MIC2950/2951

Micrel

February 1999

MIC2950/2951

MIC2950/2951

150mA Low-Dropout Voltage Regulator

Block Diagram

60mV

1.23V

REF.

Error

Amp.

Error Detection

Comparator

182k

60k

1.5µF

SNS

TAP

ERR

GND

OUT

5V/150mA
Output

TTL/CMOS
Compatible
Error Output

Unregulated
DC Supply

TTL/CMOS

Control Logic

Input

SHDN

330k

MIC2951-0x

General Description

The MIC2950 and MIC2951 are "bulletproof" micropower
voltage regulators with very low dropout voltage (typically
40mV at light loads and 250mV at 100mA), and very low
quiescent current. Like their predecessors, the LP2950 and
LP2951, the quiescent current of the MIC2950/MIC2951
increases only slightly in dropout, thus prolonging battery life.
The MIC2950/MIC2951 are pin for pin compatible with the
LP2950/LP2951, but offer lower dropout, lower quiescent
current, reverse battery, and automotive load dump protection.

The key additional features and protection offered include
higher output current (150mA), positive transient protection
for up to 60V (load dump), and the ability to survive an
unregulated input voltage transient of 20V below ground
(reverse battery).

The plastic DIP and SOIC versions offer additional system
functions such as programmable output voltage and logic
controlled shutdown. The 3-pin TO-92 MIC2950 is pin-
compatible with the older 5V regulators.

These system functions also include an error flag output that
warns of a low output voltage, which is often due to failing
batteries on the input. This may also be used as a power-on
reset. A logic-compatible shutdown input is also available
which enables the regulator to be switched on and off. This
part may also be pin-strapped for a 5 V output, or programmed
from 1.24 V to 29 V with the use of two external resistors.

Features

High accuracy 3.3, 4.85, or 5V, guaranteed 150mA output

Extremely low quiescent current

Low-dropout voltage

Extremely tight load and line regulation

Very low temperature coefficient

Use as regulator or reference

Needs only 1.5

F for stability

Current and thermal limiting

Unregulated DC input can withstand 20V reverse battery

and +60V positive transients

Error flag warns of output dropout (MIC2951)

Logic-controlled electronic shutdown (MIC2951)

Output programmable from 1.24V to 29V (MIC2951)

Applications

Automotive Electronics

Battery Powered Equipment

Cellular Telephones

SMPS Post-Regulator

Voltage Reference

Avionics

High Efficiency Linear Power Supplies

Micrel, Inc. · 1849 Fortune Drive · San Jose, CA 95131 · USA · tel + 1 (408) 944-0800 · fax + 1 (408) 944-0970 · http://www.micrel.com

MIC2950/2951

Micrel

MIC2950/2951

February 1999

Pin Description

Pin #

Pin Name

Pin Function

MIC2950

MIC2951

OUT

Regulated Output

SNS

Sense (Input): Output-voltage sensing end of internal voltage divider for
fixed 5V operation. Not used in adjustable configuration.

SHDN

Shutdown/Enable (Input): TTL compatible input. High = shutdown,
low or open = enable.

GND

Ground

ERR

Error Flag (Output): Active low, open-collector output (low = error,
floating = normal).

TAP

3.3V/4.85/5V Tap: Output of internal voltage divider when the regulator is
configured for fixed operation. Not used in adjustable configuration.

Feedback (Input): 1.235V feedback from internal voltage divider's TAP (for
fixed operation) or external resistor network (adjustable configuration).

Unregulated Supply Input

Pin Configuration

TAP

ERR

OUT

SNS

SHDN

GND

MIC2951-xx

DIP (N), SOIC (M), MM8TM (MM)

(Top View)

OUT

GND

MIC2950-xx

TO-92 (Z)

(Bottom View)

Ordering Information

Part Number

Voltage

Accuracy Temperature Range*

Package

MIC2950-05BZ

5.0V

0.5%

C to +125

TO-92

MIC2950-06BZ

5.0V

1.0%

C to +125

TO-92

MIC2951-02BM

5.0V

0.5%

C to +125

8-pin SOIC

MIC2951-03BM

5.0V

1.0%

C to +125

8-pin SOIC

MIC2951-02BN

5.0V

0.5%

C to +125

8-pin plastic DIP

MIC2951-03BN

5.0V

1.0%

C to +125

8-pin plastic DIP

MIC2951-03BMM

5.0V

1.0%

C to +125

8-lead MM8TM

MIC2951-3.3BM

3.3V

1.0%

C to +125

8-pin SOIC

MIC2951-4.8BM

4.85V

1.0%

C to +125

8-pin SOIC

* junction temperature

The MIC2950 is available as either an -05 or -06 version. The
-05 and -06 versions are guaranteed for junction temperatures
from 40

C to +125

C; the -05 version has a tighter output and

reference voltage specification range over temperature. The
MIC2951 is available as an -02 or -03 version.

