MAX1774 PDF VIEW DOWNLOAD, MAX1774 データシート

MAX1774(2002) データシートの表示（PDF） - Maxim Integrated

部品番号

コンポーネント説明

メーカー

MAX1774
(Rev.:2002)

Dual, High-Efficiency, Step-Down Converter with Backup Battery Switchover

Maxim Integrated

MAX1774 Datasheet PDF : 21 Pages

First Prev 11 12 13 14 15 16 17 18 19 20

Dual, High-Efficiency, Step-Down

Converter with Backup Battery Switchover

Pin Description (continued)

QSOP QFN

—

17, 25,

NAME

LXB2

BIN

BKOFF

ACI

DBI

LBI

REF

N.C.

FBM

CS+

CS-

FBC

GND

INC

ACO

LBO

INS

LXC

FUNCTION

Backup Converter Switching Node. Connect LXB2 to LXB as close to the IC as possible.

Backup Battery Input. Connect BIN to the output of the backup boost regulator. Bypass BIN with a 10µF or

greater capacitor to GND. When the MAX1774 is in backup mode, BIN powers the main output.

Backup Disable Input. Driving BKOFF below +0.5V disables the backup mode. In backup mode, the

device enters shutdown when this pin is pulled low. BKOFF can be driven from a digital signal or can be

used as a low battery detector to disable the backup converter when the backup battery is low.

AC Adapter Low-Voltage Detect Input. Connect to adapter DC input. When the voltage at ACI falls

below the voltage at INS plus +0.22V, ACO asserts.

Dead Battery Input. Connect DBI to the main battery through a resistive voltage-divider. When DBI drops

below +1.20V, no AC adapter is connected (ACO is low, but main output still available), BKUP asserts.

Low-Battery Input. Connect LBI to the main battery through a resistive voltage-divider. When the

voltage at LBI drops below +1.20V, LBO asserts.

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

No Connection. Not Internally Connected.

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-.

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

inductor current approaches zero.

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

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

to +5.0V.

Analog Ground

Core Supply Input

Low AC Output. Open drain ACO asserts when ACI falls below the main output voltage plus 0.22V.

Open-Drain Low-Battery Output. LBO asserts when LBI falls below +1.20V.

Power-Supply Input Voltage Sense Input. Connect INS to the power-supply input voltage.

Core Converter Switching Node

Detailed Description

The MAX1774 dual step-down DC-DC converter is

designed to power PDA, palmtop, and subnotebook

computers. Normally, these devices require two sepa-

rate power supplies–one for the processor and another

higher voltage supply for the peripheral circuitry. The

MAX1774 provides an adjustable +1.25V to +5.5V main

output designed to power the peripheral circuitry of

PDAs and similar devices. The main output delivers up

to 2A output current. The lower voltage core converter

has an adjustable +1.0V to +5.0V output, providing up

to 1.5A output current. Both regulators utilize a propri-

etary regulation scheme allowing PWM operation at

medium to heavy loads, and automatically switch to

pulse skipping at light loads for improved efficiency.

Under low-battery conditions, the MAX1774 enters

backup mode, making use of a low-voltage backup

battery and a step-up regulator to power the output.

Figure 1 is the MAX1774 typical application circuit.

Operating Modes for the

Step-Down Converters

When delivering low output currents, the MAX1774 oper-

ates in discontinuous conduction mode. Current through

the inductor starts at zero, rises as high as the minimum

current limit (IMIN), then ramps down to zero during

_______________________________________________________________________________________ 11

Share Link: