LP2953 MDS_技术文档

March 2005

LP2952/LP2952A/LP2953/LP2953A

Adjustable Micropower Low-Dropout Voltage Regulators

General Description

Features

n Output voltage adjusts from 1.23V to 29V

n Guaranteed 250 mA output current

n Extremely low quiescent current

n Low dropout voltage

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.

n Extremely tight line and load regulation

n Very low temperature coefficient

n Current and thermal limiting

n Reverse battery protection

n 50 mA (typical) output pulldown crowbar

n 5V and 3.3V versions available

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.

LP2953 Versions Only

The error flag goes low if the output voltage drops out of

regulation.

n Auxiliary comparator included with CMOS/TTL

compatible output levels. Can be used for fault

detection, low input line detection, etc.

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.

Applications

n High-efficiency linear regulator

n Regulator with under-voltage shutdown

n Low dropout battery-powered regulator

n Snap-ON/Snap-OFF regulator

The parts are available in DIP and surface mount packages.

Block Diagrams

LP2953

LP2952

01112702

01112701

DS011127

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Pinout Drawings

Ordering Information

LP2952

14-Pin DIP

LP2952

Temp.

Package

NSC

Drawing

Number

N14A

Order

Range

Number

(T_J) ˚C

LP2952IN,

−40 to

+125

14-Pin

Molded

DIP

LP2952AIN,

LP2952IN-3.3,

LP2952AIN-3.3

LP2952IM,

−40 to

+125

16-Pin

Surface

Mount

M16A

01112711

01112713

01112712

01112714

LP2952AIM,

LP2952IM-3.3,

LP2952AIM-3.3

LP2953

16-Pin DIP

LP2953

Temp.

Range

(T_J) ˚C

−40 to

+125

Package

NSC

Drawing

Number

N16A

Order

Number

LP2953IN,

16-Pin

LP2953AIN,

Molded DIP

LP2953IN-3.3,

LP2953AIN-3.3

LP2953IM,

−40 to

+125

16-Pin

Surface

Mount

M16A

LP2953AIM,

LP2953IM-3.3,

LP2952

16-Pin SO

LP2953AIM-3.3

LP2953AMJ/883

5962-9233601MEA

LP2953AMJ-QMLV

5962-9233601VEA

LP2953AMWG/883

5962-9233601QXA

LP2953AMWG-QMLV

5962-9233601VXA

−55 to

+150

16-Pin

Ceramic DIP

J16A

−55 to

+150

16-Pin

Ceramic

Surface

Mount

WG16A

LP2953

16-Pin SO

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2

Absolute Maximum Ratings (Note 1)

Maximum Junction Temperature

LP2952I, LP2953I, LP2952AI,

LP2953AI, LP2952I-3.3,

LP2953I-3.3, LP2952AI-3.3,

LP2953AI-3.3

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

+125˚C

+150˚C

Storage Temperature Range

−65˚C ≤ T_A≤

LP2953AM

+150˚C

Input Supply Voltage

−20V to +30V

−0.3V to +5V

−0.3V to +30V

Operating Temperature Range

LP2952I, LP2953I, LP2952AI,

LP2953AI, LP2952I-3.3,

LP2953I-3.3, LP2952AI-3.3,

LP2953AI-3.3

Feedback Input Voltage (Note 3)

Comparator Input Voltage (Note 4)

Shutdown Input Voltage (Note 4)

Comparator Output Voltage (Note

4)

−40˚C ≤ T_J≤ +125˚C

LP2953AM

−55˚C ≤ T_A≤

−0.3V to +30V

2 kV

+125˚C

ESD Rating (Note 15)

Lead Temp. (Soldering, 5 seconds)

Power Dissipation (Note 2)

260˚C

Internally Limited

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

3.317

3.340

3.346

Min

Max

3.333

3.366

3.379

V_O

Output Voltage

3.3

3.284

3.260

3.254

3.267

3.234

3.221

V

1 mA ≤ I_L≤ 250 mA

5V Versions

Symbol

Parameter

Conditions

Typical

LP2952AI, LP2953AI,

LP2952I, LP2953I

Units

LP2953AM (Note 17)

Min

Max

5.025

5.060

5.070

Min

Max

5.050

5.100

5.120

V_O

Output Voltage

5.0

4.975

4.940

4.930

4.950

4.900

4.880

V

1 mA ≤ I_L≤ 250 mA

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, LP2952I, LP2953I, Units

LP2952AI-3.3,

LP2953AI-3.3,

LP2953AM

LP2952I-3.3,

LP2953I-3.3

(Notes 16, 17)

Min

Max

100

Min

Max

150

REGULATOR

Output Voltage Temp.

