LP2952,LP2952A,LP2953,LP2953A
LP2952/LP2952A/LP2953/LP2953A Adjustable Micropower Low-Dropout Voltage
Regulators
Literature Number: SNVS095C
LP2952/LP2952A/LP2953/LP2953A
Adjustable Micropower Low-Dropout Voltage Regulators
General Description
The LP2952 and LP2953 are micropower voltage regulators
with very low quiescent current (130 µA typical at 1 mA load)
and very low dropout voltage (typ. 60 mV at light load and
470 mV at 250 mA load current). They are ideally suited for
battery-powered systems. Furthermore, the quiescent cur-
rent increases only slightly at dropout, which prolongs bat-
tery life.
The LP2952 and LP2953 retain all the desirable character-
istics of the LP2951, but offer increased output current,
additional features, and an improved shutdown function.
The internal crowbar pulls the output down quickly when the
shutdown is activated.
The error flag goes low if the output voltage drops out of
regulation.
Reverse battery protection is provided.
The internal voltage reference is made available for external
use, providing a low-T.C. reference with very good line and
load regulation.
The parts are available in DIP and surface mount packages.
Features
nOutput voltage adjusts from 1.23V to 29V
nGuaranteed 250 mA output current
nExtremely low quiescent current
nLow dropout voltage
nExtremely tight line and load regulation
nVery low temperature coefficient
nCurrent and thermal limiting
nReverse battery protection
n50 mA (typical) output pulldown crowbar
n5V and 3.3V versions available
LP2953 Versions Only
nAuxiliary comparator included with CMOS/TTL
compatible output levels. Can be used for fault
detection, low input line detection, etc.
Applications
nHigh-efficiency linear regulator
nRegulator with under-voltage shutdown
nLow dropout battery-powered regulator
nSnap-ON/Snap-OFF regulator
Block Diagrams
LP2952
01112701
LP2953
01112702
March 2005
LP2952/LP2952A/LP2953/LP2953A Adjustable Micropower Low-Dropout Voltage Regulators
© 2005 National Semiconductor Corporation DS011127 www.national.com
Pinout Drawings
LP2952
14-Pin DIP
01112711
LP2953
16-Pin DIP
01112713
LP2952
16-Pin SO
01112712
LP2953
16-Pin SO
01112714
Ordering Information
LP2952
Order
Number
Temp.
Range
(T
J
)˚C
Package NSC
Drawing
Number
LP2952IN,
LP2952AIN,
LP2952IN-3.3,
LP2952AIN-3.3
−40 to
+125
14-Pin
Molded
DIP
N14A
LP2952IM,
LP2952AIM,
LP2952IM-3.3,
LP2952AIM-3.3
−40 to
+125
16-Pin
Surface
Mount
M16A
LP2953
Order
Number
Temp.
