MIC2940A/2941A
1.2A Low-Dropout Voltage Regulator
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
408
) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
July 2007
M9999-071307
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
MIC2940A-xx devices are three pin, fixed voltage
regulators. A logic-compatible shutdown input is provided
on the adjustable MIC2941A, which enables the regulator
to be switched on and off.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
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 VPP regulation/switching
• Bar code scanners
• Automotive electronics
• SMPS post-regulator/ DC-to-DC modules
• Voltage reference
• High efficiency linear power supplies
___________________________________________________________________________________________________________
Pin Configur ation
123
12 34 5
12 3
TO-263-3
(MIC2940A-xxBU/WU)
MIC2940A Pinout
1) Input
2) Ground
3) Output
12345
TO-263-5
(MIC2941ABU/WU)
MIC2941A Pinout
1) Adjust
2) Shutdown
3) Ground
4) Input
5) Output
TO-220-3
(MIC2940A-xxBT/WT)
The TAB is Ground on TO-220 and TO-263 packages
TO-220-5
(MIC2941ABT/WT)
Micrel, Inc. MIC2940A/2941A
July 2007
2 M9999-071307
Ordering Information
Part Number Voltage Temperature Rang e Package Lead Finish
MIC2940A-3.3BT 3.3V –40° to +125°C 3-Pin TO-220 Standard
MIC2940A-3.3BU 3.3V –40° to +125°C 3-Pin TO-263 Standard
MIC2940A-3.3WT 3.3V –40° to +125°C 3-Pin TO-220 RoHS Comliant
(1)
MIC2940A-3.3WU 3.3V –40° to +125°C 3-Pin TO-263 RoHS Comliant
(1)
MIC2940A-5.0BT 5V –40° to +125°C 3-Pin TO-220 Standard
MIC2940A-5.0BU 5V –40° to +125°C 3-Pin TO-263 Standard
MIC2940A-5.0WT 5V –40° to +125°C 3-Pin TO-220 RoHS Comliant
(1)
MIC2940A-5.0WU 5V –40° to +125°C 3-Pin TO-263 RoHS Comliant
(1)
MIC2940A-12BT 12V –40° to +125°C 3-Pin TO-220 Standard
MIC2940A-12BU 12V –40° to +125°C 3-Pin TO-263 Standard
MIC2940A-12WT 12V –40° to +125°C 3-Pin TO-220 RoHS Comliant
(1)
MIC2940A-12WU 12V –40° to +125°C 3-Pin TO-263 RoHS Comliant
(1)
MIC2941ABT Adj. –40° to +125°C 5-Pin TO-220 Standard
MIC2941ABU Adj. –40° to +125°C 5-Pin TO-263 Standard
MIC2941AWT Adj. –40° to +125°C 5-Pin TO-220 RoHS Comliant
(1)
MIC2941AWU Adj. –40° to +125°C 5-Pin TO-263 RoHS Comliant
(1)
Note:
1. RoHS compliant with ‘hot-melting solder’ exemption.
Schematic Diagram
Micrel, Inc. MIC2940A/2941A
July 2007
3 M9999-071307
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 sec.)........................ 260°C
Storage Temperature ................................–65°C to +150°C
Operating Junction Temperature ..............–40°C to +125°C
TO-220 (θ
JC
) ........................................................2°C/W
TO-263 (θ
JC
) ........................................................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.
Electrical Characteristics
Limits in standard typeface are for T
J
= 25°C and limits in boldface apply over the full operating temperature range.
Unless otherwise specified, V
IN
= V
OUT
+ 1V, I
L
= 1000mA, C
L
= 10µF. The MIC2941A is programmed to output 5V and
has V
SHUTDOWN
0.6V.
