to 34V.
READY (Pin 16): Active-Low Ready-to-Charge Output.
The LTC4010 connects this pin to GND if proper operating
voltages for charging are present. Refer to the Operation
section for complete details on charge qualification. This
output is capable of driving an LED and should be left
floating if not used. READY is an open-drain output to GND
with an operating voltage range of GND to VCC.
Exposed Pad (Pin 17): This pin provides enhanced thermal
properties for the TSSOP. It must be soldered to the PCB
copper ground to obtain optimum thermal performance.
4010fa
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LTC4010
W
BLOCK DIAGRA
1
2
FAULT
READY
VCC
UVLO AND
SHUTDOWN
4 GND
3
6
15
CHEM
TGATE
THERMISTOR
INTERFACE
5
16
CHRG
VTEMP
VCELL
A/D
CONVERTER
BGATE
CHARGER
STATE
CONTROL
LOGIC
PGND
PWM
SENSE
BAT
14
12
13
9
10
BATTERY
DETECTOR
INTVDD
VOLTAGE
REGULATOR
8
7
TIMER
11
CHARGE
TIMER
INTERNAL
VOLTAGE
REGULATOR
VCDIV
4010 BD
VOLTAGE
REFERENCE
4010fa
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LTC4010
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OPERATIO
(Refer to Figure 1)
SHUTDOWN
NO DC ADAPTER
DC ADAPTER PRESENT
NO BATTERY
OR
VCC < 4.25V
CHARGE
QUALIFICATION
VCELL > 350mV, ADEQUATE VCC,
CHARGER ENABLED AND
TEMPERATURE OK (OPTIONAL)
CHECK
BATTERY
VCELL < 900mV
V CELL
VCELL > 900mV
NiMH
∆T/∆t
TOP-OFF
CHARGE**
(C/10)
FAST CHARGE**
(1C)
VCELL < 900mV
VCELL < 1.22V AT tMAX*/12
OR TIME = tMAX
NiCd OR
NiMH – ∆V
tMAX/3
PRECHARGE**
(C/5 FOR
tMAX/12)
0mV
> 90
VCELL < 1.325V
AUTOMATIC
RECHARGE
FAULT
VCELL > 1.95V
OR PWM FAULTS
4010 F01
*tMAX IS PROGRAMMED MAXIMUM FAST CHARGE DURATION
**OPTIONAL TEMPERATURE LIMITS APPLY
Figure 1. LTC4010 State Diagram
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OPERATIO
(Refer to Figure 1)
Shutdown State
The LTC4010 remains in micropower shutdown until VCC
(Pin 15) is driven above BAT (Pin 10). In shutdown all
status and PWM outputs and internally generated supply
voltages are inactive. Current consumption from VCC and
BAT is reduced to a very low level.
Charge Qualification State
Once VCC is greater than BAT, the LTC4010 exits micropower shutdown, enables its own internal supplies and
switches VCDIV to GND to allow measurement of the
average single-cell voltage. The IC also verifies that VCC is
at or above 4.2V, VCC is 510mV above BAT and VCELL is
between 350mV and 1.95V. If VCELL is above 1.95V, the
fault state is entered, which is described in more detail
below. Once adequate voltage conditions exist for charging, READY is asserted.
If the voltage between VTEMP and GND is below 200mV,
the LTC4010 is paused. If VTEMP is above 200mV but
below 2.85V, the LTC4010 verifies that the sensed
temperature is between 5°C and 45°C. If these temperature limits are not met or if its own die temperature is too
high, the LTC4010 will indicate a fault and not allow
charging to begin. If VTEMP is greater than 2.85V, battery
temperature related charge qualification, monitoring and
termination are disabled.
Once charging is fully qualified, precharge begins (unless
the LTC4010 is paused). In that case, the VTEMP pin is
monitored for further control. The charge status indicators
and PWM outputs remain inactive until charging begins.
Charge Monitoring
The LTC4010 continues to monitor important voltage and
temperature parameters during all charging states. If VCC
drops to the BAT voltage or lower, charging stops and the
shutdown state is entered. If VCC drops below 4.25V or
VCELL drops below 350mV, charging stops and the LTC4010
returns to the charge qualification state. If VCELL exceeds
1.95V, charging stops and the IC enters the fault state. If
an external thermistor indicates sensed temperature is
beyond a range of 5°C to 60°C, or the internal die temperature exceeds a resonable value, charging is suspended,
the charge timer is paused and the LTC4010 indicates a
fault condition. Normal charging resumes from the previous state when the sensed temperature returns to a satisfactory range. In addition, other battery faults are detected
during specific charging states as described below.
