LTC4002ES8-4.2 [Linear]
Standalone Li-Ion Switch Mode Battery Charger; 独立的锂离子开关模式电池充电器
| 型号： | LTC4002ES8-4.2 |
| 厂家： | 
Linear |
| 描述： | Standalone Li-Ion Switch Mode Battery Charger |
| 文件： | 总16页 (文件大小：198K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Final Electrical Specifications
LTC4002-4.2
Standalone Li-Ion
Switch Mode Battery Charger
June 2003
U
FEATURES
DESCRIPTIO
Wide Input Supply Range: 4.7V to 24V
TheLTC®4002-4.2isacompletebatterychargercontroller
for single cell 4.2V lithium-ion batteries. With a 500kHz
switching frequency, the LTC4002-4.2 provides a small,
simpleandefficientsolutiontofastchargeLi-Ionbatteries
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.
■
■
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
When the input supply is removed, the LTC4002-4.2
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, a new charge cycle will automatically
begin.
■
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 1U0-Lead DFN Packages
APPLICATIO S
■
The LTC4002-4.2 is available in the 8-lead SO and 10-lead
DFN packages.
Portable Computers
Charging Docks
, LTC and LT are registered trademarks of Linear Technology Corporation.
■
■
Handheld Instruments
U
TYPICAL APPLICATIO
V
IN
5V TO 24V
B330B-13
Efficiency vs Input Voltage
2
0.1µF
10µF
100
90
80
70
60
V
CER
CC
CER
BAT
2k
I
R
= 1.5A
SENSE
CHRG
3
GATE
Si6435ADQ
= 68mΩ
(CURVES INCLUDE
INPUT DIODE)
LTC4002ES8-4.2
B330B-13
L1
6.8µH
CHARGE
STATUS
V
BAT
= 4V
5
7
6
CHRG
SENSE
V
BAT
= 3.8V
68mΩ
1
COMP
NTC
BAT
GND
+
22µF
CER
0.47µF
Li-Ion
BATTERY
8
4
2.2k
10k
NTC
400242 F01
T
NTC: DALE NTHS-1206N02
15
INPUT VOLTAGE (V)
5
10
20
25
400242 TA02
Figure 1. 1.5A Single Cell Li-Ion Battery Charger
400242i
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-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
1
LTC4002-4.2
W W U W
ABSOLUTE AXI U RATI GS (Note 1)
Supply Voltage (VCC) .............................................. 24V
GATE .................................................. (VCC –8V) to VCC
BAT, SENSE .............................................. –0.3V to 14V
CHRG, COMP, NTC ..................................... –0.3V to 8V
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
U
W
U
PACKAGE/ORDER I FOR ATIO
TOP VIEW
ORDER PART
NUMBER
ORDER PART
TOP VIEW
NUMBER
COMP
1
2
3
4
5
10 NC
COMP
1
2
3
4
8
7
6
5
NTC
V
CC
9
8
7
6
NTC
LTC4002EDD-4.2
LTC4002ES8-4.2
11
GATE
PGND
SGND
SENSE
BAT
V
SENSE
BAT
CC
GATE
GND
CHRG
CHRG
DD PART MARKING
LAGG
S8 PART MARKING
400242
DD PACKAGE
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 110°C/W
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD IS GND (PIN 11)
MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
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
DC Characteristics
