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MAX1982

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

Maxim Integrated 

Low-Voltage, Low-Dropout Linear Regulators

with External Bias Supply

Current Limit

The MAX1982/MAX1983 limit the output current to

600mA (typ) in the event of an overload or output short

circuit. The current limit prevents damage to the inter-

nal power transistor, but the device can enter thermal

shutdown if the power dissipation is great enough to

increase the die temperature above +160°C (see the

Thermal-Overload Protection section).

Thermal-Overload Protection

Thermal-overload protection limits the power dissipa-

tion in the MAX1982/MAX1983. When the die tempera-

ture exceeds +160°C, the pass transistor turns off,

allowing the device to cool. Normal operation resumes

when the die temperature cools by 20°C. A continuous

thermal-overload condition results in a pulsed output.

For continuous operation, do not exceed a junction

temperature of +150°C.

Applications Information

Output Voltage Selection

The MAX1982 output is fixed at 1.2V. The MAX1983

provides an adjustable output (0.8V to 2.0V). Connect

ADJ to a resistive voltage-divider between OUT and

GND as shown in Figure 4. Set the output voltage using

the following equation:

VOUT

=

0.8V

⎛⎝⎜1+

R1⎞

R2 ⎠⎟

Set R2 at 40kΩ and choose R1 to achieve the desired

output voltage. Set VIN to higher than (VOUT + 400mV)

to meet the dropout voltage requirement (see the

Input/Output (Dropout) Voltage section).

To ensure stability over the specified input voltage

range, the minimum output capacitance must be 10µF

with a maximum ESR of 35mΩ.

Operating Region and Power Dissipation

The maximum power dissipation of the MAX1982/

MAX1983 depends on the thermal resistance of the 6-pin

SOT23 package and the circuit board, the temperature

difference between the die and ambient air, and the rate

of airflow. The power dissipated in the device is:

( ) PD = IOUT × VIN − VOUT

The resulting maximum power dissipation is:

4.5V TO 5.5V

BIAS

IN

0.1μF

MAX1982

GND

OUT

ON

OFF

SHDN

PGOOD

1.25V TO 5.5V

10μF

1.2V

10μF

100kΩ

Figure 3. MAX1982 Typical Application Circuit

4.5V TO 5.5V

BIAS

IN

0.1μF

MAX1983

GND

OUT

ON

SHDN

ADJ

OFF

1.5V TO 5.5V

10μF

1.2V

R1

20kΩ

10μF

R2

40kΩ

Figure 4. MAX1983 Typical Application Circuit

PDISS(MAX) =

TJ(MAX) − TA

θJC + θCA

where TJ(MAX) is the maximum junction temperature

(+150°C) and TA is the ambient temperature, θJC is the

thermal resistance from the die junction to the package

case, and θCA is the thermal resistance from the case

through the PC board, copper traces, and other materi-

als to the surrounding air. For optimum power dissipa-

tion, use a large ground plane with good thermal

contact to GND, and use wide input and output traces.

When 1 square inch of copper is connected to the

device, the maximum allowable power dissipation of a

6-pin SOT23 package is 696mW. The maximum power

dissipation is derated by 8.7mW/°C above TA = +70°C.

Extra copper on the PC board increases thermal mass,

and reduces thermal resistance of the board. Refer to

the MAX1982/MAX1983 EV kit for a layout example.

The MAX1982/MAX1983 deliver up to 300mA and oper-

ate with input voltages up to 5.5V, but not simultane-

ously. High output currents can only be achieved when

the input-output differential voltages are low (Figure 5).

Undervoltage Lockout (UVLO)

The undervoltage lockout (UVLO) circuit ensures that

the regulator starts up with adequate voltage for the

gate-drive circuitry to bias the internal pass transistor.

The UVLO circuitry monitors VBIAS

10 ______________________________________________________________________________________

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