Datasheet MIC29371-3.3BT, MIC29371-12BT, MIC2937A-12BU, MIC2937A-3.3BT, MIC2937A-3.3BU Datasheet (MICREL)

MIC2937A/29371/29372 Micrel

MIC2937A/29371/29372

750mA Low-Dropout Voltage Regulator

General Description

The MIC2937A family are “bulletproof” efficient voltage
regulators with very low dropout voltage (typically 40mV at
light loads and 300mV at 500mA), and very low quiescent
current (160µA typical). The quiescent current of the MIC2937A
increases only slightly in dropout, thus prolonging battery life.
Key MIC2937A features include protection against reversed
battery, fold-back current limiting, and automotive “load dump”
protection (60V positive transient).

The MIC2937 is available in several configurations. The
MIC2937A-xx devices are three pin fixed voltage regulators
with 3.3V, 5V, and 12V outputs available. The MIC29371 is a
fixed regulator offering logic compatible ON/OFF switching
input and an error flag output. This flag may also be used as
a power-on reset signal. A logic-compatible shutdown input is
provided on the adjustable MIC29372, which enables the
regulator to be switched on and off.

Features

• High output voltage accuracy

• Guaranteed 750mA output

• Low quiescent current

• Low dropout voltage

• Extremely tight load and line regulation

• Very low temperature coefficient

• Current and thermal limiting

• Input can withstand –20V reverse battery and +60V
positive transients

• Error flag warns of output dropout

• Logic-controlled electronic shutdown

• Output programmable from 1.24V to 26V(MIC29372)

• Available in TO-220, TO-263, TO-220-5, and TO-263-5
packages.

Applications

• Battery Powered Equipment

• Cellular Telephones

• Laptop, Notebook, and Palmtop Computers

• PCMCIA VCC and V

• Bar Code Scanners

• Automotive Electronics

• SMPS Post-Regulator/ DC to DC Modules

• High Efficiency Linear Power Supplies

Regulation/Switching

PP

Pin Configuration

GROUND

TO-263 Package

(MIC2937A-xxBU)

Five Lead Package Pin Functions:

MIC29371 MIC29372

1) Error Adjust

2) Input Shutdown

3) Ground Ground

4) Output Input

5) Shutdown Output

OUTPUTINPUT

The TAB is Ground on the TO-220 and TO-263 packages.

12345

TO-263-5 Package

(MIC29371/29372BU)

12 3
Front View

GROUND OUTPUTINPUT

TO-220 Package

(MIC2937A-xxBT)

12345

TO-220-5 Package

(MIC29371/29372BT)

3-18 October 1999

MIC2937A/29371/29372 Micrel

Ordering Information

Part Number Voltage Temperature Range* Package

MIC2937A-3.3BU 3.3 –40°C to +125°C TO-263-3
MIC2937A-3.3BT 3.3 –40°C to +125°C TO-220
MIC2937A-5.0BU 5.0 –40°C to +125°C TO-263-3
MIC2937A-5.0BT 5.0 –40°C to +125°C TO-220
MIC2937A-12BU 12 –40°C to +125°C TO-263-3
MIC2937A-12BT 12 –40°C to +125°C TO-220
MIC29371-3.3BT 3.3 –40°C to +125°C TO-220-5
MIC29371-3.3BU 3.3 –40°C to +125°C TO-263-5
MIC29371-5.0BT 5.0 –40°C to +125°C TO-220-5
MIC29371-5.0BU 5.0 –40°C to +125°C TO-263-5
MIC29371-12BT 12 –40°C to +125°C TO-220-5
MIC29371-12BU 12 –40°C to +125°C TO-263-5
MIC29372BT Adj –40°C to +125°C TO-220-5
MIC29372BU Adj –40°C to +125°C TO-263-5

Absolute Maximum Ratings

If Military/Aerospace specified devices
are required, contact your local Micrel
representative/distributor for availability
and specifications.

