MAX8885EUK50 查看數據表（PDF） - Maxim Integrated

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MAX8885EUK50

150mA, Low-Dropout Linear Regulator with Power-OK Output

Maxim Integrated 

150mA, Low-Dropout Linear Regulator

with Power-OK Output

Pin Description

PIN

NAME

FUNCTION

1

IN

Regulator Input. Supply voltage can range from +2.5V to +6.5V. Bypass with 1µF capacitor to GND

(see Capacitor Selection and Regulator Stability).

2

GND

Ground. This pin also functions as a heatsink. Solder to a large pad or the circuit-board ground

plane to maximize power dissipation.

3

SHDN

Active-Low Shutdown Input. A logic low reduces the supply current to below 1µA. Connect to IN

for normal operation.

4

POK

Power-OK Output. Active low, open-drain output indicates an out-of-regulation condition.

Connect a 100kΩ pull-up resistor to OUT for logic levels. If not used, leave this pin unconnected.

5

OUT

Regulator Output. Fixed 5.0V, 3.3V, 3.0V, 2.7V, or 2.5V output. Sources up to 150mA. Bypass

with 4.7µF (>0.5Ω typ ESR) tantalum capacitor to GND.

Detailed Description

The MAX8885 is a low-dropout, low-quiescent-current

linear regulator designed primarily for battery-powered

applications using low-cost, high-ESR tantalum capaci-

tors. The device delivers up to 150mA and is available

with preset output voltages of 2.5V, 2.7V, 3.0V, 3.3V, or

5.0V. The MAX8885 consists of a 1.25V reference, error

amplifier, P-channel pass transistor, power-OK compara-

tor, and internal feedback voltage divider (Figure 1).

The 1.25V bandgap reference is connected to the error

amplifier’s inverting input. The error amplifier compares

this reference with the feedback voltage and amplifies

the difference. If the feedback voltage is lower than the

reference voltage, the pass-transistor gate is pulled

lower, which allows more current to pass to the output

and increases the output voltage. If the feedback volt-

age 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 an internal resistor voltage

divider connected to the OUT pin.

Additional blocks include a current limiter, reverse-bat-

tery protection, thermal sensor, and shutdown logic.

Output Voltage

The MAX8885 is supplied with factory-set output volt-

ages of 2.5V, 2.7V, 3.0V, 3.3V, or 5.0V. The part num-

ber’s two-digit suffix identifies the nominal output

voltage. For example, the MAX8885EUK33 indicates a

preset output voltage of 3.3V (see Output Voltage

Selector Guide).

Internal P-Channel Pass Transistor

The MAX8885 features a 1.1Ω (typ) P-channel MOSFET

pass transistor. This provides several advantages over

similar designs using PNP pass transistors, including

longer battery life. The P-channel MOSFET requires no

base drive, which reduces quiescent current signifi-

cantly. PNP-based regulators waste considerable cur-

rent in dropout when the pass transistor saturates. They

also use high base-drive currents under large loads.

The MAX8885 does not suffer from these problems and

consumes only 100µA of quiescent current whether in

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

Typical Operating Characteristics).

Power-OK Output (POK)

When the output voltage goes out of regulation—as dur-

ing dropout, current limit, or thermal shutdown—POK

goes low. POK is an open-drain N-channel MOSFET. To

obtain a logic-level output, connect a pull-up resistor

from POK to OUT. To minimize current consumption,

make this resistor as large as practical. A 100kΩ resis-

tor works well for most applications. The POK function is

not active during shutdown. A capacitor to GND may be

added to generate a power-on-reset (POR) delay, which

can operate down to VIN ≤ 1V. (See POK Startup

Response in the Typical Operating Circuit.)

Current Limit

The MAX8885 includes a current limiter that monitors

and controls the pass transistor’s gate voltage, limiting

the output current to 390mA (typ). For design purpos-

es, consider the current limit to be 160mA (min) to

600mA (max). The output can be shorted to ground for

an indefinite period of time without damaging the part.

Thermal-Overload Protection

When the junction temperature exceeds TJ = +170°C,

the thermal sensor signals the shutdown logic, turning

off the pass transistor and allowing the IC to cool. The

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