LP2953AI - National Semiconductor

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 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

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

DS011127-1

LP2953

DS011127-2

May 1999

LP2952/LP2952A/LP2953/LP2953A Adjustable Micropower Low-Dropout Voltage Regulators

Pinout Drawings

Ordering Information

LP2952

Order

Number

Temp.

Range

)˚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

)˚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

14-Pin DIP

DS011127-11

LP2953

16-Pin DIP

DS011127-13

LP2952

16-Pin SO

DS011127-12

LP2953

16-Pin SO

DS011127-14

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.

Storage Temperature Range −65˚C ≤T

≤+150˚C

Operating Temperature Range

LP2952I, LP2953I, LP2952AI,

LP2953AI, LP2952I-3.3,

LP2953I-3.3, LP2952AI-3.3,

LP2953AI-3.3 −40˚C ≤T

≤+125˚C

LP2953AM −55˚C ≤T

≤+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

=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

(NOM) + 1V, I

=1 mA, C

=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

Output Voltage 3.3 3.284 3.317 3.267 3.333 V

3.260 3.340 3.234 3.366

1mA≤I

≤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

Output Voltage 5.0 4.975 5.025 4.950 5.050 V

4.940 5.060 4.900 5.100

1mA≤I

≤250 mA 5.0 4.930 5.070 4.880 5.120

All Voltage Options

Electrical Characteristics

Limits in standard typeface are for T

=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

(NOM) + 1V, I

=1 mA, C

=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

(NOM) + 1V to 30V 0.03 0.1 0.2 %

0.2 0.4

Output Voltage Load

Regulation (Note 6) I

=1 mA to 250 mA 0.04 0.16 0.20 %

=0.1 mA to 1 mA 0.20 0.30

www.national.com3

Electrical Characteristics (Continued)

Limits in standard typeface are for T

=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

(NOM) + 1V, I

=1 mA, C

=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

–V

Dropout Voltage

(Note 7) I

=1 mA 60 100 100 mV

150 150

=50 mA 240 300 300

420 420

=100 mA 310 400 400

520 520

=250 mA 470 600 600

800 800

GND

Ground Pin Current

(Note 8) I

=1 mA 130 170 170 µA

200 200

=50 mA 1.1 2 2 mA

2.5 2.5

=100 mA 4.5 6 6

250 mA 21 28 28

33 33

GND

Ground Pin Current at

Dropout V

(NOM) −0.5V 165 210 210 µA

=100 µA 240 240

GND

Ground Pin Current at

Shutdown (Note 8) V

SHUTDOWN

≤1.1V 105 140 140 µA

LIMIT

Current Limit V

OUT

=0 380 500 500 mA

530 530

Thermal Regulation (Note 10) 0.05 0.2 0.2 %/W

Output Noise Voltage

(10 Hz to 100 kHz)

=100 mA

=4.7 µF 400 µV

RMS

=33 µF 260

=33 µF (Note 11) 80

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

=2.5V to V

(NOM) + 1V 0.03 0.1 0.2 %

(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

(FB) Feedback Pin Bias

Current 20 40 40 nA

60 60

(SINK) Output “OFF” Pulldown

Current (Note 9) 30 30 mA

20 20

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Electrical Characteristics (Continued)

Limits in standard typeface are for T

=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

(NOM) + 1V, I

=1 mA, C

=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

DROPOUT DETECTION COMPARATOR

Output “HIGH”

Leakage V

=30V 0.01 1 1 µA

Output “LOW” Voltage V

(NOM) − 0.5V

(COMP) =400 µA 150 250 250 mV

400 400

THR

(MAX) Upper Threshold

Voltage (Note 14) −60 −80 −35 −80 −35 mV

−95 −25 −95 −25

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)

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

Input Bias V

(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)

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

Input Bias Current V

(COMP) =0V to 5V 10 −30 30 −30

−50 30

50 nA

−50 50

LP2953AM 10 −30 30

−75 75

Output “HIGH”

Leakage V

=30V 0.01 1 1

2µA

(COMP) =1.3V 2

LP2953AM 0.01 1

2.2

Output “LOW” Voltage V

(COMP) =1.1V 150 250 250

400 mV

(COMP) =400 µA 400

LP2953AM 150 250

420

Note 1: Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the de-

vice 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),

www.national.com5

Electrical Characteristics (Continued)

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 =VO(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 =VO(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 at

VIN =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.