Power Dissipation (Note 1) .............. Internally Limited

Lead Temperature (Soldering, 5 seconds) ........ 260°C

Storage Temperature Range ............ –65°C to +150°C

Operating Junction Temperature Range

................................................. –40°C to +125°C

TO-220 θJC...................................................... 2.5°C/W

TO-263 θJC...................................................... 2.5°C/W

Input Supply Voltage ...............................–20V to +60V

Operating Input Supply Voltage ...................2V† to 26V

Adjust Input Voltage (Notes 9 and 10)

......................................................–1.5V to +26V

Shutdown Input Voltage .........................–0.3V to +30V

Error Comparator Output Voltage .......... –0.3V to +30V

†

Across the full operating temperature, the minimum
input voltage range for full output current is 4.3V to 26V.
Output will remain in-regulation at lower output voltages
and low current loads down to an input of 2V at 25°C.

* Junction temperatures

October 1999 19 MIC2937A/29371/29372

MIC2937A/29371/29372 Micrel

Electrical Characteristics

Limits in standard typeface are for TJ = 25°C and limits in boldface apply over the full operating temperature range.
Unless otherwise specified, VIN = V
and V

SHUTDOWN

≤ 0.6V (MIC29371-xx and MIC29372 only).

Symbol Parameter Conditions Min Typical Max Units

V

O

Output Voltage Variation from factory trimmed V
Accuracy –2 2

∆V

O

Output Voltage (Note 2) 20 100 ppm/°C

∆T Temperature Coef. Output voltage > 10V 80 350
∆V

V
∆V
V

O

O

O

O

Line Regulation VIN = V

Load Regulation IL = 5 to 500mA 0.04 0.16 %

+ 1V, IL = 5mA, CL = 10µF. The MIC29372 are programmed for a 5V output voltage,

OUT

OUT

–1 1 %

5mA ≤ IL ≤ 500mA –2.5 2.5
MIC2937A-12 and 29371-12 only: –1.5 1.5

–3 3

5mA ≤ IL ≤ 500mA –4 4

+ 1V to 26V 0.03 0.10 %

OUT

0.40

(Note 3) 0.30

VIN – V

I

GND

I

GNDDO

I

LIMIT

∆V

O

∆P

D

e

n

O

Dropout Voltage IL = 5mA 80 150 mV
(Note 4) 180

IL = 100mA 200

Output voltage > 10V 240

IL = 500mA 300

Output voltage > 10V 420

IL = 750mA 370 600

750

Ground Pin Current IL = 5mA 160 250 µA
(Note 5) 300

IL = 100mA 1 2.5 mA

3

IL = 500mA 8 13

16

IL = 750mA 15 25

Ground Pin VIN = 0.5V less than designed V
Current at Dropout (V

≥ 3.3V)

OUT

OUT

200 500 µA

(Note 5) IO = 5mA
Current Limit V

= 0V 1.1 1.5 A

OUT

(Note 6) 2

Thermal Regulation (Note 7) 0.05 0.2 %/W

Output Noise CL = 10µF 400 µV RMS
Voltage
(10Hz to 100kHz) CL = 100µF 260
IL = 100mA

MIC2937A/29371/29372 20 October 1999

MIC2937A/29371/29372 Micrel

Electrical Characteristics (Continued)

MIC29372

Parameter Conditions Min Typical Max Units

Reference Voltage 1.223 1.235 1.247 V

1.210 1.260 V max
Reference Voltage (Note 8) 1.204 1.266 V
Adjust Pin 20 40 nA

Bias Current 60
Reference Voltage (Note 7) 20 ppm/°C

Temperature
Coefficient

Adjust Pin Bias 0.1 nA/°C
Current Temperature
Coefficient

Error Comparator

Output Leakage V
Current 2.00

Output Low V
Voltage I

MIC29371

= 26V 0.01 1.00 µA

OH

= 4.5V 150 250 mV

IN

= 250µA 400

OL

Upper Threshold (Note 9) 40 60 mV
Voltage 25

Lower Threshold (Note 9) 75 95 mV
Voltage 140

Hysteresis (Note 9) 15 mV

Shutdown Input

MIC29371/MIC29372

Input Logic Voltage 1.3 V

Low (ON) 0.7

High (OFF) 2.0

Shutdown Pin V

SHUTDOWN

= 2.4V 30 50 µA

Input Current 100

V

SHUTDOWN

= 26V 450 600 µA

750

Regulator Output (Note 10) 310µA
Current in Shutdown 20

October 1999 21 MIC2937A/29371/29372

MIC2937A/29371/29372 Micrel

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. The maximum allowable power dissipation is a function of the
maximum junction temperature, T
allowable power dissipation at any ambient temperature is calculated using: P
power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown.

