MIC2940A/2941A
Micrel
MIC2940A/2941A
1.25A Low-Dropout Voltage Regulator
Preliminary Information
General Description
Features
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).
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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.
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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
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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 Configuration
1 2 3 4 5
INPUT GROUND OUTPUT
TO-263-5 Package
(MIC2941ABU)
TO-263 Package
(MIC2940A-xxBU)
MIC2941A Pinout
1)
2)
3)
4)
5)
1 2
3
Front View
INPUT GROUND OUTPUT
TO-220 Package
(MIC2940A-xxBT)
Adjust
Shutdown
Ground
Input
Output
1 2 3 4 5
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
Voltage
Temperature Range*
Package
If Military/Aerospace specified devices
are required, contact your local Micrel
representative/distributor for availability
and specifications.
MIC2940A-3.3BT
3.3
–40°C to +125°C
TO-220
Power Dissipation (Note 1) ............... Internally Limited
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
Ordering Information
Part Number
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.
* Junction temperatures
Schematic Diagram
FEEDBACK
IN
R18
20kΩ
Q15A
Q15B
Q24
Q26
Q25
OUT
Q9
Q3
R11
18
kΩ
Q4
Q7
C1
20
pF
Q6
R11
20.6
kΩ
Q1
10
R2
50 kΩ
Q16
Q17
R27
R17
12 kΩ
Q14
V TAP
R28
Q2
Q20
R1
20 kΩ
Q42
SENSE
Q8
Q5
R5
180
kΩ
Q40
R6
140
kΩ
Q13
Q22
R10
150
kΩ
R8
31.4 kΩ
Q21
R9
27.8 kΩ
R12
110
kΩ
Q12
Q41
Q23
C2
40 pF
R13
100
kΩ
R15
100 kΩ
R14
350
kΩ
R16
30 kΩ
Q11
R17
10 Ω
Q29
R30
30
kΩ
Q18
Q19
Q28
R3
50 kΩ
R4
13 kΩ
R21 8 Ω
50 kΩ
Q30 Q31
Q37
10 kΩ
R22
150 kΩ
Q36
R23 60 kΩ
ERROR
Q38
Q34
R26
60 kΩ
DENOTES CONNECTION ON FIXED
VOLTAGE VERSIONS ONLY
R25
2.8 kΩ
GND
Q39
MIC2940A/2941A
SHDN
R24
50 kΩ
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 = VOUT + 1V, IL = 1000mA, CL = 10µF. The MIC2941A is programmed to output 5V and has
VSHUTDOWN ≤ 0.6V.
Symbol
VO
Parameter
Output Voltage
Accuracy
∆VO
∆T
∆VO
VO
∆VO
VO
Output Voltage
Temperature Coef.
Line Regulation
VIN – VO
Dropout Voltage
(Note 4)
IGND
IGNDDO
ILIMIT
∆VO
∆PD
en
June 1999
Load Regulation
Ground Pin Current
(Note 5)
Conditions
Min
–1
–2
–2.5
5 mA ≤ IL ≤ 1A
(Note 2)
Typical
20
VIN = VOUT + 1V to 26V
0.03
IL = 5mA to 1.25A
IL = 5mA to 1A
(Note 3)
IL = 5mA
0.04
IL = 250mA
200
IL = 1000mA
350
IL = 1250mA
400
IL = 5mA
240
60
Max
1
2
2.5
100
0.10
0.40
0.16
0.20
Units
%
ppm/°C
%
%
%
150
180
250
320
450
600
600
mV
µA
IL = 250mA
3
IL = 1000mA
22
IL = 1250mA
35
350
500
4.5
6
35
45
70
VIN = 0.5V less than designed VOUT
(VOUT ≥ 3.3V)
IL = 5mA
VOUT = 0V
(Note 6)
Thermal Regulation (Note 7)
330
600
µA
1.6
2.4
3
0.2
A
Ground Pin
Current at Dropout
(Note 5)
Current Limit
Output Noise
Voltage
(10Hz to 100kHz)
IL = 100mA
0.05
CL = 10µF
400
CL = 33µF
260
3
mA
%/W
µV RMS
MIC2940A/2941A
MIC2940A/2941A
Micrel