Precharge State
If the initial voltage on VCELL is below 900mV, the LTC4010
enters the precharge state and enables the PWM current
source to trickle charge using one-fifth the programmed
charge current. The CHRG status output is active during
precharge. The precharge state duration is limited to
tMAX/12 minutes, where tMAX is the maximum fast charge
period programmed with the TIMER pin. If sufficient VCELL
voltage cannot be developed in this length of time, the fault
state is entered, otherwise fast charge begins.
Fast Charge State
If adequate average single-cell voltage exists, the LTC4010
enters the fast charge state and begins charging at the
programmed current set by the external current sense
resistor connected between the SENSE and BAT pins. The
CHRG status output is active during fast charge. If VCELL
is initially above 1.325V, voltage-based termination processing begins immediately. Otherwise –∆V termination
is disabled for a stabilization period of tMAX/12. In that
case, the LTC4010 makes another fault check at tMAX/12,
requiring the average cell voltage to be above 1.22V. This
ensures the battery pack is accepting a fast charge. If
VCELL is not above this voltage threshold, the fault state is
entered. Fast charge state duration is limited to tMAX and
the fault state is entered if this limit is exceeded.
4010fa
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LTC4010
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OPERATIO
(Refer to Figure 1)
Charge Termination
Fault State
Fast charge termination parameters are dependent upon
the battery chemistry selected with the CHEM pin. Voltage-based termination (–∆V) is always active after the
initial voltage stabilization period. If an external thermistor
network is present, chemistry-specific limits for ∆T/∆t
(rate of temperature rise) are also used in the termination
algorithm. Temperature-based termination, if enabled,
becomes active as soon as the fast charge state is entered.
As discussed previously, the LTC4010 enters the fault
state based on detection of invalid battery voltages during
various charging phases. The IC also monitors the regulation of the PWM control loop and will enter the fault state
if this is not within acceptable limits. Once in the fault state,
the battery must be removed or DC input power must be
cycled in order to initiate further charging. In the fault
state, the FAULT output is active, the READY output is
inactive, charging stops and the charge indicator output is
inactive. The VCDIV output remains connected to GND to
allow detection of battery removal.
Top-Off Charge State
If NiMH fast charge termination occurs because the ∆T/∆t
limit is exceeded after an initial period of tMAX/12 has expired, the LTC4010 enters the top-off charge state. Top-off
charge is implemented by sourcing one-tenth the programmed charge current for tMAX/3 minutes to ensure that
100% charge has been delivered to the battery. The CHRG
status output is active during the top-off state. If NiCd cells
have been selected with the CHEM pin, the LTC4010 never
enters the top-off state.
Automatic Recharge State
Once charging is complete, the automatic recharge state
is entered to address the self-discharge characteristics of
nickel chemistry cells. The charge status output is inactive
during automatic recharge, but VCDIV remains switched to
GND to monitor the average cell voltage. If the VCELL
voltage drops below 1.325V without falling below 350mV,
the charge timer is reset and a new fast charge cycle is
initiated.
The internal termination algorithms of the LTC4010 are
adjusted when a fast charge cycle is initiated from automatic recharge, because the battery should be almost fully
charged. Voltage-based termination is enabled immediately and the NiMH ∆T/∆t limit is fixed at a battery
temperature rise of 1°C/minute.
Note that the LTC4010 also uses the FAULT output to
indicate that charging is suspended due to invalid battery
or internal die temperatures. However, the IC does not
enter the fault state in these cases and normal operation
will resume when all temperatures return to acceptable
levels. Refer to the Status Outputs section for more detail.
Insertion and Removal of Batteries
The LTC4010 automatically senses the insertion or removal of a battery by monitoring the VCELL pin voltage.
Should this voltage fall below 350mV, the IC considers the
battery to be absent. Removing and then inserting a
battery causes the LTC4010 to initiate a completely new
charge cycle beginning with charge qualification.
External Pause Control
After charging is initiated, the VTEMP pin may be used to
pause operation at any time. When the voltage between
VTEMP and GND drops below 200mV, the charge timer
pauses, fast charge termination algorithms are inhibited
and the PWM outputs are disabled. The status and VCDIV
outputs all remain active. Normal function is fully restored
from the previous state when pause ends.
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LTC4010
U
OPERATIO
(Refer to Figure 1)
Status Outputs
PWM Current Source Controller
The LTC4010 open-drain status outputs provide valuable
information about the IC’s operating state and can be
used for a variety of purposes in applications. Table 1
summarizes the state of the three status outputs and the
VCDIV pin as a function of LTC4010 operation. The status
outputs can directly drive current-limited LEDs terminated to the DC input. The VCDIV column in Table 1 is
strictly informational. VCDIV should only be used to terminate the VCELL resistor divider, as previously discussed.