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
V
Supply Voltage
Supply Current
●
4.7
24
V
CC
CC
CC
I
Current Mode
Shutdown Mode
Sleep Mode
3
3
10
5
5
20
mA
mA
µA
CC
V
V
Battery Regulated Float Voltage
Constant Current Sense Voltage
5V ≤ V ≤ 24V (Note 2)
4.168
4.158
4.2
4.232
4.242
V
V
BAT
CC
●
3V ≤ V
≤ 4V (Note 3)
0°C ≤ T ≤ 85°C
●
●
93
90
100
107
110
mV
mV
SNS(CHG)
BAT
A
–40°C ≤ T ≤ 85°C
A
V
V
V
Trickle Current Sense Voltage
V
V
V
= 0V (Note 3)
Rising
5
10
2.9
4.2
200
360
250
100
25
15
3.05
4.5
mV
V
SNS(TRKL)
TRKL
BAT
BAT
Trickle Charge Threshold Voltage
2.75
3.9
V
V
Undervoltage Lockout Threshold Voltage
Undervoltage Lockout Hysteresis Voltage
Rising
CC
V
UV
CC
CC
∆V
mV
mV
mV
µA
UV
MSD
V
V
Manual Shutdown Threshold Voltage
Automatic Shutdown Threshold Voltage
COMP Pin Output Current
COMP Pin Falling
200
500
V
V
V
– V
BAT
ASD
CC
I
I
= 1.2V
= 1V
COMP
CHRG
COMP
CHRG
CHRG Pin Weak Pull-Down Current
CHRG Pin Output Low Voltage
End-of-Charge Ratio
15
10
35
0.3
32
10
µA
V
I
= 1mA
CHRG
0.15
25
V
CHRG
R
V
/V
SNS(EOC) SNS(CHG)
%
EOC
t
Charge Time Accuracy
%
TIMER
400242i
2
LTC4002-4.2
ELECTRICAL CHARACTERISTICS
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
75
TYP
MAX
95
UNITS
I
NTC Pin Output Current
V
= 0.85V
●
●
85
µA
NTC
NTC
V
NTC Pin Threshold Voltage (Hot)
V
Falling
340
355
25
370
mV
mV
NTC-HOT
NTC
Hysteresis
Rising
V
NTC Pin Threshold Voltage (Cold)
V
●
2.428
100
2.465
170
2.502
200
1
V
mV
NTC-COLD
NTC
Hysteresis
∆V
RECHRG
Recharge Battery Voltage Offset from Full
Charged Battery Voltage
V
– V , V Falling
RECHRG BAT
150
mV
BAT(FULLCHARGED)
I
CHRG Pin Leakage Current
V
= 8V, Charging Stops
µA
LEAK
CHRG
Oscillator
f
Switching Frequency
Maximum Duty Cycle
450
500
550
100
kHz
%
OSC
DC
Gate Drive
t
t
Rise Time
C
C
V
= 2000pF, 10% to 90%
= 2000pF, 90% to 10%
20
50
ns
ns
V
r
f
GATE
GATE
Fall Time
∆V
∆V
∆V
Output Clamp Voltage
Output High Voltage
Output Low Voltage
– V , V ≥ 9V
GATE CC
●
●
●
8
GATE
CC
∆V
∆V
= V – V , V ≥ 7V
GATE CC
0.3
V
GATEHI
GATELO
GATEHI
GATELO
CC
= V – V
, V ≥ 7V
GATE CC
4.5
V
CC
Note 1: Absolute Maximum Rating are those values beyond which the life
of a device may be impaired.
Note 2: The LTC4002-4.2 is tested with Test Circuit 1.
Note 3: The LTC4002-4.2 is tested with Test Circuit 2.
U W
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C, VCC = 10V unless otherwise noted.
Oscillator Frequency
vs Temperature
Supply Current vs Temperature
Supply Current vs VCC
4.0
3.5
550
500
450
4
CURRENT MODE
3
3.0
2.5
2
50
TEMPERATURE (°C)
100 125
–25
0
50
75 100 125
–50 –25
0
25
75
15
(V)
–50
25
5
20
25
10
TEMPERATURE (°C)
V
CC
400242 G01
400242 G03
400242 G02
400242i
3
LTC4002-4.2
U W
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C, VCC = 10V unless otherwise noted.
