LTC1876
9
1876fa
provides a common control point to shut down both control-
lers. See the Operation section for details.
FCB (Pin 7): Forced Continuous Control Input. This input acts
on both controllers and is normally used to regulate a
secondary winding. Pulling this pin below 0.8V will force
continuous synchronous operation on both controllers. Do
not leave this pin floating.
I
TH1,
I
TH2
(Pins 8, 11): Error Amplifier Output and Switching
Regulator Compensation Point. Each associated channel’s
current comparator trip point increases with this control
voltage.
SGND (Pin 9): Small signal ground common to both control-
lers, must be routed separately from high current grounds to
the common (–) terminals of the C
OUT
capacitors.
3.3V
OUT
(Pin 10): Output of a linear regulator capable of
supplying up to 10mA DC with peak currents as high as
50mA.
AUXSGND (Pin 15): Small Signal Ground of the Auxiliary
Boost Regulator.
AUXV
FB
(Pin 16): Auxiliary Boost Regulator Feedback Volt-
age. This pin receives the feedback voltage from an external
resistive divider across the auxiliary output.
AUXSW (Pins 17, 18): Switch Node Connections to Inductor
for the Auxiliary Regulator. Voltage swing at these pins are
from ground to (V
OUT
+ voltage across Shottky diode).
Minimize trace area at these pins to keep EMI down.
AUXPGND (Pins 19, 20): The Auxiliary Power Ground Pins.
Its gate drive currents are returned to these pin.
AUXV
IN
(Pin 21): Auxiliary Boost Regulator Controller Sup-
ply Pin. Must be closely decoupled to AUXPGND.
AUXSD (Pin 22): Shutdown Pin for the Auxiliary Regulator.
Connect to 2.4V or more to enable the auxiliary regulator or
ground to shut the auxiliary regulator off.
TG1, TG2 (Pins 35, 24): High Current Gate Drives for Top
N-Channel MOSFETs. These are the outputs of floating
drivers with a voltage swing equal to INTV
CC
– 0.5V superim-
posed on the switch node voltage SW.
SW1, SW2 (Pins 34, 25): Switch Node Connections to
Inductors. Voltage swing at these pins is from a Schottky
diode (external) voltage drop below ground to V
IN
.
BOOST1, BOOST2 (Pins 33, 26): Bootstrapped Supplies to
the Top Side Floating Drivers. Capacitors are connected
between the boost and switch pins and Schottky diodes are
tied between the boost and INTV
CC
pins. Voltage swing at the
boost pins is from INTV
CC
to (V
IN
+ INTV
CC
).
BG1, BG2 (Pins 31, 27): High Current Gate Drives for Bottom
(synchronous) N-Channel MOSFETs. Voltage swing at these
pins is from ground to INTV
CC
.
PGND (Pin 28): Driver Power Ground. Connects to sources
of bottom (synchronous) N-channel MOSFETs, anode of the
Schottky rectifier and the (–) terminal(s) of C
IN
.
INTV
CC
(Pin 29): Output of the Internal 5V Linear Low
Dropout Regulator and the EXTV
CC
Switch. The driver and
control circuits are powered from this voltage source. Must
be decoupled to power ground with a minimum of 4.7µF
tantalum or other, low ESR capacitor. The INTV
CC
regulator
standby operation is determined by the STBYMD pin.
EXTV
CC
(Pin 30): External Power Input to an Internal Switch
Connected to INTV
CC
. This switch closes and supplies V
CC
power, bypassing the internal
low dropout regulator, when-
ever EXTV
CC
is higher than 4.7V. See EXTV
CC
connection in
Applications section. Do not exceed 7V on this pin.
V
IN
(Pin 32): Main Supply Pin. A bypass capacitor should be
tied between this pin and the signal ground pin.
PGOOD (Pin 36): Open-Drain Logic Output. PGOOD is pulled
to ground when the voltage on either V
OSENSE
pin is not within
7.5% of its setpoint.
PIN FUNCTIONS
UUU