Electrical Characteristics (MIC2941A Only)
Parameter
Conditions
Reference Voltage
Reference Voltage
(Note 8)
Min
Typical
Max
1.223
1.210
1.235
1.247
1.260
V
V max
1.266
V
40
60
nA
1.204
Units
Adjust Pin
Bias Current
20
Reference Voltage
Temperature
Coefficient
20
ppm/°C
Adjust Pin Bias
Current Temperature
Coefficient
0.1
nA/°C
Shutdown Input
Input Logic Voltage
1.3
Low (ON)
High (OFF)
Shutdown Pin
Input Current
Regulator Output
Current in Shutdown
V
0.7
2.0
VSHUTDOWN = 2.4V
30
50
100
µA
VSHUTDOWN = 26V
450
600
750
µA
3
30
60
µA
(Note 10)
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, TJ (MAX), the junction-to-ambient thermal resistance, θJA, and the ambient temperature, TA. The maximum
allowable power dissipation at any ambient temperature is calculated using: P(MAX) = (TJ(MAX) – TA) / θJA. 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 (VOUT = 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 VIN = 20V (a 4W pulse) for T = 10ms.
Note 8: VREF ≤ VOUT ≤ (VIN – 1 V), 4.3V ≤ VIN ≤ 26V, 5mA < IL ≤ 1.25A, TJ ≤ TJ MAX.
Note 9: Circuit of Figure 3 with R1 ≥ 150kΩ. VSHUTDOWN ≥ 2 V and VIN ≤ 26 V,VOUT = 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
Typical Characteristics
Dropout Voltage
vs. Temperature
400
300
200
100
0
0.00
0.25 0.50 0.75 1.00
OUTPUT CURRENT (A)
6
800
5
600
400
ILOAD = 1.25A
200
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
1.25
Ground Current
vs. Output Current
300
200
100
0
10
100
1000 10000
10A
OUTPUT CURRENT (mA)
0.00
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
1.0
0.8
3.34
3.32
1.4
1.2
CURRENT (A)
OUTPUT VOLTAGE (V)
30
20
10
FIXED 3.3V DEVICE
ILOAD = 1.25A
0
2
4
6
8
INPUT VOLTAGE (V)
1.0
0.8
0.6
0.4
10
50
ILOAD = 100mA
ILOAD = 1.25A
40
30
20
10
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Short Circuit and Maximum
Current vs. Temperature
1.8
1.6
6
Ground Current
vs. Temperature
0.2
0.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
3.38
3.36
June 1999
1
2
3
4
5
INPUT VOLTAGE (V)
40
0
8
0.6
0.4
2.0
3.22
3.20
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
2 3 4 5 6 7
SUPPLY VOLTAGE (V)
1.4
1.2
Fixed 3.3V Output Voltage
vs. Temperature
3.26
3.24
1
1.8
1.6
3.40
3.30
3.28
0
GROUND CURRENT (mA)
ILOAD = 5mA
GROUND CURRENT (mA)
GROUND CURRENT (mA)
0.10
FIXED 5V
ILOAD = 5mA
2.0
0.40
0.20
0
Ground Current
vs. Temperature
Ground Current
vs. Temperature
0.30
ILOAD = 1.25A
1
50
Ground Current
vs. Input Voltage
1000
VOUT = VNOMINAL – 0.5V
VOUT = 0V
FIXED 3.3V
VERSION
3 SAMPLES
0.2
0.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
5
GROUND CURRENT (µA)
1
2
Ground Current
vs. Supply Voltage
GROUND CURRENT (mA)
GROUND CURRENT (µA)
GROUND CURRENT (mA)
1
ILOAD = 5mA
3
0
400
10
4
Ground Current
vs. Supply Voltage
40
0.1
Dropout
Characteristics
1000
DROPOUT VOLTAGE (mV)
DROPOUT VOLTAGE (mV)
500
OUTPUT VOLTAGE (V)
Dropout Voltage
vs. Output Current
800
RLOAD = 100Ω
600
400
200
0
-200
-30
-20 -10 0
10 20
INPUT VOLTAGE (V)
30