Symbol Parameter Condition Min Typ Max Units
V
O
Output Voltage Accuracy
5 mA ≤ I
L
≤ 1A
–1
–2
–2.5
1
2
2.5
%
%
%
∆V
O
∆T
Output Voltage Temperature
Coefficient
(Note 2) 20 100 ppm/°C
Line Regulation I
O
= 10mA, (V
OUT
+ 1V) ≤ V
IN
≤ 26V 0.06 0.50 %
∆V
O
V
O
Load Regulation I
L
= 5mA to 1.25A
I
L
= 5mA to 1A (Note 3)
0.04
0.16
0.20
%
%
V
IN
– V
O
Dropout Voltage (Note 4) I
L
= 5mA
I
L
= 250mA
I
L
= 1000mA
I
L
= 1250mA
60
200
350
400
150
180
250
320
450
600
600
mV
mV
mV
mV
mV
mV
mV
I
GND
Ground Pin Current (Note 5) I
L
= 5mA
I
L
= 250mA
I
L
= 1000mA
I
L
= 1250mA
240
3
22
35
500
4.5
6
35
45
70
µA
mA
mA
mA
mA
mA
I
GNDDO
Ground Pin Current at Dropout
(Note 5)
V
IN
= 0.5V less than designed V
OUT
(V
OUT
3.3)
I
L
= 5mA
330 600 µA
I
LIMIT
Current Limit V
OUT
= 0V (Note 6) 1.6 3.5 A
∆V
O
∆P
D
Thermal Regulation (Note 7) 0.05 0.2 %/W
e
n
Output Noise Voltage
(10Hz to 100kHz)
I
L
= 100mA
C
L
= 10µF
C
L
= 33µF
400
260
µV
RMS
µV
RMS
Micrel, Inc. MIC2940A/2941A
July 2007
4 M9999-071307
Electrical Characteristics (MIC2941A Only)
Parameter Condition Min Typ Max Units
Reference Voltage
(Note 8)
1.223
1.210
1.204
1.235 1.247
1.260
1.266
V
V
V
Adjust Pin Bias Current 20
40
60
nA
nA
Reference Voltage Temperature Coefficient 20 ppm/°C
Adjust Pin Bias Current Temperature
Coefficient
0.1 nA/°C
Shutdown Input
Input Logic Voltage Low (ON)
High (OFF)
2.0
1.3
0.7
V
V
V
V
SHUTDOWN
= 2.4V 30 50
100
µA
µA
Shutdown Pin Input Current
V
SHUTDOWN
= 26V 450 600
750
µA
µA
Regulator Output Current in Shutdown (Note 10) 3
30
60
µA
µA
Notes:
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
J(MAX)
, the junction-to-ambient thermal resistance, θ
JA
, and the ambient temperature, T
A
. The maximum allowable power dissipation at any ambient
temperature is calculated using: P
(MAX)
= (T
J(MAX)
– T
A
) / θ
JA
. Exceeding the maximum allowable power dissipation will result in excessive die
temperature, and the regulator will go into thermal shutdown.
2. Output voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.
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.
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.
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.
6. The MIC2940A features fold-back current limiting. The short circuit (V
OUT
= 0V) current limit is less than the maximum current with normal output
voltage.
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 V
IN
= 20V (a 4W pulse) for T = 10ms.
8. V
REF
≤ V
OUT
≤ (V
IN
– 1 V), 4.3V ≤ V
IN
26V, 5mA < I
L
≤1.25A, T
J
≤T
J(MAX)
.
9. Circuit of Figure 3 with R1 ≥ 150k Ω. V
SHUTDOWN
≥ 2 V and V
IN
≤ 26 V,V
OUT
= 0.
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.
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.
Micrel, Inc. MIC2940A/2941A
July 2007
5 M9999-071307
Typical Characteristics
0
100
200
300
400
500
0.00 0.25 0.50 0.75 1.00 1.25
DROPOUT VOLTAGE (mV)
OUTPUT CURRENT (A)
Dropout Voltage
vs. Output Current
0
200
400
600
800
1000
-60 -30 0 30 60 90 120 150
DROPOUT VOLTAGE (mV)
TEMPERATURE (°C)
Dropout Voltage
vs. Temperature
I
LOAD
= 1.25A
0
1
2
3
4
5
6
0123456
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Dropout
Characteristics
I
LOAD
=5mA
I
LOAD
= 1.25A
0.1
1
10
40
11 0 100 1000 10000
GROUND CURRENT (mA)
OUTPUT CURRENT (mA)
Ground C urrent
vs. Output Current
10A
0
100
200
300
400
01234567 8
GROUND CURRENT (µA)
SUPPLY VOLTAGE (V)
Ground C urrent
vs. Supply Voltage
FIXED 5V
I
LOAD
=5mA
0
10
20
30
40
50
0246810
GROUND CURRENT (mA)
INPUT VOLTAGE (V)
Ground C urrent
vs. Supply Voltage
FIXED 3.3V DEVICE
I
LOAD
=1.25A
0.00
0.10
0.20
0.30
0.40
-60 -30 0 30 60 90 120 150
GROUND CURRENT (mA)
TEMPERATURE (°C)
Ground C urrent
vs. Temperature
I
LOAD
=5mA
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
-60 -30 0 30 60 90 120 150
GROUND CURRENT (mA)
TEMPERATURE (°C)
Ground Current
vs. Temperature
I
LOAD
=100mA
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
I
LOAD
= 100mA
3.20
3.22
3.24
3.26
3.28
3.30
3.32
3.34
3.36
3.38
3.40