Typical Performance Characteristics Unless otherwise specified: V

=6V, I

=1 mA, C

=2.2 µF,

=3V, T

=25˚C, V

OUT

=5V.

Quiescent Current

DS011127-27

Quiescent Current

DS011127-28

Ground Pin Current vs Load

DS011127-29

Ground Pin Current

DS011127-30

Ground Pin Current

DS011127-31

Output Noise Voltage

DS011127-32

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Typical Performance Characteristics Unless otherwise specified: V

=6V, I

=1 mA, C

=2.2 µF,

VSD =3V, T

=25˚C, V

OUT

=5V. (Continued)

Ripple Rejection

DS011127-33

Ripple Rejection

DS011127-34

Ripple Rejection

DS011127-35

Line Transient Response

DS011127-36

Line Transient Response

DS011127-37

Output Impedance

DS011127-38

Load Transient Response

DS011127-39

Load Transient Response

DS011127-40

Dropout Characteristics

DS011127-41

Enable Transient

DS011127-42

Enable Transient

DS011127-43

Short-Circuit Output Current

and Maximum Output Current

DS011127-44

www.national.com7

Typical Performance Characteristics Unless otherwise specified: V

=6V, I

=1 mA, C

=2.2 µF,

VSD =3V, T

=25˚C, V

OUT

=5V. (Continued)

Feedback Bias Current

DS011127-45

Feedback Pin Current

DS011127-46

Error Output

DS011127-47

Comparator Sink Current

DS011127-48

Divider Resistance

DS011127-49

Dropout Detection

Comparator Threshold

Voltages

DS011127-50

Thermal Regulation

DS011127-51

Minimum Operating Voltage

DS011127-52

Dropout Voltage

DS011127-53

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Schematic Diagram

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

≤+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).

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

DS011127-6

www.national.com9

Application Hints (Continued)

The next parameter which must be calculated is the maxi-

mum allowable temperature rise, T

(max). This is calculated

by using the formula:

(max) =T

(max) − T

(max)θ

(J–A)

(max)/P(max)

where: T

(max) is the maximum allowable junction tem-

perature

(max) is the maximum ambient temperature

Using the calculated values for T

(max) and P(max), the re-

quired value for junction-to-ambient thermal resistance,

(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 dissi-

pate 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

The military temperature range (−55˚C ≤T

≤+150˚C) parts

are manufactured in ceramic DIP packages which contain a

DS011127-7

FIGURE 1. P

TOTAL

=(V

−V

OUT

+(V

Current/Voltage Diagram

DS011127-8

* For best results, use L =2H

** 14-Pin DIP is similar, refer to

Table 1

for pins designated for heatsinking.

FIGURE 2. Copper Heatsink Patterns

www.national.com 10

Application Hints (Continued)

KOVAR lead frame (unlike the industrial parts, which have a

copper lead frame). The KOVAR material is necessary to at-

tain 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 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:

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 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 aluminum

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 be-

low 1 mA.

Programming the output for voltages below 5V runs the error

amplifier at lower gains requiring

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 in-

put 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 to-

gether.

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

is the Feedback

pin bias current (−20 nA typical). The minimum recom-

mended load current of 1 µAsets 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

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.

DS011127-26

FIGURE 3. Power Derating Curve for LP2953AMJ

www.national.com11

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 mea-

sured with a 1V differential. The dropout voltage is

independent 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 pro-

grammed output voltage. An out-of-regulation condition can

result from low input voltage, current limiting, or thermal lim-

iting.

