LM2990
Negative Low Dropout Regulator
General Description
The LM2990 is a three-terminal, low dropout, 1 ampere
negative voltage regulator available with fixed output volt-
ages of −5, −5.2, −12, and −15V.
The LM2990 uses new circuit design techniques to provide
low dropout and low quiescent current. 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
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
−V
IN
≤3V).
Output voltage accuracy is guaranteed to ±5%over load,
and temperature extremes.
The LM2990 is short-circuit proof, and thermal shutdown in-
cludes hysteresis to enhance the reliability of the device
when overloaded for an extended period of time. The
LM2990 is available in a 3-lead TO-220 package and is rated
for operation over the automotive temperature range of
−40˚C to +125˚C.
Features
n5%output accuracy over entire operating range
nOutput current in excess of 1A
nDropout voltage typically 0.6V at 1A load
nLow quiescent current
nInternal short circuit current limit
nInternal thermal shutdown with hysteresis
nFunctional complement to the LM2940 series
Applications
nPost switcher regulator
nLocal, on-card, regulation
nBattery operated equipment
Typical Application
Ordering Information and Connection Diagrams
Temperature
Range Output Voltage Package
-5.0 -5.2 -12 -15
−40˚C to
+125˚C LM2990T-5.0 LM2990T-5.2 LM2990T-12 LM2990T-15 TO-220
LM2990S-5.0 LM2990S-12 LM2990S-15 TO-263
−55˚C to
+125˚C LM2990J-5.0-QML
5962-9571101QEA LM2990J-12-QML
5962-9571001QEA LM2990J-15-QML
5962-9570901QEA J16A
LM2990WG5.0-QML
5962-9571101QXA WG16A
DS010801-1
*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.
**Required for stability. Must be at least a 10 µF aluminum electrolytic ora1µFsolid 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 10Ωover the same operating temperature range as the regulator.
June 1999
LM2990 Negative Low Dropout Regulator
© 1999 National Semiconductor Corporation DS010801 www.national.com
Ordering Information and
Connection Diagrams (Continued)
3-Lead TO-220
DS010801-2
Front View
Order Number LM2990T-5.0, LM2990T-5.2, LM2990T-12
or LM2990T-15
See NS Package Number T03B
TO-263 Surface-Mount Package
DS010801-11
Top View
DS010801-12
Side View
Order Number LM2990S-5.0, LM2990S-12 or
LM2990S-15
See NS Package Number TS3B
16-Lead Ceramic Dual-in-Line Package
DS010801-33
Top View
Order Number
LM2990J-5.0-QML (5962-9571101QEA),
LM2990J-12-QML (5962-9571001QEA), or
LM2990J-15-QML (5962-9570901QEA),
See NS Package Number J16A
16-Lead Ceramic Surface Mount Package
DS010801-34
Top View
Order Number
LM2990WG5.0-QML (5962-9571101QXEA)
See NS Package Number WG16A
www.national.com 2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Voltage −26V to +0.3V
ESD Susceptibility (Note 2) 2 kV
Power Dissipation (Note 3) Internally Limited
Junction Temperature (T
Jmax
) 125˚C
Storage Temperature −65˚C to +150˚C
Lead Temperature
(Soldering, 10 sec.) 260˚C
Operating Ratings(Note 1)
Junction Temperature Range (T
J
) −40˚C to +125˚C
Maximum Input Voltage (Operational) −26V
Electrical Characteristics
V
IN
=−5V+V
O(NOM)
(Note 6) , I
O
=1A, C
O
=47 µF, unless otherwise specified. Boldface limits apply over the entire operat-
ing temperature range, −40˚C ≤T
J
≤125˚C, all other limits apply for T
J
=25˚C.
LM2990-5.0 LM2990-5.2 Units
(Limit)
Parameter Conditions Typ Limit Typ Limit
(Note 4) (Note 5) (Note 4) (Note 5)
Output Voltage (V
O
)5mA≤I
O
≤1A
−5
−4.90
−5.2
−5.10 V (max)
−5.10 −5.30 mV (min)
V
5mA≤I
O
≤1A −4.75 −4.94 V (max)
−5.25 −5.46 V (min)
Line Regulation I
O
=5 mA, 4 40 4 40 mV (max)
V
O(NOM)
−1V >V
IN
>−26V
Load Regulation 50 mA ≤I
O
≤1A 1 40 1 40 mV (max)
Dropout Voltage I
O
=0.1A, ∆V
O
≤100 mV 0.1 0.3 0.1 0.3 V (max)
I
O
=1A, ∆V
O
≤100 mV 0.6 10.6 1V (max)
Quiescent Current (I
q
)I
O
≤1A 1515mA(max)
I
O
=1A, V
IN
=V
O(NOM)
9 50 9 50 mA (max)
Short Circuit Current R
L
=1Ω(Note 7) 1.8 1.5 1.8 1.5 A (min)
Maximum Output Current (Note 7) 1.8 1.5 1.8 1.5 A (min)
Ripple Rejection V
ripple
=1V
rms
, 58 50 58 50 dB (min)
ƒ
ripple
=1 kHz, I
O
=5mA
Output Noise Voltage 10 Hz–100 kHz, I
O
=5 mA 250 750 250 750 µV (max)
Long Term Stability 1000 Hours 2000 2000 ppm
Electrical Characteristics
V
IN
=−5V+V
O(NOM)
(Note 6) , I
O
=1A, C
O
=47 µF, unless otherwise specified. Boldface limits apply over the entire operat-
ing temperature range, −40˚C ≤T
J
≤125˚C, all other limits apply for T
J
=25˚C.
