LTC4002
Standalone Li-Ion
Switch Mode Battery Charger
U
FEATURES
DESCRIPTIO
■
The LTC®4002 is a complete battery charger controller for
one (4.2V) or two (8.4V) cell lithium-ion batteries. With a
500kHz switching frequency, the LTC4002 provides a
small, simple and efficient solution to fast charge Li-Ion
batteries from a wide range of supply voltages. An external
sense resistor sets the charge current with ±5% accuracy.
An internal resistor divider and precision reference set the
final float voltage to 4.2V per cell with ±1% accuracy.
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Wide Input Supply Range:
4.7V to 22V – 4.2 Version
8.9V to 22V – 8.4 Version
High Efficiency Current Mode PWM Controller with
500kHz Switching Frequency
±1% Charge Voltage Accuracy
End-of-Charge Current Detection Output
3 Hour Charge Termination Timer
Constant Switching Frequency for Minimum Noise
±5% Charge Current Accuracy
Low 10µA Reverse Battery Drain Current
Automatic Battery Recharge
Automatic Shutdown When Input Supply is Removed
Automatic Trickle Charging of Low Voltage Batteries
Battery Temperature Sensing and Charge
Qualification
Stable with Ceramic Output Capacitor
8-Lead SO and 10-Lead DFN Packages
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APPLICATIO S
■
■
The LTC4002 is available in the 8-lead SO and 10-lead DFN
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Portable Computers
Charging Docks
Handheld Instruments
U
■
When the input supply is removed, the LTC4002 automatically enters a low current sleep mode, dropping the battery
drain current to 10µA. An internal comparator detects the
near end-of-charge condition while an internal timer sets
the total charge time and terminates the charge cycle. After
the charge cycle ends, if the battery voltage drops below
4.05V per cell, a new charge cycle will automatically begin.
TYPICAL APPLICATIO
1.5A Single Cell Li-Ion Battery Charger
Efficiency vs Input Voltage
VIN
5V TO 22V
100
(CURVES INCLUDE
INPUT DIODE)
0.1µF
10µF
VCC
BAT
GATE
2k
LTC4002ES8-4.2
CHARGE
STATUS
6.8µH
CHRG
SENSE
COMP
NTC
BAT
GND
EFFICIENCY (%)
90
VBAT = 4V
VBAT = 3.8V
80
70
68mΩ
0.47µF
2.2k
60
22µF
+
10k
T
NTC
Li-Ion
BATTERY
5
10
15
20
25
INPUT VOLTAGE (V)
4002 TA02
4002 TA01
NTC: DALE NTHS-1206N02
4002f
1
LTC4002
W W
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W
ABSOLUTE
AXI U RATI GS (Note 1)
Supply Voltage (VCC) .............................................. 24V
GATE .................................................. (VCC – 8V) to VCC
BAT, SENSE .............................................. – 0.3V to 14V
CHRG, NTC ................................................. – 0.3V to 8V
Operating Temperature Range (Note 4) .. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
Lead Temperature (S8 Package)
(Soldering, 10 sec) ........................................... 300°C
U
W
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PACKAGE/ORDER I FOR ATIO
TOP VIEW
ORDER PART
NUMBER
10 NC
COMP
1
VCC
2
GATE
3
PGND
4
7 BAT
SGND
5
6 CHRG
9 NTC
11
8 SENSE
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD IS GND (PIN 11)
MUST BE SOLDERED TO PCB
LTC4002EDD-4.2
LTC4002EDD-8.4
DD PART MARKING
LAGG
LBGY
ORDER PART
NUMBER
TOP VIEW
COMP 1
8
NTC
VCC 2
7
SENSE
GATE 3
6
BAT
GND 4
5
CHRG
LTC4002ES8-4.2
LTC4002ES8-8.4
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 110°C/W
400242
400284
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
(LTC4002-4.2) The ● denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at TA = 25°C. VCC = 10V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
DC Characteristics
●
VCC
VCC Supply Voltage
ICC
VCC Supply Current
Current Mode
Shutdown Mode
Sleep Mode
VBAT(FLT)
Battery Regulated Float Voltage
5V ≤ VCC ≤ 22V (Note 2)
0°C ≤ TA ≤ 85°C
–40°C ≤ TA ≤ 85°C
4.7
22
V
3
3
10
5
5
20
mA
mA
µA
4.168
4.158
4.2
●
4.232
4.242
V
V
●
●
93
90
100
107
110
mV
mV
5
10
15
mV
2.9
3.05
