LTC1876 datasheet(9/36 Pages) LINER

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LTC1876

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.

ITH1, ITH2 (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 COUT capacitors.

3.3VOUT (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.

AUXVFB (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 (VOUT + 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.

AUXVIN (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 INTVCC– 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 VIN.

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 INTVCCpins. Voltage swing at the

boost pins is from INTVCC to (VIN + INTVCC).

BG1, BG2 (Pins 31, 27): High Current Gate Drives for Bottom

(synchronous) N-Channel MOSFETs. Voltage swing at these

pins is from ground to INTVCC.

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 CIN.

INTVCC (Pin 29): Output of the Internal 5V Linear Low

Dropout Regulator and the EXTVCC Switch. The driver and

control circuits are powered from this voltage source. Must

be decoupled to power ground with a minimum of 4.7

µF

tantalum or other, low ESR capacitor. The INTVCC regulator

standby operation is determined by the STBYMD pin.

EXTVCC (Pin 30): External Power Input to an Internal Switch

Connected to INTVCC. This switch closes and supplies VCC

power, bypassing the internal low dropout regulator, when-

ever EXTVCC is higher than 4.7V. See EXTVCC connection in

Applications section. Do not exceed 7V on this pin.

VIN (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 VOSENSE pinisnotwithin

7.5% of its setpoint.

PIN FUNCTIONS

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