The MIC2950 and MIC2951 have a tight initial tolerance
(0.5% typical), a very low output voltage temperature coefficient
which allows use as a low-power voltage reference, and
extremely good load and line regulation (0.04% typical). This
greatly reduces the error in the overall circuit, and is the result
of careful design techniques and process control.

MIC2950/2951

Micrel

February 1999

MIC2950/2951

Electrical Characteristics

(Note 16)

= 6V; I

= 100

A; C

= 1

F; T

= 25

C, bold values indicate 40

+125

C; Note 8; unless noted.

Parameter

Condition

Min

Typ

Max

Units

Output Voltage

MIC295x-02/-05 (

0.5%), T

= 25

4.975

5.000

5.025

MIC295x-03/-06 (

1%), T

= 25

4.950

5.000

5.050

MIC2951-3.3 (

1%), T

= 25

3.267

3.300

3.333

MIC2951-4.8 (

1%), T

= 25

4.802

4.850

4.899

Output Voltage

MIC295x-02/-05 (

0.5%), 25

+85

4.950

5.050

MIC295x-03/-06 (

1%), 25

+85

4.925

5.075

MIC2951-3.3 (

1%), 25

+85

3.251

3.350

MIC2951-4.8 (

1%), 25

+85

4.777

4.872

Output Voltage

MIC295x-02/-05 (

0.5%), 40

C to +125

4.940

5.060

Over Full Temperature Range

MIC295x-03/-06 (

1%), 40

C to +125

4.900

5.100

MIC2951-3.3 (

1%), 40

C to +125

3.234

3.366

MIC2951-4.8 (

1%), 40

C to +125

4.753

4.947

Output Voltage

MIC295x-02/-05 (

0.5%), 100

150mA, T

J(max)

4.930

5.070

Over Load Variation

MIC295x-03/-06 (

1%), 100

150mA, T

J(max)

4.880

5.120

MIC2951-3.3 (

1%), 100

150mA, T

J(max)

3.221

3.379

MIC2951-4.8 (

1%), 100

150mA, T

J(max)

4.733

4.967

Output Voltage

MIC295x-02/-05 (

0.5%), Note 9

100

ppm/

Temperature Coefficient

MIC295x-03/-06 (

1%), Note 9

150

ppm/

MIC2951-3.3 (

1%), Note 9

150

ppm/

MIC2951-4.8 (

1%), Note 9

150

ppm/

Line Regulation

MIC295x-02/-05 (

0.5%), Note 10, 11

0.03

0.10

0.20

MIC295x-03/-06 (

1%), Note 10, 11

0.04

0.20

0.40

MIC2951-3.3 (

1%), Note 10, 11

0.04

0.20

0.40

MIC2951-4.8 (

1%), Note 10, 11

0.04

0.20

0.40

Absolute Maximum Ratings

(Note 1)

Input Suppy Voltage (V

) Note 5 ................. 20V to +60V

Feedback Input Voltage (V

) Note 6, 7 ...... 1.5V to +26V

Shutdown Input Voltage (V

SHDN

) Note 6 ..... 0.3V to +30V

Power Dissipation (P

) Note 4 ................ Internally Limited

Storage Temperature .............................. 65

C to + 150

Lead Temperature (soldering, 5 sec.) ....................... 260

ESD, Note 3

Operating Ratings

(Note 2)