4.2
4.5
VSNS(CHG) Constant Current Sense Voltage
3V ≤ VBAT ≤ 4V (Note 3)
VSNS(TRKL) Trickle Current Sense Voltage
VBAT = 0V (Note 3)
VTRKL
Trickle Charge Threshold Voltage
VBAT Rising
2.75
VUV
VCC Undervoltage Lockout Threshold Voltage
VCC Rising
3.9
∆VUV
VCC Undervoltage Lockout Hysteresis Voltage
VMSD
Manual Shutdown Threshold Voltage
VASD
Automatic Shutdown Threshold Voltage
VCC – VBAT
250
mV
ICOMP
COMP Pin Output Current
VCOMP = 1.2V
100
µA
ICHRG
CHRG Pin Weak Pull-Down Current
VCHRG = 1V
VCHRG
CHRG Pin Output Low Voltage
ICHRG = 1mA
REOC
End-of-Charge Ratio
VSNS(EOC)/VSNS(CHG)
tTIMER
Charge Time Accuracy
200
COMP Pin Falling
200
15
10
360
V
V
mV
500
mV
25
35
0.15
0.3
V
25
32
%
10
%
µA
4002f
2
LTC4002
ELECTRICAL CHARACTERISTICS
(LTC4002-4.2) The ● denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at TA = 25°C. VCC = 10V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
INTC
NTC Pin Output Current
VNTC = 0.85V
●
75
85
95
µA
VNTC-HOT
NTC Pin Threshold Voltage (Hot)
VNTC Falling
Hysteresis
●
340
355
25
370
mV
mV
VNTC-COLD NTC Pin Threshold Voltage (Cold)
VNTC Rising
Hysteresis
●
2.428
2.465
170
2.502
V
mV
∆VRECHRG Recharge Battery Voltage Offset from Full
Charged Battery Voltage
VBAT(FULLCHARGED) – VRECHRG, VBAT Falling
100
150
200
mV
ILEAK
VCHRG = 8V, Charging Stops
1
µA
550
kHz
100
%
CHRG Pin Leakage Current
UNITS
Oscillator
fOSC
Switching Frequency
DC
Maximum Duty Cycle
450
500
Gate Drive
tr
Rise Time
CGATE = 2000pF, 10% to 90%
20
ns
tf
Fall Time
CGATE = 2000pF, 90% to 10%
50
ns
∆VGATE
Output Clamp Voltage
VCC – VGATE, VCC ≥ 9V
●
8
V
∆VGATEHI
Output High Voltage
∆VGATEHI = VCC – VGATE, VCC ≥ 7V
●
0.3
V
∆VGATELO
Output Low Voltage
∆VGATELO = VCC – VGATE, VCC ≥ 7V
●
4.5
V
(LTC4002-8.4) The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at
TA = 25°C. VCC = 12V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
DC Characteristics
●
VCC
VCC Supply Voltage
ICC
VCC Supply Current
Current Mode
Shutdown Mode
Sleep Mode
VBAT(FLT)
Battery Regulated Float Voltage
9V ≤ VCC ≤ 22V (Note 2)
22
V
3
3
10
5
5
20
mA
mA
µA
8.336
8.316
8.4
●
8.464
8.484
●
95
93
100
100
105
107
mV
mV
5
10
15
mV
4.7
5
5.3
V
7.5
8.5
VSNS(CHG) Constant Current Sense Voltage
6V ≤ VBAT ≤ 8V (Note 3)
8.9
V
V
VSNS(TRKL) Trickle Current Sense Voltage
VBAT = 0V (Note 3)
VTRKL
Trickle Charge Threshold Voltage
VBAT Rising
VUV
VCC Undervoltage Lockout Threshold Voltage
VCC Rising
∆VUV
VCC Undervoltage Lockout Hysteresis Voltage
VMSD
Manual Shutdown Threshold Voltage
VASD
Automatic Shutdown Threshold Voltage
VCC – VBAT
250
mV
ICOMP
COMP Pin Output Current
VCOMP = 1.2V
100
µA
ICHRG
CHRG Pin Weak Pull-Down Current
VCHRG = 1V
VCHRG
CHRG Pin Output Low Voltage
ICHRG = 1mA
REOC
End-of-Charge Ratio
VSNS(EOC)/VSNS(CHG)
tTIMER
Charge Time Accuracy
INTC
NTC Pin Output Current
500
COMP Pin Falling
VNTC = 0.85V
200
15
5
●
75
350
V
mV
500
mV
25
35
0.15
0.3
V
10
15
%
10
%
95
µA
85
µA
4002f
3
LTC4002
ELECTRICAL CHARACTERISTICS
(LTC4002-8.4) The ● denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at TA = 25°C. VCC = 12V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VNTC-HOT
NTC Pin Threshold Voltage (Hot)
VNTC Falling
Hysteresis
●
340
355
25
370
mV
mV
VNTC-COLD NTC Pin Threshold Voltage (Cold)
VNTC Rising
Hysteresis
●
2.428
2.465
170
2.502
V
mV
∆VRECHRG Recharge Battery Voltage Offset from Full
Charged Battery Voltage
VBAT(FULLCHARGED) – VRECHRG, VBAT Falling
200
300
400
mV
ILEAK
VCHRG = 8V, Charging Stops
1
µA
550
kHz
100
%
CHRG Pin Leakage Current
Oscillator
fOSC
Switching Frequency
DC
Maximum Duty Cycle
450
500
Gate Drive
tr
Rise Time
CGATE = 2000pF, 10% to 90%
20
ns
tf
Fall Time
CGATE = 2000pF, 90% to 10%
50
ns
∆VGATE
Output Clamp Voltage
VCC – VGATE
●
∆VGATEHI
Output High Voltage
∆VGATEHI = VCC – VGATE
●
∆VGATELO
Output Low Voltage
∆VGATELO = VCC – VGATE
●
Note 1: Absolute Maximum Rating are those values beyond which the life
of a device may be impaired.
