LTC4068-4.2/LTC4068X-4.2 - Standalone Linear Li

LTC4068-4.2/LTC4068X-4.2
Standalone Linear
Li-Ion Battery Charger with
Programmable Termination
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FEATURES
DESCRIPTIO
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The LTC®4068 is a complete constant-current/constantvoltage linear charger for single cell lithium-ion batteries.
Its DFN package and low external component count make
the LTC4068 ideally suited for portable applications. Furthermore, the LTC4068 is designed to work within USB
power specifications.
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Programmable Charge Current Up to 950mA
Complete Linear Charger in DFN Package
No MOSFET, Sense Resistor or Blocking Diode
Required
Thermal Regulation Maximizes Charge Rate
Without Risk of Overheating*
Charges Directly from a USB Port
Programmable Charge Current Termination
Preset 4.2V Charge Voltage with ±1% Accuracy
Charge Current Monitor Output for Gas Gauging*
Automatic Recharge
Charge Status Output
“AC Present” Output
2.9V Trickle Charge Threshold (LTC4068)
Available Without Trickle Charge (LTC4068X)
Soft-Start Limits Inrush Current
Low Profile (3mm × 3mm × 0.75mm) DFN Package
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APPLICATIO S
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Cellular Telephones, PDAs, MP3 Players
Bluetooth Applications
No external sense resistor or external blocking diode are
required due to the internal MOSFET architecture. Thermal
feedback regulates the charge current to limit the die
temperature during high power operation or high ambient
temperature conditions. The charge voltage is fixed at
4.2V and the charge current is programmed with a resistor. The LTC4068 terminates the charge cycle when the
charge current drops below the programmed termination
threshold after the final float voltage is reached.
When the input supply (wall adapter or USB supply) is
removed, the LTC4068 enters a low current state dropping
the battery drain current to less than 2µA. Other features
include charge current monitor, undervoltage lockout,
automatic recharge and status pins to indicate charge
termination and the presence of adequate input voltage.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Protected by U.S. Patents, including 6522118.
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TYPICAL APPLICATIO
Complete Charge Cycle (750mAh Battery)
700
Single Cell Li-Ion Battery Charger with C/5 Termination
VCC
BAT
LTC4068-4.2
1µF
CHRG
ACPR ITERM
EN
PROG
GND
+
1-CELL
Li-Ion
BATTERY
825Ω
1.65k
CHARGE CURRENT (mA)
VIN
4.5V TO 6.5V
600
4.50
CONSTANT
VOLTAGE
500
4.25
400
4.00
300
3.75
200
100
406842 TA01
0
VCC = 5V
θJA = 40°C/W
RPROG = 1.65k
RTERM = 825Ω
TA = 25°C
3.50
BATTERY VOLTAGE (V)
600mA
4.75
CONSTANT
CURRENT
3.25
3.00
0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25
406842 TA02
TIME (HOURS)
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LTC4068-4.2/LTC4068X-4.2
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ABSOLUTE
RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
Input Supply Voltage (VCC) ....................... –0.3V to 10V
PROG, ITERM ................................ – 0.3V to VCC + 0.3V
BAT ............................................................. –0.3V to 7V
CHRG, ACPR, EN ...................................... –0.3V to 10V
BAT Short-Circuit Duration .......................... Continuous
BAT Pin Current ........................................................ 1A
PROG Pin Current ................................................... 1mA
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
ORDER PART
NUMBER
TOP VIEW
ITERM 1
8
EN
BAT 2
7
ACPR
6
VCC
5
PROG
CHRG 3
9
GND 4
LTC4068EDD-4.2
LTC4068XEDD-4.2
DD PART MARKING
DD PACKAGE
8-LEAD (3mm × 3mm) PLASTIC DFN
LBHZ
LBQB
TJMAX = 125°C, θJA = 40°C/W (NOTE 3)
EXPOSED PAD IS GROUND (PIN 9)
MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted.
