LTC4088-1/LTC4088-2
8
40881fc
pin FuncTions
CHRG (Pin 7): Open-Drain Charge Status Output. The
CHRG pin indicates the status of the battery charger. Four
possible states are represented by CHRG: charging, not
charging (or float charge current less than programmed
end of charge indication current), unresponsive battery and
battery temperature out of range. CHRG is modulated at
35kHz and switches between a low and a high duty cycle
for easy recognition by either humans or microprocessors.
CHRG requires a pull-up resistor and/or LED to provide
indication.
GATE (Pin 8): Ideal Diode Amplifier Output. This pin con-
trols the gate of an external P-channel MOSFET transistor
used to supplement the internal ideal diode. The source
of the P-channel MOSFET should be connected to V
OUT
and the drain should be connected to BAT.
BAT (Pin 9): Single Cell Li-Ion Battery Pin. Depending on
available power and load, a Li-Ion battery on BAT will either
deliver system power to V
OUT
through the ideal diode or
be charged from the battery charger.
V
OUT
(Pin 10): Output voltage of the switching PowerPath
controller and input voltage of the battery charger. The
majority of the portable product should be powered from
V
OUT
. The LTC4088-1/LTC4088-2 will partition the available
power between the external load on V
OUT
and the internal
battery charger. Priority is given to the external load and
any extra power is used to charge the battery. An ideal
diode from BAT to V
OUT
ensures that V
OUT
is powered even
if the load exceeds the allotted power from V
BUS
or if the
V
BUS
power source is removed. V
OUT
should be bypassed
with a low impedance multilayer ceramic capacitor.
V
BUS
(Pin 11): Input voltage for the switching PowerPath
controller. V
BUS
will usually be connected to the USB port
of a computer or a DC output wall adapter. V
BUS
should
be bypassed with a low impedance multilayer ceramic
capacitor.
SW (Pin 12): The SW pin delivers power from V
BUS
to
V
OUT
via the step-down switching regulator. An inductor
should be connected from SW to V
OUT
. See the Applica-
tions Information section for a discussion of inductance
value and current rating.
D0 (Pin 13): Mode Select Input Pin. D0, in combina-
tion with the D1 pin and the D2 pin, controls the current
limit and battery charger functions of the LTC4088-1/
LTC4088-2 (see Table 1). This pin is pulled low by a weak
current sink.
D1 (Pin 14): Mode Select Input Pin. D1, in combination
with the D0 pin and the D2 pin, controls the current limit
and battery charger functions of the LTC4088-1/LTC4088-2
(see Table 1). This pin is pulled low by a weak current sink.
Exposed Pad (Pin 15): GND. Must be soldered to the
PCB to provide a low electrical and thermal impedance
connection to ground.