Note 2: The LTC4002 is tested with Test Circuit 1.
Note 3: The LTC4002 is tested with Test Circuit 2.
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4
0.3
V
4.5
V
TA = 25°C, VCC = 10V unless otherwise noted.
Oscillator Frequency
vs Temperature
Supply Current vs VCC
4.0
V
Note 4: The LTC4002 is 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.
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Temperature
8
550
CURRENT MODE
fOSC (kHz)
ICC (mA)
ICC (mA)
3.5
3
500
3.0
2.5
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
2
5
10
15
20
25
VCC (V)
4002 G01
4002 G02
450
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
4002 G03
4002f
4
LTC4002
U W
TYPICAL PERFOR A CE CHARACTERISTICS
TA = 25°C, VCC = 10V unless otherwise noted.
Undervoltage Lockout Threshold
vs Temperature
Oscillator Frequency vs VCC
510
8
CHRG Pin Output Low Voltage
vs VCC
150
VCC RISING
ILOAD = 1mA
LTC4002-8.4
500
VCHRG (mV)
VUV (V)
fOSC (kHz)
7
6
140
5
LTC4002-4.2
490
5
15
10
20
4
– 50 – 25
25
130
0
50
75
25
TEMPERATURE (°C)
VCC (V)
4002 G04
0
50
75
25
TEMPERATURE (°C)
100
28
25
50
75
25
TEMPERATURE (°C)
100
125
5
100
125
15
VCC (V)
20
320
150
140
10
15
20
25
LTC4002-8.4
300
280
5
25
Recharge Voltage Offset from Full
Charged Voltage vs VCC
LTC4002-4.2
5
10
15
20
25
VCC (V)
VCC (V)
4002 G10
10
4002 G09
∆VRECHRG (mV)
∆VRECHRG (mV)
∆VRECHRG/CELL (mV)
160
50
75
25
TEMPERATURE (°C)
25
Recharge Voltage Offset from Full
Charged Voltage vs VCC
190
25
VCHRG = 8V
4002 G08
Recharge Voltage Offset
Per Cell from Full Charged
Voltage vs Temperature
0
20
22
0
4002 G07
110
– 50 – 25
15
CHRG Output Pin Weak Pull-Down
Current vs VCC
VCHRG = 8V
21
– 50 – 25
125
150
10
4002 G06
ICHRG (µA)
ICHRG (µA)
VCHG (mV)
29
140
5
VCC (V)
CHRG Pin Weak Pull-Down
Current vs Temperature
ILOAD = 1mA
100
– 50 – 25
125
4002 G05
CHRG Pin Output Low Voltage
vs Temperature
180
100
4002 G11
4002 G12
4002f
5
LTC4002
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Current Mode Sense Voltage
vs VCC
Current Mode Sense Voltage
vs Temperature
102
100
50
75
25
TEMPERATURE (°C)
100
102
VBAT = 4V
LTC4002-4.2
100
98
0
125
5
15
10
20
100
15
20
86
100
96
– 50 – 25
25
50
75
25
TEMPERATURE (°C)
100
125
20
5.2
LTC4002-4.2
2.9
5
10
15
25
Trickle Charge Voltage
vs Temperature
20
25
VCC (V)
4002 G19
15
10
4002 G18
VTRKL (V)
VTRKL (V)
VTRKL (V)
3.0
2.8
50
75
25
TEMPERATURE (°C)
5
VCC (V)
Trickle Charge Voltage
vs VCC
2.9
0
125
4002 G17
LTC4002-4.2
2.8
– 50 – 25
100
VNTC = 0V
85
84
0
4002 G16
Trickle Charge Voltage
vs Temperature
25
NTC Pin Output Current
vs VCC
VCOMP = 0V
VCC (V)
3.0
20
4002 G15
INTC (µA)
ICOMP (µA)
ICOMP (µA)
104
10
15
10
VCC (V)
COMP Pin Output Current
vs Temperature
VCOMP = 0V
5
5
4002 G14
COMP Pin Output Current
vs VCC
98
100
98
25
VBAT = 8V
LTC4002-8.4
VCC (V)
4002 G13
102
Current Mode Sense Voltage
vs VCC
VSNS (mV)
VSNS (mV)
VSNS (mV)
104
96
– 50 – 25
TA = 25°C, VCC = 10V unless otherwise noted.
