LTC3553-2
12
35532f
HPWR (Pin 1): High Power Logic Input. When this pin is
low the input current limit is set to 100mA and when this
pin is driven high it is set to 500mA. The SUSP pin needs
to be low for the input current limit circuit to be enabled.
This pin has a conditional internal pull-down resistor when
power is applied to the V
BUS
pin.
PGOOD (Pin 2): Power Good. This open-drain output
indicates that all enabled regulators have been in regula-
tion for at least 1.8ms.
PBSTAT (Pin 3): Pushbutton Status. This open-drain output
is a debounced and buffered version of the ON pushbut-
ton input. It may be used to interrupt a microprocessor.
ON (Pin 4): Pushbutton Input. Weak internal pull-up
forces a high state if ON is left fl oating. A normally open
pushbutton is connected from ON to ground to force a
low state on this pin.
GND (Pin 5, Exposed Pad Pin 21): Ground. The exposed
package pad is ground and must be soldered to the PC board
for proper functionality and for maximum heat transfer.
STBY (Pin 6): Standby Mode. When this pin is driven
high, the buck regulator quiescent current is reduced
to very low levels, while still maintaining output voltage
regulation. In this mode, the buck regulator is limited to
10mA maximum load current. This pin must be driven to
a valid logic level. Do not fl oat this pin.
BUCK_ON (Pin 7): Logic Input Enables the Buck Regula-
tor. This pin must be driven to a valid logic level. Do not
fl oat this pin.
BUCK_FB (Pin 8): Feedback Input for the Buck Regulator.
This pin servos to a fi xed voltage of 0.8V when the control
loop is complete.
LDO_FB (Pin 9): Feedback Input for the Low Dropout
Regulator. This pin servos to a fi xed voltage of 0.8V when
the control loop is complete.
LDO (Pin 10): Low Dropout (LDO) Linear Regulator Out-
put. This pin should be bypassed with a low impedance
multilayer ceramic capacitor.
V
INLDO
(Pin 11): Power Input Pin for the LDO Regulator.
This pin is to be connected to V
OUT
or any supply volt-
age below V
OUT
, such as the buck regulator output. This
pin should be bypassed with a low impedance multilayer
ceramic capacitor.
BVIN (Pin 12): Power Input for the Buck Regulator. It is
recommended that this pin be connected to the V
OUT
pin.
It should be bypassed with a low impedance multilayer
ceramic capacitor.
SW (Pin 13): Power Transmission (Switch) Pin for the
Buck Regulator.
CHRG (Pin 14): O p e n - D r a i n C h a r g e S t a t u s O u t p u t . T h i s p i n
indicates the status of the battery charger. It is internally
pulled low while charging. Once the battery charge cur-
rent reduces to less than one-tenth of the programmed
charge current, this pin goes into a high impedance state.
An external pull-up resistor and/or LED is required to
provide indication.
NTC (Pin 15): The NTC pin connects to a battery’s therm-
istor to determine if the battery is too hot or too cold to
charge. If the battery’s temperature is out of range, charging
is paused until it drops back into range. A low drift bias
resistor is required from V
BUS
to NTC and a thermistor is
required from NTC to ground. If the NTC function is not
desired, the NTC pin should be grounded.
PROG (Pin 16): Charge Current Program and Charge
Current Monitor Pin. Connecting a resistor from PROG to
ground programs the charge current as given by:
I
CHG
(A)=
750V
R
PROG
If suffi cient input power is available in constant-current
mode, this pin servos to 1V. The voltage on this pin always
represents the actual charge current.
BAT (Pin 17): 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.
PIN FUNCTIONS