Range
(T
J
)˚C
Package NSC
Drawing
Number
LP2953IN,
LP2953AIN,
LP2953IN-3.3,
LP2953AIN-3.3
−40 to
+125
16-Pin
Molded DIP
N16A
LP2953IM,
LP2953AIM,
LP2953IM-3.3,
LP2953AIM-3.3
−40 to
+125
16-Pin
Surface
Mount
M16A
LP2953AMJ/883
5962-9233601MEA
LP2953AMJ-QMLV
5962-9233601VEA
−55 to
+150
16-Pin
Ceramic DIP J16A
LP2953AMWG/883
5962-9233601QXA
LP2953AMWG-QMLV
5962-9233601VXA
−55 to
+150
16-Pin
Ceramic
Surface
Mount
WG16A
LP2952/LP2952A/LP2953/LP2953A
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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 ≤T
A
≤
+150˚C
Operating Temperature Range
LP2952I, LP2953I, LP2952AI,
LP2953AI, LP2952I-3.3,
LP2953I-3.3, LP2952AI-3.3,
LP2953AI-3.3 −40˚C ≤T
J
≤+125˚C
LP2953AM −55˚C ≤T
A
≤
+125˚C
Lead Temp. (Soldering, 5 seconds) 260˚C
Power Dissipation (Note 2) Internally Limited
Maximum Junction Temperature
LP2952I, LP2953I, LP2952AI,
LP2953AI, LP2952I-3.3,
LP2953I-3.3, LP2952AI-3.3,
LP2953AI-3.3 +125˚C
LP2953AM +150˚C
Input Supply Voltage −20V to +30V
Feedback Input Voltage (Note 3) −0.3V to +5V
Comparator Input Voltage (Note 4) −0.3V to +30V
Shutdown Input Voltage (Note 4) −0.3V to +30V
Comparator Output Voltage (Note
4) −0.3V to +30V
ESD Rating (Note 15) 2 kV
Electrical Characteristics Limits in standard typeface are for T
J
= 25˚C, bold typeface applies over the full
operating temperature range. Limits are guaranteed by production testing or correlation techniques using standard Statistical
Quality Control (SQC) methods. Unless otherwise specified: V
IN
=V
O
(NOM) + 1V, I
L
= 1 mA, C
L
= 2.2 µF for 5V parts and
4.7µF for 3.3V parts. Feedback pin is tied to V Tap pin, Output pin is tied to Output Sense pin.
3.3V Versions
Symbol Parameter Conditions Typical LP2952AI-3.3, LP2953AI-3.3 LP2952I-3.3, LP2953I-3.3 Units
Min Max Min Max
V
O
Output Voltage 3.3 3.284 3.317 3.267 3.333 V
3.260 3.340 3.234 3.366
1mA≤I
L
≤250 mA 3.3 3.254 3.346 3.221 3.379
5V Versions
Symbol Parameter Conditions Typical LP2952AI, LP2953AI, LP2952I, LP2953I Units
LP2953AM (Note 17)
Min Max Min Max
V
O
Output Voltage 5.0 4.975 5.025 4.950 5.050 V
4.940 5.060 4.900 5.100
1mA≤I
L
≤250 mA 5.0 4.930 5.070 4.880 5.120
All Voltage Options
Electrical Characteristics
Limits in standard typeface are for T
J
= 25˚C, bold typeface applies over the full operating temperature range. Limits are guar-
anteed by production testing or correlation techniques using standard Statistical Quality Control (SQC) methods. Unless other-
wise specified: V
IN
=V
O
(NOM) + 1V, I
L
= 1 mA, C
L
= 2.2 µF for 5V parts and 4.7µF for 3.3V parts. Feedback pin is tied to V
Tap pin, Output pin is tied to Output Sense pin.
Symbol Parameter Conditions Typical LP2952AI, LP2953AI,
LP2952AI-3.3,
LP2953AI-3.3,
LP2953AM
(Notes 16, 17)
LP2952I, LP2953I,
LP2952I-3.3,
LP2953I-3.3
Units
Min Max Min Max
REGULATOR
Output Voltage Temp.
Coefficient
(Note 5) 20 100 150 ppm/˚C
Output Voltage Line
Regulation
V
IN
=V
O
(NOM) + 1V to 30V 0.03 0.1 0.2 %
0.2 0.4
LP2952/LP2952A/LP2953/LP2953A
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All Voltage Options (Continued)
Electrical Characteristics (Continued)
Limits in standard typeface are for T
J
= 25˚C, bold typeface applies over the full operating temperature range. Limits are guar-
anteed by production testing or correlation techniques using standard Statistical Quality Control (SQC) methods. Unless other-
wise specified: V
IN
=V
O
(NOM) + 1V, I
L
= 1 mA, C
L
= 2.2 µF for 5V parts and 4.7µF for 3.3V parts. Feedback pin is tied to V
Tap pin, Output pin is tied to Output Sense pin.
