Datasheet RC2951 Datasheet (Fairchild Semiconductor)

www.fairchildsemi.com

RC2951

Adjustable Micropower Voltage Regulator

Features

• High accuracy output voltage

• Guaranteed 100 mA output current

• Extremely low quiescent current

• Extremely tight load and line regulation

• Requires only a 1.0µF output capacitor for stability

• Internal Current and Thermal Limiting

• Error ﬂag warns of output dropout

• Logic-controlled electronic shutdown

• Output programmable from 1.24 to 29V

• Fixed 3.3V version available

• -25°C to +85°C operating range

• 8 lead SOIC package

Block Diagram

Description

The RC2951 is a voltage regulator speciﬁcally designed to maintain proper regulation with a very low dropout voltage (Typ. 40mV at light loads and 380 mV at 100mA). It has a low quiescent bias current of 75µA and is capable of supplying output currents in excess of 100mA. It has internal current and thermal limiting protection. The output can be programmed from 1.24V to 29V with two external resistors. A ﬁxed output voltage (3.3V) is also available.

The error ﬂag output can be used as power-on reset for warning of a low output voltage. The Shutdown input feature allows a logic level signal to turn on and off the regulator output. The RC2951 is ideally suited for battery powered computer, consumer, and industrial equipment where an extension of useful battery life is desirable. The RC2951 is available in an 8-pin SOIC package.

V

Unregulated DC

+

From CMOS or TTL

PRELIMINARY INFORMATION describes products that are not in full production at the time of printing. Specifications are based on design goals and limited characterization. They may change without notice. Contact Raytheon for current information.

3

Shut

Down

781

Feed-

Back

60 mV

+

1.23V Reference

Error Detection Comparator

Input Output

+

–

Error Amplifier

+

–

Sense

V

Error

Ground

IL ≤ 100 mA

2

6

TAP

5

4

OUT

+

See Application

Discussion

330kΩ

To CMOS or TTL

REV. 1.0.1 4/8/02

RC2951 PRODUCT SPECIFICATION

Pin Assignments

8 Lead SOIC Package

Output

Sense

Shutdown

Ground

1

2

3

4

Input

8

Feedback

7

V

6

5

TA P

Error

Top View

Absolute Maximum Ratings

Power Dissipation Internally Limited Lead Temp. (Soldering, 5 seconds) 260°C Storage Temperature Range –65° to +150°C

Operating Junction Temperature Range

Input Supply/Voltage –0.3 to +30V

Feedback Input Voltage

Shutdown Input Voltage

2,3

2

Error Comparator Output Voltage

Notes:

1. Junction to ambient thermal resistance for the S.O. (M) package is 160°C/W. 2 May exceed input supply voltage.

3. When used in dual-supply systems where the output terminal sees loads returned to a negative supply, the output voltage should be diode-clamped to ground.

1

–55° to +150°C

–1.5 to +30V

–0.3 to +30V

2

–0.3 to +30V

Electrical Characteristics

The • denotes that the limits apply at temperature extremes.

Parameter Conditions

Output Voltage

TJ = 25°C 5.0 5.025

(RC2951M)

-25°C ≤ TJ ≤ 85°C •

Output Voltage (RC2951M)

Output Voltage

100µA ≤ IL ≤ 100mA TJ ≤ T

TJ = 25°C 3.3 3.317

(RC2951M-3.3)

-25°C ≤ TJ ≤ 85°C •

Output Voltage (RC2951M-3.3)

Output Voltage Temperature Coefficient

Line Regulation

Load Regulation

7

9, 10

9

100µA ≤ IL ≤ 100mA TJ ≤ T

(VONOM + 1)V ≤ Vin ≤ 20V

100 µA ≤ IL ≤ 100 mA

1

JMAX

Typ. Tested Limit

2

Units

V max

5.0 5.06

•

5.0 5.075

•

4.975

4.94

4.925

V min

V max

V min

V max

V min

V max

3.3 3.340

•

3.3 3.346

•

3.284

3.260

3.254

V min

V max

V min

V max

V min

• 20 120 ppm/°C

0.03 0.1

•

0.08 0.2

•

0.5

0.4

% max % max

2 REV. 1.0.1 4/8/02

PRODUCT SPECIFICATION RC2951

Electrical Characteristics (continued)

The • denotes that the limits apply at temperature extremes.

