MAX798 查看數據表（PDF） - Maxim Integrated

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MAX798

High-Accuracy Step-Down Controller with Synchronous Rectifier for CPU Power

Maxim Integrated 

High-Accuracy Step-Down Controller

with Synchronous Rectifier for CPU Power

______________________________________________________________Pin Description

PIN NAME

FUNCTION

1

SS

Soft-Start Timing Capacitor Connection. Ramp time to full current limit is approximately 1ms/nF.

Disables pulse-skipping mode when high. Connect to GND for normal use. Don’t leave SKIP unconnected.

2

SKIP

With SKIP grounded, the device will automatically change from pulse-skipping operation to full PWM opera-

tion when the load current exceeds approximately 30% of maximum.

3

REF

Reference Voltage Output. Bypass to GND with 0.33µF minimum.

4

GND

Low-Noise Analog Ground and Feedback Reference Point

Oscillator Synchronization and Frequency Select. Tie to GND or VL for 150kHz operation; tie to REF for

5

SYNC 300kHz operation. A high-to-low transition begins a new cycle. Drive SYNC with 0V to 5V logic levels (see the

Electrical Characteristics table for VIH and VIL specifications). SYNC capture range is 195kHz to 340kHz.

6

SHDN

Shutdown Control Input, active low. Logic threshold is set at approximately 1V (VTH of an internal N-channel

MOSFET). Tie SHDN to V+ for automatic start-up.

7

FB

Feedback Input. Regulates at FB = 1.6V. Connect FB to a resistor divider to set the output voltage.

8

CSH

Current-Sense Input, high side. Current-limit level is 100mV referred to CSL.

9

CSL

Current-Sense Input, low side

10

V+

Battery Voltage Input (4.5V to 30V). Bypass V+ to PGND close to the IC with a 0.1µF capacitor. Connects to a

linear regulator that powers VL.

5V Internal Linear-Regulator Output. VL is also the supply voltage rail for the chip. VL is switched to the out-

11

VL

put voltage via CSL (VCSL > 4.5V) for automatic bootstrapping. Bypass to GND with 4.7µF. VL can supply

up to 5mA for external loads.

12 PGND Power Ground

13

DL

Low-Side Gate-Drive Output. Normally drives the synchronous-rectifier MOSFET. Swings 0V to VL.

14

BST

Boost Capacitor Connection for high-side gate drive (0.1µF)

15

LX

Switching Node (inductor) Connection. Can swing 2V below ground without hazard.

16

DH

High-Side Gate-Drive Output. Normally drives the main buck switch. DH is a floating driver output that swings

from LX to BST, riding on the LX switching-node voltage.

_______________________________________________________________________________________ 5

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