MAX604C Просмотр технического описания (PDF) - Maxim Integrated

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MAX604C

5V/3.3V or Adjustable, Low-Dropout, Low IQ, 500mA Linear Regulators

Maxim Integrated 

5V/3.3V or Adjustable, Low-Dropout,

Low IQ, 500mA Linear Regulators

IN

OFF

SHUTDOWN

LOGIC

THERMAL

SENSOR

1.20V

REFERENCE

GND

Figure 2. Functional Diagram

SHUTDOWN

ERROR AMP

MOSFET DRIVER

WITH FOLDBACK

CURRENT LIMIT

REVERSE

P

CURRENT

PROTECTION

DUAL-MODE

COMPARATOR

80mV

OUT

SET

R1

R2

MAX603

MAX604

_______________Detailed Description

The MAX603/MAX604 are low-dropout, low-quiescent-

current linear regulators designed primarily for battery-

powered applications. They supply an adjustable 1.25V

to 11V output or a preselected 5V (MAX603) or 3.3V

(MAX604) output for load currents up to 500mA. As

illustrated in Figure 2, they consist of a 1.20V reference,

error amplifier, MOSFET driver, P-channel pass transis-

tor, dual-mode comparator, and internal feedback volt-

age divider.

The 1.20V bandgap reference is connected to the error

amplifier’s inverting input. The error amplifier compares

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 pass transistor. If the feedback voltage is lower

than the reference, the pass transistor gate is pulled

lower, allowing more current to pass and increasing the

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

pass transistor gate is pulled up, allowing less current

to pass to the output.

The output voltage is fed back through either an internal

resistor voltage divider connected to the OUT pin, or an

external resistor network connected to the SET pin. The

dual-mode comparator examines the SET voltage and

selects the feedback path used. If SET is below 80mV,

internal feedback is used and the output voltage is regulat-

ed to 5V for the MAX603 or 3.3V for the MAX604.

Additional blocks include a foldback current limiter, reverse

current protection, thermal sensor, and shutdown logic.

Internal P-Channel Pass Transistor

The MAX603/MAX604 feature a 500mA P-channel

MOSFET pass transistor. This provides several advan-

tages over similar designs using PNP pass transistors,

including longer battery life.

The P-channel MOSFET requires no base drive, which

reduces quiescent current considerably. PNP based

regulators waste considerable amounts of current in

dropout when the pass transistor saturates. They also

use high base-drive currents under large loads. The

MAX603/MAX604 do not suffer from these problems

and consume only 15µA of quiescent current under

light and heavy loads, as well as in dropout.

6 _______________________________________________________________________________________

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