Parameter Conditions

Dropout Voltage

Ground Current I

Dropout Ground Current V

3

IL = 100 µA

= 100 mA

I

L

= 100 µA

L

= 100 mA

I

L

= (VONOM - 0.5)V

in

IL = 100 µA •

Current Limit V

Thermal Regulation

8

Output Noise, 10 Hz to 100 KHz

= 0

out

CL = 1 µF (5V Only) 430 µV rms

CL = 200 µF 160 µV rms

CL = 3.3 µF (Bypass = 0.01 µF Pins 7 to 1 (RC2951)

Reference Voltage

5

Feedback Pin Bias Current

Reference Voltage Temperature Coefficient

7

Feedback Pin Bias Current Temperature Coefficient

Error Comparator

Output Leakage Current VOH = 30V

Output Low Voltage V

= (VONOM - 0.5)V

in

IOL = 400 µA •

Upper Threshold Voltage

Lower Threshold Voltage

Hysteresis

4

1

Typ. Tested Limit

50 80

•

150

380 500

•

700

75 120

•

140

81415mA max

•

110 250

300

160 200

•

220

0.05 0.2 %/W max

100 µV rms

1.235 1.25

•

1.26

1.22

•

1.2

1.27

1.19

20 40

•

60

20 ppm/°C

0.1 nA/°C

0.01 1

•

150 250

400

60 40

•

25

75 95

•

140

15 mV

2

Units

mV max mV max

µA max µA max

mA max

µA max µA max

mA max mA max

V max V max

V min V min

V max

V min

nA max nA max

µA max

2

µA max

mV max mV max

mV min mV min

mV max mV max

REV. 1.0.1 4/8/02 3

RC2951 PRODUCT SPECIFICATION

Electrical Characteristics (continued)

The • denotes that the limits apply at temperature extremes.

Parameter Conditions

1

Typ. Tested Limit

Shutdown Input

Input Logic Voltage

Low (Regulator ON) High (Regulator OFF)

Shutdown Pin Input Current V

Regulator Output Current in Shutdown

Notes:

1. Unless otherwise specified all limits guaranteed for T versions, and 2.2 µF for 3V and 3.3V versions. Additional conditions for the 8-pin versions are Feedback tied to V Output tied to Output Sense and V

2. Guaranteed and 100% production tested.

3. Dropout Voltage is defined as the input to output differential at which the output voltage drops 100 mV below its nominal value measured at 1V differential. At very low values of programmed output voltage, the minimum input supply voltage of 2V (2.3V over temperature) must be taken into account.

4. Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage measured at V by the error amplifier gain = V is guaranteed to go low when the output drops by 95 mV x 5V/1.235V = 384 mV. Thresholds remain constant as a percent of V

as V

out

5. V

< V

ref

6. V

shutdown

7. Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.

8. Thermal regulation is defined as the change in output voltage at a time T after a change in power dissipation is applied, excluding load or line regulation effects. Specifications are for a 50 mA load pulse at V T = 10 ms.

9. Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are covered under the specification for thermal regulation.

10. Line regulation for the RC2951 is tested at 150°C for I by design to 0.2%. See Typical Performance Characteristics for line regulation versus temperature and load current.

≤ (V

out

≥ 2V, Vin ≤ 30V, V

6

is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed.

– 1V), 2.3V ≤ Vin ≤ 30V, 100µA ≤ IL ≤ 100 mA, TJ ≤ T

in

shutdown

V

shutdown

= (VONOM + 1)V. To express these thresholds in terms of output voltage change, multiply

in

out/Vref

= 0, Feedback pin tied to V

out

= 2.4V

= 30V

= 25°C, Vin = (VONOM + 1)V, IL = 100µA and CL = 1 µF for 5V

J

< 0.8V.

= (R1 + R2)/R2. For example, at a programmed output voltage of 5V, the Error output

JMAX

.

TAP

= 1 mA. For IL = 100 µA and TJ = 125°C, line regulation is guaranteed

L

1.3

•

30 50

•

450 600

•

31020µA max

•

.

