LTC4008 Datasheet, PDF (6/24 Pages) Linear Technology – 4A, High Efficiency, Multi-Chemistry Battery Charger

LTC4008
PI FU CTIO S
DCIN (Pin 1): External DC Power Source Input. Bypass
this pin with at least 0.01µF. See Applications Information
section.
I_CL (Pin 2): Input Current Limit Indicator. Active low digital
output. Internal 10µA pull-up to 3.5V. Pulled low if the
charger current is being reduced by the input current
limiting function. The pin is capable of sinking at least
100µA. If V_LOGIC > 3.3V, add an external pull-up.
ACP/SHDN (Pin 3): Open-drain output used to indicate if
the AC adapter voltage is adequate for charging. Active high
digital output. Internal 10µA pull-up to 3.5V. The charger
can also be shutdown by pulling this pin below 1V. The pin
is capable of sinking at least 100µA. If V_LOGIC > 3.3V, add
an external pull-up. (LTC4008-1: ACP function disabled.)
R_T (Pin 4): Thermistor Clocking Resistor. Use a 150k
resistor as a nominal value. This resistor is always re-
quired. If this resistor is not present, the charger will not
start.
FAULT (Pin 5): Active low open-drain output that indicates
that charger operation has suspended due to the ther-
mistor exceeding allowed values. A pull-up resistor is
required if this function is used. The pin is capable of
sinking at least 100µA.
GND (Pin 6): Ground for Low Power Circuitry.
V_FB (Pin 7): Input of Voltage Feedback Error Amplifier, EA,
in the Block Diagram.
NTC (Pin 8): A thermistor network is connected from NTC
to GND. This pin determines if the battery temperature is
safe for charging. The charger and timer are suspended
and the FAULT pin is driven low if the thermistor indicates
a temperature that is unsafe for charging. The thermistor
function may be disabled with a 300k to 500k resistor from
DCIN to NTC.
I_TH (Pin 9): Control Signal of the Inner Loop of the Current
Mode PWM. Higher I_TH voltage corresponds to higher
charging current in normal operation. A 6k resistor in
series with a capacitor of at least 0.1µF to GND provides
loop compensation. Typical full-scale output current is
40µA. Nominal voltage range for this pin is 0V to 3V.
PROG (Pin 10): Current Programming/Monitoring Input/
Output. An external resistor to GND programs the peak
6
charging current in conjunction with the current sensing
resistor. The voltage at this pin provides a linear indication
of charging current. Peak current is equivalent to 1.19V.
Zero current is approximately 0.309V. A capacitor from
PROG to ground is required to filter higher frequency
components. The maximum program resistance to ground
is 100k. Values higher than 100k can cause the charger to
shut down.
CSP (Pin 11): Current Amplifier CA1 Input. The CSP and
BAT pins measure the voltage across the sense resistor,
R_SENSE, to provide the instantaneous current signals re-
quired for both peak and average current mode operation.
BAT (Pin 12): Battery Sense Input and the Negative
Reference for the Current Sense Resistor.
BATMON (Pin 13): Output Voltage Representing Battery
Voltage. Switched off to reduce standby current drain
when AC is not present. An external voltage divider from
BATMON to V_FB sets the charger float voltage. Recom-
mended minimum load resistance is 100k.
FLAG (Pin 14): Active low open-drain output that indicates
when charging current has declined to 10% of max pro-
grammed current. A pull-up resistor is required if this
function is used. The pin is capable of sinking at least
100µA. This function is latching. To clear it, user must
cycle the ACP/SHDN pin.
CLN (Pin 15): Negative Input to the Input Current Limiting
Amplifier CL1. The threshold is set at 100mV below the
voltage at the CLP pin. When used to limit input current, a
filter is needed to filter out the switching noise. If no
current limit function is desired, connect this pin to CLP.
CLP (Pin 16): This pin serves as a positive reference for the
input current limit amplifier, CL1. It also serves as the
power supply for the IC.
TGATE (Pin 17): Drives the top external PMOSFET of the
battery charger buck converter.
PGND (Pin 18): High Current Ground Return for BGATE
Driver.
BGATE (Pin 19): Drives the bottom external N-MOSFET of
the battery charger buck converter.
INFET (Pin 20): Drives the gate of the external input
P-MOSFET. (LTC4008-1: No Connection)
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