LM2991J [NSC]
Negative Low Dropout Adjustable Regulator; 负低压差稳压器可调
| 型号： | LM2991J |
| 厂家： | 
National Semiconductor |
| 描述： | Negative Low Dropout Adjustable Regulator |
| 文件： | 总11页 (文件大小：341K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
May 1999
LM2991
Negative Low Dropout Adjustable Regulator
General Description
Features
n Output voltage adjustable from −3V to −24V, typically
−2V to −25V
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.
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
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).
Applications
n Post switcher regulator
n Local, on-card, regulation
n Battery operated equipment
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.
Typical Application
DS011260-1
=
V
V
(1 + R2/R1)
REF
OUT
*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
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Connection Diagrams and Ordering Information
5-Lead TO-220
Straight Leads
5-Lead TO-220
Bent, Staggered Leads
DS011260-9
DS011260-2
Front View
Order Number LM2991T
See NS Package Number T05A
Front View
Order Number LM2991T Flow LB03
See NS Package Number T05D
TO263
5-Lead Surface-Mount Package
DS011260-11
Top View
DS011260-12
Side View
Order Number LM2991S
See NS Package Number TS5B
16-Lead Ceramic Dual-in-Line Package
16-Lead Ceramic Surface-Mount Package
DS011260-29
DS011260-30
Top View
Order Number LM2991J-QMLV
5962-9650501VEA
Order Number LM2991J-QML
5962-9650501QEA
Top View
Order Number LM2991WG-QML
5962-9650501QXA
See NS Package Number WG16A
See NS Package Number J16A
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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.
Storage Temperature Range
−65˚C to +150˚C
230˚C
Lead Temperature (Soldering, 10 sec.)
Operating Ratings (Note 1)
Input Voltage
−26V to +0.3V
2 kV
Junction Temperature Range (TJ)
−40˚C to +125˚C
−26V
ESD Susceptibility (Note 2)
Power Dissipation (Note 3)
Junction Temperature (TJmax
Maximum Input Voltage (Operational)
Internally limited
125˚C
)
Electrical Characteristics
=
=
=
=
=
=
VIN −10V, VO −3V, IO 1A, CO 47 µF, R1 2.7k, TJ 25˚C, unless otherwise specified. Boldface limits apply over
the entire operating junction temperature range.
Parameter
Conditions
Typical
(Note 4)
−1.210
Min
Max
Units
Reference Voltage
5 mA ≤ IO ≤ 1A
−1.234
−1.186
V
V
5 mA ≤ IO ≤ 1A,
−1.27
−1.15
VO − 1V ≥ VIN ≥ −26V
Output Voltage
Range
−2
−25
−3
V
V
=
VIN −26V
−24
=
Line Regulation
Load Regulation
Dropout Voltage
IO 5 mA, VO − 1V ≥ VIN ≥ −26V
0.004
0.04
0.1
0.04
0.4
0.2
0.3
0.8
1
%/V
%
50 mA ≤ IO ≤ 1A
=
IO 0.1A, ∆VO ≤ 100 mV
V
=
IO 1A, ∆VO ≤ 100 mV
0.6
V
Quiescent Current
Dropout Quiescent
Current
IO ≤ 1A
0.7
16
5
mA
mA
=
VIN VO, IO ≤ 1A
50
=
=
1 kHz,
Ripple Rejection
Vripple 1 Vrms, f
60
50
dB
ripple
=
IO 5 mA
=
Output Noise
ON /OFF Input
Voltage
10 Hz − 100 kHz, IO 5 mA
(VOUT: ON)
200
1.2
1.3
0.1
40
450
µV
V
0.8
(VOUT: OFF)
2.4
=
ON /OFF Input
Current
VON/OFF 0.8V (VOUT: ON)
10
µA
µA
A
=
VON/OFF 2.4V (VOUT: OFF)
100
250
=
=
Output Leakage
Current
VIN −26V, VON/OFF 2.4V
60
=
VOUT 0V
=
Current Limit
VOUT 0V
2
1.5
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the deivce 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 kΩ resistor.
=
D
Note 3: The maximum power dissipation is a function of T
, θ and T . The maximum allowable power dissipation at any ambient temperature is P
(T
Jmax
Jmax JA
A
−
T )/θ . If this dissipation is exceeded, the die temperature will rise above 125˚C and the LM2991 will go into thermal shutdown. For the LM2991, the
A JA
junction-to-ambient thermal resistance is 53˚C/W for the TO-220, 73˚C/W for the TO-263, and junction-to-case thermal resistance is 3˚C. If the TO-263 package is
used, the thermal resistance can be reduced by increasing the PC board copper area thermally connected to the package. Using 0.5 square inches of copper area,
θ
is 50˚C/W; with 1 square inch of copper area, θ is 37˚C/W; and with 1.6 or more square inches of copper area, θ is 32˚C/W.
JA JA
JA
Note 4: Typicals are at T
=
25˚C and represent the most likely parametric norm.
J
3
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Typical Performance Characteristics
Dropout Voltage
Normalized Output Voltage
Output Voltage
DS011260-13
DS011260-15
DS011260-14
Output Noise Voltage
Line Transient Response
Ripple Rejection
Quiescent Current
Maximum Output Current
Maximum Output Current
ON /OFF Control Voltage
DS011260-16
DS011260-17
DS011260-18
Load Transient Response
DS011260-19
DS011260-20
DS011260-21
Output Impedance
DS011260-22
DS011260-23
DS011260-24
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4
Typical Performance Characteristics (Continued)
Adjust Pin Current
Low Voltage Behavior
Maximum Power
Dissipation (TO-220)
DS011260-26
DS011260-25
DS011260-27
Maximum Power Dissipation
(TO-263) (See Note 3)
DS011260-28
Application Hints
EXTERNAL CAPACITORS
Output Capacitor ESR Range
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.
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
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FORCING THE OUTPUT POSITIVE
Application Hints (Continued)
Due to an internal clamp circuit, the LM2991 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 LM2991 could damage
the device. The LM2991 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.
greater range of −2V to −25V. The adjust pin current is about
60 nA, causing a slight error in the output voltage. However,
using resistors lower than 100 kΩ makes the adjust pin cur-
rent negligible. For example, neglecting the adjust pin cur-
rent, and setting R2 to 100 kΩ and VOUT to −5V, results in an
output voltage error of only 0.16%.
ON/OFF PIN
The LM2991 regulator can be turned off by applying a TTL or
CMOS level high signal to the ON/OFF pin (see Adjustable
Current Sink Application).
Typical Applications
Fully Isolated Post-Switcher Regulator
DS011260-6
Adjustable Current Sink
DS011260-10
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6
Equivalent Schematic
7
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Physical Dimensions inches (millimeters) unless otherwise noted
5-Lead T0-220, Straight Leads (T)
Order Number LM2991T
NS Package Number T05A
5-Lead T0-220, Bent, Staggered Leads (T)
Order Number LM2991T Flow LBO3
NS Package Number T05D
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8
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
TO-263 5-Lead Plastic Surface Mount Package
Ordering Number LM2991S
NS Package Number TS5B
9
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
16-Lead Ceramic Dual-in-Line Package
Order Number LM2991J-QMLV
5962-9650501VEA
Order Number LM2991J-QML
5962-9650501QEA
NS Package Number J16A
www.national.com
10
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
16-Lead Ceramic Surface-Mount Package
Order Number LM2991WG-QML
5962-9650501QXA
NS Package Number WG16A
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