0.6

2.0

100

750

= 30V (1.25W pulse) for

IN

2

Units

V

V max

V min

µA max µA max

µA max

,

TAP

4 REV. 1.0.1 4/8/02

PRODUCT SPECIFICATION RC2951

Applications Discussion

The RC2951 regulator is designed with internal current limiting and thermal shutdown. It is not internally compensated and requires a 1.0µF (or greater) capacitor between the output terminal and ground for stability. At lower output voltages, more capacitance is required (2.2µF or more is recommended for 3V and 3.3V versions) for stability. Most types of aluminum, tantalum or multilayer ceramic capacitors will perform adequately. Solid tantalums or appropriate multilayer ceramic capacitors are suggested for operation below 25°C. At lower values of output current, less capacitance is needed to maintain stability at output. The capacitor at the output can be reduced to 0.33µF for currents less that 10mA, or 0.1µF for currents below 1.0mA.

Figure 1 is a timing diagram showing the ERR

OR signal and the regulated output voltage as the RC2951 input is ramped up and down. For 5V versions, the ERR

OR signal becomes valid (low) at about 1.3V input. It goes high at about 5V input (the input voltage at which V

= 4.75.) Since the

OUT

RC2951’s dropout voltage is load-dependent (see curve in typical performance characteristics), the input voltage trip point (about 5V) will vary with the load current. The output voltage trip point (approx. 4.75V) does not vary with load.

Output

Voltage

4.75V

Using the adjustable versions at voltages below 5V runs the error ampliﬁer at lower gains so that more output capacitance is needed. For the worst-case situation of a 100 mA load at 1.23V output (Output shorted to Feedback) a

3.3 µF (or greater) capacitor should be used.

When setting the output voltage of the RC2951 versions with external resistors, a minimum load of 1 µA is recommended. A 1 µF tantalum or aluminum electrolytic capacitor should be placed from the RC2951 input to ground if there is more than 10 inches of wire between the input and the AC ﬁlter capacitor or if a battery is used as the input.

Stray capacitance to the RC2951 Feedback terminal can cause instability. This may especially be a problem when using high value external resistors to set the output voltage. Adding a 100 pF capacitor between Output and Feedback and increasing the output capacitor to at least 3.3 µF will ﬁx this problem.

Error Detection Comparator Output

The comparator switches to a logic low whenever the RC2951 output falls out of regulation by more than approximately 5%. This value is the comparator’s built-in offset of about 60 mV divided by the 1.235 internal reference voltage. This trip level remains “5% below normal” regardless of the value of the output voltage. For example, the error ﬂag trip level is typically 4.75V for a 5V output or 11.4V for a 12V output. The out of regulation condition may be due either to low input voltage, current limiting, or thermal limiting.

Error*

Input

Voltage

Figure 1. ERROR

5V

1.3V

2950-10

Output Timing

The error comparator has an open-collector output which requires an external pullup resistor. This resistor may be returned to the output or some other supply voltage depending on system requirements. In determining a value for this resistor, note that while the output is rated to sink 400 µA, this sink current adds to battery drain in a low battery condition. Suggested values range from 100k to 1MΩ. The resistor is not required if this output is unused.

Programming the Output Voltage (RC2951)

The RC2951 may be pin-strapped for the nominal ﬁxed output voltage using its internal voltage divider by tying the output and sense pins together, and also tying the feedback and V for any output voltage between its 1.235V reference and its 30V maximum rating. As seen in Figure 2 an external pair of resistors is required.

pins together. Alternatively, it may be programmed

TA P

REV. 1.0.1 4/8/02 5

RC2951 PRODUCT SPECIFICATION

V

OUT

V

REF

R1R2+

R

2

-------------------





=

.

+V

IN

Error Output

**Shutdown

Input

100K

5

3

8

+V

IN

ERROR

RC2951

SD

GND FB

V

OUT

1.2 30V

1

V

OUT

V

74

REF

1.23V

++

R

1

R

2

.01 µF

3.3µF

2950-11

V

OUT

V

=

REF

** Drive with TTL-high to shut down. Ground or leave open if shutdown feature is not to be used.

Figure 2. Adjustable Regulator

The complete equation for the output voltage is

R

1

V

REF

OUT



1

------+

IFBR



+•=

R

2

V

OUT

V

REF

-------------R

2

V

-------------------= R1R2+

1

Reducing Output Noise

In reference applications it may be advantageous to reduce the AC noise present at the output. One method is to reduce the regulator bandwidth by increasing the size of the output capacitor.

