LT8471 View Datasheet(PDF) - Linear Technology

Part Name

Description

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LT8471

Dual Multitopology DC/DC Converters with 2A Switches and Synchronization

Linear Technology 

LT8471

Pin Functions

C1, C2 (Pins 1, 20): Collector Pins. These are the collec-

tors of the primary internal NPN power switches. If either

pin is tied to a DC voltage, it must be locally bypassed; if

either pin is a switching pin, minimize trace area connected

to the pin to minimize EMI. When the Skyhook channel is

used, the C2 pin must be tied to the input voltage of the

Skyhook channel.

C3 (Pin 13): Skyhook Collector Pin. This is the collector of

the internal NPN power switch for the Skyhook channel.

If the Skyhook channel is used, minimize the metal trace

area connected to this pin to minimize EMI. If the Skyhook

channel is not used, tie the C3 pin to GND.

E1, E2 (Pins 2, 19): Emitter Pins. These are the emit-

ters of the primary internal NPN power switches. Unless

grounded, minimize trace area connected to these pins

to minimize EMI.

FB1, FB2 (Pins 5, 16): Feedback Pins for Primary Chan-

nels. Connect a resistor divider between VOUT, FB and

GND to set the output voltage.

GND (Pins 10, 11,12, Exposed Pad 21): Ground. All of the

ground pins must be soldered directly to the local ground

plane. The exposed pad metal of the package provides both

electrical contact to ground and good thermal contact to

the printed circuit board.

OV/UV (Pin 6): Overvoltage/Undervoltage Pin. Tie to 1.215V

(typical) or more to enable the device; ground to shut down.

Configurable as a UVLO and OVLO by connecting to an

external resistor divider. See the Applications Information

section for more information.

PG1, PG2 (Pins 4, 17): Power Good Pins. Connect pull-up

resistors to these pins. These open-drain output pins are

pulled low when their respective output voltages are more

than 7.5% below their target output voltages (as set by

the external feedback resistors). When the output voltage

is above 92.5% of the target voltage, the respective PG

pin driver turns off, allowing the PG voltage to rise and

indicate that the regulated output voltage is good.

RT (Pin 7): Timing Resistor Pin. Adjusts the switching

frequency. Place a resistor from this pin to ground to set

the frequency to a fixed free-running level. Do not float

this pin.

SHOUT (Pin 14): Skyhook Output Voltage Pin. This is the

cathode of the internal Schottky diode and the output of

the Skyhook boost converter.

SS1, SS2 (Pins 8, 15): Soft Start Pins. Place a soft-start

capacitor on each pin. Upon start-up, the SS pins will be

charged by (nominally) 250k resistors to about 2.15V.

SYNC (Pin 9): To synchronize the switching frequency

to an outside clock, simply drive this pin with a clock.

The high voltage level of the clock needs to exceed 1.3V,

and the low level should be less than 0.4V. Drive this pin

to less than 0.4V to revert to the internal free running

clock. See the Applications Information section for more

information.

VIN1 (Pin 3): Input Supply Pin 1. This is the power supply

pin for primary channel 1 and the Skyhook channel. This

pin also provides power to additional circuitry common

to all channels. VIN1 must be greater than 2.6V for any

channel to operate. VIN1 must be locally bypassed.

VIN2 (Pin 18): Input Supply Pin 2. This is the power supply

pin for primary channel 2 and must be greater than 2.6V

when channel 2 is in use. VIN2 must be locally bypassed.

For more information www.linear.com/8471

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