TL/H/11127
LP2952/LP2952A/LP2953/LP2953A
Adjustable Micropower Low-Dropout Voltage Regulators
March 1994
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 mA 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
current increases only slightly at dropout, which prolongs
battery life.
The LP2952 and LP2953 retain all the desirable characteris-
tics of the LP2951, but offer increased output current, addi-
tional 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
YOutput voltage adjusts from 1.23V to 29V
YGuaranteed 250 mA output current
YExtremely low quiescent current
YLow dropout voltage
YExtremely tight line and load regulation
YVery low temperature coefficient
YCurrent and thermal limiting
YReverse battery protection
Y50 mA (typical) output pulldown crowbar
Y5V and 3.3V versions available
LP2953 Versions Only
YAuxiliary comparator included with CMOS/TTL compati-
ble output levels. Can be used for fault detection, low
input line detection, etc.
Applications
YHigh-efficiency linear regulator
YRegulator with under-voltage shutdown
YLow dropout battery-powered regulator
YSnap-ON/Snap-OFF regulator
Block Diagrams
LP2952
TL/H/11127–1
LP2953
TL/H/11127–2
C1995 National Semiconductor Corporation RRD-B30M75/Printed in U. S. A.
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 b65§CsTAsa150§C
Operating Temperature Range
LP2952I, LP2953I, LP2952AI,
LP2953AI, LP2952I-3.3, LP2953I-3.3,
LP2952AI-3.3, LP2953AI-3.3 b40§CsTJsa125§C
LP2953AM b55§CsTAsa125§C
Maximum Junction Temperature
LP2952I, LP2953I, LP2952AI,
LP2953AI, LP2952I-3.3, LP2953I-3.3,
LP2952AI-3.3, LP2953AI-3.3 a125§C
LP2953AM a150§C
Lead Temp. (Soldering, 5 seconds) 260§C
Power Dissipation (Note 2) Internally Limited
Input Supply Voltage b20V to a30V
Feedback Input Voltage (Note 3) b0.3V to a5V
Comparator Input Voltage (Note 4) b0.3V to a30V
Shutdown Input Voltage (Note 4) b0.3V to a30V
Comparator Output Voltage (Note 4) b0.3V to a30V
ESD Rating (Note 15) 2 kV
Electrical Characteristics Limits in standard typeface are for TJe25§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: VIN eVO(NOM) a1V, ILe1 mA, CLe2.2 mF for 5V parts and
4.7mF 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
VOOutput Voltage 3.3 3.284 3.317 3.267 3.333
V
3.260 3.340 3.234 3.366
1mAsI
Ls250 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
VOOutput Voltage 5.0 4.975 5.025 4.950 5.050
V
4.940 5.060 4.900 5.100
1mAsI
Ls250 mA 5.0 4.930 5.070 4.880 5.120
All Voltage Options
Symbol Parameter Conditions Typical
LP2952AI, LP2953AI, LP2952I, LP2953I,
Units
LP2952AI-3.3, LP2953AI-3.3, LP2952I-3.3, LP2953I-3.3
LP2953AM (Note 17)
Min Max Min Max
DVO
DT
Output Voltage (Note 5) 20 100 150 ppm/§C
Temp. Coefficient
DVO
VO
Output Voltage VIN eVO(NOM) a1V 0.03 0.1 0.2 %
Line Regulation to 30V 0.2 0.4
DVO
VO
Output Voltage ILe1mAto250mA 0.04 0.16 0.20 %
Load Regulation ILe0.1 mA to 1 mA 0.20 0.30
(Note 6)
VIN–VODropout Voltage ILe1mA 60 100 100
mV
(Note 7) 150 150
ILe50 mA 240 300 300
420 420
ILe100 mA 310 400 400
520 520
ILe250 mA 470 600 600
800 800
2
Electrical Characteristics Limits in standard typeface are for TJe25§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: VIN eVO(NOM) a1V, ILe1 mA, CLe2.2 mF for 5V parts and
4.7mF for 3.3V parts. Feedback pin is tied to V Tap pin, Output pin is tied to Output Sense pin. (Continued)
