MAX1928 Просмотр технического описания (PDF) - Maxim Integrated

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MAX1928

Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters

Maxim Integrated 

Low-Output-Voltage, 800mA, PWM Step-Down

DC-DC Converters

Pin Description

PIN

NAME

FUNCTION

1

PWM Forced-PWM Input. Drive to GND to use PWM at medium to heavy loads and pulse-skipping at light loads.

Drive to BATT to force PWM operation at all loads.

2

GND Ground

3

REF Internal 1.25V Reference. Bypass to GND with a 0.1µF capacitor.

Output Feedback Sense Input. To set the output voltage to the preset voltage (MAX1928), connect FB directly

4

FB to the output. To adjust the output voltage (MAX1927R), connect FB to the center of an external resistor-

divider between the output and GND. FB regulation voltage is 0.75V.

5

COMP

Compensation Input. See the Compensation, Stability, and Output Capacitor section for compensation

component selection.

6

SHDN Shutdown Control Input. Drive low to shut down the converter. Drive high for normal operation.

7

PGND Power Ground

8

LX Inductor Connection to the drains of the internal power MOSFETs.

9

BATT Supply Voltage Input. Connect to a 2.6V to 5.5V source. Bypass to GND with a low-ESR 10µF capacitor.

10

POK

Power-OK Open-Drain Output. Once the soft-start routine has completed, POK goes high impedance 20ms

after FB exceeds 90% of its expected final value.

COMP

SLOPE

COMPENSATION

PWM

COMPARATOR

MAX1927

MAX1928

BATT

BIAS

P

P

LX

1MHz

OSC

PFM CURRENT

COMPARATOR

PWM

PWM

CONTROL

SHDN

TO

COMP

REF

1.25V

REFERENCE

ILIM

COMPARATOR

N

N-CHANNEL

CURRENT COMPARATOR

N

PGND

MAX1927R

ONLY

POWER-OK

POK

CONTROL

FB

MAX1928

ONLY

GND

Figure 1. Simplified Functional Diagram

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