4002 G20
LTC4002-8.4
5.0
4.8
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
4002 G21
4002f
6
LTC4002
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Trickle Charge Sense Voltage
vs Temperature
Trickle Charge Voltage
vs VCC
10.4
5.0
4.8
5
15
10
20
11
VBAT = 2.5V
LTC4002-4.2
10.0
9.6
– 50 – 25
25
0
50
75
25
TEMPERATURE (°C)
VCC (V)
100
100
125
89
VBAT = 4V
LTC4002-8.4
10
9
5
10
15
20
85
0
50
75
25
TEMPERATURE (°C)
VCC (V)
100
125
4002 G27
4002 G26
End-of-Charge Ratio
vs Temperature
End-of-Charge Ratio
vs VCC
28
REOC (%)
LTC4002-4.2
25
21
– 50 – 25
25
VNTC = 0V
81
– 50 – 25
25
4002 G25
29
20
NTC Pin Output Current
vs Temperature
INTC (µA)
VSNS (mV)
50
75
25
TEMPERATURE (°C)
REOC (%)
VSNS (mV)
11
VBAT = 4V
LTC4002-8.4
0
15
10
4002 G24
Trickle Charge Sense Voltage
vs VCC
10.0
5
4002 G23
Trickle Charge Sense Voltage
vs Temperature
9.6
– 50 – 25
10
9
125
VBAT = 2.5V
LTC4002-4.2
VCC (V)
4002 G22
10.4
Trickle Charge Sense Voltage
vs VCC
VSNS (mV)
LTC4002-8.4
VBAT = 4V
VSNS (mV)
VTRKL (V)
5.2
TA = 25°C, VCC = 10V unless otherwise noted.
LTC4002-4.2
25
22
0
50
75
25
TEMPERATURE (°C)
100
125
4002 G28
5
10
15
VCC (V)
20
25
4002 G29
4002f
7
LTC4002
U W
TYPICAL PERFOR A CE CHARACTERISTICS
End-of-Charge Ratio
vs Temperature
End-of-Charge Ratio
vs VCC
14
LTC4002-8.4
13
13
12
12
11
11
REOC (%)
REOC (%)
14
10
9
8
8
7
7
6
0
50
75
25
TEMPERATURE (°C)
100
125
4002 G30
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PI FU CTIO S
LTC4002-8.4
10
9
6
– 50 – 25
TA = 25°C, VCC = 10V unless otherwise noted.
5
10
15
VCC (V)
20
25
4002 G31
(DFN/SO-8)
COMP (Pin 1/Pin 1): Compensation, Soft-Start and Shutdown Control Pin. The COMP pin is the control signal of the
inner loop of the current mode PWM. Charging begins when
the COMP pin reaches 800mV. The recommended compensation components are a 0.47µF (or larger) capacitor and
a 2.2k series resistor. A 100µA current into the compensation capacitor also sets the soft-start slew rate. Pulling
the COMP pin below 360mV will shut down the charger.
VCC (Pin 2/Pin 2): Positive Supply Voltage Input. VCC can
range from VBAT(FLT) + 0.5V to 22V. A 0.1µF or higher capacitor is required at the VCC pin with the lead length kept
to a minimum. A 10µF low ESR capacitor is also required
at the source pins of the power P-channel MOSFET.
GATE (Pin 3/Pin 3): Gate Drive Output. Driver Output for
the P-Channel MOSFET. The voltage at this pin is internally
clamped to 8V below VCC, allowing a low voltage MOSFET
with gate-to-source breakdown voltage of 8V or less to be
used.
PGND, SGND, Exposed Pad, GND (Pins 4, 5, 11/Pin 4):
IC Ground. The exposed pad (DFN) must be soldered to PCB
ground to provide both electrical contact and optimum
thermal performance.
CHRG (Pin 6/Pin 5): Open-Drain Charge Status Output.
When the battery is being charged, the CHRG pin is pulled
low by an internal N-channel MOSFET. When the charge
current drops below the End-of-Charge threshold for more
than 120µs, the N-channel MOSFET turns off and a 25µA
current source is connected from the CHRG pin to GND.
When the timer runs out or the input supply is removed,
the 25µA current source is turned off and the CHRG pin
becomes high impedance.
BAT (Pin 7/Pin 6): Battery Sense Input. A bypass capacitor of 22µF is required to minimize ripple voltage. An
internal resistor divider, which is disconnected in sleep
mode, sets the final float voltage at this pin. If the battery
connection is opened when charging, an overvoltage
circuit will limit the charger output voltage to 10% above
the programmed float voltage.