Coefficient

(Note 5)

20

ppm/˚C

%

Output Voltage Line

Regulation

V_IN= V_O(NOM) + 1V to 30V

0.03

0.1

0.2

0.4

3

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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, LP2952I, LP2953I, Units

LP2952AI-3.3,

LP2953AI-3.3,

LP2953AM

LP2952I-3.3,

LP2953I-3.3

(Notes 16, 17)

Min

Max

Min

Max

Output Voltage Load

Regulation (Note 6)

I_L= 1 mA to 250 mA

I_L= 0.1 mA to 1 mA

I_L= 1 mA

0.04

0.16

0.20

%

0.20

0.30

V_IN–V_ODropout Voltage

(Note 7)

60

240

310

470

130

1.1

100

150

300

420

400

520

600

800

170

200

2

100

150

300

420

400

520

600

800

170

200

2

mV

I_L= 50 mA

I_L= 100 mA

I_L= 250 mA

I_L= 1 mA

I_GND

Ground Pin Current

(Note 8)

µA

I_L= 50 mA

I_L= 100 mA

I_L= 250 mA

mA

2.5

6

2.5

6

4.5

8

21

28

33

I_GND

I_LIMIT

Ground Pin Current at

Dropout

V_IN= V_O(NOM) −0.5V

I_L= 100 µA

165

105

380

0.05

210

240

140

210

240

140

µA

Ground Pin Current at

Shutdown (Note 8)

Current Limit

V_SHUTDOWN≤ 1.1V

V_OUT= 0

(Note 10)

500

530

0.2

500

530

0.2

mA

Thermal Regulation

%/W

e_n

Output Noise Voltage

(10 Hz to 100 kHz)

I_L= 100 mA

C_L= 4.7 µF

400

260

µV

RMS

C_L= 33 µF

C_L= 33 µF (Note 11)

(Note 12)

80

V_REF

Reference Voltage

1.230

1.215

1.245

1.255

0.1

1.205

1.255

1.270

0.2

V

1.205

1.190

Reference Voltage Line V_IN= 2.5V to V_O(NOM) + 1V

0.03

%

Regulation

V_IN= V_O(NOM) + 1V to 30V

(Note 13)

0.2

0.4

Reference Voltage Load I_REF= 0 to 200 µA

Regulation

0.25

0.4

0.8

%

0.6

1.0

Reference Voltage

Temp. Coefficient

(Note 5)

20

ppm/˚C

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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, LP2952I, LP2953I, Units

LP2952AI-3.3,

LP2953AI-3.3,

LP2953AM

LP2952I-3.3,

LP2953I-3.3

(Notes 16, 17)

Min

Max

40

Min

Max

40

I_B(FB)

Feedback Pin Bias

Current

20

nA

60

I_O(SINK) Output “OFF” Pulldown (Note 9)

Current

30

mA

20

DROPOUT DETECTION COMPARATOR

I_OH

Output “HIGH” Leakage V_OH= 30V

0.01

150

−60

−85

15

1

µA

mV

2

V_OL

Output “LOW” Voltage

V_IN= V_O(NOM) − 0.5V

I_O(COMP) = 400 µA

250

400

−35

−25

−55

−40

250

400

−35

−25

−55

−40

V_THR

Upper Threshold

Voltage

(Note 14)

−80

−95

−80

−95

(MAX)

V_THR

(MIN)

Lower Threshold

Voltage

−110

−160

−110

−160

HYST

Hysteresis

SHUTDOWN INPUT (Note 15)

