LM2991| Datasheet

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LM2991 Negative Low Dropout Adjustable Regulator

September 2000

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 temperature 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 temperature 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 (VOUT - VIN 3V). The LM2991 is short-circuit proof, and thermal shutdown includes 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 package
s and is rated for operation over the automotive temperature range of -40 C to +125 C. Mil-Aero versions are also available.

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

VOUT = VREF (1 + R2/R1) *Required if the regulator is located further than 6 inches from the power supply filter capacitors. A 1 uF solid tantalum or a 10 uF aluminum electrolytic capacitor is recommended. **Required for stability. Must be at least a 10 uF aluminum electrolytic or a 1 uF solid tantalum to maintain stability. May be increased without bound to 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 over the same operating temperature range as the regulator.

2000 National Semiconductor Corporation

DS011260

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