Current Mode Sense Voltage
vs Temperature
Current Mode Sense Voltage
vs VCC
Oscillator Frequency vs VCC
104
100
96
510
500
102
V
BAT
= 4V
V
BAT
= 4V
100
490
98
–25
0
50
75 100 125
15
(V)
20
–50
25
15
(V)
20
5
25
5
25
10
10
TEMPERATURE (°C)
V
V
CC
CC
400242 G05
400242 G04
400242 G04
Trickle Charge Voltage
vs Temperature
Trickle Charge Voltage
vs VCC
CHRG Pin Output Low Voltage
vs VCC
3.0
2.9
150
140
3.0
2.9
2.8
V
BAT
= 4V
I
= 1mA
LOAD
2.8
130
15
(V)
20
15
(V)
20
5
25
5
25
–50 –25
0
25
50
75 100 125
10
10
V
V
TEMPERATURE (°C)
CC
CC
400242 G08
400242 G09
400242 G07
CHRG Pin Weak Pull-Down
Current vs Temperature
CHRG Output Pin Weak Pull-Down
Current vs VCC
CHRG Pin Output Low Voltage
vs Temperature
28
25
22
180
140
100
29
25
21
V
CHRG
= 8V
I
= 1mA
V
CHRG
= 8V
LOAD
5
10
15
(V)
20
25
–25
0
50
75 100 125
–25
0
50
75 100 125
–50
25
–50
25
V
TEMPERATURE (°C)
TEMPERATURE (°C)
CC
400242 G11
400242 G10
400242 G23
400242i
4
LTC4002-4.2
U W
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C, VCC = 10V unless otherwise noted.
Trickle Charge Sense Voltage
vs Temperature
COMP Pin Output Current
vs VCC
Trickle Charge Sense Voltage
vs VCC
11
102
10.4
10.0
9.6
V
BAT
= 2.5V
V
COMP
= 0V
V
BAT
= 2.5V
10
100
9
98
15
(V)
20
15
(V)
20
5
25
5
25
10
10
–25
0
50
75 100 125
–50
25
V
V
TEMPERATURE (°C)
CC
CC
400242 G13
400242 G14
400242 G12
NTC Pin Output Current
vs Temperature
COMP Pin Output Current
vs Temperature
NTC Pin Output Current
vs VCC
104
100
96
86
85
89
85
81
V
= 0V
V
NTC
= 0V
V
= 0V
COMP
NTC
84
–25
0
50
75 100 125
–50
25
15
(V)
20
5
25
–25
0
50
75 100 125
10
–50
25
TEMPERATURE (°C)
V
TEMPERATURE (°C)
CC
400242 G15
400242 G16
400242 G17
End-of-Charge Ratio
vs Temperature
Recharge Voltage Offset from Full
Charged Voltage vs Temperature
Recharge Voltage Offset from Full
Charged Voltage vs VCC
160
150
190
150
110
29
25
21
140
15
(V)
20
–25
0
50
75 100 125
5
10
25
–25
0
50
75 100 125
–50
25
–50
25
V
TEMPERATURE (°C)
TEMPERATURE (°C)
CC
400242 G19
400242 G18
400242 G20
400242i
5
LTC4002-4.2
U W
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C, VCC = 10V unless otherwise noted.
End-of-Charge Ratio
vs VCC
Undervoltage Lockout Threshold
vs Temperature
29
25
21
4.4
4.2
4.0
V
CC
RISING
5
10
15
(V)
20
25
–25
0
50
75 100 125
–50
25
V
CC
TEMPERATURE (°C)
400242 G21
400242 G22
U
U
U
PI FU CTIO S (DFN/SO-8)
COMP (Pin 1/Pin 1): Compensation, Soft-Start and Shut-
downControlPin.TheCOMPpinisthecontrolsignalofthe
innerloopofthecurrentmodePWM.Chargingbeginswhen
theCOMPpinreaches800mV.Therecommendedcompen-
sation components are a 0.47µF (or larger) capacitor and
a 2.2k series resistor. A 100µA current into the compen-
sation capacitor also sets the soft-start slew rate. Pulling
the COMP pin below 350mV will shut down the charger.