SYMBOL
PARAMETER
VCC
Input Supply Voltage
CONDITIONS
MIN
ICC
Input Supply Current
Charge Mode (Note 4), RPROG = 10k
Standby Mode (Charge Terminated)
Shutdown Mode (EN = 5V, VCC < VBAT
or VCC < VUV)
VFLOAT
Regulated Output (Float) Voltage
0°C ≤ TA ≤ 85°C, 4.3V < VCC < 6.5V
IBAT
BAT Pin Current
RPROG = 10k, Current Mode
RPROG = 2k, Current Mode
Standby Mode, VBAT = 4.2V
Shutdown Mode (EN = 5V, VCC < VBAT or
VCC < VUV)
Sleep Mode, VCC = 0V
●
●
●
●
●
ITRIKL
Trickle Charge Current
VBAT < VTRIKL, RPROG = 2k (Note 5)
VTRIKL
Trickle Charge Threshold Voltage
RPROG = 10k, VBAT Rising (Note 5)
VTRHYS
Trickle Charge Hysteresis Voltage
RPROG = 10k (Note 5)
VUV
VCC Undervoltage Lockout Voltage
From VCC Low to High
VUVHYS
VEN(IL)
TYP
MAX
UNITS
6.5
V
0.4
200
25
1
500
50
mA
µA
µA
4.158
4.2
4.242
92
465
100
500
–2.5
±1
105
535
–6
±2
mA
mA
µA
µA
±1
±2
µA
30
45
60
mA
2.8
2.9
3
4.25
●
●
●
80
V
V
mV
●
3.7
3.8
3.92
V
VCC Undervoltage Lockout Hysteresis
●
150
200
300
mV
EN Pin Input Low Voltage
●
0.4
0.7
VEN(IH)
EN Pin Input High Voltage
●
REN
EN Pin Pull-Down Resistor
VASD
VCC – VBAT Lockout Threshold
VCC from Low to High
VCC from High to Low
ITERM
Charge Termination Current Threshold
RTERM = 1k
RTERM = 5k
VPROG
PROG Pin Voltage
RPROG = 10k, Current Mode
VCHRG
CHRG Pin Output Low Voltage
VACPR
ACPR Pin Output Low Voltage
∆VRECHRG
Recharge Battery Threshold Voltage
VFLOAT – VRECHRG, 0°C ≤ TA ≤ 85°C
●
0.7
V
1
V
1.2
2
5
MΩ
70
5
100
30
140
50
mV
mV
90
17.5
100
20
110
22.5
mA
mA
0.93
1
1.07
V
ICHRG = 5mA
0.35
0.6
V
IACPR = 5mA
0.35
0.6
V
100
140
mV
●
●
60
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LTC4068-4.2/LTC4068X-4.2
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
TLIM
Junction Temperature in Constant
Temperature Mode
120
°C
RON
Power FET “ON” Resistance
(Between VCC and BAT)
600
mΩ
tSS
Soft-Start Time
IBAT = 0 to IBAT =1000V/RPROG
tRECHARGE
Recharge Comparator Filter Time
VBAT High to Low
0.75
2
4.5
ms
tTERM
Termination Comparator Filter Time
IBAT Drops Below Charge Termination Threshold
400
1000
2500
µs
100
µs
Note 3: Failure to solder the exposed backside of the package to the PC
board will result in a thermal resistance much higher than 40°C/W.
Note 4: Supply current includes PROG pin current and ITERM pin current
(approximately 100µA each) but does not include any current delivered to
the battery through the BAT pin (approximately 100mA).
Note 5: This parameter is not applicable to the LTC4068X.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: The LTC4068E-4.2/LTC4068XE-4.2 are guaranteed to meet
performance specifications from 0°C to 70°C. Specifications over the
–40°C to 85°C operating temperature range are assured by design,
characterization and correlation with statistical process controls.