When VBAT is within 250mV of VCC, the LTC4002 is forced
into sleep mode, dropping ICC to 10µA.
SENSE (Pin 8/Pin 7): Current Amplifier Sense Input. A sense
resistor, RSENSE, must be connected between the SENSE
and BAT pins. The maximum charge current is equal to
100mV/RSENSE.
NTC (Pin 9/Pin 8): NTC (Negative Temperature Coefficient)
Thermistor Input. With an external 10kΩ NTC thermistor
to ground, this pin senses the temperature of the battery
pack and stops the charger when the temperature is out of
range. When the voltage at this pin drops below 355mV at
4002f
8
LTC4002
U
U
U
PI FU CTIO S
(DFN/SO-8)
hot temperature or rises above 2.465V at cold temperature,
charging is suspended and the internal timer stops. The
CHRG pin output is not affected during this hold state. To
disable the temperature qualification function, ground the
NTC pin.
NC (Pin 10/NA): No Connect.
W
BLOCK DIAGRA
VCC
CLK:
100µA
COMP
ISLOP
IL
DRIVER
–
GATE
S
Q
+
CPWM
R
RSLOP
25mV or 10mV
R
+
+–
CEOC
–
RIL
100mV
+
M1
SENSE
–+
CA
–
BAT
+
M2
VA
–
4.2V/CELL
+
M3
CLB
–
90µA
2.9V OR 5V
+
COV
–
UVLO
4.2V
+
UV
CSD
360mV
CHRG
–
+
EOC
SD
RQ
CRQ
LOGIC
Q4
C/10
STOP
Q5
TEMP
4.62V/CELL
–
4.05V/CELL
+
2.465V
VCC
CCOLD
NTC_DISABLE
–
25µA
85µA
NTC
–
GND
CHOT
+
355mV
+
–
4002 BD
50mV
4002f
9
LTC4002
TEST CIRCUITS
Test Circuit 1
15V
–
1.5V
LT1006
LT1006
+
+
0V
0V
SENSE
LTC4002
–
100µA
SENSE
CA
BAT
RSENSE
10Ω
+
1mA
COMP
100µA
CA
BAT
RSENSE
10Ω
+
COMP
15V
–
–
1.5V
Test Circuit 2
VBAT
–
4002 TC01
VA
4.2V
+
LTC4002
4002 TC02
U
OPERATIO
The LTC4002 is a constant current, constant voltage
Li-Ion battery charger controller that uses a current mode
PWM step-down (buck) switching architecture. The charge
current is set by an external sense resistor (RSENSE)
across the SENSE and BAT pins. The final battery float
voltage is internally set to 4.2V per cell. For batteries like
lithium-ion that require accurate final float voltage, the
internal 2.465V reference, voltage amplifier and the resistor divider provide regulation with ±1% accuracy.
A charge cycle begins when the voltage at the VCC pin rises
above the UVLO level and is 250mV or more greater than
the battery voltage. At the beginning of the charge cycle,
if the battery voltage is less than the trickle charge threshold, 2.9V for the 4.2 version and 5V for the 8.4 version, the
charger goes into trickle charge mode. The trickle charge
current is internally set to 10% of the full-scale current. If
the battery voltage stays low for 30 minutes, the battery
is considered faulty and the charge cycle is terminated.
When the battery voltage exceeds the trickle charge threshold, the charger goes into the full-scale constant current
charge mode. In constant current mode, the charge current is set by the external sense resistor RSENSE and an
internal 100mV reference; IBAT = 100mV/RSENSE.
When the battery voltage approaches the programmed
float voltage, the charge current will start to decrease.
When the current drops to 25% (4.2 version) or 10% (8.4
version) of the full-scale charge current, an internal comparator turns off the internal pull-down N-channel MOSFET
at the CHRG pin, and connects a weak current source to
ground to indicate a near end-of-charge condition.
An internal 3 hour timer determines the total charge time.
After a time out occurs, the charge cycle is terminated
and the CHRG pin is forced high impedance. To restart
the charge cycle, remove and reapply the input voltage or
momentarily shut the charger down. Also, a new charge
cycle will begin if the battery voltage drops below the
recharge threshold voltage of 4.05V per cell.
When the input voltage is present, the charger can be shut
down (ICC = 3mA) by pulling the COMP pin low. When the
input voltage is not present, the charger goes into sleep
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10
LTC4002
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OPERATIO
mode, dropping ICC to 10µA. This will greatly reduce the
current drain on the battery and increase the standby time.
A 10kΩ NTC (negative temperature coefficient) thermistor
can be connected from the NTC pin to ground for battery
temperature qualification. The charge cycle is suspended
when the temperature is outside of the 0°C to 50°C
window (with DALE NTHS-1206N02).