LM2990-12 LM2990-15 Units
(Limit)
Parameter Conditions Typ Limit Typ Limit
(Note 4) (Note 5) (Note 4) (Note 5)
Output Voltage (V
O
)5mA≤I
O
≤1A
−12
−11.76
−15
−14.70 V (max)
−12.24 −15.30 V (min)
V
5mA≤I
O
≤1A −11.40 −14.25 V (max)
−12.60 −15.75 V (min)
Line Regulation I
O
=5 mA, 6 60 6 60 mV (max)
V
O(NOM)
−1V >V
IN
>−26V
Load Regulation 50 mA ≤I
O
≤1A 3 50 3 50 mV (max)
Dropout Voltage I
O
=0.1A, ∆V
O
≤100 mV 0.1 0.3 0.1 0.3 V (max)
I
O
=1A, ∆V
O
≤100 mV 0.6 10.6 1V (max)
Quiescent Current (I
q
)I
O
≤1A 1515mA(max)
I
O
=1A, V
IN
=V
O(NOM)
9 50 9 50 mA (max)
www.national.com3
Electrical Characteristics (Continued)
V
IN
=−5V+V
O(NOM)
(Note 6) , I
O
=1A, C
O
=47 µF, unless otherwise specified. Boldface limits apply over the entire operat-
ing temperature range, −40˚C ≤T
J
≤125˚C, all other limits apply for T
J
=25˚C.
LM2990-12 LM2990-15 Units
(Limit)
Parameter Conditions Typ Limit Typ Limit
(Note 4) (Note 5) (Note 4) (Note 5)
Short Circuit Current R
L
=1Ω(Note 7) 1.2 0.9 1.0 0.75 A (min)
Maximum Output Current (Note 7) 1.8 1.4 1.8 1.4 A (min)
Ripple Rejection V
ripple
=1V
rms
, 52 42 52 42 dB (min)
ƒ
ripple
=1 kHz, I
O
=5mA
Output Noise Voltage 10 Hz–100 kHz, I
O
=5 mA 500 1500 600 1800 µV (max)
Long Term Stability 1000 Hours 2000 2000 ppm
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is in-
tended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: Human body model, 100 pF discharged through a 1.5 kΩresistor.
Note 3: The maximum power dissipation is a function of TJmax,θJA, and TA. The maximum allowable power dissipation at any ambient temperature is PD=(TJmax
−T
A
)/θJA. If this dissipation is exceeded, the die temperature will rise above 125˚C, and the LM2990 will eventually go into thermal shutdown at a TJof approximately
160˚C. For the LM2990, the junction-to-ambient thermal resistance, is 53˚C/W, 73˚C/W for the TO-263, and the junction-to-case thermal resistance is 3˚C. If the
TO-263 package is used, the thermal resistance can be reduced by increasing the P.C. board copper area thermally connected to the package. Using 0.5 square
inches of copper area, θJA is 50˚C/W; with 1 square inch of copper area, θJA is 37˚C/W; and with 1.6 or more square inches of copper area, θJA is 32˚C/W.
Note 4: Typicals are at TJ=25˚C and represent the most likely parametric norm.
Note 5: Limits are guaranteed and 100%production tested.
Note 6: VO(NOM) is the nominal (typical) regulator output voltage, −5V, −5.2V, −12V or −15V.
Note 7: The short circuit current is less than the maximum output current with the −12V and −15V versions due to internal foldback current limiting. The −5V and
−5.2V versions, tested with a lower input voltage, does not reach the foldback current limit and therefore conducts a higher short circuit current level. If the LM2990
output is pulled above ground, the maximum allowed current sunk back into the LM2990 is 1.5A.