Symbol Parameter Conditions Typical LP2952AI, LP2953AI,
LP2952AI-3.3,
LP2953AI-3.3,
LP2953AM
(Notes 16, 17)
LP2952I, LP2953I,
LP2952I-3.3,
LP2953I-3.3
Units
Min Max Min Max
Output Voltage Load
Regulation (Note 6)
I
L
= 1 mA to 250 mA 0.04 0.16 0.20 %
I
L
= 0.1 mA to 1 mA 0.20 0.30
V
IN
–V
O
Dropout Voltage
(Note 7)
I
L
= 1 mA 60 100 100 mV
150 150
I
L
= 50 mA 240 300 300
420 420
I
L
= 100 mA 310 400 400
520 520
I
L
= 250 mA 470 600 600
800 800
I
GND
Ground Pin Current
(Note 8)
I
L
= 1 mA 130 170 170 µA
200 200
I
L
= 50 mA 1.1 2 2 mA
2.5 2.5
I
L
= 100 mA 4.5 6 6
88
I
L
= 250 mA 21 28 28
33 33
I
GND
Ground Pin Current at
Dropout
V
IN
=V
O
(NOM) −0.5V 165 210 210 µA
I
L
= 100 µA 240 240
I
GND
Ground Pin Current at
Shutdown (Note 8)
V
SHUTDOWN
≤1.1V 105 140 140 µA
I
LIMIT
Current Limit V
OUT
= 0 380 500 500 mA
530 530
Thermal Regulation (Note 10) 0.05 0.2 0.2 %/W
e
n
Output Noise Voltage
(10 Hz to 100 kHz)
I
L
= 100 mA
C
L
= 4.7 µF 400 µV
RMS
C
L
=33µF 260
C
L
= 33 µF (Note 11) 80
V
REF
Reference Voltage (Note 12) 1.230 1.215 1.245 1.205 1.255 V
1.205 1.255 1.190 1.270
Reference Voltage Line
Regulation
V
IN
= 2.5V to V
O
(NOM) + 1V 0.03 0.1 0.2 %
V
IN
=V
O
(NOM) + 1V to 30V
(Note 13)
0.2 0.4
Reference Voltage Load
Regulation
I
REF
= 0 to 200 µA 0.25 0.4 0.8 %
0.6 1.0
Reference Voltage
Temp. Coefficient
(Note 5) 20 ppm/˚C
LP2952/LP2952A/LP2953/LP2953A
www.national.com 4
All Voltage Options (Continued)
Electrical Characteristics (Continued)
Limits in standard typeface are for T
J
= 25˚C, bold typeface applies over the full operating temperature range. Limits are guar-
anteed by production testing or correlation techniques using standard Statistical Quality Control (SQC) methods. Unless other-
wise specified: V
IN
=V
O
(NOM) + 1V, I
L
= 1 mA, C
L
= 2.2 µF for 5V parts and 4.7µF for 3.3V parts. Feedback pin is tied to V
Tap pin, Output pin is tied to Output Sense pin.
Symbol Parameter Conditions Typical LP2952AI, LP2953AI,
LP2952AI-3.3,
LP2953AI-3.3,
LP2953AM
(Notes 16, 17)
LP2952I, LP2953I,
LP2952I-3.3,
LP2953I-3.3
Units
Min Max Min Max
I
B
(FB) Feedback Pin Bias
Current
20 40 40 nA
60 60
I
O
(SINK) Output “OFF” Pulldown
Current
(Note 9) 30 30 mA
20 20
DROPOUT DETECTION COMPARATOR
I
OH
Output “HIGH” Leakage V
OH
= 30V 0.01 1 1 µA
22
V
OL
Output “LOW” Voltage V
IN
=V
O
(NOM) − 0.5V
I
O
(COMP) = 400 µA
150 250 250 mV
400 400
V
THR
(MAX)
Upper Threshold
Voltage
(Note 14) −60 −80 −35 −80 −35 mV
−95 −25 −95 −25
V
THR
(MIN)
Lower Threshold
Voltage
(Note 14) −85 −110 −55 −110 −55 mV
−160 −40 −160 −40
HYST Hysteresis (Note 14) 15 mV
SHUTDOWN INPUT (Note 15)
V
OS
Input Offset (Referred to V
REF
)±3 −7.5 7.5 −7.5 7.5 mV
Voltage −10 10 −10 10
HYST Hysteresis 6 mV
I
B
Input Bias V
IN
(S/D) = 0V to 5V 10 −30 30 −30
−50
−30
50
nA
Current −50 50
LP2953AM 10 −30 30
−75 75
AUXILIARY COMPARATOR (LP2953 Only)
V
OS
Input Offset Voltage (Referred to V
REF
)±3 −7.5 7.5 −7.5
−10
7.5
10
mV
−10 10
LP2953AM ±3 −7.5 7.5
−12 12
HYST Hysteresis 6 mV
I
B
Input Bias Current V
IN
(COMP) = 0V to 5V 10 −30 30 −30
−50
30
50
nA
−50 50
LP2953AM 10 −30 30
−75 75
I
OH
Output “HIGH” Leakage V
OH
= 30V 0.01 1 1
2
µA
V