Input Supply Voltage (V

) ........................... +2.0V to +30V

Junction Temperature (T

) ....................................... Note 4

MIC2950-05/MIC2950-06 ..................... 40

C to +125

MIC2951-02/MIC2950-03 ..................... 40

C to +125

MIC2950/2951

Micrel

MIC2950/2951

February 1999

Parameter

Condition

Min

Typ

Max

Units

Load Regulation

MIC295x-02/-05 (

0.5%), 100

150mA, Note 10

0.04

0.10

0.20

MIC295x-03/-06 (

1%), 100

150mA, Note 10

0.10

0.20

0.30

MIC2951-3.3 (

1%), 100

150mA, Note 10

0.10

0.20

0.30

MIC2951-4.8 (

1%), 100

150mA, Note 10

0.10

0.20

0.30

Dropout Voltage

MIC295x-02/-03/-05/-06, I

= 100

A, Note 12

140

MIC295x-02/-03/-05/-06, I

= 100mA, Note 12

250

300

MIC295x-02/-03/-05/-06, I

= 150mA, Note 12

300

450

600

MIC2951-3.3 (

1%), I

= 100

A, Note 12

150

MIC2951-3.3 (

1%), I

= 100mA, Note 12

250

350

MIC2951-3.3 (

1%), I

= 150mA, Note 12

320

450

600

MIC2951-4.8 (

1%), I

= 100

A, Note 12

140

MIC2951-4.8 (

1%), I

= 100mA, Note 12

250

300

MIC2951-4.8 (

1%), I

= 150mA, Note 12

300

450

600

Ground Current

MIC295x-02/-03/-05/-06, I

= 100

120

180

300

MIC295x-02/-03/-05/-06, I

= 100mA

1.7

2.5

3.5

MIC295x-02/-03/-05/-06, I

= 150mA

MIC2951-3.3 (

1%), I

= 100

100

180

300

MIC2951-3.3 (

1%), I

= 100mA

1.7

2.5

MIC2951-3.3 (

1%), I

= 150mA

MIC2951-4.8 (

1%), I

= 100

120

180

300

MIC2951-4.8 (

1%), I

= 100mA

1.7

2.5

3.5

MIC2951-4.8 (

1%), I

= 150mA

Dropout Ground Current

MIC295x-02/-03/-05/-06 (

0.5%), V

= 4.5V, I

= 100

280

350

400

MIC2951-3.3 (

1%), V

= 3.0V, I

= 100

150

350

400

MIC2951-4.8 (

1%), V

= 4.3V, I

= 100

280

350

400

MIC2950/2951

Micrel

February 1999

MIC2950/2951

Parameter

Condition

Min

Typ

Max

Units

Current Limit

OUT

= 0V

300

400

450

Thermal Regulation

Note 13

0.05

0.20

%/W

Output Noise

10Hz to 100kHz, C

= 1.5

430

RMS

10Hz to 100kHz, C

= 200

160

RMS

10Hz to 100kHz, C

= 3.3

100

RMS

0.01

F bypass Feedback to Output

Reference Voltage

MIC295x-02/-05 (

0.5%)

1.220

1.235

1.250

1.200

1.260

MIC295x-03/-06 (

1%)

1.210

1.235

1.260

1.200

1.270

MIC2951-3.3 (

1%)

1.210

1.235

1.260

1.200

1.270

MIC2951-4.8 (

1%)

1.210

1.235

1.260

1.200

1.270

Reference Voltage

MIC295x-02/-05 (

0.5%), Note 14

1.190

1.270

MIC295x-03/-06 (

1%), Note 14

1.185

1.285

MIC2951-3.3 (

1%), Note 14

1.185

1.285

MIC2951-4.8 (

1%), Note 14

1.185

1.285

Feedback Bias Current

Reference Voltage

MIC295x-02/-05 (

0.5%), Note 9

ppm/

Temperature Coefficient

MIC295x-03/-06 (

1%), Note 9

ppm/

MIC2951-3.3 (

1%), Note 9

ppm/

MIC2951-4.8 (

1%), Note 9

ppm/

Feedback Bias Current

0.1

nA/

Temperature Coefficient

Error Comparator (Flag)

= 30V

0.01

1.00

Output Leakage Current

2.00

Error Comparator (Flag)

= 4.5V, I

= 200

150

250

Output Low Voltage

400

Error Comparator

Note 15

Upper Threshold Voltage

Error Comparator

Note 15

Lower Threshold Voltage

140

Error Comparator Hysteresis

Note 15

MIC2950/2951

Micrel

MIC2950/2951

February 1999

Parameter

Condition

Min

Typ

Max

Units

Shutdown Input Logic Voltage

MIC295x-02/-05 (

0.5%)

1.3

Low

0.7

High

2.0

MIC295x-03/-06 (

1%)

1.3

Low

0.7

High

2.0

MIC2951-3.3 (

1%)

1.3

Low

0.7

High

2.0

MIC2951-4.8 (

1%)

1.3

Low

0.7

High

2.0

Shutdown Input Current

SHUTDOWN

= 2.4V

100

SHUTDOWN

= 30V

450

600

750

Regulator Output Current

Note 7

in Shutdown

Note 1.

