Detailed Description

The MAX1793 features Dual Mode™ operation, allow-

ing a fixed output or an adjustable output from +1.25V

to +5V. The regulators are guaranteed to supply 1A of

output current.

As Figure 1 shows, the device consists of a +1.25V ref-

erence, error amplifier, MOSFET driver, p-channel pass

transistor, internal feedback voltage-divider, Dual Mode

comparator, and 4ms reset output.

The +1.25V reference is connected to the inverting

input of the error amplifier. The error amplifier com-

pares this reference with the selected feedback voltage

and amplifies the difference. The MOSFET driver reads

the error signal and applies the appropriate drive to the

p-channel transistor. If the feedback voltage is lower

than the reference, the pass transistor’s gate is pulled

lower, allowing more current to pass and increase the

output voltage. If the feedback voltage is high, the pass

transistor’s gate is pulled up, allowing less current to

when the feedback voltage has dropped 6% below its

expected level, causing RST to go low.

The output voltage is fed back through either an inter-

nal resistor-divider connected to OUT or an external

resistor network connected to SET. The Dual Mode

is used and the output is regulated to the factory-preset

voltage.

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Dual Mode is a trademark of Maxim Integrated Products, Inc.

1175mV

IN

OUT

100mV

NMOS

4ms

4ms DELAY TIMER

R1

R2

PMOS

OUT

SET

GND

SHDN

IN

RST

SHUTDOWN

LOGIC

1.25V

REFERENCE

MOSFET DRIVER

WITH FOLDBACK

CURRENT LIMIT

ERROR AMP

SHUTDOWN

THERMAL

SENSOR

DETECTOR

DUAL MODE

COMPARATOR

MAX1793

Figure 1. Functional Diagram