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TYPICAL PERFOR A CE CHARACTERISTICS
PROG Pin Voltage vs Supply
Voltage (Constant Current Mode)
1.0100
VCC = 5V
VBAT = 4V
TA = 25°C
RPROG = 10k
1.010
1.0075
Charge Current
vs PROG Pin Voltage
600
VCC = 5V
VBAT = 4V
RPROG = 10k
VCC = 5V
TA = 25°C
RPROG = 2k
RTERM = 2k
500
1.0050
VPROG (V)
VPROG (V)
1.005
1.000
0.995
400
1.0025
IBAT (mA)
1.015
PROG Pin Voltage
vs Temperature
1.0000
0.9975
300
200
0.9950
0.990
0.985
100
0.9925
4
4.5
5
5.5
VCC (V)
6
6.5
7
405842 G01
0.9900
–50
–25
0
50
25
TEMPERATURE (°C)
0
75
100
405842 G02
0
0.2
0.4
0.6
0.8
VPROG (V)
1
1.2
405842 G03
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LTC4068-4.2/LTC4068X-4.2
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TYPICAL PERFOR A CE CHARACTERISTICS
Regulated Output (Float) Voltage
vs Charge Current
Regulated Output (Float) Voltage
vs Temperature
4.26
4.215
4.215
VCC = 5V
RPROG = 10k
4.210
4.16
4.205
VFLOAT (V)
4.18
TA = 25°C
RPROG = 10k
4.210
4.205
4.20
VFLOAT (V)
VFLOAT (V)
VCC = 5V
4.24 TA = 25°C
RPROG = 1.25k
4.22
Regulated Output (Float) Voltage
vs Supply Voltage
4.200
4.200
4.195
4.195
4.190
4.190
4.14
4.12
4.10
0
100
200
300 400
IBAT (mA)
500
600
4.185
–50
700
–25
0
25
50
TEMPERATURE (°C)
75
CHRG Pin I-V Curve
(Pull-Down State)
60
TA = 90°C
15
10
25
TA = 25°C
5
20
TA = 90°C
1
4
3
VCHRG (V)
2
5
6
1
4
3
VACPR (V)
2
5
405842 G07
3.000
2.975
RPROG = 2k
VTRKL (V)
30
VCC = 5V
RPROG = 10k
6
0
25
50
TEMPERATURE (°C)
75
100
405842 G09
Charge Current vs Battery Voltage
600
LTC4068 ONLY
LTC4068 ONLY
500
400
2.925
2.900
300
200
6.5
7
405842 G10
2.800
–50
VCC = 5V
θJA = 40°C/W
RPROG = 2k
100
2.825
5.5
VCC (V)
–25
2.850
RPROG = 10k
5
0
–50
7
2.875
20
4.5
RPROG = 10k
2.950
40
4
30
Trickle Charge Threshold Voltage
vs Temperature
50
10
LTC4068 ONLY
405842 G08
LTC4068 ONLY
VBAT = 2.5V
TA = 25°C
6
IBAT (mA)
60
VCC = 5V
VBAT = 2.5V
10
VCC = 5V
VBAT = 4V
0
Trickle Charge Current
vs Supply Voltage
7
20
0
7
6.5
40
15
5
VCC = 5V
VBAT = 4V
0
6
RPROG = 2k
10
0
5.5
VCC (V)
50
ITRKL (mA)
20
TA = –40°C
IACPR (mA)
ICHRG (mA)
25
TA = 25°C
5
4.5
Trickle Charge Current
vs Temperature
30
TA = –40°C
4
405842 G06
ACPR Pin I-V Curve
(Pull-Down State)
30
ITRKL (mA)
4.185
405842 G05
405842 G04
0
100
–25
0
50
25
TEMPERATURE (°C)
75
100
405842 G11
0
2.4
2.7
3
3.3 3.6
VBAT (V)
3.9
4.2
4.5
405842 G12
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LTC4068-4.2/LTC4068X-4.2
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TYPICAL PERFOR A CE CHARACTERISTICS
Charge Current
vs Ambient Temperature
Charge Current vs Supply Voltage
600
600
ONSET OF THERMAL REGULATION
RPROG = 2k
500
500
RPROG = 2k
400
IBAT (mA)
IBAT (mA)
400
VBAT = 4V
300 TA = 25°C
θJA = 40°C/W
200
200
RPROG = 10k
100
0
VCC = 5V
VBAT = 4V
θJA = 40°C/W
300
4
5
4.5
5.5
VCC (V)
RPROG = 10k
100
6
6.5
0
–50
7
–25
50
25
75
0
TEMPERATURE (°C)
100
405842 G13
405842 G14
Power FET “ON” Resistance
vs Temperature
700
650
125
Recharge Threshold Voltage
vs Temperature
4.16
VCC = 4.2V
IBAT = 100mA
RPROG = 2k
4.14
VCC = 5V
RPROG = 10k
4.12
VRECHRG (V)
RDS(ON) (mΩ)
600
550
500
4.10
4.08
450
4.06
400
350
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
405842 G17
4.04
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
405842 G15
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PI FU CTIO S
ITERM (Pin 1): Charge Termination Program. The charge