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APPLICATIO S I FOR ATIO
Undervoltage Lockout (UVLO)
CHRG Status Output Pin
An undervoltage lockout circuit monitors the input voltage
and keeps the charger off until VCC rises above the UVLO
threshold (4.2V for the 4.2 version, 7.5V for the 8.4
version) and at least 250mV above the battery voltage. To
prevent oscillation around the threshold voltage, the UVLO
circuit has 200mV per cell of built-in hysteresis. When
specifying minimum input voltage requirements, the voltage drop across the input blocking diode must be added
to the minimum VCC supply voltage specification.
When a charge cycle starts, the CHRG pin is pulled to
ground by an internal N-channel MOSFET which is capable
of driving an LED. When the charge current drops below
the End-of-Charge threshold for more than 120µs, the
N-channel MOSFET turns off and a weak 25µA current
source to ground is connected to the CHRG pin. This weak
25µA pull-down remains until the timer ends the charge
cycle, or the charger is in manual shutdown or sleep mode.
Trickle Charge and Defective Battery Detection
At the beginning of a charge cycle, if the battery voltage is
below the trickle charge threshold, the charger goes into
trickle charge mode with the charge current reduced to
10% of the full-scale current. If the low-battery voltage
persists for 30 minutes, the battery is considered defective, the charge cycle is terminated and the CHRG pin is
forced high impedance.
Shutdown
After a time out occurs (charge cycle ends), the pin will
become high impedance. By using two different value resistors, a microprocessor can detect three states from this
pin (charging, end-of-charge and charging stopped) see
Figure 1.
VDD
VCC
LTC4002
390k
2k
CHRG
µPROCESSOR
OUT
IN
4002 F02
The LTC4002 can be shut down by pulling the COMP pin
to ground which pulls the GATE pin high turning off the
external P-channel MOSFET. When the COMP pin is released, the internal timer is reset and a new charge cycle
starts. In shutdown, the output of the CHRG pin is high
impedance and the quiescent current remains at 3mA.
Removing the input power supply will put the charger
into sleep mode. If the voltage at the VCC pin drops below
(VBAT + 250mV) or below the UVLO level, the LTC4002
goes into a low current (ICC = 10µA) sleep mode, reducing
the battery drain current.
Figure 1. Microprocessor Interface
To detect the charge mode, force the digital output pin,
OUT, high and measure the voltage at the CHRG pin. The
N-channel MOSFET will pull the pin low even with a 2k
pull-up resistor. Once the charge current drops below the
End-of-Charge threshold, the N-channel MOSFET is turned
off and a 25µA current source is connected to the CHRG
pin. The IN pin will then be pulled high by the 2k resistor
connected to OUT. Now force the OUT pin into a high
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11
LTC4002
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APPLICATIO S I FOR ATIO
impedance state, the current source will pull the pin low
through the 390k resistor. When the internal timer has
expired, the CHRG pin changes to a high impedance state
and the 390k resistor will then pull the pin high to indicate
charging has stopped.
Gate Drive
The LTC4002 gate driver can provide high transient currents to drive the external pass transistor. The rise and fall
times are typically 20ns and 50ns respectively when
driving a 2000pF load, which is typical for a P-channel
MOSFET with RDS(ON) in the range of 50mΩ.
A voltage clamp is added to limit the gate drive to 8V below
VCC. For example, if VCC is 10V then the GATE output will
pull down to 2V max. This allows low voltage P-channel
MOSFETs with superior RDS(ON) to be used as the pass
transistor thus increasing efficiency.
Stability
Both the current loop and the voltage loop share a common, high impedance, compensation node (COMP pin). A
series capacitor and resistor on this pin compensates both
loops. The resistor is included to provide a zero in the loop
response and boost the phase margin.
The compensation capacitor also provides a soft-start
function for the charger. Upon start-up, the COMP pin
voltage will quickly rise to 0.22V, due to the 2.2k series
resistor, then ramp at a rate set by the internal 100µA pullup current source and the external capacitor. Battery
charge current starts ramping up when the COMP pin
voltage reaches 0.8V and full current is achieved with the
COMP pin at 1.3V. With a 0.47µF capacitor, time to reach
full charge current is about 2.35ms. Capacitance can be
increased up to 1µF if a longer start-up time is needed.
Automatic Battery Recharge
After the 3 hour charge cycle is completed and both the
battery and the input power supply (wall adapter) are still
connected, a new charge cycle will begin if the battery
voltage drops below 4.05V per cell due to self-discharge
or external loading. This will keep the battery capacity at
more than 80% at all times without manually restarting the
charge cycle.
Battery Temperature Detection
A negative temperature coefficient (NTC) thermistor
located close to the battery pack can be used to monitor
battery temperature and will not allow charging unless the
battery temperature is within an acceptable range.