Exceeding the absolute maximum rating may damage the device.

Note 2.

The device is not guaranteed to function outside its operating rating.

Note 3.

Devices are ESD sensitive. Handling precautions are recommended.

Note 4.

The junction-to-ambient thermal resistance of the TO-92 package is 180

C/W with 0.4" leads and 160

C/W with 0.25" leads to a PC board.

The thermal resistance of the 8-pin DIP package is 105

C/W junction-to-ambient when soldered directly to a PC board. Junction-to-ambient

thermal resistance for the SOIC (M) package is 160

C/W. Junction-to-ambient thermal resistance for the MM8TM (MM) is 250

C/W.

Note 5.

The maximum positive supply voltage of 60V must be of limited duration (

100ms) and duty cycle (

1%). The maximum continuous supply

voltage is 30V.

Note 6.

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.

Note 7.

SHDN

2V, V

30 V, V

OUT

= 0, with the FB pin connected to TAP.

Note 8.

Additional conditions for 8-pin devices are V

= 5V, TAP and OUT connected to SNS (V

OUT

= 5V) and V

SHDN

0.8V.

Note 9.

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

Note 10. 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 in the specification for thermal regulation.

Note 11. Line regulation for the MIC2951 is tested at 150

C for I

= 1mA. For I

= 100

A and T

= 125

C, line regulation is guaranteed by design to

0.2%. See Typical Performance Characteristics for line regulation versus temperature and load current.

Note 12. Dropout voltage is defined as the input to output differential at which the output voltage drops 100mV 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.

Note 13. 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 50mA load pulse at V

= 30V (1.25W pulse) for t = 10ms.

Note 14. V

REF

OUT

1 V), 2.3V

30V, 100

A < I

150mA, T

JMAX

Note 15. Comparator thresholds are expressed in terms of a voltage differential at the FB terminal below the nominal reference voltage measured at 6V

input. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = V

OUT

REF

(R1 + R2)/R2. For example, at a programmed output voltage of 5V, the error output is guaranteed to go low when the output drops by
95mV x 5V/1.235V = 384mV. Thresholds remain constant as a percent of V

OUT

as V

OUT

is varied, with the dropout warning occurring at

typically 5% below nominal, 7.5% guaranteed.

Note 16. Specification for packaged product only.

MIC2950/2951

Micrel

February 1999

MIC2950/2951

Typical Characteristics

Ground Pin Current

Dropout Characteristics

Input Current

Ground Pin Current

Output Voltage vs.
Temperature of 3
Representative Units

Input Current

Ground Pin Current

Dropout Voltage

Short Circuit Current

Dropout Voltage

0.1

150

0.1

0.01

100

150

200

250

300

350

400

1 2

3 4

5 6

7 8 9 10

120
110
100

90
80
70
60
50
40
30
20
10

6 7

9 10

5.06

5.04

5.02

5.0

4.98

4.96

4.94

-75 -50 -25 0 25 50 75 100 125 150

100

120

140

180

350

300

250

200

150

100

-75 -50 -25 0 25 50 75 100 125 150

450

400

350

300

250

200

150

100

-75 -50 -25 0 25 50 75 100 125 150

600

500

400

300

100

-75 -50 -25 0 25 50 75 100 125 150

500

400

300

200

100

0.1

100

R = 50k

R = 33

0.2%

V = 6V
I = 100

V = 6V
I = 150 mA

I = 150 mA

I = 100

T = 25

LOAD CURRENT (mA)

INPUT VOLTAGE (V)

TEMPERATURE (

INPUT VOLTAGE (V)

TEMPERATURE (

INPUT VOLTAGE (V)

TEMPERATURE (

OUTPUT CURRENT (mA)

QUIESCENT CURRENT

OUTPUT VOLTAGE (V)