An integral part of the LTC4010 is the PWM current source
controller. The charger uses a synchronous step-down
architecture to produce high efficiency and limited thermal
dissipation. The nominal operating frequency of 550kHz
allows use of a smaller external inductor. The TGATE and
BGATE outputs have internally clamped voltage swings.
They source peak currents tailored to smaller surfacemount power FETs likely to appear in applications providing an average charge current of 3A or less. During the
various charging states, the LTC4010 uses the PWM
controller to regulate an average voltage between SENSE
and BAT that ranges from 10mV to 100mV.
Table 1. LTC4010 Status Pins
READY
FAULT
CHRG
VCDIV
CHARGER STATE
Off
Off
Off
Off
Off
On
Off
Off
On
Ready to Charge
(VTEMP Held Low)
or Automatic Recharge
On
Off
On
On
Precharge, Fast or Top Off
Charge (May be Paused)
On
On
On or Off
On
Temperature Limits
Exceeded
Off
On
Off
On
Fault State (Latched)
A conceptual diagram of the LTC4010 PWM control loop
is shown in Figure 2.
The voltage across the external current programming
resistor RSENSE is averaged by integrating error amplifier
EA. An internal programming current is also pulled from
input resistor R1. The IPROG • R1 product establishes the
desired average voltage drop across RSENSE, and hence,
the average current through RSENSE. The ITH output of the
LTC4010
VCC
14
12
9
TGATE
Q
BGATE
SENSE
R3
BAT
R4
RSENSE
10
PWM CLOCK
S
R
R1
CC
–
ITH
R2
+
EA
IPROG
4010 F02
Figure 2. LTC4010 PWM Control Loop
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OPERATIO
(Refer to Figure 1)
error amplifier is a scaled control current for the input of
the PWM comparator CC. The ITH • R3 product sets a peak
current threshold for CC such that the desired average
current through RSENSE is maintained. The current comparator output does this by switching the state of the SR
latch at the appropriate time.
At the beginning of each oscillator cycle, the PWM clock
sets the SR latch and the external P-channel MOSFET is
switched on (N-channel MOSFET switched off) to refresh
the current carried by the external inductor. The inductor
current and voltage drop across RSENSE begin to rise
linearly. During normal operation, the PFET is turned off
(NFET on) during the cycle by CC when the voltage
difference across RSENSE reaches the peak value set by
the output of EA. The inductor current then ramps down
linearly until the next rising PWM clock edge. This closes
the loop and maintains the desired average charge current
in the external inductor.
Low Dropout Charging
After charging is initiated, the LTC4010 does not require
that VCC remain at least 500mV above BAT because
situations exist where low dropout charging might occur.
In one instance, parasitic series resistance may limit PWM
headroom (between VCC and BAT) as 100% charge is
reached. A second case can arise when the DC adapter
selected by the end user is not capable of delivering the
current programmed by RSENSE, causing the output voltage of the adapter to collapse. While in low dropout, the
LTC4010 PWM runs near 100% duty cycle with a frequency that may not be constant and can be less than
550kHz. The charge current will drop below the programmed value to avoid generating audible noise, so the
actual charge delivered to the battery may depend primarily on the LTC4010 charge timer.
Internal Die Temperature
The LTC4010 provides internal overtemperature detection to protect against electrical overstress, primarily at
the FET driver outputs. If the die temperature rises above
this thermal limit, the LTC4010 stops switching and
indicates a fault as previously discussed.
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External DC Source
Battery Chemistry Selection
The external DC power source should be connected to the
charging system and the VCC pin through a power diode
acting as an input rectifier. This prevents catastrophic
system damage in the event of an input short to ground or
reverse-voltage polarity at the DC input. The LTC4010
automatically senses when this input drives the VCC pin
above BAT. The open-circuit voltage of the DC source
should be between 5.5V and 34V, depending on the
number of cells being charged. In order to avoid low
dropout operation, ensure 100% capacity at charge termination, and allow reliable detection of battery insertion,
removal or overvoltage, the following equation can be
used to determine the minimum full-load voltage that
should be produced at VCC when the external DC power
source is connected.
The desired battery chemistry is selected by programming
the CHEM pin to the proper voltage. If it is wired to GND,
a set of parameters specific to charging NiMH cells is
selected. When CHEM is left floating, charging is optimized for NiCd cells. The various charging parameters are
detailed in Table 2.
VCC(MIN) = (n • 2V) + 0.3V
where n is the number of series cells in the battery pack.
The LTC4010 will properly charge over a wide range of VCC
and BAT voltage combinations. Operating the LTC4010 in
low dropout or with VCC much greater than BAT will force
the PWM frequency to be much less than 550kHz. The
LTC4010 disables charging and sets a fault if a large VCC
to BAT differential would cause generation of audible noise.
