LM2991

Negative Low Dropout Adjustable Regulator

General Description

The LM2991 is a low dropout adjustable negative regulator

with a output voltage range between −3V to −24V. The

LM2991 provides up to 1A of load current and features a On

/Off pin for remote shutdown capability.

The LM2991 uses new circuit design techniques to provide a

low dropout voltage, low quiescent current and low tempera-

ture coefficient precision reference. The dropout voltage at

1A load current is typically 0.6V and a guaranteed

worst-case maximum of 1V over the entire operating tem-

perature range. The quiescent current is typically 1 mA with

a 1A load current and an input-output voltage differential

greater than 3V. A unique circuit design of the internal bias

supply limits the quiescent current to only 9 mA (typical)

when the regulator is in the dropout mode (V

The LM2991 is short-circuit proof, and thermal shutdown in-

cludes hysteresis to enhance the reliability of the device

when inadvertently overloaded for extended periods. The

LM2991 is available in 5-lead TO-220 and TO-263 packages

and is rated for operation over the automotive temperature

range of −40˚C to +125˚C. Mil-Aero versions are also avail-

able.

Features

n Output voltage adjustable from −3V to −24V, typically

−2V to −25V

n Output current in excess of 1A

n Dropout voltage typically 0.6V at 1A load

n Low quiescent current

n Internal short circuit current limit

n Internal thermal shutdown with hysteresis

n TTL, CMOS compatible ON/OFF switch

n Functional complement to the LM2941 series

Applications

n Post switcher regulator

n Local, on-card, regulation

n Battery operated equipment

Typical Application

DS011260-1

*Required if the regulator is located further than 6 inches from the power supply filter capacitors. A 1 µF solid tantalum or a 10 µF aluminum electrolytic

capacitor is recommended.

maintain regulation during transients. Locate the capacitor as close as possible to the regulator. The equivalent series resistance (ESR) is critical, and

should be less than 10

Ω over the same operating temperature range as the regulator.

May 1999

© 1999 National Semiconductor Corporation

DS011260

www.national.com