Note 2: Output voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.
Note 3: Regulation is measured at constant junction temperature using low duty cycle pulse testing. Changes in output voltage due to

heating effects are covered by the thermal regulation specification.
Note 4: 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 low values of programmed output voltage, the minimum input supply voltage of 4.3V over temperature must
be taken into account. The MIC2937A operates down to 2V of input at reduced output current at 25°C.
Note 5: Ground pin current is the regulator quiescent current. The total current drawn from the source is the sum of the load current plus
the ground pin current.
Note 6: The MIC2937A family features fold-back current limiting. The short circuit (V
with normal output voltage.
Note 7: 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 200mA load pulse at VIN = 20V (a 4W pulse) for T = 10ms.

Note 8: V
Note 9: Comparator thresholds are expressed in terms of a voltage differential at the Adjust terminal below the nominal reference voltage

REF

≤ V

≤ (VIN – 1 V), 4.3V ≤ VIN ≤ 26V, 5mA < I

OUT

measured at 6V input (for a 5V regulator). To express these thresholds in terms of output voltage change, multiply by the error amplifier gain
= V

/V

OUT

drops by 95 mV x 5V/1.235 V = 384 mV. Thresholds remain constant as a percent of V

= (R1 + R2)/R2. For example, at a programmed output voltage of 5V, the Error output is guaranteed to go low when the output

REF

occurring at typically 5% below nominal, 7.7% guaranteed.

Note 10: Circuit of Figure 3 with R1 ≥ 150kΩ. V
Note 11: 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 12: Maximum positive supply voltage of 60V must be of limited duration (< 100ms) and duty cycle ( ≤ 1%). The maximum continuous
supply voltage is 26V.

, the junction-to-ambient thermal resistance, θJA, and the ambient temperature, TA. The maximum

J (MAX)

≤ 750 mA, T

L

J

(MAX)

≤ T

= (T

– TA) / θ

J(MAX)

= 0V) current limit is less than the maximum current

OUT

Exceeding the maximum allowable

JA.

J MAX.

OUT as VOUT is varied, with the dropout warning

SHUTDOWN

≥ 2V and VIN ≤ 26V,V

OUT

= 0.

Schematic Diagram

50 kΩ

10 kΩ

IN

Q15A

R11

Q4Q3

18
kΩ

Q6

Q1

10

R1

20 kΩ

Q42

R2

Q40

50 kΩ

Q41

R30

30

kΩ

50 kΩ

R3

R5

180

kΩ

ERROR

C1
20
pF

Q13

13 kΩ

Q5

R11

20.6
kΩ

Q2

R8

31.4 kΩ

R6

R9

140

27.8 kΩ

kΩ

Q12

R4

Q37

Q38

R26
60 kΩ

Q39

Q7

Q11

Q36

Q9

Q8

R25

2.8 kΩ

Q34

Q20

R12
110

kΩ

R10
150

kΩ

Q18

Q16

R13
100

kΩ

GND

R22
150 kΩ

Q15B

Q17

C2
40 pF

R14
350
kΩ

FEEDBACK

Q25

R17

Q14

12 kΩ

Q21

Q19

Q31

Q30

DENOTES CONNECTION ON
MIC2937A-xx AND MIC29371-xx
VERSIONS ONLY

Q22

R15
100 kΩ

R16
30 kΩ

Q29

Q28

R21 8 Ω

R23 60 kΩ

R24
50 kΩ

R18
20kΩ

Q26

10 Ω

Q24

OUT

SENSE

R27

V TAP

R28

Q23

R17

SHDN

MIC2937A/29371/29372 22 October 1999

MIC2937A/29371/29372 Micrel

0

50

100

150

200

012345678

GROUND CURRENT (µA)

SUPPLY VOLTAGE (V)

0

5

10

15

20

25

30

-60 -30 0 30 60 90 120 150

GROUND CURRENT (mA)

TEMPERATURE (°C)

Ground Current

vs. Temperature

I

LOAD

= 750mA

Typical Characteristics

Dropout Voltage

vs. Output Current

500

400

300

200

100

DROPOUT VOLTAGE (mV)