INPUT CURRENT (

INPUT CURRENT (mA)

OUTPUT VOLTAGE (V)

QUIESCENT CURRENT (

QUIESCENT CURRENT (mA)

SHORT CIRCUIT CURRENT (mA)

DROPOUT VOLTAGE (mV)

R =

130

140

150

160

R = 50

R = 50k

I = 1 mA

I = 0

I = 150 mA

150

MIC2950/2951

Micrel

MIC2950/2951

February 1999

MIC2951
Error Comparator Output

MIC2951
Minimum Operating Voltage

Line Transient Response

Load Transient Response

Ripple Rejection

Output Impedance

2.2

2.0

1.9

1.6

-30

-20

-10

-250

-200

-150

-100

-50

-2.0 -1.5 -1.0 -0.5

0.5

1.0

-2

2.5

2.0

1.5

1.0

0.5

0.0

200

400

200

400

600

800

125
100

75
50
25

-25
-50

7
6

2
1

-100 0 100 200 300 400 500 600 700

0.5

0.2
0.1

0.05

100

10K 100K

T = 125

C = 4.7

V = 5V

OUT

I = 10 mA
V = 8V
V = 5V

I = 0

I = 100

TEMPERATURE (

FEEDBACK VOLTAGE (V)

TIME (

OUTPUT LOW VOLTAGE (V)

INPUT VOLTAGE (V)

TIME (mS)

FREQUENCY (Hz)

MINIMUM OPERATING VOLTAGE (V)

BIAS CURRENT (nA)

FEEDBACK CURRENT (

COMPARATOR OUTPUT (V)

SINK CURRENT (mA)

OUTPUT VOLTAGE

CHANGE (mV)

OUTPUT IMPEDANCE (OHMS)

RIPPLE REJECTION (dB)

MIC2951
Feedback Bias Current

MIC2951
Feedback Pin Current

MIC2951
Comparator Sink Current

MIC2951
Enable Transient

Ripple Rejection

2.1

1.8

1.7

-75 -50 -25 0 25 50 75 100 125 150

TEMPERATURE (

PIN 7 DRIVEN BY EXTERNAL
SOURCE (REGULATOR RUN
OPEN LOOP)

T = 25

V = 5V

OUT

T = 125

T = 25

T = -55

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-50

100

LOAD

CURRENT

C = 4.7

I = 1 mA
V = 5V

OUT

60
40
20

-20
-40
-60

100

OUTPUT VOLTAGE

CHANGE (mV)

LOAD

CURRENT

C = 15

V = 5V

OUT

OUTPUT VOLTAGE

CHANGE

INPUT

VOLTAGE

OUTPUT

VOLTAGE (V)

SHUTDOWN

PIN VOLTAGE (V)

-2

C = 10

OUT

0.02

0.01

I = 100

I = 1 mA

I = 100 mA

V = 5V
C = 4.7

OUT

C = 1.5

V = 6V
V = 5V

OUT

C = 1.5

V = 6V
V = 5V

OUT

I = 10 mA

I = 1 mA

HYSTERESIS

PULLUP RESISTOR TO
SEPARATE 5V SUPPLY

FREQUENCY (Hz)

T = 55

TIME (

C = 1.5

MIC2950/2951

Micrel

February 1999

MIC2950/2951

120

100

130

140

150

Ripple Rejection

Shutdown Threshold Voltage

0.6

0.8

1.0

1.2

1.4

1.6

1.8

-75 -50 -25 0 25 50 75 100 125 150

FREQUENCY (Hz)

TEMPERATURE (

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

30
25
20

-10

400

300

200

100

-75 -50 -25 0 25 50 75 100 125 150

Output Noise

MIC2951 Divider Resistance

Line Regulation

MIC2951 Maximum
Rated Output Current

15
10

-5

FREQUENCY (Hz)

TEMPERATURE (

RIPPLE REJECTION (dB)

VOLTAGE NOISE

SPECTRAL DENSITY (

V/ Hz)

PIN 2 TO PIN 4 RESISTANCE (k )

SHUTDOWN THRESHOLD VOLTAGE (V)

INPUT VOLTAGE (V)

OUTPUT VOLTAGE CHANGE (mV)

OUTPUT CURRENT (mA)

