LTC4002-4.2
1
400242i
s
Portable Computers
s
Charging Docks
s
Handheld Instruments
, LTC and LT are registered trademarks of Linear Technology Corporation.
s
Wide Input Supply Range: 4.7V to 24V
s
High Efficiency Current Mode PWM Controller with
500kHz Switching Frequency
s
1% Charge Voltage Accuracy
s
End-of-Charge Current Detection Output
s
3 Hour Charge Termination Timer
s
Constant Switching Frequency for Minimum Noise
s
5% Charge Current Accuracy
s
Low 10
A Reverse Battery Drain Current
s
Automatic Battery Recharge
s
Automatic Shutdown When Input Supply is Removed
s
Automatic Trickle Charging of Low Voltage Batteries
s
Battery Temperature Sensing and Charge
Qualification
s
Stable with Ceramic Output Capacitor
s
8-Lead SO and 10-Lead DFN Packages
Standalone Li-Ion
Switch Mode Battery Charger
June 2003
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
Final Electrical Specifications
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
The LTC
4002-4.2 is a complete battery charger controller
for single cell 4.2V lithium-ion batteries. With a 500kHz
switching frequency, the LTC4002-4.2 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 with
1% accuracy.
When the input supply is removed, the LTC4002-4.2
automatically enters a low current sleep mode, dropping
the battery drain current to 10
A. 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, a new charge cycle will automatically
begin.
The LTC4002-4.2 is available in the 8-lead SO and 10-lead
DFN packages.
L1
6.8
H
Si6435ADQ
2
3
7
6
1
5
4
8
B330B-13
B330B-13
22
F
CER
+
400242 F01
NTC: DALE NTHS-1206N02
10
F
CER
0.1
F
CER
0.47
F
2.2k
68m
Li-Ion
BATTERY
10k
NTC
SENSE
GATE
BAT
CHRG
LTC4002ES8-4.2
V
CC
V
IN
5V TO 24V
BAT
NTC
GND
COMP
2k
CHARGE
STATUS
T
Figure 1. 1.5A Single Cell Li-Ion Battery Charger
INPUT VOLTAGE (V)
5
EFFICIENCY (%)
80
V
BAT
= 4V
90
25
400242 TA02
70
60
10
15
20
100
V
BAT
= 3.8V
I
CHRG
= 1.5A
R
SENSE
= 68m
(CURVES INCLUDE
INPUT DIODE)
Efficiency vs Input Voltage
LTC4002-4.2
2
400242i
Supply Voltage (V
CC
) .............................................. 24V
GATE .................................................. (V
CC
8V) to V
CC
BAT, SENSE .............................................. 0.3V to 14V
CHRG, COMP, NTC ..................................... 0.3V to 8V
ORDER PART
NUMBER
Consult LTC Marketing for parts specified with wider operating temperature ranges.
LTC4002EDD-4.2
ABSOLUTE AXI U
RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
(Note 1)
T
JMAX
= 125
C,
JA
= 110
C/W
1
2
3
4
8
7
6
5
TOP VIEW
NTC
SENSE
BAT
CHRG
COMP
V
CC
GATE
GND
S8 PACKAGE
8-LEAD PLASTIC SO
DD PART MARKING
LAGG
Operating Temperature Range (Note 2) .. 40
C to 85
C
Storage Temperature Range ................. 65
C to 150
C
Lead Temperature (Soldering, 10 sec).................. 300
C
TOP VIEW
11
DD PACKAGE
10-LEAD (3mm
3mm) PLASTIC DFN
10
9
6
7
8
4
5
3
2
1
NC
NTC
SENSE
BAT
CHRG
COMP
V
CC
