MAX1774EMJ(2002) 查看數據表（PDF） - Maxim Integrated

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MAX1774EMJ
(Rev.:2002)

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

Maxim Integrated 

Dual, High-Efficiency, Step-Down

Converter with Backup Battery Switchover

Typical Operating Characteristics (continued)

(Circuit of Figure 1, VIN = +5V, VINC = +3.3V, TA = +25°C, unless otherwise noted.)

5V

VSHDN

5V/div

0

TURN-ON RESPONSE

MAX1774-14

VMAIN

VCORE

INPUT CURRENT

3V

VOUT

2V

1V/div

1V

0

400µA

200µA

0

INPUT

CURRENT

200mA/div

BACKUP SWITCHOVER RESPONSE

MAX1774-15

VBKUP

5V/div

IBBATT

50mA/div

VBIN

10mV/div

VMAIN

10mV/div

100µs/div

5µs/div

Pin Description

PIN

QSOP QFN

1

30

2

31

3

32

4

1

5

2

6

3

7

4

8

5

9

6

10

7

11

8

12

9

NAME

SHDNM

SHDNC

BKUP

MDRV

PGNDC

PGND

NDRV

CVL

IN

PDRV

CVH

LXB

FUNCTION

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

operation, connect SHDNM to IN.

Shutdown for Core Regulator. Low voltage on SHDNC shuts off the core output. For normal

operation, connect SHDNC to CVL.

Open-Drain Backup Input/Output. The device is in backup mode when BKUP is low. BKUP can be

externally pulled low to place the device in backup mode.

Open-Drain Drive Output. MDRV goes low when the ACI voltage drops below the main voltage plus

220mV and device is not in backup. Connect MDRV to the gate of the main battery P-channel

MOSFET to switch the battery to IN when the AC adapter voltage is not present.

Power Ground for the Core Converter. Connect all grounds together close to the IC.

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 CVL and PGND.

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

Power Supply Input

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

CVH. The voltage at CVH is regulated at VIN - 4.2V unless the input voltage is less than 5.5V.

High-Side Drive Bypass. This is the 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.

Backup Converter Switching Node. Connect an inductor from LXB to the backup battery and a

Schottky diode to BIN to complete the backup converter. In backup mode, this step-up converter

powers the main output from the backup battery through BIN.

10 ______________________________________________________________________________________

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