V_OS

Input Offset

Voltage

(Referred to V_REF

)

3

−7.5

7.5

−7.5

7.5

−10

10

−10

10

HYST

I_B

Hysteresis

Input Bias

Current

6

mV

nA

V_IN(S/D) = 0V to 5V

10

−30

−50

−30

−75

30

50

30

75

−30

−50

50

LP2953AM

10

AUXILIARY COMPARATOR (LP2953 Only)

V_OS

Input Offset Voltage

(Referred to V_REF

)

3

−7.5

−10

−7.5

−12

7.5

10

−7.5

7.5

mV

−10

10

LP2953AM

7.5

12

HYST

I_B

Hysteresis

6

mV

nA

Input Bias Current

V_IN(COMP) = 0V to 5V

10

−30

−50

−30

−75

30

50

30

75

1

−30

30

−50

50

LP2953AM

10

I_OH

Output “HIGH” Leakage V_OH= 30V

0.01

150

1

µA

2

V_IN(COMP) = 1.3V

2

LP2953AM

1

2.2

250

400

250

420

V_OL

Output “LOW” Voltage

V_IN(COMP) = 1.1V

I_O(COMP) = 400 µA

250

mV

400

LP2953AM

5

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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, T (MAX), the junction-to-ambient thermal resistance, θ

,

J–A

J

and the ambient temperature, T . The maximum allowable power dissipation at any ambient temperature is calculated using the equation for P(MAX),

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 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: V

≤ 1.1V, V = V (NOM).

OUT O

SHUTDOWN

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 V = V (NOM)+15V (3W pulse) for T = 10 ms.

IN

O

Note 11: Connect a 0.1 µF capacitor from the output to the feedback pin.

Note 12: V ≤ V ≤ (V − 1V), 2.3V ≤ V ≤ 30V, 100 µA ≤ I ≤ 250 mA.

REF

OUT

IN

L

Note 13: Two separate tests are performed, one covering 2.5V ≤ V ≤ V (NOM)+1V and the other test for V (NOM)+1V ≤ V ≤ 30V.

IN

O

IN

Note 14: Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage measured atV

=

IN

V

(NOM) + 1V. To express these thresholds in terms of output voltage change, multiply by the Error amplifier gain, which is V

/V

= (R1 + R2)/R2(refer to

O

OUT REF

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.

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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

Ground Pin Current

Output Noise Voltage

01112727

01112728

Ground Pin Current vs Load

01112730

01112729

Ground Pin Current

01112731

01112732

7

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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. (Continued)

Ripple Rejection

01112733

01112734

Ripple Rejection

Line Transient Response

01112736

01112735

Line Transient Response

Output Impedance

01112737

01112738

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8

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. (Continued)

Load Transient Response

01112739

01112740

Dropout Characteristics

Enable Transient

01112741

01112742

Short-Circuit Output Current

and Maximum Output Current

Enable Transient

01112743

01112744

9

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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. (Continued)

Feedback Bias Current

Feedback Pin Current

01112745

01112746

Error Output

Comparator Sink Current

01112747

01112748

Dropout Detection

Comparator Threshold

Voltages

Divider Resistance

01112749

01112750

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10

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. (Continued)

Thermal Regulation

Minimum Operating Voltage

01112751

01112752

Dropout Voltage

01112753

11

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Schematic Diagram

01112706

the ground pins of the IC, and into the copper of the PC

board. Details on heatsinking using PC board copper are

covered later.

Application Hints

HEATSINK REQUIREMENTS (Industrial Temperature

Range Devices)

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:

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

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12

Application Hints (Continued)

01112707

FIGURE 1. P_TOTAL= (V_IN− V_OUT) I_L+ (V_IN) I_G

Current/Voltage Diagram

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.

01112708

* 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

TABLE 1. Heat Conducting Pins

Part

Package

Pins

LP2952IN, LP2952AIN,

LP2952IN-3.3,

14-Pin DIP

3, 4, 5,

TABLE 2. Thermal Resistance for Various Copper

Heatsink Patterns

10, 11, 12

LP2952AIN-3.3

Package

L (in.)