GATE
PGND
SGND
ORDER PART
NUMBER
LTC4002ES8-4.2
S8 PART MARKING
400242
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. V
CC
= 10V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
DC Characteristics
V
CC
V
CC
Supply Voltage
q
4.7
24
V
I
CC
V
CC
Supply Current
Current Mode
3
5
mA
Shutdown Mode
3
5
mA
Sleep Mode
10
20
A
V
BAT
Battery Regulated Float Voltage
5V
V
CC
24V (Note 2)
4.168
4.2
4.232
V
q
4.158
4.242
V
V
SNS(CHG)
Constant Current Sense Voltage
3V
V
BAT
4V (Note 3)
0
C
T
A
85
C
q
93
100
107
mV
40
C
T
A
85
C
q
90
110
mV
V
SNS(TRKL)
Trickle Current Sense Voltage
V
BAT
= 0V (Note 3)
5
10
15
mV
V
TRKL
Trickle Charge Threshold Voltage
V
BAT
Rising
2.75
2.9
3.05
V
V
UV
V
CC
Undervoltage Lockout Threshold Voltage
V
CC
Rising
3.9
4.2
4.5
V
V
UV
V
CC
Undervoltage Lockout Hysteresis Voltage
200
mV
V
MSD
Manual Shutdown Threshold Voltage
COMP Pin Falling
200
360
500
mV
V
ASD
Automatic Shutdown Threshold Voltage
V
CC
V
BAT
250
mV
I
COMP
COMP Pin Output Current
V
COMP
= 1.2V
100
A
I
CHRG
CHRG Pin Weak Pull-Down Current
V
CHRG
= 1V
15
25
35
A
V
CHRG
CHRG Pin Output Low Voltage
I
CHRG
= 1mA
0.15
0.3
V
R
EOC
End-of-Charge Ratio
V
SNS(EOC)
/V
SNS(CHG)
10
25
32
%
t
TIMER
Charge Time Accuracy
10
%
T
JMAX
= 125
C,
JA
= 43
C/W
EXPOSED PAD IS GND (PIN 11)
MUST BE SOLDERED TO PCB
LTC4002-4.2
3
400242i
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. V
CC
= 10V unless otherwise noted.
Note 1: Absolute Maximum Rating are those values beyond which the life
of a device may be impaired.
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Supply Current vs Temperature
Supply Current vs V
CC
Oscillator Frequency
vs Temperature
Note 2: The LTC4002-4.2 is tested with Test Circuit 1.
Note 3: The LTC4002-4.2 is tested with Test Circuit 2.
TEMPERATURE (
C)
50
I
CC
(mA)
3.5
4.0
25
75
400242 G01
3.0
25
0
50
100
125
2.5
V
CC
(V)
5
I
CC
(mA)
3
25
400242 G02
2
10
15
20
4
CURRENT MODE
TEMPERATURE (
C)
50
f
OSC
(kHz)
25
400242 G03
500
25
0
50
450
550
75
100
125
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
NTC
NTC Pin Output Current
V
NTC
= 0.85V
q
75
85
95
A
V
NTC-HOT
NTC Pin Threshold Voltage (Hot)
V
NTC
Falling
q
340
355
370
mV
Hysteresis
25
mV
V
NTC-COLD
NTC Pin Threshold Voltage (Cold)
V
NTC
Rising
q
2.428
2.465
2.502
V
Hysteresis
170
mV
V
RECHRG
Recharge Battery Voltage Offset from Full
V
BAT(FULLCHARGED)
V
RECHRG
, V
BAT
Falling
100
150
200
mV
Charged Battery Voltage
I
LEAK
CHRG Pin Leakage Current
V
CHRG
= 8V, Charging Stops
1
A
Oscillator
f
OSC
Switching Frequency
450
500
550
kHz
DC
Maximum Duty Cycle
100
%
Gate Drive
t
r
Rise Time
C
GATE
= 2000pF, 10% to 90%
20
ns
t
f
Fall Time
C
GATE
= 2000pF, 90% to 10%
50
ns
V
GATE
Output Clamp Voltage
V
CC
V
GATE
, V
CC
9V
q
8
V
V
GATEHI
Output High Voltage
V
GATEHI
= V
CC
V
GATE
, V
CC
7V
q
0.3
V
V
GATELO
Output Low Voltage
V
GATELO
= V
CC
V
GATE
, V
CC
7V
q
4.5
V
T
A
= 25
C, V
CC
= 10V unless otherwise noted.