Load Control
Proper load current control is an important consideration
when fast charging nickel cells. This control ensures that
the system load remains powered at all times, but that
normal system operation and associated load transients
do not adversely affect fast charge termination. The input
protecton detailed in the previous paragraph is an integral
part of the necessary load control.
The battery should also be connected to the raw system
supply by some rectifying means, thus forming a switch that
selects the battery for system power only if an external DC
source is not present.
Programming Charge Current
Charge current is programmed using the following
equation:
RSENSE =
100mV
IPROG
RSENSE is an external resistor connected between the
SENSE and BAT pins. A 1% resistor with a low temperature
coefficient and sufficient power dissipation capability to
avoid self-heating effects is recommended.
Programming Maximum Charge Times
Connecting the appropriate resistor between the TIMER
pin and GND programs the maximum duration of various
charging states. To some degree, the value should reflect
how closely the programmed charge current matches the
1C rate of targeted battery packs. The maximum fast
charge period is determined by the following equation:
RTIMER =
tMAX (Hours)
(Ω )
30 • 10 –6
Some typical timing values are detailed in Table 3. RTIMER
should not be less than 15k. The actual time limits used by
the LTC4010 have a resolution of approximately ±30
seconds in addition to the tolerances given the Electrical
Characteristics table. The maximum time period is approximately 4.3 hours.
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Table 2. LTC4010 Charging Parameters
STATE
CHEM
PIN
BAT
CHEMISTRY TIMER
PC
FC
TMIN
TMAX
ICHRG
TERMINATION CONDITION
Both
tMAX/12
5°C
45°C
IPROG/5
Open
NiCd
tMAX
5°C
60°C
IPROG
Timer Expires
–20mV per Cell or 2°C/Minute
GND
NiMH
tMAX
5°C
60°C
IPROG
1.5°C/Minute for First tMAX/12 Minutes if Initial
VCELL < 1.325V
–10mV per Cell or 1°C/Minute After tMAX/12 Minutes
or if Initial VCELL > 1.325V
TOC
GND
NiMH
AR
tMAX/3
Both
5°C
60°C
IPROG/10
Timer Expires
5°C
45°C
0
VCELL < 1.325V
PC: Precharge
FC: Fast Charge (Initial –∆V Termination Hold Off of tMAX/12 Minutes May Apply)
TOC: Top-Off Charge (Only for NiMH ∆T/∆t FC Termination After Initial tMAX/12 Period)
AR: Automatic Recharge (Temperature Limits Apply to State Termination Only)
Table 3. LTC4010 Time Limit Programming Examples
TYPICAL FAST
CHARGE RATE
PRECHARGE LIMIT
(MINUTES)
FAST CHARGE
VOLTAGE STABILIZATION
(MINUTES)
FAST CHARGE LIMIT
(HOURS)
24.9k
2C
3.8
3.8
0.75
15
33.2k
1.5C
5
5
1
20
49.9k
1C
7.5
7.5
1.5
30
66.5k
0.75C
10
10
2
40
100k
C/2
15
15
3
60
RTIMER
FOR TWO OR
MORE SERIES CELLS
Cell Voltage Network Design
An external resistor network is required to provide the
average single-cell voltage to the VCELL pin of the LTC4010.
The proper circuit for multicell packs is shown in Figure
3. The ratio of R2 to R1 should be a factor of (n – 1), where
n is the number of series cells in the battery pack. The
value of R1 should be between 1k and 100k. This range
limits the sensing error caused by VCELL leakage current
and prevents the ON resistance of the internal NFET
between VCDIV and GND from causing a significant error
in the VCELL voltage. The external resistor network is also
used to detect battery insertion and removal. The filter
formed by C1 and the parallel combination of R1 and R2
is recommended for rejecting PWM switching noise. The
value of C1 should be chosen to yield a 1st order lowpass
TOP-OFF
CHARGE
(MINUTES)
BAT 10
LTC4010
VCELL
VCDIV
+
R2
6
R1
C1
7
R2 = R1(n – 1)
GND
4
4010 F03
Figure 3. Multiple Cell Voltage Divider
frequency of less than 500Hz. In the case of a single cell,
the external application circuit shown in Figure 4 is
recommended to provide the necessary noise filtering
and missing battery detection.
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10
7
6
BAT
1 CELL
VCDIV
10k
10k
VCELL
33nF
4010 F04
Figure 4. Single-Cell Monitor Network
External Thermistor
The network for proper temperature sensing using a
thermistor with a negative temperature coefficient (NTC)
is shown in Figure 5. The LTC4010 is designed to work
best with a 1% 10k NTC thermistor with a β of 3750.