I = 50

C = 1.5

V = 6V
V = 5V

OUT

0.01

BYPASS
PIN 1 TO
PIN 7

C = 220

I = 100 mA

C = 4.7

C =
3.3

I = 100

I = 1 mA

I = 100

T = 150

T = 125

MAX

V = 5V

OUT

T = 25

T = 50

T = 85

8-PIN SOIC
SOLDERED
TO PC BOARD

I = 100 mA

OUTPUT CURRENT (mA)

-2

-1

Thermal Response

POWER

DISSIPATION (W)

OUTPUT VOLTAGE

CHANGE (mV)

1.25W

TIME (

MAX

TO-92 PACKAGE

.25" LEADS SOLDERED

TO PC BOARD

T = 125

T = 25

T = 85

120

100

130

140

150

MIC2950 Maximum
Rated Output

INPUT VOLTAGE (V)

Fold-Back Current Limiting

OUTPUT CURRENT (mA)

OUTPUT VOLTAGE (V)

600

500

400

300

100

200

MIC2950/2951

Micrel

MIC2950/2951

February 1999

offset of about 60mV divided by the 1.235V reference voltage.
(Refer to the block diagram on Page 1). This trip level remains
"5% below normal" regardless of the programmed output
voltage of the MIC2951. 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, thermal limiting, or overvoltage on
input (over

40V).

Figure 1 is a timing diagram depicting the ERROR signal and
the regulated output voltage as the MIC2951 input is ramped
up and down. The ERROR signal becomes valid (low) at
about 1.3V input. It goes high at about 5V input (the input
voltage at which V

OUT

= 4.75--for 5.0V applications). Since

the MIC2951'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 does not vary with load.

The error comparator has an open-collector output which
requires an external pull-up resistor. Depending on system
requirements, this resistor may be returned to the output or
some other supply voltage. In determining a value for this
resistor, note that while the output is rated to sink 200

A, this

sink current adds to battery drain in a low battery condition.
Suggested values range from 100k to 1M

. The resistor is not

required if this output is unused.

Programming the Output Voltage (MIC2951)

The MIC2951 may be pin-strapped for 5V (or 3.3V or 4.85V)
using its internal voltage divider by tying Pin 1 (output) to Pin
2 (sense) and Pin 7 (feedback) to Pin 6 (5V Tap). Alternatively,
it may be programmed for any output voltage between its
1.235V reference and its 30V maximum rating. An external
pair of resistors is required, as shown in Figure 2.

The complete equation for the output voltage is

OUT

= V

REF

x { 1 + R

} + I

where V

REF

is the nominal 1.235 reference voltage and I

the feedback pin bias current, nominally 20nA. The minimum
recommended load current of 1

A forces an upper limit of

1.2M

on the value of R

, if the regulator must work with no

load (a condition often found in CMOS in standby), I

will

produce a 2% typical error in V

OUT

which may be eliminated

at room temperature by trimming R

. For better accuracy,

choosing R

= 100k reduces this error to 0.17% while

increasing the resistor program current to 12

Reducing Output Noise

In some 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. This is the only method by which noise can be
reduced on the 3 lead MIC2950 and is relatively inefficient, as
increasing the capacitor from 1

F to 220

F only decreases

the noise from 430

V to 160

V rms for a 100kHz bandwidth

at 5V output.

Applications Information

Automotive Applications

The MIC2950/2951 are ideally suited for automotive
applications for a variety of reasons. They will operate over a
wide range of input voltages, have very low dropout voltages
(40mV at light loads), and very low quiescent currents. These
features are necessary for use in battery powered systems,
such as automobiles. They are also "bulletproof" devices; with
the ability to survive both reverse battery (negative transients
up to 20V below ground), and load dump (positive transients
up to 60V) conditions. A wide operating temperature range
with low temperature coefficients is yet another reason to use
these versatile regulators in automotive designs.

External Capacitors

A 1.5

F (or greater) capacitor is required between the

MIC2950/MIC2951 output and ground to prevent oscillations
due to instability. Most types of tantalum or aluminum
electrolytics will be adequate; film types will work, but are
costly and therefore not recommended. Many aluminum
electrolytics have electrolytes that freeze at about 30

C, so

solid tantalums are recommended for operation below 25

The important parameters of the capacitor are an effective
series resistance of about 5

or less and a resonant frequency

above 500kHz. The value of this capacitor may be increased
without limit.