LTC4002-4.2
4
400242i
Oscillator Frequency vs V
CC
Current Mode Sense Voltage
vs Temperature
Trickle Charge Voltage
vs Temperature
Trickle Charge Voltage
vs V
CC
V
CC
(V)
5
f
OSC
(kHz) 500
25
400242 G04
490
10
15
20
510
TEMPERATURE (
C)
50
V
SNS
(mV)
25
400242 G05
100
25
0
50
96
104
75
100
125
V
BAT
= 4V
Current Mode Sense Voltage
vs V
CC
V
CC
(V)
5
V
SNS
(mV) 100
25
400242 G04
98
10
15
20
102
V
BAT
= 4V
TEMPERATURE (
C)
50
V
TRKL
(V)
25
400242 G07
2.9
25
0
50
2.8
3.0
75
100
125
V
CC
(V)
5
V
TRKL
(V)
2.9
25
400242 G08
2.8
10
15
20
3.0
V
BAT
= 4V
CHRG Pin Output Low Voltage
vs V
CC
CHRG Pin Output Low Voltage
vs Temperature
V
CC
(V)
5
V
CHRG
(mV)
140
25
400242 G09
130
10
15
20
150
I
LOAD
= 1mA
TEMPERATURE (
C)
50
V
CHG
(mV)
25
400242 G10
140
25
0
50
100
180
75
100
125
I
LOAD
= 1mA
CHRG Pin Weak Pull-Down
Current vs Temperature
CHRG Output Pin Weak Pull-Down
Current vs V
CC
TEMPERATURE (
C)
50
I
CHRG
(
A)
25
400242 G23
25
25
0
50
21
29
75
100
125
V
CHRG
= 8V
V
CC
(V)
5
22
I
CHRG
(
A)
25
28
10
15
20
25
400242 G11
V
CHRG
= 8V
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
T
A
= 25
C, V
CC
= 10V unless otherwise noted.
LTC4002-4.2
5
400242i
NTC Pin Output Current
vs V
CC
Recharge Voltage Offset from Full
Charged Voltage vs Temperature
Recharge Voltage Offset from Full
Charged Voltage vs V
CC
End-of-Charge Ratio
vs Temperature
Trickle Charge Sense Voltage
vs Temperature
Trickle Charge Sense Voltage
vs V
CC
TEMPERATURE (
C)
50
V
SNS
(mV)
25
400242 G12
10.0
25
0
50
9.6
10.4
75
100
125
V
BAT
= 2.5V
V
CC
(V)
5
V
SNS
(mV)
10
25
400242 G13
9
10
15
20
11
V
BAT
= 2.5V
NTC Pin Output Current
vs Temperature
COMP Pin Output Current
vs V
CC
COMP Pin Output Current
vs Temperature
V
CC
(V)
5
I
COMP
(
A)
100
25
400242 G14
98
10
15
20
102
V
COMP
= 0V
TEMPERATURE (
C)
50
I
COMP
(
A)
25
400242 G15
100
25
0
50
96
104
75
100
125
V
COMP
= 0V
V
CC
(V)
5
I
NTC
(
A)
85
25
400242 G16
84
10
15
20
86
V
NTC
= 0V
TEMPERATURE (
C)
50
I
NTC
(
A)
25
400242 G17
85
25
0
50
81
89
75
100
125
V
NTC
= 0V
TEMPERATURE (
C)
50
V
RECHRG
(mV)
25
400242 G18
150
25
0
50
110
190
75
100
125
V
CC
(V)
5
V
RECHRG
(mV)
150
25
400242 G19
140
10
15
20
160
TEMPERATURE (
C)
50
R
EOC
(%)
25
400242 G20
25
25
0
50
21
29
75
100
125
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
T
A
= 25
C, V
CC
= 10V unless otherwise noted.
LTC4002-4.2
6
400242i
U
U
U
PI FU CTIO S
COMP (Pin 1/Pin 1): Compensation, Soft-Start and Shut-
down 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 compen-
sation components are a 0.47
F (or larger) capacitor and
a 2.2k series resistor. A 100
A current into the compen-
sation capacitor also sets the soft-start slew rate. Pulling
the COMP pin below 350mV will shut down the charger.
V
CC
(Pin 2/Pin 2): Positive Supply Voltage Input. V
CC
can
range from 4.7V to 24V. A 0.1
F or higher capacitor is
required at the V
CC
pin with the lead length kept to a mini-
mum. A 10
F 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 V
CC
, 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, 11/4): IC
Ground.
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 to 25% of the full-scale current for more than
120
s, the N-channel MOSFET turns off and a 25
A cur-
rent source is connected from the CHRG pin to GND. When
the timer runs out or the input supply is removed, the 25
A
current source is turned off and the CHRG pin becomes high
impedance.
BAT (Pin 7/Pin 6): Battery Sense Input. A bypass capaci-
tor of 22
F 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 V
BAT
is within 250mV of V
CC
, the LTC4002-4.2 is
forced into sleep mode, dropping I
CC
to 10
A.
