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MAX1775

Dual-Output Step-Down DC-DC Converter for PDA/Palmtop Computers

Maxim Integrated 

Dual-Output Step-Down

DC-DC Converter for PDA/Palmtop Computers

Pin Description

PIN

NAME

FUNCTION

1

SHDNM

Shutdown for Main Regulator. A low voltage on SHDNM shuts off the main output. For normal

operation, connect SHDNM to IN.

2

SHDNC

Shutdown for Core Regulator. A low voltage on SHDNC shuts off the core output. For normal operation,

connect SHDNC to CVL.

3

PGND

Power Ground. Ground for NDRV and core output synchronous rectifier. Connect all grounds together

close to the IC.

N-Channel Drive Output. Drives the main output synchronous rectifier MOSFET. NDRV swings between

4

NDRV

CVL and PGND.

Low-Side Regulator Bypass. CVL is the output of an internal LDO regulator. This is the internal power

5

CVL

supply for the device control circuitry as well as the N-channel driver. Bypass CVL with a 1.0µF or

greater capacitor to GND. When CS- is above the CVL switchover threshold (2.47V), CVL is powered

from the main output.

6

IN

Power Supply Input

P-Channel Drive Output. Drives the main output high-side MOSFET switch. PDRV swings between IN

7

PDRV

and CVH. The voltage at CVH is regulated at VIN - 4.3V unless the input voltage is less than 5.5V.

High-Side Drive Bypass. CVH is the output of an internal LDO regulator with respect to VIN. This is the

8

CVH

low-side of the P-channel driver output. Bypass with a 1.0µF capacitor or greater to IN. When the input

voltage is less than +5.5V, CVH is switched to PGND.

9

REF

Reference Voltage Output. Bypass REF to GND with a 0.22µF or greater capacitor.

10

FBM

Main Output Feedback. Connect FBM to a resistive voltage-divider to set main output voltage between

+1.25V to +5.5V.

Main Regulator High-Side Current-Sense Input. Connect the sense resistor between CS+ and CS-.

11

CS+

This voltage is used to set the current limit and to turn off the synchronous rectifier when the inductor

current approaches zero.

12

CS-

Main Regulator Low-Side Current-Sense Input. Connect CS- to the main output.

13

FBC

Core Output Feedback. Connect FBC to a resistive voltage-divider to set core output between +1.0V to

+5.0V.

14

GND

Analog Ground

15

INC

Core Supply Input

16

LXC

Core Converter Switching Node

_______________________________________________________________________________________ 9

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