LTC3576 Datasheet, PDF (15/48 Pages) Linear Technology – Switching Power Manager with USB On-the-Go + Triple Step-Down DC/DCs

LTC3576/LTC3576-1
PIN FUNCTIONS
ACPR (Pin 28): External Power Source Present Output
(Active Low). ACPR indicates that the output of the external
high voltage step-down switching regulator is suitable for
use by the LTC3576/LTC3576-1. It should be connected to
the gate of an external P-channel MOSFET whose source
is connected to V_OUT and whose drain is connected to
WALL. ACPR has a high level of V_OUT and a low level of
GND. The USB bidirectional switcher is disabled when
ACPR is low.
PROG (Pin 29): Charge Current Program and Charge Cur-
rent Monitor Pin. Connecting a 1% resistor from PROG
to ground programs the charge current. 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 by using the following formula:
I_BAT
=
V_PROG
R_PROG
• 1030
CHRG (Pin 30): Open-Drain Charge Status Output. The
CHRG pin indicates the status of the battery charger.
Four possible charger states are represented by CHRG:
charging, not charging, unresponsive battery and battery
temperature out of range. In addition, CHRG is used to
indicate whether there is a short-circuit condition on V_BUS
when the bidirectional switching regulator is in step-up
mode (on-the-go). CHRG is modulated at 35kHz and
switches between a low and a high duty cycle for easy
recognition by either humans or microprocessors. See
Table 1. CHRG requires a pull-up resistor and/or LED to
provide indication.
IDGATE (Pin 31): Ideal Diode Amplifier Output. This pin
controls the gate of an optional external P-channel MOSFET
used as an ideal diode between V_OUT and BAT. The external
ideal diode operates in parallel with 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. If the
external ideal diode MOSFET is not used, IDGATE should
be left floating.
BAT (Pin 32): Single Cell Li-Ion Battery Pin. Depending on
available V_BUS power, a Li-Ion battery on BAT will either
deliver power to V_OUT through the ideal diode or be charged
from V_OUT via the battery charger.
V_OUT (Pin 33): Output Voltage of the Bidirectional Pow-
erPath Switching Regulator in step-down mode and
Input Voltage of the Battery Charger. The majority of
the portable product should be powered from V_OUT. The
LTC3576/LTC3576-1 will partition the available power
between the external load on V_OUT and the internal bat-
tery 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. In on-the-go mode, this
pin delivers power to V_BUS via the SW pin. V_OUT should
be bypassed with a low impedance ceramic capacitor.
V_BUS (Pins 34, 35): Power Pins. These pins deliver power
to V_OUT via the SW pin by drawing controlled current from
a DC source such as a USB port or DC output wall adapter.
In on-the-go mode these pins provide power to external
loads. Tie the two V_BUS pins together at the part and bypass
with a low impedance multilayer ceramic capacitor.
SW (Pin 36): The SW pin transfers power between V_BUS
and V_OUT via the bidirectional switching regulator. See
the Applications Information section for a discussion of
inductance value and current rating.
I_LIM0, I_LIM1 (Pins 37, 38): I_LIM0 and I_LIM1 control the current
limit of the PowerPath switching regulator. See Table 1.
Both the I_LIM0 and I_LIM1 pins are logically ORed with their
corresponding bits in the I²C serial port. See Tables 3 and
6. Each has a 2μA internal pull-down current source.
Exposed Pad (Pin 39): Ground. The Exposed Pad should
be connected to a continuous ground plane on the second
layer of the printed circuit board by several vias directly
under the LTC3576/LTC3576-1.
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