SENSE (Pin 8/Pin 7): Current Amplifier Sense Input. A sense
resistor, R
SENSE
, must be connected between the SENSE
and BAT pins. The maximum charge current is equal to
100mV/R
SENSE
.
NTC (Pin 9/Pin 8): NTC (Negative Temperature Coefficient)
Thermistor Input. With an external 10k
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 350mV at
Undervoltage Lockout Threshold
vs Temperature
End-of-Charge Ratio
vs V
CC
V
CC
(V)
5
21
R
EOC
(%)
25
29
10
15
20
25
400242 G21
TEMPERATURE (
C)
50
V
UV
(V)
25
400242 G22
4.2
25
0
50
4.0
4.4
75
100
125
V
CC
RISING
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
T
A
= 25
C, V
CC
= 10V unless otherwise noted.
(DFN/SO-8)
LTC4002-4.2
7
400242i
BLOCK DIAGRA
W
+
+
C
EOC
20mV
DRIVER
+
100mV
SENSE
+
CA
+
VA
+
C
LB
+
C
OV
+
C
RQ
+
C
COLD
+
C
HOT
+
GATE
BAT
4.2V
2.9V
4.62V
4.05V
2.465V
350mV
50mV
400242 BD
NTC
V
CC
85
A
TEMP
RQ
UV
LOGIC
NTC_DISABLE
EOC
STOP
SD
C/10
UVLO
4.2V
R
R
S
CLK:
Q
+
C
PWM
R
SLOP
I
L
I
SLOP
100
A
R
IL
M1
M2
M3
V
CC
COMP
CHRG
GND
+
C
SD
350mV
Q4
Q5
25
A
90
A
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.
LTC4002-4.2
8
400242i
TEST CIRCUITS
Test Circuit 1
Test Circuit 2
+
+
100
A
LTC4002-4.2
SENSE
BAT
V
BAT
400242 TC01
R
SENSE
10
CA
COMP
0V
LT1006
15V
1.5V
+
+
100
A
LTC4002-4.2
SENSE
BAT
4.2V
400242 TC02
R
SENSE
10
CA
+
VA
COMP
0V
LT1006
15V
1.5V
1mA
LTC4002-4.2
9
400242i
OPERATIO
U
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 (R
SENSE
)
across the SENSE and BAT pins. The final battery float
voltage is internally set to 4.2V. For batteries like lithium-
ion that require accurate final float voltage, the internal
2.465V reference, voltage amplifier and the resistor di-
vider provide regulation with
1% accuracy.
A charge cycle begins when the voltage at the V
CC
pin rises
above the UVLO level (4.2V) and is 250mV or more greater
than the battery voltage. At the beginning of the charge
cycle, if the battery voltage is less than 2.9V, 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 2.9V, the charger goes
into the full-scale constant current charge mode. In con-
stant current mode, the charge current is set by the
external sense resistor R
SENSE
and an internal 100mV
reference; I
BAT
= 100mV/R
SENSE
.
When the battery voltage approaches the programmed
float voltage, the charge current will start to decrease.
When the current drops to 25% 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.
When the input voltage is present, the charger can be shut
down (I
CC
= 3mA) by pulling the COMP pin low. When the
input voltage is not present, the charger goes into sleep
mode, dropping I
CC
to 10
A. This will greatly reduce the
current drain on the battery and increase the standby time.
A 10k
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).
LTC4002-4.2
10
400242i
APPLICATIO S I FOR ATIO
W
U
U
U
Undervoltage Lockout (UVLO)
An undervoltage lockout circuit monitors the input voltage
and keeps the charger off until V
CC
rises above 4.2V and
at least 250mV above the battery voltage. To prevent
oscillation around the threshold voltage, the UVLO circuit
has 200mV of built-in hysteresis.
Trickle Charge and Defective Battery Detection
At the beginning of a charge cycle, if the battery voltage is
below 2.9V, the charger goes into trickle charge mode with
the charge current reduced to 10% of the full-scale cur-
rent. If the low-battery voltage persists for 30 minutes, the
battery is considered defective, the charge cycle is termi-
nated and the CHRG pin is forced to be high impedance.
Shutdown
The LTC4002 can be shut down by pulling the COMP pin
to ground which pulls the GATE pin high and turns off the
external P-channel MOSFET. When the COMP pin is re-
leased, 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 V
CC
pin drops below
(V
BAT
+ 250mV) or below the UVLO level (4.2V), the
LTC4002-4.2 goes into a low current (I
CC
= 10
A) sleep
mode, reducing the battery drain current.