termination current threshold current is programmed by
connecting a 1% resistor, RTERM, to ground. The current
threshold ITERM, is set by the following formula:
ITERM =
100V
100V
, RTERM =
RTERM
ITERM
BAT (Pin 2): Charge Current Output. Provides charge
current to the battery from the internal P-channel MOSFET,
and regulates the final float voltage to 4.2V. An internal
precision resistor divider from this pin sets the float
voltage. This divider is disconnected in shutdown mode to
minimize current drain from the battery.
CHRG (Pin 3): Charge Status Open-Drain Output. When
the battery is charging, the CHRG pin is pulled low by an
internal N-channel MOSFET. When the charge cycle is
completed, CHRG becomes high impedance.
GND (Pins 4, 9): Ground/Exposed Pad. The exposed
backside package pad (Pin 9) is electrical ground and
must be soldered to the PC board for maximum heat
transfer.
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LTC4068-4.2/LTC4068X-4.2
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PI FU CTIO S
PROG (Pin 5): Charge Current Program and Charge Current Monitor. Charge current is programmed by connecting a 1% resistor, RPROG, to ground. When charging in
constant-current mode, this pin servos to 1V. In all modes,
the voltage on this pin can be used to measure the charge
current using the following formula:
When VCC is within 100mV of the BAT pin voltage, the
LTC4068 enters shutdown mode dropping the battery
drain current to less than 2µA.
ACPR (Pin 7): Power Supply Status Open-Drain Output.
When VCC is greater than the undervoltage lockout threshold and at least 100mV above VBAT, the ACPR pin is pulled
to ground; otherwise, the pin is high impedance.
IBAT = (VPROG/RPROG) • 1000
This pin is clamped to approximately 2.4V. Driving this pin
to voltages beyond the clamp voltage can draw large
currents and should be avoided.
EN (Pin 8): Enable Input . A logic high on the EN pin will put
the LTC4068 into shutdown mode where the battery drain
current is reduced to less than 2µA and the supply current
is reduced to less than 50µA. A logic low or floating the EN
pin (allowing an internal 2MΩ pull-down resistor to pull
this pin low) enables charging.
VCC (Pin 6): Positive Input Supply Voltage. Provides
power to the charger. VCC can range from 4.25V to 6.5V.
This pin should be bypassed with at least a 1µF capacitor.
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BLOCK DIAGRA
6
VCC
120°C
TA
1×
1×
TDIE
1000×
–
+
BAT
5µA
MA
2
R1
+
ACPR
7
VA
R2
–
CHRG
CA
3
+
–
REF
1.211V
R3
*
1V
CHARGE ACPR
R4
LOGIC
+
TERM
0.1V
C1
R5
–
EN
SHDN
EN
8
C2*
–
+
2.9V
TO BAT
*TRICKLE
CHARGE
DISABLED
ON THE
LTC4068X
PROG
ITERM
1
5
RTERM
GND
4, 9
RPROG
406842 BD
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LTC4068-4.2/LTC4068X-4.2
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OPERATIO
The LTC4068 is a single cell lithium-ion battery charger
using a constant-current/constant-voltage algorithm. It
can deliver up to 950mA of charge current (using a good
thermal PCB layout) with a final float voltage accuracy of
±1%. The LTC4068 includes an internal P-channel power
MOSFET and thermal regulation circuitry. No blocking
diode or external current sense resistor is required; thus,
the basic charger circuit requires only two external components. Furthermore, the LTC4068 is capable of operating from a USB power source.