Definition of Terms
Dropout Voltage: The input-output voltage differential at
which the circuit ceases to regulate against further reduction
in input voltage. Measured when the output voltage has
dropped 100 mV from the nominal value obtained at (V
O
+
5V) input, dropout voltage is dependent upon load current
and junction temperature.
Input Voltage: The DC voltage applied to the input terminals
with respect to ground.
Input-Output Differential: The voltage difference between
the unregulated input voltage and the regulated output volt-
age for which the regulator will operate.
Line Regulation: The change in output voltage for a change
in the input voltage. The measurement is made under condi-
tions of low dissipation or by using pulse techniques such
that the average chip temperature is not significantly af-
fected.
Load Regulation: The change in output voltage for a
change in load current at constant chip temperature.
Long Term Stability: Output voltage stability under accelle-
rated life-test conditions after 1000 hours with maximum
rated voltage and junction temperature.
Output Noise Voltage: The rms AC voltage at the output,
with constant load and no input ripple, measured over a
specified frequency range.
Quiescent Current: That part of the positive input current
that does not contribute to the positive load current. The
regulator ground lead current.
Ripple Rejection: The ratio of the peak-to-peak input ripple
voltage to the peak-to-peak output ripple voltage.
Temperature Stability of V
O
:The percentage change in
output voltage for a thermal variation from room temperature
to either temperature extreme.
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Typical Performance Characteristics
Dropout Voltage
DS010801-14
Normalized Output Voltage
DS010801-15
LM2990-5.0 and LM2990-5.2
Quiescent Current
DS010801-16
LM2990-12
Quiescent Current
DS010801-17
LM2990-15
Quiescent Current
DS010801-18
LM2990-5 and LM2990-5.2
Low Voltage Behavior
DS010801-19
LM2990-5 and LM2990-5.2
Line Transient Response
DS010801-20
LM2990-5 and LM2990-5.2
Load Transient Response
DS010801-21
LM2990-12 and LM2990-15
Low Voltage Behavior
DS010801-22
LM2990-12 and LM2990-15
Line Transient Response
DS010801-23
LM2990-12 and LM2990-15
Load Transient Response
DS010801-24
www.national.com5
Typical Performance Characteristics (Continued)
LM2990-5 and LM2990-5.2
Ripple Rejection
DS010801-25
LM2990-5 and LM2990-5.2
Output Impedance
DS010801-26
Maximum Output Current
DS010801-27
LM2990-12 and LM2990-15
Ripple Rejection
DS010801-28
LM2990-12 and LM2990-15
Output Impedance
DS010801-29
Maximum Output Current
DS010801-30
Maximum Power
Dissipation (TO-220)
DS010801-31
Maximum Power Dissipation
(TO-263) (See (Note 3))
DS010801-32
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Typical Applications
The LM2940 is a positive 1A low dropout regulator; refer to its datasheet for further information.
Application Hints
EXTERNAL CAPACITORS
The LM2990 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 (refer to the graph on the
right).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" from the input power supply filter.
FORCING THE OUTPUT POSITIVE
Due to an internal clamp circuit, the LM2990 can withstand
positive voltages on its output. If the voltage source pulling
the output positive is DC, the current must be limited to 1.5A.
A current over 1.5A fed back into the LM2990 could damage
the device. The LM2990 output can also withstand fast posi-
tive voltage transients up to 26V, without any current limiting
of the source. However, if the transients have a duration of
over 1 ms, the output should be clamped with a Schottky di-
ode to ground.
Post Regulator for an Isolated Switching Power Supply
DS010801-5
Fixed Current Sink
DS010801-7
Adjustable Current Sink
DS010801-10
Output Capacitor ESR
DS010801-9
www.national.com7
Equivalent Schematic
DS010801-8
www.national.com 8
Physical Dimensions inches (millimeters) unless otherwise noted
TO-220 3–Lead Molded Package
Order Number LM2990T-5.0, LM2990T-5.2, LM2990T-12 or LM2990T-15
NS Package Number T03B
www.national.com9
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
TO-263 3-Lead Plastic Surface Mount Package
Order Number LM2990S-5.0, LM2990S-12 or LM2990S-15
NS Package Number TS3B
www.national.com 10
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
16–Lead Ceramic Dual–in–Line Package
LM2990J-5.0-QML (5962-9571101QEA), LM2990J-12-QML (5962-9571001QEA), or LM2990J-15-QML (5962-9570901QEA),
NS Package Number J16A
16–Lead Ceramic Surface–Mount Package
LM2990WG5.0-QML (5962-9571101QXA)
NS Package Number WG16A
www.national.com11
Notes
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
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Fax: 81-3-5639-7507
www.national.com
LM2990 Negative Low Dropout Regulator
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.
