MIC2937A/29371/29372
Micrel
MIC2937A/29371/29372
750mA Low-Dropout Voltage Regulator
General Description
Features
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).
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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.
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•
•
•
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
•
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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
High Efficiency Linear Power Supplies
Pin Configuration
INPUT
GROUND OUTPUT
TO-263 Package
(MIC2937A-xxBU)
1 2 3 4 5
TO-263-5 Package
(MIC29371/29372BU)
Five Lead Package Pin Functions:
MIC29371 MIC29372
1) Error
Adjust
2) Input
Shutdown
3) Ground
Ground
4) Output
Input
5) Shutdown Output
1 2
3
Front View
1 2 3 4 5
INPUT GROUND OUTPUT
TO-220 Package
(MIC2937A-xxBT)
TO-220-5 Package
(MIC29371/29372BT)
The TAB is Ground on the TO-220 and TO-263 packages.
3-18
October 1999
MIC2937A/29371/29372
Micrel
Absolute Maximum Ratings
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
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 = VOUT + 1V, IL = 5mA, CL = 10µF. The MIC29372 are programmed for a 5V output voltage,
and VSHUTDOWN ≤ 0.6V (MIC29371-xx and MIC29372 only).
Symbol
VO
Parameter
Output Voltage
Accuracy
Conditions
Variation from factory trimmed VOUT
5mA ≤ IL ≤ 500mA
MIC2937A-12 and 29371-12 only:
5mA ≤ IL ≤ 500mA
(Note 2)
Output voltage > 10V
VIN = VOUT + 1V to 26V
∆VO
∆T
∆VO
VO
∆VO
VO
Output Voltage
Temperature Coef.
Line Regulation
Load Regulation
IL = 5 to 500mA
(Note 3)
VIN – VO
Dropout Voltage
(Note 4)
IL = 5mA
IL = 750mA
200
240
300
420
370
IL = 5mA
160
IL = 500mA
Output voltage > 10V
IGNDDO
ILIMIT
∆VO
∆PD
en
150
180
Units
%
ppm/°C
%
%
mV
600
750
µA
IL = 100mA
1
IL = 500mA
8
IL = 750mA
15
200
500
µA
1.1
1.5
2
0.2
A
VIN = 0.5V less than designed VOUT
(VOUT ≥ 3.3V)
IO = 5mA
VOUT = 0V
(Note 6)
Thermal Regulation (Note 7)
MIC2937A/29371/29372
Max
1
2
2.5
1.5
3
4
100
350
0.10
0.40
0.16
0.30
250
300
2.5
3
13
16
25
Ground Pin
Current at Dropout
(Note 5)
Current Limit
Output Noise
Voltage
(10Hz to 100kHz)
IL = 100mA
20
80
0.03
80
Output voltage > 10V
Ground Pin Current
(Note 5)
Typical
0.04
IL = 100mA
IGND
Min
–1
–2
–2.5
–1.5
–3
–4
0.05
CL = 10µF
400
CL = 100µF
260
20
mA
%/W
µV RMS
October 1999
MIC2937A/29371/29372
Micrel
Electrical Characteristics (Continued)
MIC29372
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
Adjust Pin
Bias Current
Reference Voltage
Temperature
Coefficient
20
(Note 7)
Adjust Pin Bias
Current Temperature
Coefficient
Error Comparator
Units
20
ppm/°C
0.1
nA/°C
MIC29371
Output Leakage
Current
VOH = 26V
0.01
1.00
2.00
µA
Output Low
Voltage
VIN = 4.5V
IOL = 250µA
150
250
400
mV
Upper Threshold
Voltage
(Note 9)
Lower Threshold
Voltage
(Note 9)
75
Hysteresis
(Note 9)
15
Shutdown Input
40
25
October 1999
95
140
mV
mV
1.3
V
0.7
High (OFF)
Regulator Output
Current in Shutdown
mV
MIC29371/MIC29372
Input Logic Voltage
Low (ON)
Shutdown Pin
Input Current
60
2.0
VSHUTDOWN = 2.4V
30
50
100
µA
VSHUTDOWN = 26V
450
600
750
µA
3
10
20
µA
(Note 10)
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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, 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. 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 (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 ≤ 750 mA, TJ ≤ TJ MAX.
Note 9: Comparator thresholds are expressed in terms of a voltage differential at the Adjust terminal below the nominal reference voltage
measured at 6V input (for a 5V regulator). To express these thresholds in terms of output voltage change, multiply by the error amplifier gain
= VOUT /VREF = (R1 + R2)/R2. For example, at a programmed output voltage of 5V, the Error output is guaranteed to go low when the output
drops by 95 mV x 5V/1.235 V = 384 mV. Thresholds remain constant as a percent of VOUT as VOUT is varied, with the dropout warning
occurring at typically 5% below nominal, 7.7% guaranteed.
Note 10: Circuit of Figure 3 with R1 ≥ 150kΩ. VSHUTDOWN ≥ 2V and VIN ≤ 26V,VOUT = 0.
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.