IN
(COMP) = 1.3V 2
LP2953AM 0.01 1
2.2
V
OL
Output “LOW” Voltage V
IN
(COMP) = 1.1V 150 250 250
400
mV
I
O
(COMP) = 400 µA 400
LP2953AM 150 250
420
LP2952/LP2952A/LP2953/LP2953A
www.national.com5
All Voltage Options (Continued)
Electrical Characteristics (Continued)
Note 1: Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the
device outside of its rated operating conditions.
Note 2: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance, θJ–A,
and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated using the equation for P(MAX),
.
Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. See APPLICATION
HINTS for additional information on heatsinking and thermal resistance.
Note 3: When used in dual-supply systems where the regulator load is returned to a negative supply, the output voltage must be diode-clamped to ground.
Note 4: May exceed the input supply voltage.
Note 5: Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.
Note 6: Load regulation is measured at constant junction temperature using low duty cycle pulse testing. Two separate tests are performed, one for the range of
100 µA to 1 mA and one for the 1 mA to 250 mA range. Changes in output voltage due to heating effects are covered by the thermal regulation specification.
Note 7: Dropout voltage is defined as the input to output differential at which the output voltage drops 100 mV below the value measured with a 1V differential. At
very low values of programmed output voltage, the input voltage minimum of 2V (2.3V over temperature) must be observed.
Note 8: Ground pin current is the regulator quiescent current. The total current drawn from the source is the sum of the ground pin current, output load current, and
current through the external resistive divider (if used).
Note 9: VSHUTDOWN ≤1.1V, VOUT =V
O(NOM).
Note 10: Thermal regulation is the change in output voltage at a time T after a change in power dissipation, excluding load or line regulation effects. Specifications
are for a 200 mA load pulse at VIN =V
O(NOM)+15V (3W pulse) for T = 10 ms.
Note 11: Connect a 0.1 µF capacitor from the output to the feedback pin.
Note 12: VREF ≤VOUT ≤(VIN − 1V), 2.3V ≤VIN ≤30V, 100 µA ≤IL≤250 mA.
Note 13: Two separate tests are performed, one covering 2.5V ≤VIN ≤VO(NOM)+1V and the other test for VO(NOM)+1V ≤VIN ≤30V.
Note 14: Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage measured atVIN =
VO(NOM) + 1V. To express these thresholds in terms of output voltage change, multiply by the Error amplifier gain, which is VOUT/VREF = (R1 + R2)/R2(refer to
Figure 4).
Note 15: Human body model, 200 pF discharged through 1.5 kΩ.
Note 16: Drive Shutdown pin with TTL or CMOS-low level to shut regulator OFF, high level to turn regulator ON.
Note 17: A military RETS specification is available upon request. For more information on military products, please refer to the Mil-Aero web page at
http://www.national.com/appinfo/milaero/index.html.
LP2952/LP2952A/LP2953/LP2953A
www.national.com 6
Typical Performance Characteristics
Unless otherwise specified: V
IN
= 6V, I
L
= 1 mA, C
L
= 2.2
µF, V
SD
= 3V, T
A
= 25˚C, V
OUT
= 5V.
