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SC4609EVB

Low Input, MHz Operation, High Efficiency Synchronous Buck

Semtech Corporation 

SC4609

POWER MANAGEMENT

Pin Descriptions (Cont.)

Pin #

Pin Name Pin Function

7

AGND

Analog ground.

8

PGND

Power ground.

9

DRVL

DRVL drives the gate of the low side (synchronous rectifier) MOSFET. The output drivers

are rated for 1A peak currents. The PWM circuitry provides complementary drive signals to

the output stages. The cross conduction of the external MOSFETs is prevented by

monitoring the voltage on the driver pins of the MOSFET pair in conjunction with a time

delay optimized for FET turn-off characteristics.

10

PHASE

The PHASE pin is used to limit current in the high side MOSFET. The SC4609 uses the

voltage across the VIN and ISET pin in order to set the current limit. The current limit

threshold is set by the value of an external resistor (R3 in the Typical Application Circuit

Diagram). Current limiting is performed by comparing the voltage drop across the sense

resistor with the voltage drop across the drain to source resistance of the high side

MOSFET during the MOSFET’s conduction period. The voltage drop across the drain to

source resistance of the high side MOSFET is obtained from the VIN and PHASE pin.

11

DRVH

DRVH drives the gate of the high side (main switch) MOSFET. The output drivers are rated

for 1A peak currents. The PWM circuitry provides complementary drive signals to the

output stages. The cross conduction of the external MOSFETs is prevented by monitoring

the voltage on the driver pins of the MOSFET pair in conjunction with a time delay

optimized for FET turn-off characteristics.

12

BST

This pin enables the converter to drive an N-Channel high side MOSFET. BST connects to

the external charge pump circuit. The charge pump circuit boosts the BST pin voltage to a

sufficient gate-to-source voltage level for driving the gate of the high side MOSFET.

THERMAL PAD Pad for heatsinking purposes. Connect to ground plane using multiple vias. Not connected

internally.

 2006 Semtech Corp.

5

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