Normal Charge Cycle
A charge cycle begins when the voltage at the VCC pin rises
above the UVLO threshold level and a 1% program resistor
is connected from the PROG pin to ground. If the BAT pin
is less than 2.9V, the charger enters trickle charge mode.
In this mode, the LTC4068 supplies approximately 1/10th
the programmed charge current to bring the battery voltage up to a safe level for full current charging. (Note: The
LTC4068X does not include this trickle charge feature.)
When the BAT pin voltage rises above 2.9V, the charger
enters constant-current mode where the programmed
charge current is supplied to the battery. When the BAT pin
approaches the final float voltage (4.2V), the LTC4068
enters constant-voltage mode and the charge current
begins to decrease. When the charge current drops to the
programmed termination threshold (set by the external
resistor RTERM), the charge cycle ends.
Programming Charge Current
The charge current is programmed using a single resistor
from the PROG pin to ground. The charge current out of
the BAT pin is 1000 times the current out of the PROG pin.
The program resistor and the charge current are calculated using the following equations:
RPROG =
1000 V
1000 V
, I CHG =
ICHG
RPROG
Charge current out of the BAT pin can be determined at any
time by monitoring the PROG pin voltage and using the
following equation:
IBAT =
VPROG
• 1000
RPROG
Programming Charge Termination
The charge cycle terminates when the charge current
falls below the programmed termination threshold. This
threshold is set by connecting an external resistor, RTERM,
from the ITERM pin to ground. The charge termination
current threshold (ITERM) is set by the following equation:
ITERM =
100V ICHG RPROG
100V
=
•
, RTERM =
RTERM
10 RTERM
ITERM
The termination condition is detected by using an internal
filtered comparator to monitor the ITERM pin. When the
ITERM pin voltage drops below 100mV* for longer than
tTERM (typically 1ms), charging is terminated. The charge
current is latched off and the LTC4068 enters standby
mode where the input supply current drops to 200µA.
(Note: Termination is disabled in trickle charging and
thermal limiting modes.)
ITERM can be set to be 1/10th of ICHG by shorting the ITERM
pin to the PROG pin, thus eliminating the need for external
resistor RTERM. When configured in this way, ITERM is
always set to ICHG/10, and the programmed charge current
is set by the equation:
500V
500V
ICHG =
,RPROG =
RPROG
ICHG
**
When charging, transient loads on the BAT pin can cause
the ITERM pin to fall below 100mV for short periods of
time before the DC charge current has dropped to 10% of
the programmed value. The 1ms filter time (tTERM) on the
termination comparator ensures that transient loads of
this nature do not result in premature charge cycle termination. Once the average charge current drops below the
programmed termination threshold, the LTC4068 terminates the charge cycle and ceases to provide any current
out of the BAT pin. In this state, any load on the BAT pin
must be supplied by the battery.
The LTC4068 constantly monitors the BAT pin voltage in
standby mode. If this voltage drops below the 4.1V recharge
* Any external sources that hold the ITERM pin above 100mV will prevent the LTC4068 from
terminating a charge cycle.
** These equations apply only when the ITERM pin is shorted to the PROG pin.
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LTC4068-4.2/LTC4068X-4.2
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OPERATIO
threshold (VRECHRG), another charge cycle begins and
charge current is once again supplied to the battery. To
manually restart a charge cycle when in standby mode, the
input voltage must be removed and reapplied or the charger
must be shut down and restarted using the EN pin. Figure 1
shows the state diagram of a typical charge cycle.