All Voltage Options (Continued)
Symbol Parameter Conditions Typical
LP2952AI, LP2953AI, LP2952I, LP2953I,
Units
LP2952AI-3.3, LP2953AI-3.3, LP2952I-3.3, LP2953I-3.3
LP2953AM (Note 17)
Min Max Min Max
IGND Ground Pin Current ILe1mA 130 170 170 mA
(Note 8) 200 200
ILe50 mA 1.1 22
mA
2.5 2.5
ILe100 mA 4.5 66
88
I
L
e
250 mA 21 28 28
33 33
IGND Ground Pin Current VIN eVO(NOM) b0.5V 165 210 210 mA
at Dropout (Note 8) ILe100 mA240 240
IGND Ground Pin Current (Note 9) 105 140 140 mA
at Shutdown (Note 8)
ILIMIT Current Limit VOUT e0380 500 500 mA
530 530
DVO
DPd
Thermal Regulation (Note 10) 0.05 0.2 0.2 %/W
enOutput Noise Voltage CLe4.7 mF 400
mV RMS
(10 Hz to 100 kHz) CLe33 mF 260
ILe100 mA
CLe33 mF (Note 11) 80
VREF Reference Voltage (Note 12) 1.230 1.215 1.245 1.205 1.255 V
1.205 1.255 1.190 1.270
DVREF
VREF
Reference Voltage VIN e2.5V to VO(NOM)a1V 0.03 0.1 0.2 %
Line Regulation VIN eVO(NOM)a1V to 30V 0.2 0.4
(Note 13)
DVREF
VREF
Reference Voltage IREF e0to200mA0.25 0.4 0.8 %
Load Regulation 0.6 1.0
DVREF
DT
Reference Voltage (Note 5) 20 ppm/§C
Temp. Coefficient
IB(FB) Feedback Pin 20 40 40 nA
Bias Current 60 60
IOOutput ‘‘OFF’’ (Note 9) 50 30 30 mA
(SINK) Pulldown Current 20 20
3
Electrical Characteristics Limits in standard typeface are for TJe25§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: VIN eVO(NOM) a1V, ILe1 mA, CLe2.2 mF for 5V parts and
4.7mF for 3.3V parts. Feedback pin is tied to V Tap pin, Output pin is tied to Output Sense pin. (Continued)
Symbol Parameter Conditions Typical
LP2952AI, LP2953AI, LP2952I, LP2953I,
Units
LP2952AI-3.3, LP2953AI-3.3, LP2952I-3.3, LP2953I-3.3
LP2953AM (Note 17)
Min Max Min Max
DROPOUT DETECTION COMPARATOR
IOH Output ‘‘HIGH’’ VOH e30V 0.01 11
mA
Leakage 22
V
OL Output ‘‘LOW’’ VIN eVO(NOM) b0.5V 150 250 250 mV
Voltage IO(COMP) e400 mA400 400
VTHR Upper Threshold (Note 14) b60 b80 b35 b80 b35 mV
(MAX) Voltage b95 b25 b95 b25
VTHR Lower Threshold (Note 14) b85 b110 b55 b110 b55 mV
(MIN) Voltage b160 b40 b160 b40
HYST Hysteresis (Note 14) 15 mV
SHUTDOWN INPUT (Note 16)
VOS Input Offset Voltage (Referred to VREF)g3b7.5 7.5 b7.5 7.5 mV
b10 10 b10 10
HYST Hysteresis 6 mV
IBInput Bias Current VIN(S/D) e0V to 5V 10 b30 30
b50
b30 b30
50 nA
b50 50
LP2953AM 10 b30 30
b75 75
AUXILIARY COMPARATOR (LP2953 Only)
VOS Input Offset Voltage (Referred to VREF)g3b7.5 7.5
b10
b7.5
10
7.5 mV
b10 10
LP2953AM g3b7.5 7.5
b12 12
HYST Hysteresis 6 mV
IBInput Bias Current VIN(COMP) e0V to 5V 10 b30 30
b50
b30
50
30 nA
b50 50
LP2953AM 10 b30 30
b75 75
IOH Output ‘‘HIGH’’ VOH e30V 0.01 1
2
1mA
Leakage VIN(COMP) e1.3V 2
LP2953AM 0.01 1
2.2
VOL Output ‘‘LOW’’ VIN(COMP) e1.1V 150 250
400
250 mV
Voltage IO(COMP) e400 mA400
LP2953AM 150 250
420
4
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, iJ–A,
and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated using: P (MAX) eTJ(MAX) bTA
iJ–A
.
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 mA 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 s1.1V, VOUT eVO(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 eVO(NOM)a15V (3W pulse) for T e10 ms.
Note 11: Connect a 0.1 mF capacitor from the output to the feedback pin.
Note 12: VREF sVOUT s(VIN b1V), 2.3V sVIN s30V, 100 mAsILs250 mA.
Note 13: Two separate tests are performed, one covering 2.5V sVIN sVO(NOM)a1V and the other test for VO(NOM)a1V sVIN s30V.
