MAX8860EUA(1999) Просмотр технического описания (PDF) - Maxim Integrated

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MAX8860EUA
(Rev.:1999)

Low-Dropout, 300mA Linear Regulator in µMAX

Maxim Integrated 

Low-Dropout, 300mA

Linear Regulator in µMAX

IN

REVERSE

BATTERY

SHDN PROTECTION

CC

MAX8860

GND

SHUTDOWN

LOGIC

THERMAL

SENSOR

ERROR

AMP

MOS DRIVER

WITH ILIMIT

1.25V

REF

FAULT

DETECT

DUAL-MODE

COMPARATOR

60mV

P

OUT

SET

FAULT

Figure 1. Functional Diagram

Internal P-Channel Pass Transistor

The MAX8860 features a 0.5Ω typical P-channel

MOSFET pass transistor. This provides several advan-

tages over similar designs using PNP pass transistors,

including longer battery life. 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 P-channel

MOSFET requires no base-drive current, which reduces

quiescent current considerably. The MAX8860 con-

sumes less than 165µA of quiescent current whether in

dropout, light-load, or heavy-load applications (see

Typical Operating Characteristics).

Output Voltage Selection

The MAX8860 features Dual Mode operation: it operates

in either a preset voltage mode or an adjustable mode.

In preset voltage mode, internal, trimmed feedback

resistors set the output voltage to an adjustable +1.25V

to +6.5V output voltage or a fixed-voltage output of

+1.8V (MAX8860EUA18), +2.5V (MAX8860EUA25),

+2.77V (MAX8860EUA27), +2.82V (MAX8860EUA28),

+3.V (MAX8860EUA30), or +3.3V (MAX8860EUA33).

Select this mode by connecting SET to ground. In

adjustable mode, select an output between 1.25V and

6.5V using two external resistors connected as a voltage

divider to SET (Figure 2). Calculate the output voltage

with the following equation:

BATTERY

CIN

2.2µF

33nF

IN

OUT

MAX8860

SHDN

SET

CC

FAULT

GND

OUTPUT

VOLTAGE

R1

COUT

2.2µF

100k

R2

Figure 2. Adjustable Output Using External Feedback

Resistors

VOUT

=

VSET

1

+

R1

R2 

where VSET = 1.25V. To simplify resistor selection, use

the following equation:

R1

=

R2





VOUT



− 1

 VSET 

6 _______________________________________________________________________________________

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