120µs, the N-channel MOSFET turns off and a 25µA cur-
rentsourceisconnectedfromtheCHRGpintoGND.When
thetimerrunsoutortheinputsupplyisremoved,the25µA
currentsourceisturnedoffandtheCHRGpinbecomeshigh
impedance.
BAT (Pin 7/Pin 6): Battery Sense Input. A bypass capaci-
tor 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.
VCC (Pin 2/Pin 2): Positive Supply Voltage Input. VCC can
range from 4.7V to 24V. A 0.1µF or higher capacitor is
required at the VCC pin with the lead length kept to a mini-
mum. A 10µF low ESR capacitor is also required at the
source pins of the power P-channel MOSFET.
When VBAT is within 250mV of VCC, the LTC4002-4.2 is
forced into sleep mode, dropping ICC to 10µA.
GATE (Pin 3/Pin 3): Gate Drive Output. Driver Output for
theP-ChannelMOSFET. Thevoltageatthispinisinternally
clamped to 8V below VCC, allowing a low voltage MOSFET
with gate-to-source breakdown voltage of 8V or less to be
used.
SENSE(Pin8/Pin7):CurrentAmplifierSenseInput.Asense
resistor, RSENSE, must be connected between the SENSE
and BAT pins. The maximum charge current is equal to
100mV/RSENSE
.
PGND, SGND, Exposed Pad, GND (Pins 4, 5, 11/4): IC
Ground.
NTC(Pin9/Pin8):NTC(NegativeTemperatureCoefficient)
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 350mV at
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
currentdropsto25%ofthefull-scalecurrentformorethan
400242i
6
LTC4002-4.2
U
U
U
(DFN/SO-8)
PI FU CTIO S
hottemperatureorrisesabove2.465Vatcoldtemperature,
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
V
CC
CLK:
100µA
I
I
L
SLOP
COMP
DRIVER
–
+
GATE
S
Q
C
PWM
R
R
20mV
R
SLOP
IL
+
–
+
–
C
EOC
R
100mV
SENSE
+
–
+
–
M1
CA
VA
BAT
+
–
M2
4.2V
2.9V
4.62V
+
–
M3
C
LB
OV
RQ
90µA
+
–
C
C
UVLO
4.2V
+
–
+
–
UV EOC
C
SD
SD
RQ
350mV
4.05V
LOGIC
CHRG
C/10
Q4
+
–
2.465V
V
CC
STOP
TEMP
C
COLD
Q5
NTC_DISABLE
85µA
25µA
NTC
–
+
GND
C
HOT
350mV
50mV
400242 BD
+
–
400242i
7
LTC4002-4.2
TEST CIRCUITS
Test Circuit 1
15V
–
1.5V
LT1006
+
0V
LTC4002-4.2
100µA
SENSE
BAT
–
+
COMP
R
SENSE
CA
10Ω
V
BAT
400242 TC01
Test Circuit 2
15V
–
+
1.5V
LT1006
0V
SENSE
–
100µA
COMP
R
SENSE
CA
VA
BAT
10Ω
+
1mA
–
+
4.2V
LTC4002-4.2
400242 TC02
400242i
8
LTC4002-4.2
U
OPERATIO
The LTC4002 is a constant current, constant voltage
Li-Ion battery charger controller that uses a current mode
PWMstep-down(buck)switchingarchitecture.Thecharge
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.
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. 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.
Aninternal3hourtimerdeterminesthetotalchargetime.
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.
AchargecyclebeginswhenthevoltageattheVCC pinrises
abovetheUVLOlevel(4.2V)andis250mVormoregreater
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 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
mode, dropping ICC to 10µA. This will greatly reduce the
currentdrainonthebatteryandincreasethestandbytime.
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 RSENSE and an internal 100mV
A10kΩNTC(negativetemperaturecoefficient)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).
reference; IBAT = 100mV/RSENSE
.
When the battery voltage approaches the programmed
float voltage, the charge current will start to decrease.