However, the LTC4010 will operate satisfactorily with
other 10k NTC thermistors having slightly different nominal exponential temperature coefficients. For these thermistors, the temperature related limits given in the Electrical Characteristics table may not strictly apply. The filter
formed by C1 in Figure 5 is optional but recommended for
rejecting PWM switching noise.
VTEMP
C1
68nF
5
RT
10k NTC
4010 F05
INTVDD Regulator Output
If BGATE is left open, the INTVDD pin of the LTC4010 can
be used as an additional source of regulated voltage in the
host system any time READY is active. Switching loads on
INTVDD may reduce the accuracy of internal analog circuits used to monitor and terminate fast charging. In
addition, DC current drawn from the INTVDD pin can
greatly increase internal power dissipation at elevated VCC
voltages. A minimum ceramic bypass capacitor of 0.1µF is
recommended.
Calculating Average Power Dissipation
The user should ensure that the maximum rated IC junction temperature is not exceeded under all operating conditions. The thermal resistance of the LTC4010 package
(θJA) is 38°C/W, provided the exposed metal pad is properly soldered to the PCB. The actual thermal resistance in
the application will depend on the amount of PCB copper
to which the package is soldered. Feedthrough vias directly below the package that connect to inner copper
layers are helpful in lowering thermal resistance. The following formula may be used to estimate the maximum
average power dissipation PD (in watts) of the LTC4010
under normal operating conditions.
PD = VCC (9mA + IDD + 615k(Q TGATE + QBGATE ))
⎛V –V ⎞
– 3.85IDD + 60n ⎜ CC LED ⎟
⎝ RLED + 30 ⎠
Figure 5. External NTC Thermistor Network
Disabling Thermistor Functions
Temperature sensing is optional in LTC4010 applications.
For low cost systems where temperature sensing may not
be required, the VTEMP pin may simply be wired to INTVDD
through 8.66k to disable temperature qualification of all
charging operations. Alternatively, a 10k resistor may be
connected between VTEMP and GND. However, this practice is not recommended for NiMH cells charged well
above or below their 1C rate, because fast charge termination based solely on voltage inflection may not be adequate to protect the battery from a severe overcharge.
2
where:
IDD = Average external INTVDD load current, if any
QTGATE = Gate charge of external P-channel MOSFET
in coulombs
QBGATE = Gate charge of external N-channel MOSFET
(if used) in coulombs
VLED = Maximum external LED forward voltage
RLED = External LED current-limiting resistor used in
the application
n = Number of LEDs driven by the LTC4010
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Sample Applications
Figures 6 through 8 detail sample charger applications
of various complexities. Combined with the Typical
Application on the first page of this data sheet, these
figures demonstrate some of the proper configurations
of the LTC4010. MOSFET body diodes are shown in these
figures strictly for reference only.
Figure 6 shows a minimum application, which might be
encountered in low cost NiCd fast charge applications. The
LTC4010 uses –∆V to terminate the fast charge state, as
no external temperature information is available.
Nonsynchronous PWM switching is employed to reduce
external component cost. A single LED indicates charging
status.
A full-featured 2A LTC4010 application is shown in Figure 7. The inherent voltage ratings of the VCELL, VCDIV,
SENSE and BAT pins allow charging of one to sixteen
series nickel cells in this application, governed only by the
VCC overhead limits previously discussed. The application
includes all average cell voltage and battery temperature
sensing circuitry required for the LTC4010 to utilize its full
range of charge qualification, safety monitoring and fast
charge termination features. The VTEMP thermister network allows the LTC4010 to accurately terminate fast
FROM
ADAPTER
5.5V TO 34V
10µF
3k
R
charge under a variety of applied charge rates. Use of a
synchronous PWM topology improves efficiency and reduces excess heat generation. A green LED indicates valid
DC input voltage and installed battery, while a red LED
indicates charging. Fault conditions are indicated by a
yellow LED. The grounded CHEM pin selects the NiMH
charge termination parameter set.
P-channel MOSFET Q4 functions as a switch to connect
the battery to the system load whenever the DC input
adapter is removed. If the maximum battery voltage is less
than the maximum rated VGS of Q4, diode D1 and resistor
R1 are not required. Otherwise choose the Zener voltage
of D1 to be less than the maximum rated VGS of Q4. R1
provides a bias current of (VBAT – VZENER)/(R1 + 20k) for
D1 when the input adapter is removed. Choose R1 to make
this current, which is drawn from the battery, just large
enough to develop the desired VGS across D1.