Note 14: Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage measured at
VIN eVO(NOM) a1V. To express these thresholds in terms of output voltage change, multiply by the Error amplifier gain, which is VOUT/VREF e(R1 aR2)/R2
(refer to Figure 4).
Note 15: Human body model, 200 pF discharged through 1.5 kX.
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. At the time of printing, the LP2953AMJ/883C RETS specification complied with the boldface
limits in this column.
5
Typical Performance Characteristics Unless otherwise specified: VIN e6V, ILe1 mA, CLe2.2 mF,
VSD e3V, TAe25§C, VOUT e5V.
Quiescent Current Quiescent Current Ground Pin Current vs Load
Ground Pin Current Ground Pin Current Output Noise Voltage
Ripple Rejection Ripple Rejection Ripple Rejection
Line Transient Response Line Transient Response Output Impedance
TL/H/11127–3
6
Typical Performance Characteristics Unless otherwise specified: VIN e6V, ILe1 mA, CLe2.2 mF,
VSD e3V, TAe25§C, VOUT e5V. (Continued)
Load Transient Response Load Transient Response Dropout Characteristics
Enable Transient Enable Transient and Maximum Output Current
Short-Circuit Output Current
Feedback Bias Current Feedback Pin Current Error Output
Comparator Sink Current Divider Resistance Voltages
Comparator Threshold
Dropout Detection
TL/H/11127–4
7
Typical Performance Characteristics Unless otherwise specified: VIN e6V, ILe1 mA, CLe2.2 mF,
VSD e3V, TAe25§C, VOUT e5V. (Continued)
Thermal Regulation Minimum Operating Voltage Dropout Voltage
TL/H/11127–5
Schematic Diagram
TL/H/11127–6
8
Application Hints
HEATSINK REQUIREMENTS (Industrial Temperature
Range Devices)
The maximum allowable power dissipation for the
LP2952/LP2953 is limited by the maximum junction temper-
ature (a125§C) and the external factors that determine how
quickly heat flows away from the part: the
ambient tempera-
ture
and the
junction-to-ambient thermal resistance
for the
specific application.
The industrial temperature range (b40§CsTJsa125§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).
Fig-
ure 1
shows the voltages and currents which are present in
the circuit. The formula for calculating the power dissipated
in the regulator is also shown in
Figure 1
:
TL/H/11127–7
PTOTAL e(VIN bVOUT)I
La(VIN)I
G
FIGURE 1. Current/Voltage Diagram
The next parameter which must be calculated is the maxi-
mum allowable temperature rise, TR(max). This is calculat-
ed by using the formula:
TR(max) eTJ(max) bTA(max)
where: TJ(max) is the maximum allowable junction tempera-
ture
TA(max) is the maximum ambient temperature
Using the calculated values for TR(max) and P(max), the
required value for junction-to-ambient thermal resistance,
i(J–A), can now be found:
i(J–A) eTR(max)/P(max)
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:
TABLE I
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 dissi-
pate heat from the LP2952 and LP2953:
TL/H/11127–8
*For best results, use L e2H
**14-Pin DIP is similar, refer to Table I for pins designated for heatsinking.
FIGURE 2. Copper Heatsink Patterns
Table II shows some values of junction-to-ambient thermal
resistance (iJ–A) for values of L and W for 1 oz. copper:
TABLE II
Package L (in.) H (in.) iJ–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
9
Application Hints (Continued)
HEATSINK REQUIREMENTS (Military Temperature
Range Devices)
The maximum allowable power dissipation for the
LP2953AMJ is limited by the maximum junction temperature
(a150§C) and the two parameters that determine how
quickly heat flows away from the die:
the ambient tempera-
ture and the junction-to-ambient thermal resistance of the
part
.
The military temperature range (b55§CsTJsa150§C)
parts are manufactured in ceramic DIP packages which con-
tain a KOVAR lead frame (unlike the industrial parts, which
have a copper lead frame). The KOVAR material is neces-
sary to attain the hermetic seal required in military applica-
tions.
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 i(J–A),
the junction-to-ambient thermal resistance, is fixed at
95§C/W and can not be changed by adding copper foil pat-
terns to the PC board. This leads to an important fact: The
maximum allowable power dissipation in any application us-
ing the LP2953AMJ is dependent only on the ambient tem-
perature:
P(max) eTR(max) /i(J–A)
P(max) eTJ(max) bTA(max)
i(J–A)
P(max) e150 bTA(max)
95
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 i(J–A) and assuming a maxi-
mum junction temperature of 150§C (caution: the
maximum
ambient temperature which will be reached in a given appli-
cation must always be used to calculate maximum allowable
power dissipation).