CHRG Status Output Pin
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 to 25%
of the full-scale current for more than 120
s, the N-channel
MOSFET turns off and a weak 25
A current source to
ground is connected to the CHRG pin. This weak 25
A
pull-down remains until the timer ends the charge cycle,
or the charger is in manual shutdown or sleep mode.
After a time out occurs (charge cycle ends), the pin will go
into high impedance. By using two different value resis-
tors, a microprocessor can detect three states from this
pin (charging, end-of-charge and charging stopped) see
Figure 2.
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 to 25% of
the full-scale current, the N-channel MOSFET is turned off
and a 25
A 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
impedance state, the current source will pull the pin low
through the 400k resistor. When the internal timer has
expired, the CHRG pin changes to a high impedance state
and the 400k resistor will then pull the pin high to indicate
the charging has stopped.
2k
400k
V
DD
V
CC
OUT
CHRG
PROCESSOR
LTC4002-4.2
IN
400242 F02
Figure 2. Microprocessor Interface
LTC4002-4.2
11
400242i
Gate Drive
The LTC4002-4.2 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 R
DS(ON)
in the range of 50m
.
A voltage clamp is added to limit the gate drive to 8V below
V
CC
. For example, if V
CC
is 10V then the GATE output will
pull down to 2V max. This allows low voltage P-channel
MOSFETs with superior R
DS(ON)
to be used as the pass
transistor thus increasing efficiency.
Stability
Both the current loop and the voltage loop share a com-
mon, 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 0.05V, due to the 2.2k series
resistor, then ramp at a rate set by the internal 100
A pull-
up 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 0.47
F capacitor, time to reach
full charge current is about 235ms. Capacitance can be
increased up to 1
F 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 due to self-discharge or exter-
nal 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 10k
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 4.1k
. With
the 85
A pull-up current source, the Hot temperature
voltage threshold is 350mV. For Cold temperature, the
voltage threshold is set at 2.456V which is equal to 0
C
(R
NTC
28.4k
) with 85
A of pull-up current. If the
temperature is outside the window, the GATE pin will be
pulled up to V
CC
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.
APPLICATIO S I FOR ATIO
W
U
U
U
LTC4002-4.2
12
400242i
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 cur-
rent 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 pos-
sible voltage rating on the capacitor will minimize prob-
lems. Consult with the manufacturer before use.
The selection of output capacitor C
OUT
is primarily deter-
mined by the ESR required to minimize ripple voltage and
load step transients. The output ripple
V
OUT
is approxi-
mately bounded by:
+
V
I ESR
f
C
OUT
L
OSC OUT
1
8
Since
I
L
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.
APPLICATIO S I FOR ATIO
W
U
U
U
Switching ripple current splits between the battery and the
output capacitor depending on the ESR of the output ca-
pacitor 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 0.2
and
the battery impedance is raised to 4
with a bead or induc-
tor, only 5% of the current ripple will flow in the battery.
Design Example
As a design example, take a charger with the following
specifications: V
IN
= 5V to 24V, V
BAT
= 4V nominal, I
BAT
=
1.5A, f
OSC
= 500kHz, see Figure 1.
First, calculate the SENSE resistor :
R
SENSE
= 100mV/1.5A = 68m
Choose the inductor for about 65% ripple current at the
maximum V
IN
:
L
V
kHz
A
V
V
H
=
(
)( )( )
=
4
500
0 65 1 5
1
4
24
6 838
.
.
.
Selecting a standard value of 6.8
H results in a maximum
ripple current of :
=
(
)
(
)
=
I
V
kHz
H
V
V
mA
L
4
500
6 8
1
4
24
980 4
.
.
LTC4002-4.2
13
400242i
APPLICATIO S I FOR ATIO
W
U
U
U
Next, choose the P-channel MOSFET. The Si6435ADQ in
a TSSOP-8 package with R
DS(ON)
= 42m
(nom), 55m
(max) offers a small solution. The maximum power dissi-
pation with V
IN
= 5V and V
BAT
= 4V at 50
C ambient
temperature is:
P
A
m
V
V
W
D
=
( )
(
)( )
=
1 5
55
4
5
0 099
2
.
.
T
J
= 50
C + (0.099W)(65
C/W) = 56.5
C
C
IN
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 100m
. The ripple voltage
on the BAT pin is:
V
I
ESR
A
mV
OUT RIPPLE
L MAX
(
)
(
)
.