Noise can be reduced fourfold by a bypass capacitor across R1, since it reduces the high frequency gain from 4 to unity. Pick

V

OUT

=



V

1

REF



Adding the error term,

V

OUT



V

1

REF



R

1

------+ R

2

C

BYPASS

or about 0.01 µF. When doing this, the output capacitor must be increased to 3.3 µF to maintain stability. These changes

R

1

------+

IFBR

+=

R

2

reduce the output noise from 430 µV to 100 µV rms for a 100 kHz bandwidth at 5V output. With the bypass capacitor added, noise no longer scales with output voltage so that

------------------------------------

≅

2πR

improvements are more dramatic at higher output voltages.

where V

is the nominal 1.235 reference voltage and IFB

REF

is the feedback pin bias current, nominally -20 nA. The minimum recommended load current of 1 µA forces an upper limit of 1.2 MΩ on the value of R2, if the regulator must work with no load (a condition often found in CMOS in standby). IFB will produce a 2% typical error in V

OUT

which may be eliminated at room temperature by trimming R1. For better accuracy, choosing R2 = 100k reduces this error to 0.17% while increasing the resistor program current to 12 µA. Since the RC2951 typically draws 60 µA at no load with Pin 2 open-circuited, this is a small price to pay.

R

1



1

------+



R

2

1

200Hz•

1

6 REV. 1.0.1 4/8/02

PRODUCT SPECIFICATION RC2951

Typical Applications

Unregulated

Input

1µF

6

V

TAP

7

FB

1MΩ

Figure 3. 1A Regulator with 1.2V Dropout

10kΩ

8

IN

RC2951

GND

4

0.01µF

SENSE

OUT

0.002µF

Supertex VP12C

+

220µF

I

400µA

Q

Output 5V±1%@ 0 to 1A

2

1

2kΩ

Unregulated

Input

8

IN

RC2951

6

V

TAP

GNDFB

7

OUT

SENSE

4

1

2

4.7µF

27kΩ

+

Load 50mA to 300mA

330Ω

Figure 4. 300 mA Regulator with 0.75 Dropout

+V = 2 30V

Load

L

8

V

IN

RC2951

Shutdown Input

3

SD

GND

4

R

1%

V

FB

IL=I

OUT

7

2N5432 (2)

5V Output

1.23 R

1

1 µF

+V

IN

8

+V Error Output

**Shutdown

Input

*Minimum input-output voltage ranges from 40 mV to 400 mV, depending on load current. Current limit is typically 160 mA.

Figure 5. Wide Input Voltage Range

0.1µF

+

5

3

Current Limiter

IN

ERROR

RC2951

SD

GND

4

*V

OUT≈VIN

1

V

OUT

FB

4

2950-12

Figure 6. Low Drift Current Source

REV. 1.0.1 4/8/02 7

RC2951 PRODUCT SPECIFICATION

Typical Applications (continued)

+V

IN

8

+V

IN

6

V

TAP

RC2951

#1

FB

7

SENSE

V

ERROR

OUT

D

1

2

1

5

+

GND

4

27kΩ

D

2.7MΩ

Q

1

6

7

3

V

FB

SD

+V

TAP

8

IN

RC2951

D

4

SENSE

#2

ERROR

V

OUT

3

2

1

5

330kΩ

Main 5V Output

+

GND

4

• Early warning flag on low input voltage

• Main output latches of f at lower input voltages

• Battery backup on auxillary output

Operation Reg. #1’s V flag becomes active when V flag of Reg. #2 becomes active and via Q1 latches the main output off. When V

again exceeds 5.7V Reg. #1 is back in regulation and the early

in

warning signal rises unlatching Reg. #2 via D3.

is programmed one diode drop above 5V. Its error

OUT

≤ 5.7V. WhenVin drops below 5.3V, the error

in

Figure 7. Regulator with Early Warning and Auxillary Output

+V

IN

8

+V

IN

RC2951

GND

1

V

OUT

R

7

FB

R

Reset

470kΩ

5

ERROR

3

SD

4

Figure 8. Latch Off When Error Flag Occurs

5V Memory

D

2

Supply

20

1µF

3.6V Nicad

EARLY WARNING

RESET

µP

V

DD

1µF

V

OUT

1

+

1µF

2

Current Limit Section

+V

= V

+5.0V

IN

OUT

680 0.05

470

MJE2955

2N3906

10kΩ

5

Error Flag

R

1

7

FBSD

1

1%

R

2

47

4.7MΩ

+V

8

IN

ERROR

RC2951

3

V

OUT

220

20kΩ

= 1.23V

V

OUT

,use internal resistors. Wire pin 6 to 7, & wire pin 2 +V

For 5V

OUT

GND

4

.033

R

1

1 +

()

R

2

Figure 9. 2 Ampere Low Dropout Regulator

+V

IN

C-MOS

*Sleep Input

Error Output

Shutdown Input

47kΩ

5

3

+V

ERROR

RC2951

SD

GND

4

GATE

100 pF

470kΩ

2N3906

200kΩ

1%

100kΩ

1%

8

IN

1

V

OUT

FB

7

100kΩ

*High input lowers V

OUT

to 2.5V.