At lower values of output current, less output capacitance is
required for output stability. The capacitor can be reduced to
0.5

F for current below 10mA or 0.15

F for currents below 1

mA. Using the 8-pin 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 150mA load at
1.23V output (Output shorted to Feedback) a 5

F (or greater)

capacitor should be used.

The MIC2950 will remain stable and in regulation with no load
in addition to the internal voltage divider, unlike many other
voltage regulators. This is especially important in CMOS RAM
keep-alive applications. When setting the output voltage of
the MIC2951 version with external resistors, a minimum load
of 1

A is recommended.

A 0.1

F capacitor should be placed from the MIC2950/

MIC2951 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 MIC2951 Feedback terminal (pin 7)
can cause instability. This may especially be a problem when
using high value external resistors to set the output voltage.
Adding a 100pF capacitor between Output and Feedback and
increasing the output capacitor to at least 3.3

F will remedy

this.

Error Detection Comparator Output

A logic low output will be produced by the comparator whenever
the MIC2951 output falls out of regulation by more than
approximately 5%. This figure is the comparator's built-in

MIC2950/2951

Micrel

February 1999

MIC2950/2951

MIC2951

OUT

GND

ERROR

ERROR
OUTPUT

SHUTDOWN
INPUT

100k

OUT

1.2

30V

R 100

3.3µF

1.23V

REF

OUT

REF

= V

x (1 + )

OFF

Noise can be reduced fourfold by a bypass capacitor across
R

, since it reduces the high frequency gain from 4 to unity.

Pick:

870 23

or about 0.01

F. When doing this, the output capacitor must

be increased to 3.3

F to maintain stability. These changes

reduce the output noise from 430

V to 100

V rms for a 100

kHz bandwidth at 5V output. With the bypass capacitor
added, noise no longer scales with output voltage so that
improvements are more dramatic at higher output voltages.

MIC2951

ERROR

GND

OUT

+V IN

ERROR
OUTPUT

SHUTDOWN
INPUT

47k

*SLEEP
INPUT

100pF

2N3906

200k

100k

C-MOS
GATE

+V IN

100k

3.3µF

+V OUT

470 k

OFF

*HIGH INPUT LOWERS V

OUT

TO 2.5V

Typical Applications

870 25

*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40

V TO 400

DEPENDING ON LOAD CURRENT.

MIC2951

OUT

ERROR

GND

+VIN

VIN

OUT

ERROR
OUTPUT

SHUTDOWN
INPUT

OFF

Wide Input Voltage Range Current Limiter

5V Regulator with 2.5V Sleep Function

Figure 1. ERROR Output Timing

Figure 2. Adjustable Regulator

NOTE: PINS 2 AND 6 ARE LEFT OPEN

*SEE APPLICATIONS
INFORMATION

* SEE APPLICATIONS INFORMATION

BYPASS

2 R

· 200 Hz

OUTPUT

VOLTAGE

INPUT

VOLTAGE

ERROR

NOT

VALID

NOT

VALID

1.3V

4.75V

MIC2950/2951

Micrel

MIC2950/2951

February 1999

Low Drift Current Source

5-Volt Current Limiter

* MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV,
DEPENDING ON LOAD CURRENT.

870 27

870 29

MIC2950Z

OUT

GND

+V IN

OUT

5V BUS

1µF

MIC2951

GND

VIN

OUT

SHUTDOWN
INPUT

LOAD

+V = 2

30V

I L

I L=

1.23V

0.1µF

1µF

OFF

Regulator with Early Warning and Auxiliary Output

· EARLY WARNING FLAG ON LOW INPUT VOLTAGE
· MAIN OUTPUT LATCHES OFF AT LOWER INPUT VOLTAGES
· BATTERY BACKUP ON AUXILIARY OUTPUT

OPERATION: REG. #1'S V

OUT

IS PROGRAMMED ONE DIODE DROP ABOVE 5 V.

ITS ERROR FLAG BECOMES ACTIVE WHEN V

5.7 V. WHEN V

DROPS

BELOW 5.3 V, THE ERROR FLAG OF REG. #2 BECOMES ACTIVE AND VIA Q1
LATCHES THE MAIN OUTPUT OFF. WHEN V

AGAIN EXCEEDS 5.7 V REG. #1

IS BACK IN REGULATION AND THE EARLY WARNING SIGNAL RISES,
UNLATCHING REG. #2 VIA D3.

