LTC3520 Datasheet, PDF(9/24 Page) Linear Technology – Synchronous 1A Buck-Boost and 600mA Buck Converters

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LTC3520 Datasheet, PDF (9/24 Pages) Linear Technology – Synchronous 1A Buck-Boost and 600mA Buck Converters

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LTC3520

PIN FUNCTIONS

SS2 (Pin 13): Buck Converter Soft-Start Pin. This pin must

be connected to a soft-start capacitor. The value of the

capacitor determines the duration of the soft-start period.

For information on choosing the value of this capacitor, see

the Applications Information section of this datasheet.

FB2 (Pin 14): Feedback Voltage for the Buck Converter.

This pin is derived from a resistor divider on the buck

output voltage. The buck output voltage is given by the

following equation where R1 is a resistor between FB2

and ground and R2 is a resistor between FB2 and the

buck output voltage:

VOUT

0.790V

ââ

R2 â

R1â â

VC1 (Pin 15): Buck-Boost Error Ampliï¬er Output. A fre-

quency compensation network is connected to FB1 to

compensate the loop. During Burst Mode operation, VC1

is driven internally by a clamp circuit.

SGND (Pin 16): Small Signal Ground. This pin is used

as a ground reference for the internal circuitry of the

LTC3520.

SS1 (Pin 17): Buck-Boost Converter Soft-Start Pin. This

pin must be connected to a soft-start capacitor. The value

of the capacitor determines the duration of the soft-start

period. For information on choosing the value of this

capacitor, see the Applications Information section of

this datasheet.

FB1 (Pin 18): Feedback Voltage for the Buck-Boost Con-

verter. This pin is derived from a resistor divider on the

buck-boost output voltage. The buck-boost output voltage

is given by the following equation where R1 is a resistor

between FB1 and ground and R2 is a resistor between

FB1 and the buck-boost output voltage:

VOUT

0.782V

ââ

R2 â

R1â â

VOUT1 (Pin 19): Buck-Boost Output Voltage Node. This

pin should be connected to a low ESR buck-boost output

capacitor. The capacitor should be placed as close to the

IC as possible and should have a short return path to

ground.

SW1B (Pin 20): Buck-Boost Switch Node. This pin must

be connected to one side of the buck-boost inductor.

PGND1 (Pin 21): High Current Ground Connection for

the Buck-Boost NMOS Power Devices. The PCB trace

connecting this pin to ground should be made as short

and wide as possible.

SW1A (Pin 22): Buck-Boost Switch Node. This pin must

be connected to one side of the buck-boost inductor.

PVIN1 (Pin 23), PVIN3 (Pin 24): High Current Power Sup-

ply Connections Used to Power the Buck-Boost Converter

Power Switch A. These pins should be connected together

and bypassed by a 22ÂµF or larger ceramic capacitor. The

bypass capacitor should be placed as close to the pin as

possible and should have a short return path to ground.

Pins PVIN1, PVIN2, PVIN3, and SVIN must be connected

together in the application circuit.

Exposed Pad (Pin 25): Ground. The Exposed Pad must be

electrically connected to ground and soldered to the PCB.

Pins PGND1, PGND2, SGND, and the Exposed Pad must

be connected together in the application circuit.

3520f

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