LTC3577-4_15 Datasheet, PDF (18/52 Pages) Linear Technology – Highly Integrated Portable Product PMIC

LTC3577-3/LTC3577-4
PIN FUNCTIONS
V_OUT (Pin 39): Output Voltage of the PowerPath Controller
and Input Voltage of the Battery Charger. The majority of
the portable product should be powered from V_OUT. The
LTC3577-3/LTC3577-4 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 input current 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 40): USB Input Voltage. 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 imped-
ance multilayer ceramic capacitor.
ACPR (Pin 41): Wall Adapter Present Output (Active Low).
A low on this pin indicates that the wall adapter input com-
parator has had its input pulled above its input threshold
(typically 4.3V). This pin can be used to drive the gate of
an external P-channel MOSFET to provide power to V_OUT
from a power source other than a USB port.
EXTPWR (Pin 42): External Power Present Output (Active
Low, Open-Drain Output). A low on this pin indicates that
external power is present at either the V_BUS or WALL input.
For EXTPWR to signal V_BUS present, V_BUS must exceed
the V_BUS undervoltage lockout threshold. For EXTPWR to
signal WALL present, WALL must exceed the absolute and
differential WALL input thresholds. The EXTPWR signal is
independent of the I_LIM1 and I_LIM0 pins. Thus, it is possible
to have the input current limit circuitry in suspend with
EXTPWR showing a valid charging level on V_BUS.
CLPROG (Pin 43): Input Current Program and Input
Current Monitor Pin. A resistor from CLPROG to ground
determines the upper limit of the current drawn from the
V_BUS pin (i.e., the input current limit). A precise fraction
of the input current, h_CLPROG, is sent to the CLPROG pin.
The input PowerPath delivers current until the CLPROG
pin reaches 2V (10x mode), 1V (5x mode) or 0.2V (1x
mode). Therefore, the current drawn from V_BUS will be
limited to an amount given by h_CLPROG and R_CLPROG. In
USB applications the resistor R_CLPROG should be set to
no less than 2.1k.
CHRG (Pin 44): Open-Drain Charge Status Output. The
CHRG pin indicates the status of the battery charger. If
CHRG is high then the charger is near the float voltage
(charge current less than 1/10th programmed charge cur-
rent) or charging is complete and charger is disabled. A low
on CHRG indicates that the charger is enabled. For more
information see the “Charge Status Indication” section.
Ground (Exposed Pad Pin 45): The exposed package pad is
ground and must be soldered to PCB ground for electrical
contact and rated thermal performance.
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