Rainbow-electronics MAX1774 Bedienungsanleitung PDF herunterladen (Seite 10)

MAX1774

Dual, High-Efficiency, Step-Down

Converter with Backup Battery Switchover

10 ______________________________________________________________________________________

Typical Operating Characteristics (continued)

(Circuit of Figure 1, V

= +5V, V

INC

= +3.3V, T

= +25°C, unless otherwise noted.)

TURN-ON RESPONSE

MAX1774-14

OUT

1V/div

100µs/div

400µA

200µA

INPUT

CURRENT

200mA/div

SHDN

5V/div

INPUT CURRENT

MAIN

CORE

BACKUP SWITCHOVER RESPONSE

MAX1774-15

BKUP

5V/div

BBATT

50mA/div

BIN

10mV/div

MAIN

10mV/div

5µs/div

Pin Description

QSOP

QFN

NAME FUNCTION

130

SHDNM

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

operation, connect SHDNM to IN.

231

SHDNC

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

operation, connect SHDNC to CVL.

332BKUP

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.

41MDRV

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.

PGNDC

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

6 3 PGND

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

together close to the IC.

7 4 NDRV

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

between CVL and PGND.

8 5 CVL

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.

9 6 IN Power Supply Input

10 7 PDRV

P - C hannel D r i ve Outp ut. D r i ves the m ai n outp ut hi g h- si d e M OS FE T sw i tch. P D RV sw i ng s b etw een IN and

C V H . The vol tag e at C V H i s r eg ul ated at V

- 4.2V unl ess the i np ut vol tag e i s l ess than 5.5V .

11 8 CVH

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.

12 9 LXB

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.

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 20 21

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