Figure 5

gives a timing diagram showing the relationship be-

tween the output voltage, the ERROR output, and input volt-

age as the input voltage is ramped up and down to a regula-

tor 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

≤1.3V, the error flag pin becomes a high imped-

ance, allowing the error flag voltage to rise to its pull-up volt-

age. Using V

OUT

as the pull-up voltage (rather than an exter-

nal 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 kΩsug-

gested) 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 volt-

age 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

theAC 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 sta-

bility. 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.

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 kΩrec-

ommended) should be connected from the Shutdown input

to the regulator input.

DS011127-9

*See Application Hints

** Drive with TTL-low to shut down

FIGURE 4. Adjustable Regulator

DS011127-10

* 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

www.national.com 12

Application Hints (Continued)

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

DS011127-15

5V Current Limiter with Load Fault Indicator

DS011127-16

* 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

DS011127-17

5V Regulator with Error Flags for

LOW BATTERY and OUT OF REGULATION

DS011127-18

* Connect to Logic or µP 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.

www.national.com13

Typical Applications (Continued)

5V Battery Powered Supply with Backup and Low Battery Flag

DS011127-19

The circuit switches to the NI-CAD backup battery when the main battery voltage drops below about 5.6V, and returns to the main battery when its voltage is

recharged to about 6V.

The 5V MAIN output powers circuitry which requires no backup, and the 5V MEMORY output powers critical circuitry which can not be allowed to lose power.

* The BATTERY LOW flag goes low whenever the circuit switches to the NI-CAD backup battery.

5V Regulator with Timed Power-On Reset

DS011127-20

Timing Diagram for Timed Power-On Reset

DS011127-21

T=1 MEG, CT=0.1 µF

www.national.com 14

Typical Applications (Continued)

5V Regulator with Snap-On/Snap-Off

Feature and Hysteresis

DS011127-22

* Turns ON at VIN =5.87V

Turns OFF at VIN =5.64V

(for component values shown)

5V Regulator with Error Flags for

LOW BATTERY and OUT OF REGULATION

with SNAP-ON/SNAP-OFF Output

DS011127-23

* Connect to Logic or µP 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

hardware 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

DS011127-24

Timing Diagram

DS011127-25

Td =(0.28) RC =28 ms for components shown.

www.national.com15

Physical Dimensions inches (millimeters) unless otherwise noted

16-Pin Ceramic DIP

Order Number LP2953AMJ/883, 5962-9233601MEA, LP2953AMJ-QMLV, 5962-9233601VEA

NS Package Number J16A

16-Pin Surface Mount

Order Number LP2952IM, LP2952AIM, LP2952IM-3.3, LP2952AIM-3.3,

LP2953IM, LP2953AIM, LP2953IM-3.3 or LP2953AIM-3.3

NS Package Number M16A

www.national.com 16

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

14-Pin Molded DIP

Order Number LP2952IN, LP2952AIN, LP2952IN-3.3 or LP2952AIN-3.3

NS Package Number N14A

16-Pin Molded DIP

Order Number LP2953IN, LP2953AIN, LP2953IN-3.3 or LP2953AIN-3.3

NS Package Number N16A

www.national.com17

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

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: support@nsc.com

National Semiconductor

Europe Fax: +49 (0) 1 80-530 85 86

Email: europe.support@nsc.com

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

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National Semiconductor

Asia Pacific Customer

Response Group

Tel: 65-2544466

Fax: 65-2504466

Email: sea.support@nsc.com

National Semiconductor

Japan Ltd.

Tel: 81-3-5639-7560

Fax: 81-3-5639-7507

www.national.com

16-Pin Ceramic Surface-Mount

Order Number LP2953AMWG/883, 5962-9233601QXA, LP2953AMWG-QMLV, 5962-9233601VXA

NS Package Number WG16A

LP2952/LP2952A/LP2953/LP2953A Adjustable Micropower Low-Dropout Voltage Regulators

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.