POWER ON
BAT < 2.9V
TRICKLE CHARGE
MODE
EN DRIVEN LOW
OR
UVLO CONDITION
STOPS
1/10TH FULL CURRENT
LTC4068
ONLY
CHRG: STRONG
PULL-DOWN
BAT > 2.9V
SHUTDOWN MODE
CHARGE MODE
ICC DROPS TO <25µA
FULL CURRENT
CHRG: Hi-Z
Undervoltage Lockout (UVLO)
CHRG: STRONG
PULL-DOWN
STANDBY MODE
NO CHARGE CURRENT
CHRG: Hi-Z
406842 F01
An internal thermal feedback loop reduces the programmed
charge current if the die temperature attempts to rise above
a preset value of approximately 120°C. This feature protects
the LTC4068 from excessive temperature and allows the
user to push the limits of the power handling capability of
a given circuit board without risk of damaging the LTC4068.
The charge current can be set according to typical (not worst
case) ambient temperature with the assurance that the
charger will automatically reduce the current in worst-case
conditions. DFN power considerations are discussed further in the Applications Information section.
BAT > 2.9V
ITERM < 100mV
EN DRIVEN HIGH
OR
UVLO CONDITION
Thermal Limiting
2.9V < BAT < 4.1V
Figure 1. State Diagram of a Typical Charge Cycle
Charge Status Indicator (CHRG)
The charge status output has two states: pull-down and
high impedance. The pull-down state indicates that the
LTC4068 is in a charge cycle. Once the charge cycle has
terminated or the LTC4068 is disabled, the pin state
becomes high impedance.
Power Supply Status Indicator (ACPR)
The power supply status output has two states: pull-down
and high impedance. The pull-down state indicates that
VCC is above the UVLO threshold (3.8V) and is also 100mV
above the battery voltage. If these conditions are not met,
the ACPR pin is high impedance indicating that the LTC4068
is unable to charge the battery.
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until VCC
rises above the undervoltage lockout threshold. The UVLO
circuit has a built-in hysteresis of 200mV. Furthermore, to
protect against reverse current in the power MOSFET, the
UVLO circuit keeps the charger in shutdown mode if VCC
falls to within 30mV of the BAT voltage. If the UVLO comparator is tripped, the charger will not come out of shutdown mode until VCC rises 100mV above the BAT voltage.
Manual Shutdown
At any point in the charge cycle, the LTC4068 can be put
into shutdown mode by driving the EN pin high. This
reduces the battery drain current to less than 2µA and the
supply current to less than 50µA. When in shutdown
mode, the CHRG pin is in the high impedance state. A new
charge cycle can be initiated by driving the EN pin low. An
internal resistor pull-down on this pin forces the LTC4068
to be enabled if the pin is allowed to float.
Automatic Recharge
Once the charge cycle is terminated, the LTC4068 continuously monitors the voltage on the BAT pin using a comparator with a 2ms filter time (tRECHARGE). A charge cycle
restarts when the battery voltage falls below 4.10V (which
corresponds to approximately 80% to 90% battery capacity). This ensures that the battery is kept at, or near, a fully
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LTC4068-4.2/LTC4068X-4.2
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APPLICATIO S I FOR ATIO
charged condition and eliminates the need for periodic
charge cycle initiations. The CHRG output enters a pulldown state during recharge cycles.
If the battery is removed from the charger, a sawtooth
waveform of approximately 100mV appears at the charger
output. This is caused by the repeated cycling between
termination and recharge events. This cycling results in
pulsing at the CHRG output; an LED connected to this pin
will exhibit a blinking pattern, indicating to the user that a
battery is not present. The frequency of the sawtooth is
dependent on the amount of output capacitance.
Stability Considerations
The constant-voltage mode feedback loop is stable without an output capacitor, provided a battery is connected to
the charger output. With no battery present, an output
capacitor on the BAT pin is recommended to reduce ripple
voltage. When using high value, low ESR ceramic capacitors, it is recommended to add a 1Ω resistor in series with
the capacitor. No series resistor is needed if tantalum
capacitors are used.