H (in.)

0.5

1

θ_J–A(˚C/W)

LP2953IN, LP2953AIN,

LP2953IN-3.3,

16-Pin DIP

4, 5, 12, 13

16-Pin DIP

1

2

3

4

6

1

2

3

1

2

3

6

4

2

70

60

58

66

65

51

49

83

70

67

69

71

73

LP2953AIN-3.3

1.5

0.19

0.5

1

LP2952IM, LP2952AIM,

LP2952IM-3.3,

16-Pin Surface 1, 8, 9, 16

Mount

LP2952AIM-3.3,

LP2953IM, LP2953AIM,

LP2953IM-3.3,

14-Pin DIP

1.5

0.5

1

LP2953AIM-3.3

Surface Mount

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.

1.5

0.19

)

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.

13

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100 pF capacitor between the Output and Feedback pins

and increasing the output capacitance to 6.8 µF (or greater)

will cure the problem.

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.

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.

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.

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.

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:

01112726

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).

FIGURE 3. Power Derating Curve for LP2953AMJ

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.

EXTERNAL CAPACITORS

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:

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

5Ω or 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.

where V_REFis the 1.23V reference and I_FBis the Feedback

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

mended load current of 1 µA sets an upper limit of 1.2 MΩ on

the value of R2 in cases where the regulator must work with

no load (see MINIMUM LOAD ). I_FBwill produce a typical 2%

error in V_OUTwhich 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.

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

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14

down the error flag voltage using equal-value resistors

(10 kΩ suggested) to ensure a low-level logic signal during

any fault condition, while still allowing a valid high logic level

during normal operation.

Application Hints (Continued)

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.

01112709

* See Application Hints

** Drive with TTL-low to shut down

** Exact value depends on dropout voltage. (See Application Hints)

FIGURE 4. Adjustable Regulator

DROPOUT VOLTAGE

FIGURE 5. ERROR Output Timing

OUTPUT ISOLATION

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.

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.

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.

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:

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.

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.

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 kΩ to 1 MΩ. This

resistor is not required if the output is unused.

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.

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_OUTas 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

15

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Application Hints (Continued)

5V Current Limiter with Load Fault Indicator

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 kΩ to 100 kΩ recom-

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.

01112716

* Output voltage equals +V minum dropout voltage, which varies with

IN

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.

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.

Low T.C. Current Sink

Typical Applications

Basic 5V Regulator

01112715

01112717

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16

Typical Applications (Continued)

5V Regulator with Error Flags for

LOW BATTERY and OUT OF REGULATION

01112718

* 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.

5V Battery Powered Supply with Backup and Low Battery Flag

01112719

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.

17

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Typical Applications (Continued)

5V Regulator with Error Flags for

LOW BATTERY and OUT OF REGULATION

with SNAP-ON/SNAP-OFF Output

5V Regulator with Timed Power-On Reset

01112723

* Connect to Logic or µP control inputs.

01112720

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.

Timing Diagram for Timed Power-On Reset

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.

01112721

* R = 1 MEG, C = 0.1 µF

T

5V Regulator with Snap-On/Snap-Off

Feature and Hysteresis

01112722

* Turns ON at V = 5.87V

IN

Turns OFF at V = 5.64V

IN

(for component values shown)

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18

Typical Applications (Continued)

5V Regulator with Timed Power-On Reset, Snap-On/Snap-Off Feature and Hysteresis

Timing Diagram

01112725

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

01112724

FIGURE 6.

19

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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

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20

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

21

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

16-Pin Ceramic Surface-Mount

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

NS Package Number WG16A

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.

For the most current product information visit us at www.national.com.

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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

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(b) support or sustain life, and whose failure to perform when

properly used in accordance with instructions for use

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型号：	LP2953 MDS
厂家：	TEXAS INSTRUMENTS
描述：	-20V 至 30V、250mA、2.5V 或 5V 输出航天级 QMLV 线性稳压器 \| Y \| 0 \| -55 to 125 电源电路线性稳压器IC
文件：	总24页 (文件大小：1079K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LP2953 MDS [TI]

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