MIC2951

SENSE

ERROR

GND

27k

OUT

+VIN

SENSE

ERROR

GND

OUT

+VIN

MEMORY

V+

D 2

D 1

2.7M

D 3

D 4

330k

RESET

EARLY WARNING

µP

VDO

1µf

MAIN

OUTPUT

1µF

+VIN

3.6V
NICAD

SENSE

ERROR

GND

27k

OUT

+VIN

MIC2951

SENSE

ERROR

GND

OUT

+VIN

MEMORY

V+

D 2

D 1

2.7M

D 3

D 4

330k

RESET

EARLY WARNING

µP

VDO

1µf

MAIN

OUTPUT

1µF

+VIN

3.6V
NICAD

MIC2950/2951

Micrel

MIC2950/2951

February 1999

Low-Battery Disconnect

For values shown, Regulator shuts down when V

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

System Overtemperature Protection Circuit

* Sets disconnect voltage
** Sets disconnect hysteresis

LM34 for 125

F Shutdown

LM35 for 125

C Shutdown

1N457

Schematic Diagram

MIC2951

GND

OUT

+VIN

SENSE

1µF

LM385

1.5k

100k

120k

6V
SEALED
LEAD-
ACID
BATTERY
SOURCE

400k

FOR 5.5V

AUX. SHUTDOWN

INPUT

MIC2951

GND

OUT

+VIN

ERROR

RELAY

EXTERNAL CIRCUIT

PROTECTED FROM

OVER TEMPERATURE

(V+ GOES OFF WHEN

TEMP.> 125

)

10k

PRE-SHUTDOWN FLAG

+VIN

LM34 OR

LM35

TEMP.

SENSOR

8.2k

OFF

FEEDBACK

SENSE

Q15A

OUT

Q24

Q26

R27
182 k

5V TAP

R28
60 k

R18
20k

Q25

Q23

Q22

R15
100 k

R16
30 k

Q29

Q28

R17

R21 8

R17

12 k

Q31

Q30

R23 60 k

SHDN

R24
50 k

R22
150 k

Q21

Q19

C2
40 pF

R14
350
k

Q14

R13

100

Q18

R12

110

Q20

Q15B

R11

20.6

31.4 k

R10

150

27.8 k

Q11

Q12

Q13

140

180

13 k

50 k

20
pF

R11
18
k

20 k

50 k

Q41

R30

Q40

Q34

GND

Q36

Q37

R25
2.8 k

Q38

ERROR

R26
60 k

Q39

DENOTES CONNECTION ON MIC2950 ONLY

Q42

Q16

Q17

50 k

10 k

100 x

MIC2950/2951

Micrel

MIC2950/2951

February 1999

0.008 (0.20)
0.004 (0.10)

0.039 (0.99)
0.035 (0.89)

0.021 (0.53)

0.012 (0.03) R

0.0256 (0.65) TYP

0.012 (0.30) R

MAX

MIN

0.122 (3.10)
0.112 (2.84)

0.120 (3.05)
0.116 (2.95)

0.012 (0.03)

0.007 (0.18)
0.005 (0.13)

0.043 (1.09)
0.038 (0.97)

0.036 (0.90)
0.032 (0.81)

DIMENSIONS:

INCH (MM)

0.199 (5.05)
0.187 (4.74)

8-Lead MSOP (MM)

typ.

0.185 (4.699)
0.175 (4.445)

0.085 (2.159) Diam.

0.500 (12.70) Min.

0.090 (2.286) typ.

0.0155 (0.3937)
0.0145 (0.3683)

Seating Plane

0.025 (0.635) Max
Uncontrolled
Lead Diameter

0.016 (0.406)
0.014 (0.356)

0.105 (2.667)
0.095 (2.413)

0.055 (1.397)
0.045 (1.143)

0.090 (2.286) Radius, typ.

0.145 (3.683)
0.135 (3.429)

0.055 (1.397)
0.045 (1.143)

BOTTOM VIEW

TO-92 (Z)

MICREL INC.

1849 FORTUNE DRIVE

SAN JOSE, CA 95131

USA

TEL

+ 1 (408) 944-0800

FAX

+ 1 (408) 944-0970

WEB

http://www.micrel.com

This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or

other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.

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