MIC2940A/2941A
MIC2940A/2941A
Micrel
MIC29401/2 Shutdown Current
vs. Temperaure
VEN = 2V
25
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
COUT = 10 µF
250
0
-250
2.0
-500
1.5
1.0
0.5
5mA
0.0
-0.5
-5
MIC29402/3 Adjust Pin
Current vs. Temperature
20
10
ILOAD = 5mA
100
-100
2.0
-200
1.5
1.0
0.5
0.0
-0.5
-5
0
-20
10
-40
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
5mA
0
5
TIME (ms)
10
Line Transient
COUT = 10 µF
20
COUT = 100 µF
0
INPUT (V)
30
10
200
Line Transient
∆ OUTPUT (mV)
40
0
5
TIME (ms)
40
INPUT (V)
ADJUST PIN CURRENT (nA)
50
Load Transient
OUTPUT (A) ∆ OUTPUT (mV)
50
750
500
∆ OUTPUT (mV)
VEN = 5V
75
∆ OUTPUT (mV)
100
Load Transient
OUTPUT (A)
ENABLE CURRENT (µA)
125
8
6
4
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
TIME (ms)
20
10
COUT = 100 µF
0
10
-10
8
6
4
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
TIME (ms)
Output Impedance
vs. Frequency
1
0.1
1x106
100x103
10x103
1x103
1x100
0.01
100x100
ILOAD = 10mA
10x100
OUTPUT IMPEDANCE (Ω)
10
FREQUENCY (Hz)
MIC2940A/2941A
6
June 1999
MIC2940A/2941A
Micrel
Applications Information
Reducing Output Noise
External Capacitors
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 160µVRMS 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 R1, since it reduces the
high frequency gain from 4 to unity. Pick
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.
CBYPASS ≅
1
2 π R1 • 200 Hz
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.
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.
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.
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.
Automotive Applications
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.
The complete equation for the output voltage is
VOUT = VREF x { 1 + R1/R2 } – |IFB| R1
4.75V
OUTPUT
VOLTAGE
where VREF is the nominal 1.235 reference voltage and IFB is
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 VOUT which may be eliminated
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.
June 1999
ERROR
NOT *
VALID
NOT*
VALID
INPUT
VOLTAGE
5V
1.3V
* SEE APPLICATIONS INFORMATION
Figure 1. ERROR Output Timing
7
MIC2940A/2941A
MIC2940A/2941A
Micrel
Typical Applications
+VIN
V IN
VIN
+VIN
VOUT
*V OUT ≈5V
V
OUT
VOUT = 5V
+
SHUTDOWN
INPUT
SHUTDOWN
OFF
10µF
VOUT
1.2V
GND ADJUST
R1 100
pF
26V
22µF
ON
GND
1.23V
R1
VOUT = VREF x (1 +
)
R2
Figure 2. MIC2940A-5.0 Fixed +5V Regulator
V REF
R2
Figure 3. MIC2941A Adjustable Regulator
+5V to +7V
+VIN
+VIN
VIN
VOUT
VOUT ≈ VIN
VCC OUT
VOUT
SHUTDOWN
INPUT
SHUTDOWN
OFF
+
ON
100pF
GND
GND
10µF
ADJUST
5V
Input
0
1
*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV,
DEPENDING ON LOAD CURRENT.
470 kΩ
220kΩ
1%
180kΩ
1%
2N2222
3.3V
Output
3.3V
5.0V
ADJUST PIN LOW= ENABLE OUTPUT. Q1 ON = 3.3V, Q1 OFF = 5.0V.
Figure 4. MIC2941A Wide Input Voltage Range Current Limiter
MIC2940A/2941A
ADJUST
300kΩ
1%
Figure 5. MIC2941A 5.0V or 3.3V Selectable Regulator with
Shutdown.
8
June 1999