0

0 200 400 600 800

OUTPUT CURRENT (mA)

Ground Current

vs. Output Current

30

10

1

GROUND CURRENT (mA)

0.1
1 10 100 1000

OUTPUT CURRENT (mA)

Dropout Voltage

700
600
500
400
300
200
100

DROPOUT VOLTAGE (mV)

vs. Temperature

I

= 750mA

LOAD

0

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

Ground Current

vs. Supply Voltage

FIXED 5V VERSION

= 5mA

I

LOAD

Dropout

Characteristics

6

5

4

I

= 5mA

LOAD

3

2

1

OUTPUT VOLTAGE (V)

0

0123456

I

= 750mA

LOAD

INPUT VOLTAGE (V)

Ground Current

vs. Supply Voltage

30

25

20

15

10

5

GROUND CURRENT (mA)

0

0246810

FIXED 5V

= 750mA

I

LOAD

INPUT VOLTAGE (V)

GROUND CURRENT (mA)

October 1999 23 MIC2937A/29371/29372

OUTPUT VOLTAGE (V)

Ground Current

0.25

0.20

0.15

0.10

0.05

0.00

vs. Temperature

I

= 5mA

LOAD

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

Fixed 3.3V Output Voltage

3.40

3.38

3.36

3.34

3.32

3.30

3.28

3.26

3.24

3.22

3.20

vs. Temperature

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

Ground Current

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

GROUND CURRENT (mA)

0.2

0.0

vs. Temperature

I

= 100mA

LOAD

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

Short Circuit and Maximum

Current vs. Temperature

1.4
V

= V

OUT

1.2

1.0

0.8

0.6

CURRENT (A)

0.4

0.2

0.0

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

NOMINAL

V

= 0V

OUT

FIXED 5V
VERSION

– 0.5V

Ground Current

500

400

300

200

100

GROUND CURRENT (µA)

-100

vs. Input Voltage

R

= 100Ω

LOAD

0

-30 -20 -10 0 10 20 30

INPUT VOLTAGE (V)

MIC2937A/29371/29372 Micrel

MIC29371/2 Shutdown Current

125

vs. Temperaure

100

VEN = 5V

75

50

VEN = 2V

25

ENABLE CURRENT (µA)

0

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

MIC29372/3 Adjust Pin

Current vs. Temperature

50

40

30

20

I

10

ADJUST PIN CURRENT (nA)

0

-60 -30 0 30 60 90 120 150

= 1mA

LOAD

TEMPERATURE (°C)

300
150

-150

∆ OUTPUT (mV)

1000

-300

750
500
250

OUTPUT (mA)

-250

-20

∆ OUTPUT (mV)

-40

INPUT (V)

Load Transient

C

= 10 µF

OUT

0

5mA

0

-5 0510

40
20

0

10

8

6

4

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

TIME (ms)

Line Transient

C

= 10 µF

OUT

= 5mA

I

L

TIME (ms)

200
100

Load Transeint

C

= 100 µF

OUT

0

-100

∆ OUTPUT (mV)

1000

-200

750
500

5mA

250

0

OUTPUT (mA)

-250

-5 0510

20

10

TIME (ms)

Line Transient

C

= 100 µF

OUT

= 5mA

I

L

0

∆ OUTPUT (mV)

10

-10

8

6

INPUT (V)

4

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

TIME (ms)

OUTPUT IMPEDANCE (Ω)

0.01

Output Impedance

10

1

0.1

0

0

1x10

vs. Frequency

I

= 10mA

LOAD

0

3

100x10

1x10

10x10

FREQUENCY (Hz)

3

10x10

3

100x10

6

1x10

MIC2937A/29371/29372 24 October 1999

MIC2937A/29371/29372 Micrel

Applications Information

External Capacitors

A 10µF (or greater) capacitor is required between the
MIC2937A 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°C. The important
parameters of the capacitor are an effective series resistance
of about 5Ω 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

0.5µF for current below 10mA or 0.15µF for currents below
1 mA. Adjusting the MIC29372 to voltages below 5V runs the
error amplifier at lower gains so that more output capacitance
is needed. For the worst-case situation of a 750mA load at

1.23V output (Output shorted to Adjust) a 22µF (or greater)
capacitor should be used.

