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

_______________________________________________________________________________________

7

_______________Detailed Description

The MAX882/MAX883/MAX884 are micropower, low-

dropout linear regulators designed primarily for battery-

powered applications. They feature Dual Mode operation,

allowing a fixed output of 5V for the MAX883 and 3.3V for

the MAX882/MAX884, or an adjustable output from 1.25V

to 11V. These devices supply up to 200mA while requiring

less than 15µA quiescent current. As illustrated in Figure

1, they consist of a 1.20V reference, error amplifier, MOS-

FET driver, P-channel pass transistor, dual-mode com-

parator, and feedback voltage-divider.

The 1.20V reference is connected to the error amplifier’s

inverting input. The error amplifier compares this refer-

ence 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 refer-

ence, the pass transistor’s 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 pin

voltage and selects the feedback path used. If the SET

pin is below 65mV, internal feedback is used and the

output voltage is regulated to 5V for the MAX883 or

3.3V for the MAX882/MAX884. Additional blocks

include a foldback current limiter, reverse-current pro-

tection, a thermal sensor, shutdown or standby logic,

and a low-battery-detection comparator.

Internal P-Channel Pass Transistor

The MAX882/MAX883/MAX884 feature a 200mA P-

channel MOSFET pass transistor. This provides several

advantages over similar designs using PNP pass tran-

sistors, including longer battery life.

The P-channel MOSFET requires no base drive, which

reduces quiescent current considerably. PNP-based reg-

ulators waste large amounts of current in dropout when

the pass transistor saturates. They also use high base-

drive currents under large loads. The MAX882/MAX883/

MAX884 do not suffer from these problems and consume

only 11µA of quiescent current during light loads, heavy

loads, and dropout.

Output Voltage Selection

The MAX882/MAX883/MAX884 feature Dual Mode

operation. In preset voltage mode, the MAX883’s out-

put is set to 5V and the MAX882/MAX884’s output is set

to 3.3V, using internal trimmed feedback resistors.

Select this mode by connecting SET to ground.

In preset voltage mode, impedances between SET and

ground should be less than 100k

Ω. Otherwise, spurious

conditions could cause the voltage at SET to exceed

the 65mV dual-mode threshold.

Pin Description

PIN

MAX882

MAX883/

MAX884

NAME

DESCRIPTION

11

LBO

Low-Battery Output is an open-drain output that goes low when LBI is less than 1.2V. Connect

to IN or OUT through a pull-up resistor. LBO is undefined during shutdown mode

(MAX883/MAX884).

2

2

SET

Feedback for setting the output voltage. Connect to GND to set the output voltage to the

preselected 3.3V or 5V. Connect to an external resistor network for adjustable-output operation.

3, 6

3, 6

GND

Ground pins—also function as heatsinks in the SO package. All GND pins must be soldered to

the PC board for proper power dissipation. Connect to large copper pads or planes to channel

heat from the IC.

4

4

OUT

Regulator Output. Fixed or adjustable from 1.25V to 11.0V. Sources up to 200mA. Bypass with a

2.2µF capacitor.

5

5

IN

Regulator Input. Supply voltage can range from 2.7V to 11.5V.

7

—

STBY

Standby. Active-low comparator input. Connect to GND to disable the output or to IN for normal

operation. A resistor network (from IN) can be used to set a standby mode threshold.

—

7

OFF

Shutdown. Active-low logic input. In OFF mode, supply current is reduced below 1µA and

8

8

LBI

Low-Battery comparator Input. Tie to IN when not used.