Datasheet MIC2941ABU, MIC2940A-3.3BT, MIC2940A-3.3BU, MIC2940A-5.0BT, MIC2940A-5.0BU Datasheet (MICREL)

MIC2940A/2941A Micrel

MIC2940A/2941A

1.25A Low-Dropout Voltage Regulator
Preliminary Information

General Description

The MIC2940A and MIC2941A are “bulletproof” efficient
voltage regulators with very low dropout voltage (typically
40mV at light loads and 350mV at 1A), and low quiescent
current (240µA typical). The quiescent current of the MIC2940A
increases only slightly in dropout, thus prolonging battery life.
Key MIC2940A features include protection against reversed
battery, fold-back current limiting, and automotive “load dump”
protection (60V positive transient).

The MIC2940 is available in both fixed voltage (3.3V, 5V, and
12V) and adjustable voltage configurations. The MIC2940A­xx devices are three pin fixed voltage regulators. A logic­compatible shutdown input is provided on the adjustable
MIC2941A, which enables the regulator to be switched on and
off.

Features

• High output voltage accuracy

• Guaranteed 1.25A 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

• Logic-controlled electronic shutdown

• Output programmable from 1.24V to 26V(MIC2941A)

• 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

• Voltage Reference

• High Efficiency Linear Power Supplies

Regulation/Switching

PP

Pin Configuration

12 3
Front View

GROUNDINPUT

TO-220 Package

(MIC2940A-xxBT)

OUTPUT

INPUT GROUND OUTPUT

TO-263 Package

(MIC2940A-xxBU)

12345

TO-263-5 Package

(MIC2941ABU)

MIC2941A Pinout

1) Adjust

2) Shutdown

3) Ground

4) Input

5) Output

12345

TO-220-5 Package

(MIC2941ABT)

The Tab is Ground on TO-220 and TO-263 packages

June 1999 1 MIC2940A/2941A

MIC2940A/2941A Micrel

Absolute Maximum Ratings

If Military/Aerospace specified devices

Ordering Information

Part Number Voltage Temperature Range* Package

MIC2940A-3.3BT 3.3 –40°C to +125°C TO-220
MIC2940A-3.3BU 3.3 –40°C to +125°C TO-263
MIC2940A-5.0BT 5.0 –40°C to +125°C TO-220
MIC2940A-5.0BU 5.0 –40°C to +125°C TO-263
MIC2940A-12BT 12 –40°C to +125°C TO-220
MIC2940A-12BU 12 –40°C to +125°C TO-263
MIC2941ABT Adj –40°C to +125°C TO-220-5
MIC2941ABU Adj –40°C to +125°C TO-263-5

* Junction temperatures

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 °C/W

TO-263 θJC........................................................ 2 °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.

Schematic Diagram

Q6

R1

20 kΩ

Q42

R2

50 kΩ

Q40

Q41

R30

30

kΩ

50 kΩ

10 kΩ

IN

Q15A

Q9

R11
18
kΩ

Q1

10

R5

180

kΩ

R3

50 kΩ

ERROR

C1
20
pF

Q13

R4

13 kΩ

140

Q4Q3

R6
kΩ

Q12

Q38

Q39

Q5

Q2

31.4 kΩ

27.8 kΩ

Q37

R11

20.6
kΩ

R8

R9

R26
60 kΩ

Q7

Q11

Q36

R10
150

Q8

Q20

kΩ

R12
110

kΩ

Q34

R25

2.8 kΩ

Q16

R13
100

Q18

GND

kΩ

Q15B

R22
150 kΩ

Q17

C2
40 pF

R14
350
kΩ

FEEDBACK

R18
20kΩ

Q26

Q25

R17

Q14

12 kΩ

Q22

Q21

R15
100 kΩ

R16

R17

30 kΩ

Q29

Q19

Q31

Q30

DENOTES CONNECTION ON FIXED
VOLTAGE VERSIONS ONLY

Q28

R24
50 kΩ

10 Ω

R21 8 Ω

R23 60 kΩ

Q24

OUT

SENSE

R27

V TAP

R28

Q23

SHDN

MIC2940A/2941A 2 June 1999

MIC2940A/2941A 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
V

SHUTDOWN

≤ 0.6V.

