MAX799 查看數據表（PDF） - Maxim Integrated

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MAX799

Step-Down Controllers with Synchronous Rectifier for CPU Power

Maxim Integrated 

Step-Down Controllers 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.

Secondary winding Feedback input. Normally connected to a resistor divider from an auxiliary output.

SECFB

(MAX796/

MAX799)

Don’t leave SECFB unconnected.

• MAX796: SECFB regulates at VSECFB = 2.505V. Tie to VL if not used.

• MAX799: SECFB regulates at VSECFB = 0V. Tie to a negative voltage through a high-value current-limit-

2

ing resistor (IMAX = 100µA) if not used.

SKIP

(MAX797)

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

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. (See Table 3.)

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 190kHz to 340kHz

guaranteed.

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.

Feedback input. Regulates at FB = REF (approximately 2.505V) in adjustable mode. FB is a Dual-ModeTM

input that also selects the fixed output voltage settings as follows:

• Connect to GND for 3.3V operation.

7

FB

• Connect to VL for 5V operation.

• Connect FB to a resistor divider for adjustable mode. FB can be driven with +5V rail-to-rail logic in order to

change the output voltage under system control.

8

CSH

Current-Sense input, High side. Current-limit level is 100mV referred to CSL.

9

CSL

Current-Sense input, Low side. Also serves as the feedback input in fixed-output modes.

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 output

11

VL

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.

Dual Mode is a trademark of Maxim Integrated Products.

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