In constant-current mode, the PROG pin is in the feedback
loop, not the battery. The constant-current mode stability
is affected by the impedance at the PROG pin. With no
additional capacitance on the PROG pin, the charger is
stable with program resistor values as high as 20k; however, additional capacitance on this node reduces the
maximum allowed program resistor. The pole frequency
at the PROG pin should be kept above 100kHz. Therefore,
if the PROG pin is loaded with a capacitance, CPROG, the
following equation can be used to calculate the maximum
resistance value for RPROG:
RPROG ≤
1
2π • 105 • CPROG
Average, rather than instantaneous charge current may be
of interest to the user. For example, if a switching power
supply operating in low current mode is connected in
parallel with the battery, the average current being pulled
out of the BAT pin is typically of more interest than the
instantaneous current pulses. In such a case, a simple RC
filter can be used on the PROG pin to measure the average
battery current, as shown in Figure 2. A 10k resistor has
been added between the PROG pin and the filter capacitor
to ensure stability.
LTC4068-4.2
10k
PROG
GND
RPROG
CFILTER
CHARGE
CURRENT
MONITOR
CIRCUITRY
406842 F02
Figure 2. Isolating Capacitive Load on PROG Pin and Filtering
Power Dissipation
It is not necessary to design for worst-case power dissipation scenarios because the LTC4068 automatically
reduces the charge current during high power conditions.
The conditions that cause the LTC4068 to reduce charge
current through thermal feedback can be approximated
by considering the power dissipated in the IC. Nearly all
of this power dissipation is generated by the internal
MOSFET—this is calculated to be approximately:
PD = (VCC – VBAT) • IBAT
where PD is the power dissipated, VCC is the input supply
voltage, VBAT is the battery voltage and IBAT is the charge
current. The approximate ambient temperature at which
the thermal feedback begins to protect the IC is:
TA = 120°C – PDθJA
TA = 120°C – (VCC – VBAT) • IBAT • θJA
Example: An LTC4068 operating from a 5V supply is
programmed to supply 800mA full-scale current to a
discharged Li-Ion battery with a voltage of 3.3V. Assuming
θJA is 50°C/W (see Thermal Considerations), the ambient
temperature at which the LTC4068 will begin to reduce the
charge current is approximately:
TA = 120°C – (5V – 3.3V) • (800mA) • 50°C/W
TA = 120°C – 1.36W • 50°C/W = 120°C – 68°C
TA = 52°C
406842fa
9
LTC4068-4.2/LTC4068X-4.2
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APPLICATIO S I FOR ATIO
The LTC4068 can be used above 52°C ambient but the
charge current will be reduced from the programmed
800mA. The approximate current at a given ambient
temperature can be approximated by:
IBAT =
120°C – TA
(VCC – VBAT ) • θJA
Using the previous example with an ambient temperature
of 60°C, the charge current will be reduced to
approximately:
IBAT =
120°C – 60°C
(5V – 3.3V) • 50°C/W
=
60°C
85°C/A
IBAT = 706mA
Moreover, when thermal feedback reduces the charge current the voltage at the PROG pin is also reduced proportionally as discussed in the Operation section. It is important
to remember that LTC4068 applications do not need to be
designed for worst-case thermal conditions since the IC will
automatically reduce power dissipation when the junction
temperature reaches approximately 120°C.
Thermal Considerations
In order to deliver maximum charge current under all
conditions, it is critical that the exposed metal pad on the
backside of the LTC4068 package is soldered to the PC
board ground. Correctly soldered to a 2500mm2 doublesided 1oz copper board, the LTC4068 has a thermal
resistance of approximately 40°C/W. Failure to make
thermal contact between the exposed pad on the backside of the package and the copper board will result in
thermal resistances far greater than 40°C/W. As an
example, a correctly soldered LTC4068 can deliver over
800mA to a battery from a 5V supply at room temperature. Without a good backside thermal connection, this
number will drop considerably.
ceramic capacitors. Because of the self-resonant and high
Q characteristics of some types of ceramic capacitors,
high voltage transients can be generated under some
start-up conditions such as connecting the charger input
to a live power source. Adding a 1.5Ω resistor in series
with an X5R ceramic capacitor will minimize start-up
voltage transients. For more information, see Application
Note 88.