Quiescent Current Quiescent Current
01112727 01112728
Ground Pin Current vs Load Ground Pin Current
01112729 01112730
Ground Pin Current Output Noise Voltage
01112731 01112732
LP2952/LP2952A/LP2953/LP2953A
www.national.com7
Typical Performance Characteristics Unless otherwise specified: V
IN
= 6V, I
L
= 1 mA, C
L
= 2.2 µF,
VSD = 3V, T
A
= 25˚C, V
OUT
= 5V. (Continued)
Ripple Rejection Ripple Rejection
01112733 01112734
Ripple Rejection Line Transient Response
01112735 01112736
Line Transient Response Output Impedance
01112737
01112738
LP2952/LP2952A/LP2953/LP2953A
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Typical Performance Characteristics Unless otherwise specified: V
IN
= 6V, I
L
= 1 mA, C
L
= 2.2 µF,
VSD = 3V, T
A
= 25˚C, V
OUT
= 5V. (Continued)
Load Transient Response Load Transient Response
01112739 01112740
Dropout Characteristics Enable Transient
01112741 01112742
Enable Transient
Short-Circuit Output Current
and Maximum Output Current
01112743 01112744
LP2952/LP2952A/LP2953/LP2953A
www.national.com9
Typical Performance Characteristics Unless otherwise specified: V
IN
= 6V, I
L
= 1 mA, C
L
= 2.2 µF,
VSD = 3V, T
A
= 25˚C, V
OUT
= 5V. (Continued)
Feedback Bias Current Feedback Pin Current
01112745 01112746
Error Output Comparator Sink Current
01112747 01112748
Divider Resistance
Dropout Detection
Comparator Threshold
Voltages
01112749 01112750
LP2952/LP2952A/LP2953/LP2953A
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Typical Performance Characteristics Unless otherwise specified: V
IN
= 6V, I
L
= 1 mA, C
L
= 2.2 µF,
VSD = 3V, T
A
= 25˚C, V
OUT
= 5V. (Continued)
Thermal Regulation Minimum Operating Voltage
01112751 01112752
Dropout Voltage
01112753
LP2952/LP2952A/LP2953/LP2953A
www.national.com11
Schematic Diagram
01112706
Application Hints
HEATSINK REQUIREMENTS (Industrial Temperature
Range Devices)
The maximum allowable power dissipation for the LP2952/
LP2953 is limited by the maximum junction temperature
(+125˚C) and the external factors that determine how quickly
heat flows away from the part: the ambient temperature and
the junction-to-ambient thermal resistance for the specific
application.
The industrial temperature range (−40˚C ≤T
J
≤+125˚C)
parts are manufactured in plastic DIP and surface mount
packages which contain a copper lead frame that allows
heat to be effectively conducted away from the die, through
the ground pins of the IC, and into the copper of the PC
board. Details on heatsinking using PC board copper are
covered later.
To determine if a heatsink is required, the maximum power
dissipated by the regulator, P(max), must be calculated. It is
important to remember that if the regulator is powered from
a transformer connected to the AC line, the maximum
specified AC input voltage must be used (since this pro-
duces the maximum DC input voltage to the regulator).
Figure 1 shows the voltages and currents which are present
in the circuit. The formula for calculating the power dissi-
pated in the regulator is also shown in Figure 1:
LP2952/LP2952A/LP2953/LP2953A
www.national.com 12
Application Hints (Continued)
The next parameter which must be calculated is the maxi-
mum allowable temperature rise, T
R
(max). This is calculated
by using the formula:
T
R
(max) = T
J
(max) − T
A
(max)θ
(J–A)
=T
R
(max)/P(max)
where: T
J
(max) is the maximum allowable junction
temperature
T
A
(max) is the maximum ambient temperature
Using the calculated values for T
R
(max) and P(max), the
required value for junction-to-ambient thermal resistance,
θ
(J–A)
, can now be found:
The heatsink is made using the PC board copper. The heat
is conducted from the die, through the lead frame (inside the
part), and out the pins which are soldered to the PC board.
