MAX1982(2002) 데이터 시트보기 (PDF) - Maxim Integrated

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MAX1982
(Rev.:2002)

Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply

Maxim Integrated 

Low-Voltage, Low-Dropout Linear Regulators

with External Bias Supply

Pin Description

PIN

MAX1982 MAX1983

1

1

2

2

3

3

4

—

—

4

5

5

6

6

NAME

BIAS

GND

SHDN

PGOOD

ADJ

OUT

IN

FUNCTION

Bias Voltage. Input voltage to the control circuitry. BIAS powers all control blocks and the gate

of the pass transistor. Bypass BIAS to GND with a 0.1µF ceramic capacitor.

Ground

Shutdown Control Input. Drive SHDN low to enter the low-power shutdown state. Connect

SHDN to BIAS for normal operation.

Power-Good Output. The open-drain PGOOD output goes high at least 1ms after the output

voltage has attained regulation. PGOOD asserts low 10µs after the output falls by 10%.

Feedback for Adjustable Output. Connect ADJ to the midpoint of a resistor-divider between

OUT and GND for an adjustable output voltage between 0.8V and 2.0V.

Regulator Output. Bypass OUT to GND with a 10µF to 22µF low-ESR ceramic capacitor.

Internal Pass Transistor Input. IN connects to the drain of the internal power switch. Bypass IN

to GND with a 10µF ceramic capacitor.

Detailed Description

The MAX1982/MAX1983 are low-voltage, low-dropout

linear regulators with an external bias supply input (see

Figures 1 and 2). BIAS is powered by a 4.5V to 5.5V

supply that is commonly available in laptop and desk-

top computers. The 5V bias supply drives the gate of

the internal pass transistor, while a lower voltage input

at the drain of the transistor (IN) is regulated to provide

VOUT. Separating the bias input voltages yields higher

efficiency. These devices are ideal for applications that

require low-voltage outputs from low-voltage inputs.

The MAX1982 delivers 1.2V (±3%) at 300mA from an

input voltage of 1.25V to 5.5V. The MAX1983 delivers

an adjustable output voltage from 0.8V to 2V.

The MAX1982 features an open-drain PGOOD output

that transitions high 1ms after the output reaches regu-

lation. PGOOD goes low within 10µs of the output

falling out of regulation by 120mV.

Both devices feature current- and thermal-limiting cir-

cuitry that protect the MAX1982/MAX1983 from dam-

age during fault conditions.

Bias Supply Input

The BIAS input powers the control circuitry and pro-

vides the pass transistor gate drive. Power BIAS from a

well-regulated 5V (±10%) supply. Current drawn from

the BIAS supply remains relatively constant with varia-

tions in VIN and load current (see the Typical Operating

Characteristics). Bypass BIAS with a 0.1µF or greater

capacitor as close to the device as possible. The bias

supply current remains low (250µA) when the

MAX1982/MAX1983 are in dropout.

Power-Supply Input

IN connects to the drain of the internal N-channel

power transistor. IN may be as low as 1.25V, minimizing

power dissipation. Bypass IN with a 10µF or greater

capacitor as close to the device as possible.

Shutdown

The MAX1982/MAX1983 feature a low-power shutdown

mode that reduces quiescent current drawn to 1µA

(typ), and BIAS current consumption to less than 1µA

(typ). Driving SHDN low disables the voltage reference,

error amplifier, gate-drive circuitry, and pass transistor

(see Figure 2), and the device output enters a high-

impedance state. Connect SHDN to BIAS for normal

operation.

PGOOD Output

The MAX1982 provides an open-drain PGOOD output

that goes high 1ms (min) after the output attains regula-

tion (within 10% of the nominal output voltage). PGOOD

transitions low 10µs after the output falls out of regula-

tion by 120mV, or when the device enters shutdown.

Connect a pullup resistor from PGOOD to BIAS for a

logic-level output. Use a 100kΩ resistor to minimize

current consumption.

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