400242i
9
LTC4002-4.2
W U U
U
APPLICATIO S I FOR ATIO
Undervoltage Lockout (UVLO)
CHRG Status Output Pin
Anundervoltagelockoutcircuitmonitorstheinputvoltage
and keeps the charger off until VCC 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.
When a charge cycle starts, the CHRG pin is pulled to
groundbyaninternalN-channelMOSFETwhichiscapable
of driving an LED. When the charge current drops to 25%
ofthefull-scalecurrentformorethan120µs,theN-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
below2.9V,thechargergoesintotricklechargemodewith
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.
Afteratimeoutoccurs(chargecycleends), thepinwillgo
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 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
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.
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 VCC pin drops below
(VBAT + 250mV) or below the UVLO level (4.2V), the
LTC4002-4.2 goes into a low current (ICC = 10µA) sleep
mode, reducing the battery drain current.
V
V
DD
CC
400k
2k
LTC4002-4.2
CHRG
µPROCESSOR
OUT
IN
400242 F02
Figure 2. Microprocessor Interface
400242i
10
LTC4002-4.2
W U U
APPLICATIO S I FOR ATIO
U
Gate Drive
Automatic Battery Recharge
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 RDS(ON) in the range of 50mΩ.
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-
nalloading.Thiswillkeepthebatterycapacityatmorethan
80% at all times without manually restarting the charge
cycle.
Avoltageclampisaddedtolimitthegatedriveto8Vbelow
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.
Battery Temperature Detection
A negative temperature coefficient (NTC) thermistor
located close to the battery pack can be used to monitor
batterytemperatureandwillnotallowchargingunlessthe
battery temperature is within an acceptable range.
Stability
Both the current loop and the voltage loop share a com-
mon, high impedance, compensation node (COMP pin). A
seriescapacitorandresistoronthispincompensatesboth
loops. The resistor is included to provide a zero in the loop
response and boost the phase margin.
Connect a 10kΩ thermistor (DALE NTHS-1206N02) from
theNTCpintoground.Ifthetemperaturerisesto50°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 2.456V 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
statusattheCHRGpinremainsthesame.Thechargecycle
begins or resumes once the temperature is within the
acceptable range. Short the NTC pin to ground to disable
the temperature qualification feature.
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 100µA 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 0.47µF capacitor, time to reach
full charge current is about 235ms. Capacitance can be
increased up to 1µF if a longer start-up time is needed.
400242i
11
LTC4002-4.2
W U U
U
APPLICATIO S I FOR ATIO
Input and Output Capacitors
Switchingripplecurrentsplitsbetweenthebatteryandthe
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 0.2Ω and
thebatteryimpedanceisraisedto4Ωwithabeadorinduc-
tor, only 5% of the current ripple will flow in the battery.
Since the input capacitor is assumed to absorb all input
switching ripple current in the converter, it must have an
adequateripplecurrentrating.Worst-caseRMSripplecur-
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.
Design Example
As a design example, take a charger with the following
specifications: VIN = 5V to 24V, VBAT = 4V nominal, IBAT
1.5A, fOSC = 500kHz, see Figure 1.
=
First, calculate the SENSE resistor :
The selection of output capacitor COUT is primarily deter-
mined by the ESR required to minimize ripple voltage and
load step transients. The output ripple ∆VOUT is approxi-
mately bounded by:
RSENSE = 100mV/1.5A = 68mΩ
Choose the inductor for about 65% ripple current at the
maximum VIN:
4V
4V
24V
L =
1–
= 6.838µH
1
500kHz 0.65 1.5A
∆VOUT ≤ ∆IL ESR +
(
)(
)(
)
8fOSC OUT
C
Selecting a standard value of 6.8µH results in a maximum
Since ∆IL increases with input voltage, the output ripple is
highestatmaximuminputvoltage.Typically,oncetheESR
requirement is satisfied, the capacitance is adequate for
filtering and has the necessary RMS current rating.
ripple current of :
4V
4V
∆IL =
1–
= 980.4mA
500kHz 6.8µH
24V
(
)(
)
400242i
12
LTC4002-4.2
W U U
APPLICATIO S I FOR ATIO
U
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 dissi-
pation with VIN = 5V and VBAT = 4V at 50°C ambient
temperature is:
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.