The pins used for heat conduction are given in Table 1.
TABLE 1. Heat Conducting Pins
Part Package Pins
LP2952IN, LP2952AIN, 14-Pin DIP 3, 4, 5,
LP2952IN-3.3,
LP2952AIN-3.3
10, 11, 12
LP2953IN, LP2953AIN, 16-Pin DIP 4, 5, 12, 13
LP2953IN-3.3,
LP2953AIN-3.3
LP2952IM, LP2952AIM, 16-Pin Surface
Mount
1, 8, 9, 16
LP2952IM-3.3,
LP2952AIM-3.3,
LP2953IM, LP2953AIM,
LP2953IM-3.3,
LP2953AIM-3.3
Figure 2 shows copper patterns which may be used to
dissipate heat from the LP2952 and LP2953. Table 2 shows
some values of junction-to-ambient thermal resistance (θ
J–A
)
for values of L and W for 1 oz. copper.
TABLE 2. Thermal Resistance for Various Copper
Heatsink Patterns
Package L (in.) H (in.) θ
J–A
(˚C/W)
16-Pin DIP 1 0.5 70
21 60
3 1.5 58
4 0.19 66
6 0.19 66
14-Pin DIP 1 0.5 65
21 51
3 1.5 49
Surface Mount 1 0.5 83
21 70
3 1.5 67
6 0.19 69
4 0.19 71
2 0.19 73
HEATSINK REQUIREMENTS (Military Temperature
Range Devices)
The maximum allowable power dissipation for the
LP2953AMJ is limited by the maximum junction temperature
(+150˚C) and the two parameters that determine how quickly
heat flows away from the die: the ambient temperature and
the junction-to-ambient thermal resistance of the part.
01112707
FIGURE 1. P
TOTAL
=(V
IN
−V
OUT
)I
L
+(V
IN
)I
G
Current/Voltage Diagram
01112708
* For best results, useL=2H
** 14-Pin DIP is similar, refer to Table 1 for pins designated for
heatsinking.
FIGURE 2. Copper Heatsink Patterns
LP2952/LP2952A/LP2953/LP2953A
www.national.com13
Application Hints (Continued)
The military temperature range (−55˚C ≤T
J
≤+150˚C) parts
are manufactured in ceramic DIP packages which contain a
KOVAR lead frame (unlike the industrial parts, which have a
copper lead frame). The KOVAR material is necessary to
attain the hermetic seal required in military applications.
The KOVAR lead frame does not conduct heat as well as
copper, which means that the PC board copper can not be
used to significantly reduce the overall junction-to-ambient
thermal resistance in applications using the LP2953AMJ
part.
The power dissipation calculations for military applications
are done exactly the same as was detailed in the previous
section, with one important exception: the value for θ
(J–A)
,
the junction-to-ambient thermal resistance, is fixed at
95˚C/W and can not be changed by adding copper foil
patterns to the PC board. This leads to an important fact:
The maximum allowable power dissipation in any application
using the LP2953AMJ is dependent only on the ambient
temperature:
Figure 3 shows a graph of maximum allowable power dissi-
pation vs. ambient temperature for the LP2953AMJ, made
using the 95˚C/W value for θ
(J–A)
and assuming a maximum
junction temperature of 150˚C (caution: the maximum ambi-
ent temperature which will be reached in a given application
must always be used to calculate maximum allowable power
dissipation).
EXTERNAL CAPACITORS
A 2.2 µF (or greater) capacitor is required between the
output pin and ground to assure stability when the output is
set to 5V. Without this capacitor, the part will oscillate. Most
type of tantalum or aluminum electrolytics will work here.
