MIC2940A/2941A
Micrel
June 1999
1
MIC2940A/2941A
MIC2940A/2941A
1.25A Low-Dropout Voltage Regulator
Preliminary Information
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 V
CC
and V
PP
Regulation/Switching
Bar Code Scanners
Automotive Electronics
SMPS Post-Regulator/ DC to DC Modules
Voltage Reference
High Efficiency Linear Power Supplies
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 (240
A 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.
1
2 3 4 5
TO-220-5 Package
(MIC2941ABT)
TO-263-5 Package
(MIC2941ABU)
1
2 3 4 5
1
2
3
Front View
TO-220 Package
(MIC2940A-xxBT)
GROUND
INPUT
OUTPUT
INPUT GROUND OUTPUT
TO-263 Package
(MIC2940A-xxBU)
Pin Configuration
MIC2941A Pinout
1)
Adjust
2)
Shutdown
3)
Ground
4)
Input
5)
Output
The Tab is Ground on TO-220 and TO-263 packages
MIC2940A/2941A
Micrel
MIC2940A/2941A
2
June 1999
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
JC
........................................................ 2
C/W
TO-263
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.
FEEDBACK
SENSE
Q15A
OUT
Q24
Q26
R27
V TAP
R28
R18
20k
Q25
Q23
Q22
R15
100 k
R16
30 k
Q29
Q28
R17
10
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
k
Q18
R12
110
k
Q20
Q9
Q15B
Q8
Q7
R11
20.6
k
Q5
R8
31.4 k
R10
150
k
R9
27.8 k
Q11
Q12
Q13
R6
140
k
R5
180
k
R4
13 k
R3
50 k
Q2
C1
20
pF
Q4
Q3
R11
18
k
Q6
Q1
10
R1
20 k
R2
50 k
Q41
R30
30
k
Q40
Q34
GND
Q36
Q37
R25
2.8 k
Q38
ERROR
R26
60 k
Q39
DENOTES CONNECTION ON FIXED
VOLTAGE VERSIONS ONLY
Q42
Q16
Q17
50 k
10 k
IN
Schematic Diagram
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
MIC2940A/2941A
Micrel
June 1999
3
MIC2940A/2941A
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
= 10
F. The MIC2941A is programmed to output 5V and has
V
SHUTDOWN
0.6V.
Symbol
Parameter
Conditions
Min
Typical
Max
Units
V
O
Output Voltage
1
1
%
Accuracy
2
2
5 mA
I
L
1A
2.5
2.5
V
O
Output Voltage
(Note 2)
20
100
ppm/
C
T
Temperature Coef.
V
O
Line Regulation
V
IN
= V
OUT
+ 1V to 26V
0.03
0.10
%
V
O
0.40
V
O
Load Regulation
I
L
= 5mA to 1.25A
0.04
0.16
%
V
O
I
L
= 5mA to 1A
0.20
%
(Note 3)
V
IN
V
O
Dropout Voltage
I
L
= 5mA
60
150
mV
(Note 4)
180
I
L
= 250mA
200
250
320
I
L
= 1000mA
350
450
600
I
L
= 1250mA
400
600
I
GND
Ground Pin Current
I
L
= 5mA
240
350
A
(Note 5)
500
I
L
= 250mA
3
4.5
mA
6
I
L
= 1000mA
22
35
45
I
L
= 1250mA
35
70
I
GNDDO
Ground Pin
V
IN
= 0.5V less than designed V
OUT
330
600
A
Current at Dropout
(V
OUT
3.3V)
(Note 5)
I
L
= 5mA
I
LIMIT
Current Limit
V
OUT
= 0V
1.6
2.4
A
(Note 6)
3
V
O
Thermal Regulation
(Note 7)
0.05
0.2
%/W
P
D
e
n
Output Noise
C
L
= 10
F
400
V RMS
Voltage
(10Hz to 100kHz)
C
L
= 33
F
260
I
L
= 100mA
Electrical Characteristics
MIC2940A/2941A
Micrel
MIC2940A/2941A
4
June 1999
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
A
Input Current
100
V
SHUTDOWN
= 26V
450
600
A
750
Regulator Output
(Note 10)
3
30
A
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
J (MAX)
, the junction-to-ambient thermal resistance,
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
)
/
JA.
Exceeding the maximum allowable
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.
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
OUT
= 0V) current limit is less than the maximum current 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 V
IN
= 20V (a 4W pulse) for T = 10ms.