.
=
( )
=
(
)
(
)
=
2
0 98
0 1
2
49
C1: Taiyo Yuden TMK325BJ106MM
C2: Taiyo Yuden JMK325BJ226MM
L1: TOKO B952AS-6R8N
The Schottky diode D2 shown in Figure 1 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 V
IN
.
Board Layout Suggestions
When laying out the printed circuit board, the following
considerations should be taken to ensure proper opera-
tion of the LTC4002-4.2.
GATE pin rise and fall times are 20ns and 50ns respectively
(with C
GATE
= 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.
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 disrupt-
ing 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 V
CC
and/or high gate capacitance applications.
LTC4002-4.2
14
400242i
U
PACKAGE DESCRIPTIO
3.00
0.10
(4 SIDES)
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. 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
5. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
0.38
0.10
BOTTOM VIEW--EXPOSED PAD
1.65
0.10
(2 SIDES)
0.75
0.05
R = 0.115
TYP
2.38
0.10
(2 SIDES)
1
5
10
6
PIN 1
TOP MARK
(SEE NOTE 5)
0.200 REF
0.00 0.05
(DD10) DFN 0403
0.25
0.05
2.38
0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1.65
0.05
(2 SIDES)
2.15
0.05
0.50
BSC
0.675
0.05
3.50
0.05
PACKAGE
OUTLINE
0.25
0.05
0.50 BSC
DD Package
10-Lead Plastic DFN (3mm
3mm)
(Reference LTC DWG # 05-08-1699)
LTC4002-4.2
15
400242i
U
PACKAGE DESCRIPTIO
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.016 .050
(0.406 1.270)
.010 .020
(0.254 0.508)
45
0
8
TYP
.008 .010
(0.203 0.254)
SO8 0303
.053 .069
(1.346 1.752)
.014 .019
(0.355 0.483)
TYP
.004 .010
(0.101 0.254)
.050
(1.270)
BSC
1
2
3
4
.150 .157
(3.810 3.988)
NOTE 3
8
7
6
5
.189 .197
(4.801 5.004)
NOTE 3
.228 .244
(5.791 6.197)
.245
MIN
.160
.005
RECOMMENDED SOLDER PAD LAYOUT
.045
.005
.050 BSC
.030
.005
TYP
INCHES
(MILLIMETERS)
NOTE:
1. DIMENSIONS IN
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)
LTC4002-4.2
16
400242i
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
q
FAX: (408) 434-0507
q
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2003
LT/TP 0603 1K PRINTED IN USA
PART NUMBER
DESCRIPTION
COMMENTS
LTC1732/LTC4050
Constant Voltage/Constant Current Li-Ion Linear
Standalone Battery Charger, No uC or Firmware Required, Auto
Battery Chargers
Recharge of Low Battery, 10-Pin MSOP, Input Supply Detection
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
4A Multiple Cell Li-Ion, NiCd, NiMH, Lead Acid
6V
V
IN
28V, High Efficiency
90%, V
OUT
28V,
LTC4008
Battery Chargers
Digital Interface I/O, Small Inductor
LTC4052/LTC1730
Integrated Pulse Chargers for a 1-Cell Li-Ion Battery
0.35
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
Thermal Regulation Prevents Overheating, C/10 Termination,
with Integrated Pass Transistor in ThinSOT
TM
C/10 Indicator
LTC4056
Standalone SOT-23 Li-Ion Linear Battery Charger
Charge Termination Included, I
CH
700mA, 8-Lead ThinSOT Package
LTC4412
Low Loss PowerPath
TM
Controller in ThinSOT
Automatic Switching Between DC Sources, Simplified Load Sharing
PowerPath and ThinSOT are trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
U
Single Cell 4.2V, 2A Li-Ion Battery Charger
L1
6.8
H
B330-13
1/2 Si9933ADY
1/2 Si9933ADY
C2
22
F
CER
400242 TA01
NTC: DALE NTHS-1206N02
C1
10
F
CER
0.1
F
CER
0.47
F
2.2k
R
SENSE
50m
Li-Ion
BATTERY
10k
NTC
SENSE
GATE
3
2
7
6
1
5
8
4
BAT
CHRG
LTC4002ES8-4.2
V
CC
V
IN
5V TO 12V
NTC
GND
COMP
100k
T
+
RELATED PARTS
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