Film types will work, but are more expensive. Many alumi-
num electrolytics contain electrolytes which freeze at −30˚C,
which requires the use of solid tantalums below −25˚C. The
important parameters of the capacitor are an ESR of about
5Ωor less and a resonant frequency above 500 kHz (the
ESR may increase by a factor of 20 or 30 as the temperature
is reduced from 25˚C to −30˚C). The value of this capacitor
may be increased without limit.
At lower values of output current, less output capacitance is
required for stability. The capacitor can be reduced to
0.68 µF for currents below 10 mA or 0.22 µF for currents
below 1 mA.
Programming the output for voltages below 5V runs the error
amplifier at lower gains requiring more output capacitance
for stability. At 3.3V output, a minimum of 4.7 µF is required.
For the worst-case condition of 1.23V output and 250 mA of
load current, a 6.8 µF (or larger) capacitor should be used.
A 1 µF capacitor should be placed from the input pin to
ground if there is more than 10 inches of wire between the
input and the AC filter capacitor or if a battery input is used.
Stray capacitance to the Feedback terminal can cause insta-
bility. This problem is most likely to appear when using high
value external resistors to set the output voltage. Adding a
100 pF capacitor between the Output and Feedback pins
and increasing the output capacitance to 6.8 µF (or greater)
will cure the problem.
MINIMUM LOAD
When setting the output voltage using an external resistive
divider, a minimum current of 1 µA is recommended through
the resistors to provide a minimum load.
It should be noted that a minimum load current is specified in
several of the electrical characteristic test conditions, so this
value must be used to obtain correlation on these tested
limits.
PROGRAMMING THE OUTPUT VOLTAGE
The regulator may be pin-strapped for 5V operation using its
internal resistive divider by tying the Output and Sense pins
together and also tying the Feedback and 5V Tap pins
together.
Alternatively, it may be programmed for any voltage between
the 1.23V reference and the 30V maximum rating using an
external pair of resistors (see Figure 4). The complete equa-
tion for the output voltage is:
where V
REF
is the 1.23V reference and I
FB
is the Feedback
pin bias current (−20 nA typical). The minimum recom-
mended load current of 1 µA sets an upper limit of 1.2 MΩon
the value of R2 in cases where the regulator must work with
no load (see MINIMUM LOAD ). I
FB
will produce a typical 2%
error in V
OUT
which can be eliminated at room temperature
by trimming R1. For better accuracy, choosing R2 = 100 kΩ
will reduce this error to 0.17% while increasing the resistor
program current to 12 µA. Since the typical quiescent current
is 120 µA, this added current is negligible.
01112726
FIGURE 3. Power Derating Curve for LP2953AMJ
LP2952/LP2952A/LP2953/LP2953A
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Application Hints (Continued)
DROPOUT VOLTAGE
The dropout voltage of the regulator is defined as the mini-
mum input-to-output voltage differential required for the out-
put voltage to stay within 100 mV of the output voltage
measured with a 1V differential. The dropout voltage is in-
dependent of the programmed output voltage.
DROPOUT DETECTION COMPARATOR
This comparator produces a logic “LOW” whenever the out-
put falls out of regulation by more than about 5%. This figure
results from the comparator’s built-in offset of 60 mV divided
by the 1.23V reference (refer to block diagrams on page 1).
The 5% low trip level remains constant regardless of the
programmed output voltage. An out-of-regulation condition
can result from low input voltage, current limiting, or thermal
limiting.
Figure 5 gives a timing diagram showing the relationship
between the output voltage, the ERROR output, and input
voltage as the input voltage is ramped up and down to a
regulator programmed for 5V output. The ERROR signal
becomes low at about 1.3V input. It goes high at about 5V
input, where the output equals 4.75V. Since the dropout
voltage is load dependent, the input voltage trip points will
vary with load current. The output voltage trip point does not
vary.
The comparator has an open-collector output which requires
an external pull-up resistor. This resistor may be connected
to the regulator output or some other supply voltage. Using
the regulator output prevents an invalid “HIGH” on the com-
parator output which occurs if it is pulled up to an external
voltage while the regulator input voltage is reduced below
1.3V. In selecting a value for the pull-up resistor, note that
while the output can sink 400 µA, this current adds to battery
drain. Suggested values range from 100 kΩto 1 MΩ. This
resistor is not required if the output is unused.