The MIC2937A/29371 will remain in regulation with a minimum
load of 5mA. When setting the output voltage of the MIC29372
version with external resistors, the current through these
resistors may be included as a portion of the minimum load.

A 0.1µF capacitor should be placed from the 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.

Error Detection Comparator Output (MIC29371)

A logic low output will be produced by the comparator whenever
the MIC29371 output falls out of regulation by more than
approximately 5%. This figure is the comparator’s built-in
offset of about 75mV 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 MIC29371. 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,extremely high input voltage, current limiting, or thermal
limiting.

Figure 1 is a timing diagram depicting the ERROR signal and
the regulated output voltage as the MIC29371 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
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
(approximately 4.75V) does not vary with load.

= 4.75). Since the MIC29371’s dropout

OUT

The error comparator has an NPN open-collector output
which requires an external pull-up resistor. Depending on
system requirements, this resistor may be returned to the 5V
output or some other supply voltage. In determining a value
for this resistor, note that while the output is rated to sink
250µA, 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 (MIC29372)

The MIC29372 may programmed for any output voltage
between its 1.235V reference and its 26V maximum rating. An
external pair of resistors is required, as shown in Figure 3.

The complete equation for the output voltage is
V
where V

OUT

= V

REF

x { 1 + R1/R2 } – |I

REF

FB

| R

1

is the nominal 1.235 reference voltage and IFB is
the Adjust pin bias current, nominally 20nA. The minimum
recommended load current of 1µA forces an upper limit of

1.2MΩ 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

which may be eliminated

OUT

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 12µA. Since the MIC29372
typically draws 100µA at no load with SHUTDOWN open­circuited, this is a negligible addition.

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. This is relatively inefficient, as increasing the
capacitor from 1µF to 220µF only decreases the noise from
430µV to 160µV
Noise can be reduced by a factor of four with the adjustable

OUTPUT

VOLTAGE

ERROR

INPUT

VOLTAGE

for a 100kHz bandwidth at 5V output.

RMS

4.75V

NOT

VALID

*

5V

1.3V

NOT

VALID

*

* SEE APPLICATIONS INFORMATION

Figure 1. ERROR Output Timing

October 1999 25 MIC2937A/29371/29372

MIC2937A/29371/29372 Micrel

regulators with a bypass capacitor across R1, since it reduces
the high frequency gain from 4 to unity. Pick

C

BYPASS

≅

1

π

2R

1

• 200 Hz

or about 0.01µF. When doing this, the output capacitor must
be increased to 10µF to maintain stability. These changes
reduce the output noise from 430µV to 100µV

for a 100

RMS

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.

Typical Applications

V

IN

+V

IN

V

OUT

*V

OUT

≈5V

V

OUT

= 5V

Automotive Applications

The MIC2937A is ideally suited for automotive applications
for a variety of reasons. It will operate over a wide range of
input voltages with very low dropout voltages (40mV at light
loads), and very low quiescent currents (100µA typical).
These features are necessary for use in battery powered
systems, such as automobiles. It is a “bulletproof” device 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.

V

IN

V

OUT

V

OUT

1.2V

26V

GND

+

10µF

SHUTDOWN
INPUT

ON

SHUTDOWN

OFF

GND ADJUST

R .01

1

µF

1.23V
R

2

V

OUT

= V

x (1 + )

REF

V

R
R

REF

1
2

Figure 2. MIC2937A-5.0 Fixed +5V Regulator Figure 3. MIC29372 Adjustable Regulator

+5V to +7V

+V

IN

+V

GND

IN

V

ADJUST

OUT

100pF

300kΩ

1%

V

IN

V

OUT

V

OUT

≈ V

IN

SHUTDOWN
INPUT

ON

SHUTDOWN

OFF

GND ADJUST

10µF

VCC OUT

+

10µF

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

Figure 4. MIC29372 Wide Input Voltage Range Current Limiter

5V

3.3V
Input Output

0 3.3V
1 5.0V

SHUTDOWN PIN LOW= ENABLE OUTPUT. Q1 ON = 3.3V, Q1 OFF = 5.0V.

470 kΩ

220kΩ
1%

2N2222

Figure 5. MIC29372 5.0V or 3.3V Selectable Regulator with

180kΩ

1%

Shutdown.

MIC2937A/29371/29372 26 October 1999