Symbol Parameter Conditions Min Typical Max Units

V

O

Output Voltage –1 1 %
Accuracy –2 2

∆V

O

Output Voltage (Note 2) 20 100 ppm/°C

∆T Temperature Coef.
∆V

O

V

O

∆V

O

V

O

VIN – V

O

Line Regulation VIN = V

Load Regulation IL = 5mA to 1.25A 0.04 0.16 %

Dropout Voltage IL = 5mA 60 150 mV
(Note 4) 180

+ 1V, IL = 1000mA, CL = 10µF. The MIC2941A is programmed to output 5V and has

OUT

5 mA ≤ IL ≤ 1A –2.5 2.5

+ 1V to 26V 0.03 0.10 %

OUT

0.40

IL = 5mA to 1A 0.20 %
(Note 3)

IL = 250mA 200 250

320

IL = 1000mA 350 450

600

IL = 1250mA 400 600

I

GND

I

GNDDO

I

LIMIT

∆V
∆P

e

n

Ground Pin Current IL = 5mA 240 350 µA
(Note 5) 500

IL = 250mA 3 4.5 mA

6

IL = 1000mA 22 35

45

IL = 1250mA 35 70

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

≥ 3.3V)

OUT

OUT

330 600 µA

(Note 5) IL = 5mA
Current Limit V

= 0V 1.6 2.4 A

OUT

(Note 6) 3

O
D

Thermal Regulation (Note 7) 0.05 0.2 %/W

Output Noise CL = 10µF 400 µV RMS
Voltage
(10Hz to 100kHz) CL = 33µF 260
IL = 100mA

June 1999 3 MIC2940A/2941A

MIC2940A/2941A Micrel

Electrical Characteristics (MIC2941A Only)

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 20 ppm/°C

Temperature
Coefficient

Adjust Pin Bias 0.1 nA/°C
Current Temperature
Coefficient

Shutdown Input

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) 330µA
Current in Shutdown 60

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.

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

J (MAX)

(MAX)

= (T

J(MAX)

– TA) / θ

Exceeding the maximum allowable

JA.

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.
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 MIC2940A features fold-back current limiting. The short circuit (V
normal output voltage.

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

OUT

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: Circuit of Figure 3 with R1 ≥ 150kΩ. V

REF

≤ V

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

OUT

SHUTDOWN

≤ 1.25A, T

L

J

≤ T

J MAX.

≥ 2 V and VIN ≤ 26 V,V

OUT

= 0.
Note 10: 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 11: Maximum positive supply voltage of 60 V must be of limited duration (< 100 ms) and duty cycle ( ≤ 1%). The maximum continuous
supply voltage is 26V.

MIC2940A/2941A 4 June 1999

MIC2940A/2941A Micrel

0

100

200

300

400

012345678

GROUND CURRENT (µA)

SUPPLY VOLTAGE (V)

0

10

20

30

40

50

-60 -30 0 30 60 90 120 150

GROUND CURRENT (mA)

TEMPERATURE (°C)

Ground Current

vs. Temperature

I

LOAD

= 1.25A

Typical Characteristics

Dropout Voltage

vs. Output Current

500

400

300

200

100

DROPOUT VOLTAGE (mV)

0

0.00 0.25 0.50 0.75 1.00 1.25

OUTPUT CURRENT (A)

Ground Current

vs. Output Current

40

10

1

GROUND CURRENT (mA)

0.1
1 10 100 1000 10000

OUTPUT CURRENT (mA)

10A

Dropout Voltage

1000

800

600

400

200

DROPOUT VOLTAGE (mV)

vs. Temperature

I

= 1.25A

LOAD

0

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

Ground Current

vs. Supply Voltage

FIXED 5V

= 5mA

I

LOAD

Dropout

Characteristics

6

5

4

I

= 5mA

LOAD

3

2

1

OUTPUT VOLTAGE (V)

0

0123456

I

= 1.25A

LOAD

INPUT VOLTAGE (V)

Ground Current

vs. Supply Voltage

50

40

30

20

10

GROUND CURRENT (mA)

0

0246810

FIXED 3.3V DEVICE

= 1.25A

I

LOAD

INPUT VOLTAGE (V)

GROUND CURRENT (mA)

June 1999 5 MIC2940A/2941A

OUTPUT VOLTAGE (V)

Ground Current

0.40

0.30

0.20

0.10

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

2.0

1.8

V

= V

OUT

1.6

1.4

1.2

1.0

0.8

CURRENT (A)