-60 -30 0 30 60 90 120 150
OUTPUT VOLTAGE (V)
TEMPERATURE (°C)
Fixed 3.3V Output Voltage
vs. Temperature
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
-60 -30 0 30 60 90 120 150
CURRENT (A)
TEMPERATURE (°C)
Short Circuit and M aximum
Current vs. Temperat ure
V
OUT
=V
NOMINAL
–0.5V
V
OUT
=0V
FIXED 3.3V
VERSION
3SAMPLES
-200
0
200
400
600
800
1000
-30 -20 -10 0 10 20 30
GROUND CURRENT (µA)
INPUT VOLTAGE (V)
Ground C urrent
vs. Input Voltage
R
LOAD
= 100
Micrel, Inc. MIC2940A/2941A
July 2007
6 M9999-071307
Typical Characteristics (continued)
0
25
50
75
100
125
-60 -30 0 30 60 90 120 150
ENABLE CURRENT (µA)
TEMPERATURE (°C)
MIC29401/2 Shutdown Current
vs. Temperature
V
EN
=5V
V
EN
=2V
-500
-250
0
250
500
750
OUTPUT (mV)
-0.5
0.0
0.5
1.0
1.5
2.0
-5 0510
OUTPUT (A)
TIME (ms)
Load Transient
C
OUT
=10µF
5mA
-200
-100
0
100
200
OUTPUT (mV)
-0.5
0.0
0.5
1.0
1.5
2.0
-5 0510
OUTPUT (A)
TIME (ms)
Load Transient
C
OUT
= 100 µF
5mA
0
10
20
30
40
50
-60 -30 0 30 60 90 120 150
ADJUST PIN CURRENT (nA)
TEMPERATURE (°C)
MIC29402/3 Adjust Pin
Current vs. Temperature
I
LOAD
=5mA
-40
-20
0
20
40
OUTPUT (mV)
4
6
8
10
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
INPUT (V)
TIME (ms)
Line Transient
C
OUT
=10µF
-10
0
10
20
OUTPUT (mV)
4
6
8
10
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
INPUT (V)
TIME (ms)
Line Transient
C
OUT
= 100 µF
0.01
0.1
1
10
1x10
0
10x10
0
100x10
0
1x10
3
10x10
3
100x10
3
1x10
6
OUTPUT IMPEDANCE ( )
FREQUENCY (Hz)
Output Impedance
vs. Frequency
I
LOAD
= 10mA
Micrel, Inc. MIC2940A/2941A
July 2007
7 M9999-071307
Application 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 10mA. 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 (MI C29 41A)
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.
V
OUT
= V
REF
x { 1 + R
1
/R
2
} – |I
FB
| R
1
where V
REF
is the nominal 1.235 reference voltage and
I
FB
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 R
2
, if the regulator
must work with no load (a condition often found in
CMOS in standby), I
FB
will produce a –2% typical error in
V
OUT
which may be eliminated at room temperature by
trimming R
1
. For better accuracy, choosing R
2
= 100kΩ
reduces this error to 0.17% while increasing the resistor
program current to 12µA. Since the MIC2941A typically
draws 100µA at no load with SHUTDOWN open-
circuited, 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
RMS
for a
100kHz bandwidth at 5V output. Noise can be reduced
by a factor of four with the MIC2941A by adding a
bypass capacitor across R
1
. Pick
200HzR2
1
C
1
BYPASS
π
≅
or about 0.01µF. When doing this, the output capacitor
must be increased to 22µF to maintain stability. These
changes reduce the output noise from 430µV to
100µV
RMS
for a 100kHz 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.
NOT *
VALID
NOT *
VALID
OUTPUT
VOLTAGE
4.75V
ERROR
INPUT
VOLTAGE
5V
1.3V
Figure 1. ERROR Output Timing
Micrel, Inc. MIC2940A/2941A
July 2007 8
M9999-071307
Typical Applications
V
IN
+V
IN
V
OUT
V
OUT
= 5V
GND
10µF
+
Figure 2. MIC2940A-5.0 Fixed +5V Regulator
OUT
GND ADJUST
V
VIN
+VIN
VOUT =VIN
* Minimum Input-Output Voltage Ranges from 40mV to 400mV,
depending on Load Current.
Figure 4. MIC2941A Wide Input Voltage Range
Current Limit
IN
OUT
GND ADJUST
SHUTDOWN
V
V
SHUTDOWN
INPUT
IN
+V
OUT
V
1.2V 26V
1
R100
pF
22µF
2
R
1.23V
REF
V
VOUT =V
REF x (1 + )
1
R
2
R
OFF
ON
Figure 3. MIC2941A Adjustable Regu l ator
SHUTDOWN
V
GND
OUT
+VIN
ADJ
SHUTDOWN
INPUT
100pF
2N2222
1%
300k
+5V to +7V
1%
180k
+
10µF
470 k
OFF
ON
5V
3.3V
220k
1%
VCC OUT
Adjust Pin Low = Enable Output. Q1 ON = 3.3V, Q1 OFF = 5.0V.
Figure 5. MIC2941A 5.0V or 3.3V Selectable Regu l ator
with Shutdown
Micrel, Inc. MIC2940A/2941A
July 2007 9
M9999-071307
Package Information
3-Pin TO-220 (T)
3-Pin TO-263 (U)
Micrel, Inc. MIC2940A/2941A
July 2007 10
M9999-071307
5-Pin TO-220 (T)
5-Pin TO-263 (U)
Micrel, Inc. MIC2940A/2941A
July 2007 11
M9999-071307
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2004 Micrel, Incorporated.