Connect a 10kΩ thermistor (DALE NTHS-1206N02) from
the NTC pin to ground. If the temperature rises to 50°C, the
resistance of the NTC will be approximately 4.1kΩ. With
the 85µA pull-up current source, the Hot temperature
voltage threshold is 350mV. For Cold temperature, the
voltage threshold is set at 2.465V which is equal to 0°C
(RNTC ≅ 28.4kΩ) with 85µA of pull-up current. If the
temperature is outside the window, the GATE pin will be
pulled up to VCC and the timer frozen while the output
status at the CHRG pin remains the same. The charge cycle
begins or resumes once the temperature is within the
acceptable range. Short the NTC pin to ground to disable
the temperature qualification feature.
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12
LTC4002
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APPLICATIO S I FOR ATIO
Input and Output Capacitors
Since the input capacitor is assumed to absorb all input
switching ripple current in the converter, it must have an
adequate ripple current rating. Worst-case RMS ripple current is approximately one-half of output charge current.
Actual capacitance value is not critical. Solid tantalum
capacitors have a high ripple current rating in a relatively
small surface mount package, but caution must be used
when tantalum capacitors are used for input bypass. High
input surge currents can be created when the adapter is
hot-plugged to the charger and solid tantalum capacitors
have a known failure mechanism when subjected to very
high turn-on surge currents. Selecting the highest possible voltage rating on the capacitor will minimize problems. Consult with the manufacturer before use.
The selection of output capacitor COUT is primarily determined by the ESR required to minimize ripple voltage and
load step transients. The output ripple ∆VOUT is approximately bounded by:
⎛
⎞
1
∆VOUT ≤ ∆IL ⎜ ESR +
⎟
⎝
8 fOSCCOUT ⎠
Since ∆IL increases with input voltage, the output ripple is
highest at maximum input voltage. Typically, once the ESR
requirement is satisfied, the capacitance is adequate for
filtering and has the necessary RMS current rating.
Switching ripple current splits between the battery and the
output capacitor depending on the ESR of the output capacitor and the battery impedance. EMI considerations
usually make it desirable to minimize ripple current in the
battery leads. Ferrite beads or an inductor may be added
to increase battery impedance at the 500kHz switching
frequency. If the ESR of the output capacitor is 0.2Ω and
the battery impedance is raised to 4Ω with a bead or inductor, only 5% of the current ripple will flow in the battery.
Design Example
As a design example, take a charger with the following
specifications: VIN = 5V to 22V, VBAT = 4V nominal, IBAT =
1.5A, fOSC = 500kHz, see Figure 2.
First, calculate the SENSE resistor :
RSENSE = 100mV/1.5A = 68mΩ
Choose the inductor for about 65% ripple current at the
maximum VIN:
L=
4V
4V ⎞
⎛
⎜ 1–
⎟ = 6.713µH
(500kHz)(0.65)(1.5A) ⎝ 22V ⎠
Selecting a standard value of 6.8µH results in a maximum
ripple current of :
∆IL =
4V
4V ⎞
⎛
⎜ 1–
⎟ = 962.6mA
(500kHz)(6.8µH) ⎝ 22V ⎠
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13
LTC4002
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APPLICATIO S I FOR ATIO
Board Layout Suggestions
Next, choose the P-channel MOSFET. The Si6435ADQ in
a TSSOP-8 package with RDS(ON) = 42mΩ (nom), 55mΩ
(max) offers a small solution. The maximum power dissipation with VIN = 5V and VBAT = 4V at 50°C ambient
temperature is:
When laying out the printed circuit board, the following
considerations should be taken to ensure proper operation of the LTC4002.
GATE pin rise and fall times are 20ns and 50ns respectively
(with CGATE = 2000pF). To minimize radiation, the catch
diode, pass transistor and the input bypass capacitor
traces should be kept as short as possible. The positive
side of the input capacitor should be close to the source of
the P-channel MOSFET; it provides the AC current to the
pass transistor. The connection between the catch diode
and the pass transistor should also be kept as short as
possible. The SENSE and BAT pins should be connected
directly to the sense resistor (Kelvin sensing) for best
charge current accuracy. Avoid routing the NTC PC board
trace near the MOSFET switch to minimize coupling switching noise into the NTC pin.
2
(1.5A) (55m Ω)(4V) = 0.099 W
PD =
5V
TJ = 50°C + (0.099W)(65°C/W) = 56.5°C
CIN is chosen for an RMS current rating of about 0.8A at
85°C. The output capacitor is chosen for an ESR similar to
the battery impedance of about 100mΩ. The ripple voltage
on the BAT pin is:
∆IL(MAX) (ESR)
2
(0.96A)(0.1Ω) = 48mV
=
2
C1: Taiyo Yuden TMK325BJ106MM
C2: Taiyo Yuden JMK325BJ226MM
L1: TOKO B952AS-6R8N
VOUT(RIPPLE) =
The compensation capacitor connected at the COMP pin
should return to the ground pin of the IC or as close to it
as possible. This will prevent ground noise from disrupting the loop stability. The ground pin also works as a heat
sink, therefore use a generous amount of copper around
the ground pin. This is especially important for high VCC
and/or high gate capacitance applications.