While the LTC4010 is a complete, standalone solution,
Figure 8 shows that it can also be interfaced to a host
microprocessor. The host MCU can control the charger
directly with an open-drain I/O port connected to the
VTEMP pin, if that port is low leakage and can tolerate at
least 2V. The charger state is monitored on the three
LTC4010 status outputs. Charging of NiMH batteries is
TO
SYSTEM
LOAD
LTC4010
FAULT
CHRG
READY
TIMER
49.9k
VCC
TGATE
BGATE
10µH
PGND
SENSE
GND
0.1Ω
BAT
10k
0.1µF
VCDIV
CHEM
VCELL
INTVDD VTEMP
R2
NiCd
PACK
(1AHr)
10µF
4010 F06
33nF
8.66k
Figure 6. Minimum 1 Amp LTC4010 Application
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R1 10k
FROM
ADAPTER
5.5V TO 34V
20k
G
R
20µF
Y
D1
6V
LTC4010
FAULT
CHRG
READY
TO
SYSTEM
LOAD
VCC
TGATE
Q4
BGATE
TIMER
49.9k
10µH
PGND
SENSE
GND
CHEM
0.05Ω
BAT
10k
R2
20µF
VCDIV
VCELL
0.1µF
NiMH PACK
WITH 10k NTC
(2AHr)
INTVDD VTEMP
33nF
68nF
4010 F07
Figure 7. Full-Featured 2 Amp LTC4010 Application
FROM
ADAPTER
5.5V TO 34V
V+
10µF
LTC4010
FAULT
CHRG
READY
VCC
TGATE
BGATE
TIMER
49.9k
10µH
PGND
SENSE
GND
CHEM
0.1Ω
BAT
10k
R2
TO
SYSTEM
LOAD
10µF
VCDIV
VCELL
33nF
0.1µF
INTVDD VTEMP
68nF
PAUSE
FROM MCU
NiCd PACK
WITH 10k NTC
(2AHr)
4010 F08
Figure 8. LTC4010 with MCU Interface
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selected in this example. However, NiCd parameters could
be chosen as well.
Unlike all of the other applications discussed so far, the
battery continues to power the system during charging.
The MCU could be powered directly from the battery or
from any type of post regulator operating from the battery. In this configuration, the LTC4010 relies expressly
on the ability of the host MCU to know when load transients will be encountered. The MCU should then pause
charging (and thus –∆V processing) during those events
to avoid premature fast charge termination. If the MPU
cannot reliably perform this function, the battery should
be disconnected from the load with a rectifier or switch
during charging. Excessive battery load current variations,
such as those generated by a post-regulating PWM, can
generate sufficient voltage noise to cause the LTC4010 to
prematurely terminate a charge cycle and/or prematurely
restart a fast charge. In this case, it may be necessary to
inhibit the LTC4010 after charging is complete until external gas gauge circuitry indicates that recharging is necessary. Shutdown power is applied to the LTC4010
through the body diode of the P-channel MOSFET in this
application.
SHDN
VCC
PRECHARGE
Waveforms
Sample waveforms for a standalone application during a
typical charge cycle are shown in Figure 9. Note that these
waveforms are not to scale and do not represent the
complete range of possible activity. The figure is simply
intended to allow better conceptual understanding and to
highlight the relative behavior of certain signals generated
by the LTC4010 during a typical charge cycle.
Initially, the LTC4010 is in low power shutdown as the
system operates from a heavily discharged battery. A DC
adapter is then connected such that VCC rises above 4.25V
and is 500mV above BAT. The READY output is asserted
when the LTC4010 completes charge qualification.
When the LTC4010 determines charging should begin, it
starts a precharge cycle because VCELL is less than 900mV.
As long as the temperature remains within prescribed
limits, the LTC4010 charges (TGATE switching), applying
limited current to the battery with the PWM in order to
bring the average cell voltage to 900mV.
When the precharge state timer expires, the LTC4010 begins fast charge if VCELL is greater than 900mV. The PWM,
FAST CHARGE
TOP-OFF
VCC ≥ BAT + 500mV
AUTO
RECHARGE
SHDN
VCC < BAT + 25mV
READY
VCDIV
TGATE
VCELL
VTEMP
(PAUSE)
0.9V
200mV
CHRG
EXTERNAL
PAUSE
4010 F09
Figure 9. Charging Waveforms Example
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LTC4010
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charge timer and internal termination control are suspended if pause is asserted (VTEMP < 200mV), but all
status outputs continue to indicate charging is in progress.
The fast charge state continues until the selected voltage
or temperature termination criteria are met. Figure 9 suggests termination based on ∆T/∆t, which for NiMH would
be an increase greater than 1°C per minute.
Because NiMH charging terminated due to ∆T/∆t and the
fast charge cycle had lasted more than tMAX/12 minutes,
the LTC4010 begins a top-off charge with a current of
IPROG/10. Top-off is an internally timed charge of tMAX/3
minutes with the CHRG output continuously asserted.