0.6

0.4

0.2

0.0

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

– 0.5V

NOMINAL

V

= 0V

OUT

FIXED 3.3V

VERSION

3 SAMPLES

Ground Current

1000

800

600

400

200

GROUND CURRENT (µA)

-200

vs. Input Voltage

R

= 100Ω

LOAD

0

-30 -20 -10 0 10 20 30

INPUT VOLTAGE (V)

MIC2940A/2941A Micrel

MIC29401/2 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)

MIC29402/3 Adjust Pin

Current vs. Temperature

50

40

30

20

I

10

ADJUST PIN CURRENT (nA)

0

-60 -30 0 30 60 90 120 150

= 5mA

LOAD

TEMPERATURE (°C)

750
500
250

-250

∆ OUTPUT (mV)

2.0

-500

1.5

1.0

0.5

0.0

OUTPUT (A)

-0.5

-20

∆ OUTPUT (mV)

-40

INPUT (V)

Load Transient

C

= 10 µF

OUT

0

5mA

-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

TIME (ms)

200
100

Load Transient

C

= 100 µF

OUT

0

-100

∆ OUTPUT (mV)

2.0

-200

1.5

1.0
5mA

0.5

0.0

OUTPUT (A)

-0.5

-5 0510

20

10

TIME (ms)

Line Transient

C

= 100 µF

OUT

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)

0.1

0.01

Output Impedance

1

0

1x10

vs. Frequency

0

10x10

FREQUENCY (Hz)

10

0

100x10

I

LOAD

3

1x10

= 10mA

3

10x10

3

100x10

6

1x10

MIC2940A/2941A 6 June 1999

MIC2940A/2941A Micrel

Applications Information

External Capacitors

A 10µF (or greater) capacitor is required between the
MIC2940A 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

3.3µF for current below 100mA or 2.2µF for currents below 10
mA. Adjusting the MIC2941A 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 1.25A load at

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

The MIC2940A will remain stable and in regulation with load
currents ranging from 5mA on up to the full 1.25A rating. The
external resistors of the MIC2941A version may be scaled to
draw this minimum load current.

A 0.22µF capacitor should be placed from the MIC2940A
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.

Programming the Output Voltage (MIC2941A)

The MIC2941A may be 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.

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 1 µF to 220 µF only decreases the noise from
430µV to 160µV

for a 100kHz bandwidth at 5V output.

RMS

Noise can be reduced by a factor of four with the MIC2941A
by adding 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 0.01 µF. When doing this, the output capacitor must
be increased to 22 µF to maintain stability. These changes
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 improvements
are more dramatic at higher output voltages.

Automotive Applications

The MIC2940A 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 (240µA 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.

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

OUTPUT

VOLTAGE

4.75V

the Adjust pin bias current, nominally 20nA. The minimum
recommended load current of 1 µA 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 = 100kΩ reduces this error to 0.17% while
increasing the resistor program current to 12 µA. Since the
MIC2941A typically draws 100 µA at no load with SHUTDOWN
open-circuited, this is a negligible addition.

NOT

ERROR

INPUT

VOLTAGE

* SEE APPLICATIONS INFORMATION

*

VALID

5V

1.3V

Figure 1. ERROR Output Timing

NOT

VALID

*

June 1999 7 MIC2940A/2941A

MIC2940A/2941A Micrel

Typical Applications

+V

IN

V

+V

GND

IN

IN

V

OUT

V

IN

V

*V

≈5V

OUT

V

= 5V

OUT

+

10µF

SHUTDOWN
INPUT

ON

SHUTDOWN

OFF

GND ADJUST

OUT

1.23V

V

R

OUT

1.2V

100

1

pF

26V

22µF

R

2

V

OUT

= V

x (1 + )

REF

V

R
R

REF

1

2

Figure 2. MIC2940A-5.0 Fixed +5V Regulator Figure 3. MIC2941A 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

3.3V

5V

Input Output

0 3.3V
1 5.0V

470 kΩ

220kΩ
1%

2N2222

180kΩ

1%

VCC OUT

+

10µF

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

Figure 4. MIC2941A Wide Input Voltage Range Current Limiter

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

Figure 5. MIC2941A 5.0V or 3.3V Selectable Regulator with
Shutdown.

MIC2940A/2941A 8 June 1999