The Schottky diode D2 shown in Figure 2 conducts current
when the pass transistor is off. In a low duty cycle case, the
current rating should be the same or higher than the
charge current. Also it should withstand reverse voltage as
high as VIN.
VIN
5V TO 22V
D1
B330
BAT
2
C3
0.1µF
CER
R1
2k
VCC
GATE
3
C1
10µF
CER
M1
Si6435ADQ
D2
B330
LTC4002ES8-4.2
CHARGE
STATUS
5
1
CC
0.47µF
RC
2.2k
CHRG
COMP
NTC
SENSE
BAT
GND
8
T
4
10k
NTC
7
6
L1
6.8µH
RSENSE
68mΩ
C2
22µF
CER
+
4.2V
Li-Ion
BATTERY
4002 F02
NTC: DALE NTHS-1206N02
Figure 2. 1.5A Single Cell Li-Ion Battery Charger
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14
LTC4002
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PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115
TYP
6
0.38 ± 0.10
10
0.675 ±0.05
3.50 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
3.00 ±0.10
(4 SIDES)
PACKAGE
OUTLINE
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD10) DFN 1103
5
0.25 ± 0.05
0.50 BSC
0.75 ±0.05
0.200 REF
0.25 ± 0.05
1
0.50
BSC
2.38 ±0.05
(2 SIDES)
2.38 ±0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
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
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
NOTE 3
.045 ±.005
.050 BSC
8
.245
MIN
7
6
5
.160 ±.005
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
1
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
× 45°
(0.254 – 0.508)
.008 – .010
(0.203 – 0.254)
3
4
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
NOTE:
1. DIMENSIONS IN
2
.014 – .019
(0.355 – 0.483)
TYP
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
.050
(1.270)
BSC
SO8 0303
4002f
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.
15
LTC4002
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TYPICAL APPLICATIO
2-Cell 8.4V, 2A Li-Ion Battery Charger
VIN
9V TO 12V
R1
100k
M2
1/2 Si9933ADY
2
C3
0.1µF
CER
VCC
GATE
3
LTC4002ES8-8.4
5
1
CC
0.47µF
CHRG
SENSE
BAT
COMP
NTC
GND
8
4
RC
2.2k
T
10k
NTC
M1
1/2 Si9933ADY
C1
10µF
CER
D2
B330
L1
6.8µH
7
6
RSENSE
50mΩ
C2
22µF
CER
+
8.4V
Li-Ion
BATTERY
4002 TA03
NTC: DALE NTHS-1206N02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1732-8.4
2-Cell Li-Ion Linear Battery Charger
8.8V ≤ VIN ≤ 12V; Programmable Charge Termination Timer
Standalone Charger
LTC1733
Li-Ion Battery Charger with Termal Regulation
Standalone Charger, Constant-Current/Constant-Voltage/
Constant-Temperature, Integrated MOSFET, No External Sense
Resistor or Blocking Diodes
LTC1734/LTC1734L
SOT-23 Li-Ion Battery Chargers
Need Only Two External Components, Monitors Charge Current, No
Reverse Diode or Sense Resistor Required, 50mA to 700mA
LTC1980
Combination Battery Charger and DC/DC Converter
Wall Adapter May Be Above or Below Battery Voltage, Standalone,
1-, 2-Cell Li-Ion, Also for Charging NiMH and NiCd Batteries
LTC4006/LTC4007
LTC4008
4A Multiple Cell Li-Ion, NiCd, NiMH, Lead Acid
Battery Chargers
6V ≤ VIN ≤ 28V, High Efficiency ≥ 90%, VOUT ≤ 28V,
Digital Interface I/O, Small Inductor
LTC4052/LTC1730
Integrated Pulse Chargers for a 1-Cell Li-Ion Battery
0.35Ω Internal N-FET Requires No Blocking Diode,
Current Limit for Safety
LTC4053
USB Compatible Li-Ion Linear Battery Charger
Charges from USB Input or AC/DC, 100mA/500mA Up to 1.25A,
Thermal Regulation, Fully Integrated
LTC4054
Standalone Linear Li-Ion Battery Charger
with Integrated Pass Transistor in ThinSOTTM
Thermal Regulation Prevents Overheating, C/10 Termination,
C/10 Indicator
LTC4056
Standalone SOT-23 Li-Ion Linear Battery Charger
Charge Termination Included, ICH ≤ 700mA, 8-Lead ThinSOT Package
LTC4412/LTC4413
TM
Low Loss PowerPath Controllers in ThinSOT
Automatic Switching Between DC Sources, Simplified Load Sharing
PowerPath and ThinSOT are trademarks of Linear Technology Corporation.
4002f
16
Linear Technology Corporation
LT/TP 1104 1K PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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