EXTERNAL CAPACITORS
A 2.2 mF (or greater) capacitor is required between the out-
put 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
b30§C, which requires the use of solid tantalums below
b25§C. The important parameters of the capacitor are an
ESR of about 5Xor 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§Ctob
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 mF for currents below 10 mA or 0.22 mF for currents
below 1 mA.
Programming the output for voltages below 5V runs the er-
ror amplifier at lower gains requiring
more
output capaci-
tance for stability. At 3.3V output, a minimum of 4.7 mFis
required. For the worst-case condition of 1.23V output and
250 mA of load current, a 6.8 mF (or larger) capacitor should
be used.
A1mF 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 in-
stability. This problem is most likely to appear when using
high value external resistors to set the output voltage. Add-
ing a 100 pF capacitor between the Output and Feedback
pins and increasing the output capacitance to 6.8 mF (or
greater) will cure the problem.
MINIMUM LOAD
When setting the output voltage using an external resistive
divider, a minimum current of 1 mA 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 test-
ed limits.
TL/H/11127–26
FIGURE 3. Power Derating Curve for LP2953AMJ
10
Application Hints (Continued)
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 to-
gether.
Alternatively, it may be programmed for any voltage be-
tween the 1.23V reference and the 30V maximum rating
using an external pair of resistors (see
Figure 4
). The com-
plete equation for the output voltage is:
VOUT eVREF c#1aR1
R2 Ja(IFB cR1)
where VREF is the 1.23V reference and IFB is the Feedback
pin bias current (b20 nA typical). The minimum recom-
mended load current of 1 mA sets an upper limit of 1.2 MX
on the value of R2 in cases where the regulator must work
with no load (see MINIMUM LOAD). IFB will produce a typi-
cal 2% error in VOUT which can be eliminated at room tem-
perature by trimming R1. For better accuracy, choosing
R2 e100 kXwill reduce this error to 0.17% while increas-
ing the resistor program current to 12 mA. Since the typical
quiescent current is 120 mA, this added current is negligible.
TL/H/11127–9
FIGURE 4. Adjustable Regulator
*See Application Hints
**Drive with TTL-low to shut down
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 mea-
sured with a 1V differential. The dropout voltage is indepen-
dent 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 fig-
ure 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 con-
dition 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 be-
comes 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 re-
quires an external pull-up resistor. This resistor may be con-
nected to the regulator output or some other supply voltage.
Using the regulator output prevents an invalid ‘‘HIGH’’ on
the comparator 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 mA, this current adds to
battery drain. Suggested values range from 100 kXto
1MX. This resistor is not required if the output is unused.
When VIN s1.3V, the error flag pin becomes a high imped-
ance, allowing the error flag voltage to rise to its pull-up
voltage. Using VOUT 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 kXsuggested) to ensure a low-level logic signal during
any fault condition, while still allowing a valid high logic level
during normal operation.
TL/H/11127–10
FIGURE 5. ERROR Output Timing
*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)
OUTPUT ISOLATION
The regulator output can be left connected to an active volt-
age source (such as a battery) with the regulator input pow-
er shut off, as long as the regulator ground pin is con-
nected 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.
11
Application Hints (Continued)
REDUCING OUTPUT NOISE
In reference applications it may be advantageous to reduce
the AC noise present on the output. One method is to re-
duce regulator bandwidth by increasing output capacitance.
This is relatively inefficient, since large increases in capaci-
tance are required to get significant improvement.
Noise can be reduced more effectively by a bypass capaci-
tor placed across R1 (refer to
Figure 4
). The formula for
selecting the capacitor to be used is:
CBe1
2qR1 c20 Hz
This gives a value of about 0.1 mF. When this is used, the
output capacitor must be 6.8 mF (or greater) to maintain
stability. The 0.1 mF capacitor reduces the high frequency
gain of the circuit to unity, lowering the output noise from
260 mVto80mV using a 10 Hz to 100 kHz bandwidth. Also,
noise is no longer proportional to the output voltage, so im-
provements 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 compar-
ator. The non-inverting input and output are brought out for
external connections.
SHUTDOWN INPUT
A logic-level signal will shut off the regulator output when a
‘‘LOW’’ (k1.2V) 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-col-
lector logic, a pull-up resistor (20 kXto 100 kXrecommend-
ed) 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 pro-
tects 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.