Finally, the LTC4010 enters the automatic recharge state
where the CHRG output is deasserted. The PWM is disabled but VCDIV remains asserted to monitor VCELL. The
charge timer will be reset and fast charging will resume if
VCELL drops below 1.325V. The LTC4010 enters shutdown
when the DC adapter is removed, minimizing current draw
from the battery in the absence of an input power source.
While not a part of the sample waveforms of Figure 9,
temperature qualification is an ongoing part of the charging process, if an external thermistor network is detected
by the LTC4010. Should prescribed temperature limits be
exceeded during any particular charging state, charging
would be suspended until the sensed temperature returned to an acceptable range.
A second possibility is to configure an LTC4010-based
charger to accept battery packs with varying numbers of
cells. By including R2 of the average cell voltage divider
network shown in Figure 3, battery-based programming
of the number of series-stacked cells could be realized
without defeating LTC4010 detection of battery insertion
or removal. Figure 11 shows a 2-cell NiMH battery pack
that programs the correct number of series cells when it
is connected to the charger, along with indicating chemistry and providing temperature information.
Any of these battery pack charge control concepts could
be combined in a variety of ways to service custom
application needs.
TIMER
CHEM
VTEMP
8
3
5
NC
+
10k
NTC
66.5k
BATTERY
PACK
1200mAhr
NiCd CELLS
–
4010 F10
Figure 10. NiCd Battery Pack with Time Limit Control
CHEM
VTEMP
VCELL
3
5
6
10k
NTC
+
R2
BATTERY
PACK
1500mAhr
NiMH CELLS
Battery-Controlled Charging
Because of the programming arrangement of the LTC4010,
it may be possible to configure it for battery-controlled
charging. In this case, the battery pack is designed to provide customized information to an LTC4010-based charger,
allowing a single design to service a wide range of application batteries. Assume the charger is designed to provide
a maximum charge current of 800mA (RSENSE = 125mΩ).
Figure 10 shows a 4-cell NiCd battery pack for which 800mA
represents a 0.75C rate. When connected to the charger,
this pack would provide battery temperature information
and correctly configure both fast charge termination parameters and time limits for the internal NiCd cells.
–
4010 F11
Figure 11. NiMH Battery Pack Indicating Number of Cells
PCB Layout Considerations
To prevent magnetic and electrical field radiation and high
frequency resonant problems, proper layout of the components connected to the LTC4010 is essential. Refer to
Figure 12. For maximum efficiency, the switch node rise
and fall times should be minimized. The following PCB
design priority list will help ensure proper topology. Layout the PCB using this specific order.
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21
LTC4010
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APPLICATIO S I FOR ATIO
1. Input capacitors should be placed as close as possible
to switching FET supply and ground connections with
the shortest copper traces possible. The switching
FETs must be on the same layer of copper as the input
capacitors. Vias should not be used to make these
connections.
2. Place the LTC4010 close to the switching FET gate
terminals, keeping the connecting traces short to
produce clean drive signals. This rule also applies to
IC supply and ground pins that connect to the switching FET source pins. The IC can be placed on the
opposite side of the PCB from the switching FETs.
3. Place the inductor input as close as possible to the
drain of the switching FETs. Minimize the surface area
of the switch node. Make the trace width the minimum
needed to support the programmed charge current.
Use no copper fills or pours. Avoid running the connection on multiple copper layers in parallel. Minimize
capacitance from the switch node to any other trace or
plane.
6. Output capacitor ground connections must feed into
the same copper that connects to the input capacitor
ground before tying back into system ground.
7. Connection of switching ground to system ground, or
any internal ground plane should be single-point. If
the system has an internal system ground plane, a
good way to do this is to cluster vias into a single star
point to make the connection.
8. Route analog ground as a trace tied back to the
LTC4010 GND pin before connecting to any other
ground. Avoid using the system ground plane. A
useful CAD technique is to make analog ground a
separate ground net and use a 0Ω resistor to connect
analog ground to system ground.
9. A good rule of thumb for via count in a given high
current path is to use 0.5A per via. Be consistent when
applying this rule.
10. If possible, place all the parts listed above on the same
PCB layer.
4. Place the charge current sense resistor immediately
adjacent to the inductor output, and orient it such that
current sense traces to the LTC4010 are not long.
These feedback traces need to be run together as a
single pair with the smallest spacing possible on any
given layer on which they are routed. Locate any filter
component on these traces next to the LTC4010, and
not at the sense resistor location.
11. Copper fills or pours are good for all power connections except as noted above in Rule 3. Copper planes
on multiple layers can also be used in parallel. This
helps with thermal management and lowers trace
inductance, which further improves EMI performance.