Schematic Diagram
FEEDBACK
IN
R18
20kΩ
Q15A
Q15B
Q24
Q26
Q25
OUT
Q9
Q3
R11
18
kΩ
Q4
Q7
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
C1
20
pF
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
MIC2937A-xx AND MIC29371-xx
VERSIONS ONLY
R25
2.8 kΩ
GND
Q39
MIC2937A/29371/29372
SHDN
R24
50 kΩ
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October 1999
MIC2937A/29371/29372
Micrel
Typical Characteristics
Dropout Voltage
vs. Temperature
DROPOUT VOLTAGE (mV)
400
300
200
100
0
6
600
5
500
400
ILOAD = 750mA
300
200
100
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
200
400
600
800
OUTPUT CURRENT (mA)
Ground Current
vs. Output Current
1
150
100
2.0
0.20
1.8
1.6
0.05
GROUND CURRENT (mA)
GROUND CURRENT (mA)
0.25
ILOAD = 5mA
1.2
1.2
15
10
FIXED 5V
ILOAD = 750mA
5
0
2
4
6
8
INPUT VOLTAGE (V)
ILOAD = 100mA
ILOAD = 750mA
25
20
15
10
5
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Ground Current
vs. Input Voltage
500
VOUT = VNOMINAL – 0.5V
0.8
VOUT = 0V
0.4
0.2
10
30
1.0
0.6
6
20
Short Circuit and Maximum
Current vs. Temperature
CURRENT (A)
OUTPUT VOLTAGE (V)
1
2
3
4
5
INPUT VOLTAGE (V)
Ground Current
vs. Temperature
0.4
0.2
3.38
3.36
October 1999
0
25
0
8
0.6
1.4
3.22
3.20
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
2 3 4 5 6 7
SUPPLY VOLTAGE (V)
1.0
0.8
Fixed 3.3V Output Voltage
vs. Temperature
3.26
3.24
1
1.4
3.40
3.30
3.28
0
0.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
0.00
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
3.34
3.32
ILOAD = 750mA
1
Ground Current
vs. Temperature
Ground Current
vs. Temperature
0.10
FIXED 5V VERSION
ILOAD = 5mA
50
0
10
100
1000
OUTPUT CURRENT (mA)
0.15
2
30
GROUND CURRENT (mA)
GROUND CURRENT (µA)
GROUND CURRENT (mA)
0.1
3
Ground Current
vs. Supply Voltage
200
1
ILOAD = 5mA
Ground Current
vs. Supply Voltage
30
10
4
0
GROUND CURRENT (mA)
0
Dropout
Characteristics
700
FIXED 5V
VERSION
0.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
23
GROUND CURRENT (µA)
DROPOUT VOLTAGE (mV)
500
OUTPUT VOLTAGE (V)
Dropout Voltage
vs. Output Current
400
RLOAD = 100Ω
300
200
100
0
-100
-30
-20 -10 0
10 20
INPUT VOLTAGE (V)
30
MIC2937A/29371/29372
MIC2937A/29371/29372
Micrel
MIC29371/2 Shutdown Current
vs. Temperaure
VEN = 2V
25
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
500
250
20
10
ILOAD = 1mA
∆ OUTPUT (mV)
5mA
0
-250
-5
0
5
TIME (ms)
10
100
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
40
-100
1000
-200
750
500
250
0
-250
-5
5mA
0
5
TIME (ms)
10
Line Transient
COUT = 10 µF
IL = 5mA
20
COUT = 100 µF
0
Line Transient
∆ OUTPUT (mV)
30
= 10 µF
-150
INPUT (V)
ADJUST PIN CURRENT (nA)
40
OUT
1000
-300
750
MIC29372/3 Adjust Pin
Current vs. Temperature
50
C
0
OUTPUT (mA)
50
150
200
∆ OUTPUT (mV)
VEN = 5V
75
Load Transeint
300
0
-20
10
-40
INPUT (V)
100
Load Transient
OUTPUT (mA) ∆ OUTPUT (mV)
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
IL = 5mA
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)
MIC2937A/29371/29372
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October 1999
MIC2937A/29371/29372
Micrel
Applications Information
External Capacitors
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.
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.
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.
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 complete equation for the output voltage is
VOUT = VREF x { 1 + R1/R2 } – |IFB| R1
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 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 VOUT which may be eliminated
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.
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)
Reducing Output Noise
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.
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 160µVRMS for a 100kHz bandwidth at 5V output.
Noise can be reduced by a factor of four with the adjustable
4.75V
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 VOUT = 4.75). Since the MIC29371’s dropout
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.
OUTPUT
VOLTAGE
ERROR
NOT *
VALID
NOT*
VALID
INPUT
VOLTAGE
5V
1.3V
* 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
CBYPASS ≅
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.
1
2 π R1 • 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 100µVRMS 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.
Typical Applications
V IN
+VIN
*V OUT ≈5V
VOUT
VIN
VOUT
VOUT = 5V
+
SHUTDOWN
10µF
INPUT
SHUTDOWN
26V
10µF
OFF
GND
VOUT
1.2V
GND ADJUST
R1 .01
µF
ON
1.23V
R1
VOUT = VREF x (1 +
)
R2
Figure 2. MIC2937A-5.0 Fixed +5V Regulator
R2
V REF
Figure 3. MIC29372 Adjustable Regulator
+5V to +7V
+VIN
VIN
VOUT
+VIN
VOUT ≈ VIN
VCC OUT
VOUT
SHUTDOWN
INPUT
SHUTDOWN
OFF
+
ON
100pF
GND
GND
ADJUST
300kΩ
1%
10µF
ADJUST
5V
470 kΩ
220kΩ
1%
180kΩ
1%
2N2222
3.3V
Input
0
1
Output
3.3V
5.0V
*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV,
DEPENDING ON LOAD CURRENT.
SHUTDOWN PIN LOW= ENABLE OUTPUT. Q1 ON = 3.3V, Q1 OFF = 5.0V.
Figure 4. MIC29372 Wide Input Voltage Range Current Limiter
Figure 5. MIC29372 5.0V or 3.3V Selectable Regulator with
Shutdown.
MIC2937A/29371/29372
26
October 1999