Pinout Drawings
LP2952 LP2952
14-Pin DIP 16-Pin SO
TL/H/11127–11
TL/H/11127–12
LP2953 LP2953
16-Pin DIP 16-Pin SO
TL/H/11127–13 TL/H/11127–14
Ordering Information
LP2952
Order Temp. NSC
Number Range Package Drawing
(TJ)§C Number
LP2952IN, LP2952AIN, b40 to
a125 Molded DIP
14-Pin N14A
LP2952IN-3.3,
LP2952AIN-3.3
LP2952IM, LP2952AIM, b40 to
a125 Surface
16-Pin
Mount
M16A
LP2952IM-3.3,
LP2952AIM-3.3
LP2953
Order Temp. NSC
Number Range Package Drawing
(TJ)§C Number
LP2953IN, LP2953AIN, b40 to
a125 Molded DIP
16-Pin N16A
LP2953IN-3.3,
LP2953AIN-3.3
LP2953IM, LP2953AIM, b40 to
a125 Surface Mount
16-Pin M16A
LP2953IM-3.3,
LP2953AIM-3.3
LP2953AMJ/883
b55 to
a150
16-Pin J16A
Ceramic DIP
12
Typical Applications
Basic 5V Regulator
TL/H/11127–15
5V Current Limiter with Load Fault Indicator
TL/H/11127–16
*Output voltage equals aVIN minum dropout voltage, which varies with out-
put 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
TL/H/11127–17
5V Regulator with Error Flags for
LOW BATTERY and OUT OF REGULATION
TL/H/11127–18
*Connect to Logic or mP control inputs.
LOW BATT flag warns the user that the battery has discharged down to
about 5.8V, giving the user time to recharge the battery or power down some
hardware with high power requirements. The output is still in regulation at
this time.
OUT OF REGULATION flag indicates when the battery is almost completely
discharged, and can be used to initiate a power-down sequence.
13
Typical Applications (Continued)
5V Battery Powered Supply with Backup and Low Battery Flag
The circuit switches to the
NI-CAD backup battery
when the main battery volt-
age drops below about
5.6V, and returns to the
main battery when its volt-
age is recharged to about
6V.
The 5V MAIN output pow-
ers circuitry which requires
no backup, and the 5V
MEMORY output powers
critical circuitry which can
not be allowed to lose pow-
er.
*The BATTERY LOW flag
goes low whenever the cir-
cuit switches to the NI-CAD
backup battery. TL/H/11127–19
5V Regulator with Timed Power-On Reset
TL/H/11127–20
Timing Diagram for Timed Power-On Reset
TL/H/11127–21
*RTe1 MEG, CTe0.1 mF
14
Typical Applications (Continued)
5V Regulator with Snap-On/Snap-Off
Feature and Hysteresis
TL/H/11127–22
*Turns ON at VIN e5.87V
Turns OFF at VIN e5.64V
(for component values shown)
5V Regulator with Error Flags for
LOW BATTERY and OUT OF REGULATION
with SNAP-ON/SNAP-OFF Output
TL/H/11127–23
*Connect to Logic or mP control inputs.
OUTPUT has SNAP-ON/SNAP-OFF feature.
LOW BATT flag warns the user that the battery has discharged down to
about 5.8V, giving the user time to recharge the battery or shut down hard-
ware with high power requirements. The output is still in regulation at this
time.
OUT OF REGULATION flag goes low if the output goes below about 4.7V,
which could occur from a load fault.
OUTPUT has SNAP-ON/SNAP-OFF feature. Regulator snaps ON at about
5.7V input, and OFF at about 5.6V.
5V Regulator with Timed Power-On Reset, Snap-On/Snap-Off Feature and Hysteresis
TL/H/11127–24
Timing Diagram
TL/H/11127–25
Td e(0.28) RC e28 ms for components shown.
15
Physical Dimensions inches (millimeters) (Continued)
14-Pin Molded DIP
Order Number LP2952IN, LP2952AIN, LP2952IN-3.3 or LP2952AIN-3.3
NS Package Number N14A
17
LP2952/LP2952A/LP2953/LP2953A
Adjustable Micropower Low-Dropout Voltage Regulators
Physical Dimensions inches (millimeters) (Continued) Lit. Ý108569-002
16-Pin Molded DIP
Order Number LP2953IN, LP2953AIN, LP2953IN-3.3 or LP2953AIN-3.3
NS Package Number N16A
LIFE SUPPORT POLICY
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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL
SEMICONDUCTOR CORPORATION. As used herein:
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systems which, (a) are intended for surgical implant support device or system whose failure to perform can
into the body, or (b) support or sustain life, and whose be reasonably expected to cause the failure of the life
failure to perform, when properly used in accordance support device or system, or to affect its safety or
with instructions for use provided in the labeling, can effectiveness.
be reasonably expected to result in a significant injury
to the user.
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