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PDF 5962-9650501VEA Data sheet ( Hoja de datos )
| Número de pieza | 5962-9650501VEA | |
| Descripción | Negative Low Dropout Adjustable Regulator | |
| Fabricantes | National Semiconductor | |
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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 −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 (VOUT − VIN ≤ 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 −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
VOUT = VREF (1 + R2/R1)
*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.
**Required for stability. Must be at least a 10 µF aluminum electrolytic or a 1 µF 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 10Ω over the same operating temperature range as the regulator.
© 1999 National Semiconductor Corporation DS011260
www.national.com
1 page  
Typical Performance Characteristics (Continued)
Adjust Pin Current
Low Voltage Behavior
Maximum Power
Dissipation (TO-220)
DS011260-25
Maximum Power Dissipation
(TO-263) (See Note 3)
DS011260-26
DS011260-27
DS011260-28
Application Hints
EXTERNAL CAPACITORS
The LM2991 regulator requires an output capacitor to main-
tain stability. The capacitor must be at least 10 µF aluminum
electrolytic or 1 µF solid tantalum. The output capacitor’s
ESR must be less than 10Ω, or the zero added to the regu-
lator frequency response by the ESR could reduce the
phase margin, creating oscillations. The shaded area in the
Output Capacitor ESR graph indicates the recommended
ESR range. An input capacitor, of at least 1 µF solid tantalum
or 10 µF aluminum electrolytic, is also needed if the regulator
is situated more than 6 inches from the input power supply
filter.
Output Capacitor ESR Range
DS011260-5
MINIMUM LOAD
A minimum load current of 500 µA is required for proper op-
eration. The external resistor divider can provide the mini-
mum load, with the resistor from the adjust pin to ground set
to 2.4 kΩ.
SETTING THE OUTPUT VOLTAGE
The output voltage of the LM2991 is set externally by a resis-
tor divider using the following equation:
VOUT = VREF x (1 + R2/R1) − (IADJ x R2)
where VREF = −1.21V. The output voltage can be pro-
grammed within the range of −3V to −24V, typically an even
5 www.national.com
5 Page 
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
16-Lead Ceramic Surface-Mount Package
Order Number LM2991WG-QML
5962-9650501QXA
NS Package Number WG16A
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: [email protected]
www.national.com
National Semiconductor
Europe
Fax: +49 (0) 1 80-530 85 86
Email: [email protected]
Deutsch Tel: +49 (0) 1 80-530 85 85
English Tel: +49 (0) 1 80-532 78 32
Français Tel: +49 (0) 1 80-532 93 58
Italiano Tel: +49 (0) 1 80-534 16 80
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: [email protected]
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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| PDF Descargar | [ Datasheet 5962-9650501VEA.PDF ] | |
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