LTC3554 Datasheet, PDF (11/36 Pages) Linear Technology – Micropower USB Power Manager with Li-Ion Charger and Two Step-Down Regulators

LTC3554
PIN FUNCTIONS
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.
FSEL (Pin 2): Buck Frequency Select. When this pin is
low the buck switching frequency is set to 1.125MHz and
when this pin is driven high it is set to 2.25MHz.
PBSTAT (Pin 3): Pushbutton Status. This open-drain output
is a debounced and buffered version of the ON pushbutton
input. It may be used to interrupt a microprocessor.
PGOOD (Pin 4): Power Good. This open-drain output
indicates that all enabled buck regulators have been in
regulation for at least 230ms.
ON (Pin 5): Pushbutton Input. Weak internal pull-up
forces a high state if ON is left floating. A normally open
pushbutton is connected from ON to ground to force a
low state on this pin.
FB1 (Pin 6): Feedback Input for Step-Down Switching
Regulator 1. This pin servos to a fixed voltage of 0.8V
when the control loop is complete.
FB2 (Pin 7): Feedback Input for Step-Down Switching
Regulator 2. This pin servos to a fixed voltage of 0.8V
when the control loop is complete.
PWR_ON2 (Pin 8): Logic Input Enables Step-Down
Switching Regulator 2.
PWR_ON1 (Pin 9): Logic Input Enables Step-Down
Switching Regulator 1.
STBY (Pin 10): Standby Mode. When this pin is driven
high the part enters a very low quiescent current mode.
The buck regulators are each limited to 10mA maximum
load current in this mode.
SW2 (Pin 11): Power Transmission (Switch) Pin for Step-
Down Switching Regulator 2.
BVIN (Pin 12): Power Input for Step-Down Switching
Regulators 1 and 2. It is recommended that this pin be
connected to the V_OUT pin. It should be bypassed with a
low impedance multilayer ceramic capacitor.
SW1 (Pin 13): Power Transmission (Switch) Pin for Step-
Down Switching Regulator 1.
CHRG (Pin 14): Open-Drain Charge Status Output. This pin
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 sufficient 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.
V_OUT (Pin 18): Output Voltage of the PowerPath Controller
and Input Voltage of the Battery Charger. The majority of
the portable products should be powered from V_OUT. The
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