Note 8:
V
REF
V
OUT
(V
IN
1 V), 4.3V
V
IN
26V, 5mA < I
L
1.25A, T
J
T
J MAX.
Note 9:
Circuit of Figure 3 with R1
150k
. V
SHUTDOWN
2 V and V
IN
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
Micrel
June 1999
5
MIC2940A/2941A
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
0
1
2
3
4
5
6
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Dropout
Characteristics
I
LOAD
= 5mA
I
LOAD
= 1.25A
0.1
1
10
40
1
10
100
1000
10000
GROUND CURRENT (mA)
OUTPUT CURRENT (mA)
Ground Current
vs. Output Current
10A
0
100
200
300
400
0
1
2
3
4
5
6
7
8
GROUND CURRENT (
A)
SUPPLY VOLTAGE (V)
Ground Current
vs. Supply Voltage
FIXED 5V
I
LOAD
= 5mA
0
10
20
30
40
50
0
2
4
6
8
10
GROUND CURRENT (mA)
INPUT VOLTAGE (V)
Ground Current
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 Current
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
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 Maximum
Current vs. Temperature
V
OUT
= V
NOMINAL
0.5V
V
OUT
= 0V
FIXED 3.3V
VERSION
3 SAMPLES
-200
0
200
400
600
800
1000
-30
-20
-10
0
10
20
30
GROUND CURRENT (
A)
INPUT VOLTAGE (V)
Ground Current
vs. Input Voltage
R
LOAD
= 100
MIC2940A/2941A
Micrel
MIC2940A/2941A
6
June 1999
0
25
50
75
100
125
-60 -30
0
30
60
90 120 150
ENABLE CURRENT (
A)
TEMPERATURE (
C)
MIC29401/2 Shutdown Current
vs. Temperaure
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
0
5
10
OUTPUT (A)
TIME (ms)
Load Transient
C
OUT
= 10
F
5mA
-200
-100
0
100
200
OUTPUT (mV)
-0.5
0.0
0.5
1.0
1.5
2.0
-5
0
5
10
OUTPUT (A)
TIME (ms)
Load Transient
C
OUT
= 100
F
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
= 10
F
-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
F
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
MIC2940A/2941A
Micrel
June 1999
7
MIC2940A/2941A
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
F to 220
F only decreases the noise from
430
V to 160
V
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
, since it reduces the
high frequency gain from 4 to unity. Pick
or about 0.01
F. When doing this, the output capacitor must
be increased to 22
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.
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 (240
A 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.
Applications Information
External Capacitors
A 10
F (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 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
3.3
F for current below 100mA or 2.2
F 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 22
F (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 0.22
F 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.
The complete equation for the output voltage is
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 1
A forces an upper limit of
1.2M
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
= 100k
reduces this error to 0.17% while
increasing the resistor program current to 12
A. Since the
MIC2941A typically draws 100
A at no load with SHUTDOWN
open-circuited, this is a negligible addition.
* SEE APPLICATIONS INFORMATION
*
*
OUTPUT
VOLTAGE
INPUT
VOLTAGE
ERROR
NOT
VALID
NOT
VALID
5V
1.3V
4.75V
Figure 1. ERROR Output Timing
C
BYPASS
1
2 R
1
200 Hz
MIC2940A/2941A
Micrel
MIC2940A/2941A
8
June 1999
OUT
GND
+VIN
*V
5V
OUT
V
V
10F
+
IN
V
OUT
= 5V
Figure 2. MIC2940A-5.0 Fixed +5V Regulator
Figure 3. MIC2941A Adjustable Regulator
Typical Applications
IN
OUT
GND ADJUST
SHUTDOWN
V
V
SHUTDOWN
INPUT
IN
+V
OUT
V
1.2V
26V
1
R 100
pF
22F
2
R
1.23V
REF
V
VOUT = VREF x (1 + )
1
R
2
R
OFF
ON
*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40
m
V TO 400
m
V,
DEPENDING ON LOAD CURRENT.
SHUTDOWN
V
GND
OUT
+VIN
ADJUST
SHUTDOWN
INPUT
100pF
2N2222
1%
300k
+5V to +7V
1%
180k
+
10F
470 k
OFF
ON
5V
3.3V
220k
1%
VCC OUT
Input
Output
0
3.3V
1
5.0V
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.
Figure 4. MIC2941A Wide Input Voltage Range Current Limiter
OUT
GND
ADJUST
V
VIN
+VIN
VOUT
VIN
PDF 
ZIP