MAX8865REUA Просмотр технического описания (PDF) - Maxim Integrated

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MAX8865REUA

Dual, Low-Dropout, 100mA Linear Regulators

Maxim Integrated 

Dual, Low-Dropout, 100mA Linear Regulators

______________________________________________________________Pin Description

PIN NAME

FUNCTION

1

OUT1

Regulator 1 Output. Fixed or adjustable from 1.25V to 5.5V. Sources up to 100mA. Bypass with a 1µF

capacitor to GND.

2

IN

Regulator Input. Supply voltage can range from +2.5V to +5.5V. Bypass with 2µF to GND.

3

GND Ground. Solder to large pads or the circuit board ground plane to maximize thermal dissipation.

4

OUT2

Regulator 2 Output. Fixed or adjustable from 1.25V to 5.5V. Sources up to 100mA. Bypass with a 1µF

capacitor to GND.

Feedback Input for Setting the Output 2 Voltage. Connect to GND to set the output voltage to the preset 2.80V

5

SET2 (MAX886_R), 2.84V (MAX886_S), or 3.15V (MAX886_T). Connect to an external resistor divider for adjustable-

output operation.

6

SHDN2

Active-Low Shutdown 2 Input. A logic low turns off regulator 2. On the MAX8866, a logic low also causes the

output voltage to discharge to GND. Connect to IN for normal operation.

7

SHDN1

Active-Low Shutdown 1 Input. A logic low turns off regulator 1. On the MAX8866, a logic low also causes the

output voltage to discharge to GND. Connect to IN for normal operation.

Feedback Input for Setting the Output 1 Voltage. Connect to GND to set the output voltage to the preset 2.80V

8

SET1 (MAX886_R), 2.84V (MAX886_S), or 3.15V (MAX886_T). Connect to an external resistor divider for adjustable-

output operation.

_______________Detailed Description

The MAX8865/MAX8866 are dual, low-dropout, low-qui-

escent-current linear regulators designed primarily for

battery-powered applications. They supply adjustable

1.25V to 5.5V outputs or preselected 2.80V

(MAX886_R), 2.84V (MAX886_S), or 3.15V (MAX886_T)

outputs for load currents up to 100mA. As illustrated in

Figure 1, these devices have a 1.25V reference and two

independent linear regulators. Each linear regulator

consists of an error amplifier, MOSFET driver, P-channel

pass transistor, Dual Mode™ comparator, and internal

feedback voltage divider.

The 1.25V bandgap reference is connected to the error

amplifiers’ inverting inputs. Each 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 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 inter-

nal 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. If SET_ is below

60mV, internal feedback is used and the output voltage

is regulated to 2.80V for the MAX886_R, 2.84V for the

MAX886_S, or 3.15V for the MAX886_T. Both regulators

are preset for the same voltage. The reference and the

thermal sensor are shared between the regulators.

Duplicate blocks exist for current limiters, reverse bat-

tery protection, and shutdown logic.

Internal P-Channel Pass Transistor

The MAX8865/MAX8866 feature 1.1Ω typical P-channel

MOSFET pass transistors. This provides several advan-

tages over similar designs using PNP pass transistors,

including longer battery life.

The P-channel MOSFET requires no base-drive current,

which reduces quiescent current significantly. PNP-

based regulators waste considerable amounts of cur-

rent in dropout when the pass transistor saturates. They

also use high base-drive currents under large loads.

The MAX8865/MAX8866 do not suffer from these prob-

lems, and consume only 145µA of quiescent current,

whether in dropout, light load, or heavy load applica-

tions (see Typical Operating Characteristics).

Output Voltage Selection

The MAX8865/MAX8866 feature Dual Mode operation:

they operate in either a preset voltage mode or an

adjustable mode.

_______________________________________________________________________________________ 7

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