LM2991 Negative Low Dropout Adjustable Regulator
May 1999
LM2991
Negative Low Dropout Adjustable Regulator
General Description
The LM2991 is a low dropout adjustable negative regulator
with a output voltage range between 鈭?V to 鈭?4V. 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
OUT
鈭?V
IN
鈮?/div>
3V).
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 鈭?0藲C to +125藲C. Mil-Aero versions are also avail-
able.
Features
n
Output voltage adjustable from 鈭?V to 鈭?4V, typically
鈭?V to 鈭?5V
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
V
OUT
= V
REF
(1 + R2/R1)
*Required if the regulator is located further than 6 inches from the power supply filter capacitors. A 1 碌F solid tantalum or a 10 碌F aluminum electrolytic
capacitor is recommended.
*
*Required for stability. Must be at least a 10 碌F aluminum electrolytic or a 1 碌F 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鈩?over the same operating temperature range as the regulator.
漏 1999 National Semiconductor Corporation
DS011260
www.national.com
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