NCP3488 Просмотр технического описания (PDF) - ON Semiconductor

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NCP3488

MOSFET Driver with Dual Outputs for Synchronous Buck Converters

ON Semiconductor 

OD

DRVH

or

DRVL

NCP3488

tpdlOD

90%

tpdhOD

10%

Figure 2. Output Disable Timing Diagram

IN

DRVL

DRVH−SW

SW

tpdlDRVL

tfDRVL

90%

2V

10%

tpdhDRVH

trDRVH

90%

10%

90%

tpdlDRVH

tfDRVH

90%

10%

trDRVL

2V 10%

tpdhDRVL

Figure 3. Nonoverlap Timing Diagram

APPLICATIONS INFORMATION

Theory of Operation

The NCP3488 is a single phase MOSFET driver designed

for driving two N−channel MOSFETs in a synchronous buck

converter topology. The NCP3488 will operate from 5 V or

12 V, but it has been optimized for high current multi−phase

buck regulators that convert 12 Volt rail directly to the core

voltage required by complex logic chips. A single PWM input

signal is all that is required to properly drive the high−side and

the low−side MOSFETs. Each driver is capable of driving a

3.3 nF load at frequencies up to 500 kHz.

Low−Side Driver

The low−side driver is designed to drive a

ground−referenced low RDS(on) N−Channel MOSFET. The

voltage rail for the low−side driver is internally connected to

the VCC supply and PGND.

High−Side Driver

The high−side driver is designed to drive a floating low

RDS(on) N−channel MOSFET. The gate voltage for the high

side driver is developed by a bootstrap circuit referenced to

Switch Node (SW) pin.

The bootstrap circuit is comprised of an external diode,

and an external bootstrap capacitor. When the NCP3488 is

starting up, the SW pin is at ground, so the bootstrap

capacitor will charge up to VCC through the bootstrap diode

See Figure 4. When the PWM input goes high, the high−side

driver will begin to turn on the high−side MOSFET using the

stored charge of the bootstrap capacitor. As the high−side

MOSFET turns on, the SW pin will rise. When the high−side

MOSFET is fully on, the switch node will be at 12 volts, and

the BST pin will be at 12 volts plus the charge of the

bootstrap capacitor (approaching 24 volts).

The bootstrap capacitor is recharged when the switch

node goes low during the next cycle.

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