MAX667(1994) Просмотр технического описания (PDF) - Maxim Integrated

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MAX667
(Rev.:1994)

+5V/Programmable Low-Dropout Voltage Regulator

Maxim Integrated 

+5V/Programmable Low-Dropout

Voltage Regulator

__________________________________________Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

1000

100

10

1

1

DROPOUT VOLTAGE

vs. LOAD CURRENT

10

100

LOAD CURRENT (mA)

100,000

QUIESCENT CURRENT

vs. LOAD CURRENT

VIN = +6V

10,000

DD OUTPUT CURRENT

vs. INPUT-OUTPUT DIFFERENCE

1000

5 10

20 50 100mA LOAD

100

1000

1000

100

10

0.01

0.1

1

10 100

LOAD CURRENT (mA)

1000

10

1

1

0

2

50 100 150 200 250

INPUT-OUTPUT DIFFERENCE (mV)

_____________________Pin Description

PIN NAME

FUNCTION

Dropout Detector Output—the collec-

1

DD

tor of a PNP pass transistor. Normally

an open circuit, it sources current as

dropout is reached.

Regulated Output Voltage. OUT falls

to 0V when SHDN is above 1.5V. SET

2

OUT

determines output voltage when SET

is above 50mV; otherwise, it is 5V.

OUT must be connected to an output

filter capacitor.

Low-Battery Detector. A CMOS input

3

LBI

to an internal 1.255V comparator

whose output is the LBO pin.

4

GND Ground

Shutdown Input. Connect to GND for

normal operation (output active). Pull

5

SHDN above 1.5V to disable OUT, LBO, and

DD and to reduce quiescent current to

less than 1µA.

(Output) Voltage Set, CMOS Input.

6

SET

Connect to GND for 5V output. For

other voltages, connect external resis-

tive divider from OUT.

Low-Battery Output. An open-drain N-

7

LBO channel transistor that sinks current to

GND when LBI is less than 1.22V.

8

IN

Positive Input Voltage (unregulated)

_______________Detailed Description

Figure 1 shows a micropower bandgap reference, an

error amplifier, a PNP pass transistor, and two com-

parators as the main elements of the MAX667. One

comparator, C1, selects the fixed 5V or adjustable

operation with an external voltage divider. The other

comparator, C2, is a low-battery detector.

The bandgap reference, which is trimmed to 1.22V,

connects internally to one input of the error amplifier,

A1. The feedback signal from the regulator output sup-

plies the other input of A1 from either an on-chip volt-

age divider or two external resistors. When SET is

grounded, the internal divider provides the error ampli-

fier feedback signal for a fixed 5V output. When SET is

more than 50mV above ground, the error amplifier’s

input switches directly to SET while an external resistor

divider from OUT determines the output voltage.

A second comparator, C2, compares the LBI input to

the internal reference voltage. LBO is an open-drain

FET connected to GND. The low-battery threshold can

also be set with a voltage divider at LBI. In addition, the

MAX667 has a shutdown input (SHDN) that disables

the load and the device while reducing quiescent cur-

rent when it is pulled high.

+5V Output

Figure 2 shows the connection for a fixed 5V output.

The SET input is grounded, and no external resistors

are required. Figure 3 shows adjustable output opera-

tion. R1 and R2 set the output voltage. SHDN should be

grounded if not used.

_______________________________________________________________________________________ 3

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