GATEpinriseandfalltimesare20nsand50nsrespectively
(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.
2
1.5A 55mΩ 4V
(
) (
)(
)
PD =
= 0.099W
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
thebatteryimpedanceofabout100mΩ.Theripplevoltage
on the BAT pin is:
∆IL(MAX) ESR
(
)
VOUT(RIPPLE)
=
=
2
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 VCC
and/or high gate capacitance applications.
0.98A 0.1Ω
(
)(
)
= 49mV
2
C1: Taiyo Yuden TMK325BJ106MM
C2: Taiyo Yuden JMK325BJ226MM
L1: TOKO B952AS-6R8N
TheSchottkydiodeD2showninFigure1conductscurrent
whenthepasstransistorisoff.Inalowdutycyclecase,the
current rating should be the same or higher than the
chargecurrent.Alsoitshouldwithstandreversevoltageas
high as VIN.
400242i
13
LTC4002-4.2
U
PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
0.675 ±0.05
3.50 ±0.05
2.15 ±0.05 (2 SIDES)
1.65 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50
BSC
2.38 ±0.05
(2 SIDES)
R = 0.115
TYP
6
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.38 ± 0.10
10
3.00 ±0.10
(4 SIDES)
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 5)
(DD10) DFN 0403
5
1
0.25 ± 0.05
0.50 BSC
0.75 ±0.05
0.200 REF
2.38 ±0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
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
400242i
14
LTC4002-4.2
U
PACKAGE DESCRIPTIO
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
.045 ±.005
.160 ±.005
NOTE 3
.050 BSC
7
5
8
6
.245
MIN
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
1
3
4
2
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
(0.254 – 0.508)
× 45°
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
.008 – .010
(0.203 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
.050
(1.270)
BSC
.014 – .019
(0.355 – 0.483)
TYP
NOTE:
INCHES
1. DIMENSIONS IN
(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)
SO8 0303
400242i
15
LTC4002-4.2
U
TYPICAL APPLICATIO
Single Cell 4.2V, 2A Li-Ion Battery Charger
V
IN
5V TO 12V
100k
1/2 Si9933ADY
C1
10µF
CER
2
0.1µF
CER
V
CC
3
1/2 Si9933ADY
GATE
B330-13
LTC4002ES8-4.2
L1
6.8µH
7
6
5
1
CHRG
SENSE
R
SENSE
50mΩ
COMP
BAT
C2
22µF
CER
+
NTC
8
GND
4
Li-Ion
0.47µF
2.2k
BATTERY
400242 TA01
10k
T
NTC
NTC: DALE NTHS-1206N02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1732/LTC4050
Constant Voltage/Constant Current Li-Ion Linear
Battery Chargers
Standalone Battery Charger, No uC or Firmware Required, Auto
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
LTC4008
4A Multiple Cell Li-Ion, NiCd, NiMH, Lead Acid
Battery Chargers
6V ≤ V ≤ 28V, High Efficiency ≥90%, V
Digital Interface I/O, Small Inductor
≤ 28V,
OUT
IN
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
LTC4412
Standalone SOT-23 Li-Ion Linear Battery Charger
Low Loss PowerPathTM Controller in ThinSOT
Charge Termination Included, I ≤ 700mA, 8-Lead ThinSOT Package
CH
Automatic Switching Between DC Sources, Simplified Load Sharing
PowerPath and ThinSOT are trademarks of Linear Technology Corporation.
400242i
LT/TP 0603 1K PRINTED IN USA
16 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LINEAR TECHNOLOGY CORPORATION 2003
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