LTC3577-4_15 Datasheet, PDF (17/52 Pages) Linear Technology – Highly Integrated Portable Product PMIC

LTC3577-3/LTC3577-4
PIN FUNCTIONS
I_LED (Pin 22): Series LED Backlight Current Sink Output.
This pin is connected to the cathode end of the series LED
backlight string. The current drawn through the series LEDs
is programmed via a 6-bit 60dB DAC and can be further
dimmed via an internal PWM function. I²C is used to control
LED driver enable, brightness, gradation (soft on/soft off).
I²C default is LED driver off, current = 0mA.
LDO1_FB (Pin 23): Feedback Voltage Input for Low Drop-
out Linear Regulator 1 (LDO1). LDO1 output voltage is
set using an external resistor divider between LDO1 and
LDO1_FB.
LDO2_FB (Pin 24): Feedback Voltage Input for Low Drop-
out Linear Regulator 2 (LDO2). LDO2 output voltage is
set using an external resistor divider between LDO2 and
LDO2_FB.
FB2 (Pin 25): Feedback Input for Step-Down Switching
Regulator 2 (Buck2). This pin servos to a fixed voltage of
0.8V when the control loop is complete.
FB1 (Pin 26): Feedback Input for Step-Down Switching
Regulator 1 (Buck1). This pin servos to a fixed voltage of
0.8V when the control loop is complete.
V_INLDO1 (Pin 27): Input Supply of Low Dropout Linear
Regulator 1 (LDO1). This pin should be bypassed to ground
with a 1μF or greater ceramic capacitor.
LDO1 (Pin 28): Output of Low Dropout Linear Regulator 1.
LDO1 is an always-on LDO and will be enabled whenever
the part is not in V_OUT UVLO. This pin must be bypassed
to ground with a 1μF or greater ceramic capacitor.
LDO2 (Pin 29): Output of Low Dropout Linear Regulator 2.
This pin must be bypassed to ground with a 1μF or greater
ceramic capacitor.
V_INLDO2 (Pin 30): Input Supply of Low Dropout Linear
Regulator 2 (LDO2). This pin should be bypassed to ground
with a 1μF or greater ceramic capacitor.
SW2 (Pin 31): Power Transmission (Switch) Pin for Step-
Down Switching Regulator 2 (Buck2).
V_IN12 (Pin 32): Power Input for Step-Down Switching
Regulators 1 and 2. This pin will generally be connected
to V_OUT.
SW1 (Pin 33): Power Transmission (Switch) Pin for Step-
Down Switching Regulator 1 (Buck1).
NTCBIAS (Pin 34): Output Bias Voltage for NTC. A
resistor from this pin to the NTC pin will bias the NTC
thermistor.
NTC (Pin 35): 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 NTCBIAS to NTC and
a thermistor is required from NTC to ground.
PROG (Pin 36): Charge Current Program and Charge
Current Monitor Pin. Connecting a resistor from PROG
to ground programs the charge current:
( ) ^I_CHG
=
1000 V
R_PROG
A
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.
IDGATE (Pin 37): Ideal Diode Gate Connection. This
pin controls the gate of an optional 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. It is important to maintain high impedance on this
pin and minimize all leakage paths.
BAT (Pin 38): 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.
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