Charge Current Soft-Start
The LTC4068 includes a soft-start circuit to minimize the
inrush current at the start of a charge cycle. When a charge
cycle is initiated, the charge current ramps from zero to
full-scale current over a period of approximately 100µs.
This has the effect of minimizing the transient current load
on the power supply during start-up.
USB and Wall Adapter Power
The LTC4068 allows charging from both a wall adapter
and a USB port. Figure 3 shows how to combine wall
adapter and USB power inputs. A P-channel MOSFET,
MP1, is used to prevent back conducting into the USB port
when a wall adapter is present and a Schottky diode, D1,
is used to prevent USB power loss through the 1k pulldown resistor.
Typically a wall adapter can supply more current than
the 500mA-limited USB port. Therefore, an N-channel
MOSFET, MN1, and an extra 3.3k program resistor are
used to increase the charge current to 800mA when the
wall adapter is present. The charge termination threshold
remains fixed at 80mA.
5V WALL
ADAPTER
800mA ICHG
USB POWER
500mA ICHG
LTC4068-4.2
2
BAT
1
6
VCC ITERM
5
4, 9
GND PROG
MP1
Many types of capacitors can be used for input bypassing;
however, caution must be exercised when using multilayer
SYSTEM
LOAD
1.25k
+
3.3k
1k
VCC Bypass Capacitor
ICHG
D1
MN1
2k
Li-Ion
BATTERY
406842 F03
Figure 3. Combining Wall Adapter and USB Power
406842fa
10
LTC4068-4.2/LTC4068X-4.2
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APPLICATIO S I FOR ATIO
Reverse Polarity Input Voltage Protection
DRAIN-BULK
DIODE OF FET
In some applications, protection from reverse polarity
voltage on VCC is desired. If the supply voltage is high
enough, a series blocking diode can be used. In other
cases, where the voltage drop must be kept low, a P-channel
MOSFET can be used (as shown in Figure 4).
LTC4068
VCC
VIN
405842 F04
Figure 4. Low Loss Input Reverse Polarity Protection
U
PACKAGE DESCRIPTIO
DD Package
8-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1698)
0.675 ±0.05
3.5 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
PACKAGE
OUTLINE
0.28 ± 0.05
0.50
BSC
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
TYP
5
3.00 ±0.10
(4 SIDES)
0.38 ± 0.10
8
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(DD8) DFN 0203
0.200 REF
0.75 ±0.05
0.00 – 0.05
4
0.28 ± 0.05
1
0.50 BSC
2.38 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1)
2. ALL DIMENSIONS ARE IN MILLIMETERS
3. 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
4. EXPOSED PAD SHALL BE SOLDER PLATED
406842fa
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.
11
LTC4068-4.2/LTC4068X-4.2
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TYPICAL APPLICATIO S
Full Featured Single Cell Li-Ion Charger
Li-Ion Battery Charger with Reverse Polarity Input Protection
VIN
5V
1k
1k
5V
WALL
ADAPTER
6
500mA
VCC
1µF
6
VCC
2
7
ACPR
BAT
1
3
CHRG ITERM
LTC4068-4.2
8
5
EN
PROG
GND
BAT
LTC4068-4.2
1µF
1µF
1k
+
2k
1-CELL
Li-Ion
BATTERY
4, 9
ITERM
8
EN
PROG
GND
500mA
2
1
+
5
1-CELL
Li-Ion
BATTERY
1k
4, 9
406842 TA04
405642 TA03
USB/Wall Adapter Power Li-Ion Charger
5V WALL
ADAPTER
BAT
IBAT
2
+
LTC4068-4.2
6
USB
POWER
VCC
1µF
1k
ITERM
PROG
GND
4, 9
1
5
1-CELL
Li-Ion
BATTERY
1.25k
5k
100mA/
500mA
µC
406842 TA05
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PART NUMBER
DESCRIPTION
COMMENTS
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Up to 950mA Charge Current, Kelvin Sense for High Accuracy,
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LTC4410
USB Power Manager
For Simultaneous Operation of USB Peripheral and Battery Charging from USB
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ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
406842fa
12
Linear Technology Corporation
LT/TP 0904 1K REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2004
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