Figure 10. 5V Regulator with 2.5V Sleep Function

+5V

4

20mA

8

V

IN

1

V

1N 4001

0.1µF

RC2951

GND

OUT

FB

7

4

1N457

4.7kΩ

1

2

360

+V

OUT

+

4.7

TANT.

OUT

+V

OUT

+

Output*

5

4

* High for IL < 3.5mA

@ 2A

+

3.3µF

100 µF

Buss.

Min. Voltages ≈ 4V

2950-13

Figure 11. Open Circuit Detector for 4mA to 20mA Current Loop

8 REV. 1.0.1 4/8/02

PRODUCT SPECIFICATION RC2951

Typical Applications (continued)

+

39kΩ

–

*C4 +

6V Lead-Acid Battery

C1-C4 LP339

RESET

1%

R

3

1%

39kΩ

100 kΩ

1kΩ

10kΩ

20kΩ

5

3

+V

IN

ERROR

RC2951

SD

GND

4

–

C1

+

–

C2

+

–

C3

+

28

SENSE

V

OUT

FB

V

TAP

6

1

7

100kΩ

+V

OUT

< 5.8V**

< 6.0V**

< 6.2V**

= 5V

+

1µF

*Optional Latch off when drop out occurs. Adjust R3 for C2 Switching when V

**Outputs go low whenV

drops below designated thresholds.

in

Figure 12. Regulator with State-of-Charge Indicator

For values shown, Regulator shuts down when V

6V

+

Sealed Lead-Acid Battery Source

≈ 400kΩ* for 5.5V

*Sets disconnect Voltage

**Sets disconnect Hysteresis

< 5.5V and turns on again at 6.0V. Current drain in disconnected mode is ≈ 150 µA.

in

120kΩ

FB

LM385

1.5kΩ**

+

–

100kΩ

1N457

Figure 13. Low Battery Disconnect

3

is 6.0V.

in

SD

GND

8

+V

IN

RC2951

SENSE

V

TAP

1

V

OUT

2

7

FB

64

1µF

+

Main V+

Memory V+

20Ω

Ni-cad Backup Battery

2950-14

REV. 1.0.1 4/8/02 9

RC2951 PRODUCT SPECIFICATION

Mechanical Dimensions – 8 Lead SOIC

Symbol

A .053 .069 1.35 1.75

A1 .004 .010 0.10 0.25

B .013 0.33

C .008 .010 0.20 0.25 D .189 .197 4.80 5.00

E .150 .158 3.81 4.01

e

H

h

L .016 .050 0.40 1.27

N8 8

α

ccc .004 0.10——

85

14

Inches

Min. Max. Min. Max.

.020 0.51

.050 BSC 1.27 BSC

.228 .244 5.79 6.20

.010 .020 0.25 0.50

0° 8° 0° 8°

EH

Millimeters

Notes

5 2

2

3 6

Notes:

1.

Dimensioning and tolerancing per ANSI Y14.5M-1982.

2.

"D" and "E" do not include mold flash. Mold flash or protrusions shall not exceed .010 inch (0.25mm).

3.

"L" is the length of terminal for soldering to a substrate.

4.

Terminal numbers are shown for reference only.

5.

"C" dimension does not include solder finish thickness.

6.

Symbol "N" is the maximum number of terminals.

D

A

e

B

A1

SEATING PLANE

– C –

LEAD COPLANARITY

ccc C

α

h x 45°

C

L

10 REV. 1.0.1 4/8/02

RC2951 PRODUCT SPECIFICATION

Ordering Information

Product Number Package

RC2951MT 8-pin SOIC in tape and reel

RC2951M33 8-pin SOIC

DISCLAIMER

FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.

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FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD 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 (c) 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 of the user.

2. A critical component in 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.

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4/8/02 0.0m 001

 2001 Fairchild Semiconductor Corporation

Stock#DS30002951