5. Place output capacitors next to the sense resisitor
output and ground.
13. It is important to minimize parasitic capacitance on
the TIMER, SENSE and BAT pins. The traces connecting these pins to their respective resistors should be
as short as possible.
12. For best current programming accuracy, provide a
Kelvin connection from RSENSE to SENSE and BAT.
See Figure 13 for an example.
SWITCH NODE
L1
VBAT
VIN
CIN
HIGH
FREQUENCY
CIRCULATING
PATH
D1
COUT
DIRECTION OF CHARGING CURRENT
RSENSE
BAT
4010 F13
SWITCHING GROUND
Figure 12. High Speed Switching Path
4010 F12
SENSE
BAT
Figure 13. Kelvin Sensing of Charge Current
4010fa
22
LTC4010
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PACKAGE DESCRIPTIO
FE Package
16-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1663)
Exposed Pad Variation BC
4.90 – 5.10*
(.193 – .201)
3.58
(.141)
3.58
(.141)
16 1514 13 12 1110
6.60 ±0.10
9
2.94
(.116)
4.50 ±0.10
6.40
2.94
(.252)
(.116)
BSC
SEE NOTE 4
0.45 ±0.05
1.05 ±0.10
0.65 BSC
1 2 3 4 5 6 7 8
RECOMMENDED SOLDER PAD LAYOUT
4.30 – 4.50*
(.169 – .177)
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
MILLIMETERS
2. DIMENSIONS ARE IN
(INCHES)
3. DRAWING NOT TO SCALE
0.25
REF
1.10
(.0433)
MAX
0° – 8°
0.65
(.0256)
BSC
0.195 – 0.30
(.0077 – .0118)
TYP
0.05 – 0.15
(.002 – .006)
FE16 (BC) TSSOP 0204
4. RECOMMENDED MINIMUM PCB METAL SIZE
FOR EXPOSED PAD ATTACHMENT
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
4010fa
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
23
LTC4010
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT 1510
Constant-Voltage/Constant-Current Battery Charger
Up to 1.5A Charge Current for Li-Ion, NiCd and NiMH Batteries
LT1511
3A Constant-Voltage/Constant-Current Battery Charger
High Efficiency, Minimum External Components to Fast Charge
Lithium, NiMH and NiCd Batteries
LT1513
SEPIC Constant- or Programmable-Current/ConstantVoltage Battery Charger
Charger Input Voltage May be Higher, Equal to or Lower Than
Battery Voltage, 500kHz Switching Frequency
LTC1760
Smart Battery System Manager
Autonomous Power Management and Battery Charging for Two
Smart Batteries, SMBus Rev 1.1 Compliant
LTC1960
Dual Battery Charger/Selector with SPI
11-Bit V-DAC, 0.8% Voltage Accuracy, 10-Bit I-DAC,
5% Current Accuracy
LTC4008
High Efficiency, Programmable Voltage/Current Battery
Charger
Constant-Current/Constant-Voltage Switching Regulator, Resistor
Voltage/Current Programming, AC Adapter Current Limit and
Thermistor Sensor and Indicator Outputs
LTC4011
High Efficiency Standalone Nickel Battery Charger
Complete NiMH/NiCd Charger in a 20-Pin TSSOP Package,
PowerPathTM Control, Constant-Current Switching Regulator
LTC4060
Standalone Linear NiMH/NiCd Fast Charger
Complete NiMH/NiCd Charger in a Small Leaded or Leadless
16-Pin Package, No Sense Resistor or Blocking Diode Required
LTC4100
Smart Battery Charger Controller
Level 2 Charger Operates with or without MCU Host,
SMBus Rev. 1.1 Compliant
LTC4150
Coulomb Counter/Battery Gas Gauge
High Side Sense of Charge Quantity and Polarity in a 10-Pin MSOP
LTC4412
Low Loss PowerPath Controller
Very Low Loss Replacement for Power Supply ORing Diodes
Using Minimal External Components, VIN(MAX) = 28V
LTC4412HV
36V, Low Loss PowerPath Controller in ThinSOT
Very Low Loss Replacement for Power Supply ORing Diodes,
VIN(MAX) = 36V
LTC4413
Dual, 2.6A Ideal Diode in 3mm × 3mm DFN
2.5V ≤ VIN ≤ 5.5V, Ideal Diode ORing or Load Sharing,
Low Reverse Leakage Current
LTC4414
36V, Low Loss PowerPath Controller for Large PFETs
Higher Gate Drive for Larger QG PFETs, VIN(MAX) = 36V,
8-Pin MSOP Package
®
PowerPath is a trademark of Linear Technology Corporation.
4010fa
24 Linear Technology Corporation
LT/LWI 0606 REV A • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005
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