When V
IN
≤1.3V, the error flag pin becomes a high imped-
ance, allowing the error flag voltage to rise to its pull-up
voltage. Using V
OUT
as the pull-up voltage (rather than an
external 5V source) will keep the error flag voltage below
1.2V (typical) in this condition. The user may wish to divide
down the error flag voltage using equal-value resistors
(10 kΩsuggested) to ensure a low-level logic signal during
any fault condition, while still allowing a valid high logic level
during normal operation.
OUTPUT ISOLATION
The regulator output can be left connected to an active
voltage source (such as a battery) with the regulator input
power shut off, as long as the regulator ground pin is
connected to ground. If the ground pin is left floating,
damage to the regulator can occur if the output is pulled
up by an external voltage source.
REDUCING OUTPUT NOISE
In reference applications it may be advantageous to reduce
the AC noise present on the output. One method is to reduce
regulator bandwidth by increasing output capacitance. This
is relatively inefficient, since large increases in capacitance
are required to get significant improvement.
Noise can be reduced more effectively by a bypass capacitor
placed across R1 (refer to Figure 4). The formula for select-
ing the capacitor to be used is:
This gives a value of about 0.1 µF. When this is used, the
output capacitor must be 6.8 µF (or greater) to maintain
stability. The 0.1 µF capacitor reduces the high frequency
gain of the circuit to unity, lowering the output noise from 260
µV to 80 µV using a 10 Hz to 100 kHz bandwidth. Also, noise
is no longer proportional to the output voltage, so improve-
ments are more pronounced at high output voltages.
AUXILIARY COMPARATOR (LP2953 only)
The LP2953 contains an auxiliary comparator whose invert-
ing input is connected to the 1.23V reference. The auxiliary
comparator has an open-collector output whose electrical
characteristics are similar to the dropout detection compara-
tor. The non-inverting input and output are brought out for
external connections.
01112709
* See Application Hints
** Drive with TTL-low to shut down
FIGURE 4. Adjustable Regulator
01112710
* In shutdown mode, ERROR will go high if it has been pulled up to an
external supply. To avoid this invalid response, pull up to regulator output.
** Exact value depends on dropout voltage. (See Application Hints)
FIGURE 5. ERROR Output Timing
LP2952/LP2952A/LP2953/LP2953A
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Application Hints (Continued)
SHUTDOWN INPUT
A logic-level signal will shut off the regulator output when a
“LOW” (<1.2V) is applied to the Shutdown input.
To prevent possible mis-operation, the Shutdown input must
be actively terminated. If the input is driven from open-
collector logic, a pull-up resistor (20 kΩto 100 kΩrecom-
mended) should be connected from the Shutdown input to
the regulator input.
If the Shutdown input is driven from a source that actively
pulls high and low (like an op-amp), the pull-up resistor is not
required, but may be used.
If the shutdown function is not to be used, the cost of the
pull-up resistor can be saved by simply tying the Shutdown
input directly to the regulator input.
IMPORTANT: Since the Absolute Maximum Ratings state
that the Shutdown input can not go more than 0.3V below
ground, the reverse-battery protection feature which protects
the regulator input is sacrificed if the Shutdown input is tied
directly to the regulator input.
If reverse-battery protection is required in an application, the
pull-up resistor between the Shutdown input and the regula-
tor input must be used.
Typical Applications
Basic 5V Regulator
01112715
5V Current Limiter with Load Fault Indicator
01112716
* Output voltage equals +VIN minum dropout voltage, which varies with
output current. Current limits at a maximum of 380 mA (typical).
** Select R1 so that the comparator input voltage is 1.23V at the output
voltage which corresponds to the desired fault current value.
Low T.C. Current Sink
01112717
LP2952/LP2952A/LP2953/LP2953A
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