LTC4008
7
4008fb
PIN FUNCTIONS
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 required.
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 thermistor
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 Amplifi er,
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
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 fi lter 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 Amplifi er CA1 Input. The CSP and BAT
pins measure the voltage across the sense resistor, R
SENSE
,
to provide the instantaneous current signals required 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 fl oat voltage. Recom-
mended minimum load resistance is 100k.
FLAG (Pin 14): Active low open-drain output that indi-
cates when charging current has declined to 10% of max
programmed 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
Amplifi er CL1. The threshold is set at 100mV below the
voltage at the CLP pin. When used to limit input current,
a fi lter is needed to fi lter 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 amplifi er, 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)
