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MIC2937A/29371/29372
Micrel
MIC2937A/29371/29372
750mA Low-Dropout Voltage Regulator
General Description
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 (160A 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). 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.
Features
* * * * * * * * * * * * 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. 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
Applications
* * * * * * * *
Pin Configuration
INPUT
GROUND OUTPUT
12345
TO-263 Package (MIC2937A-xxBU)
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
INPUT GROUND OUTPUT TO-220 Package (MIC2937A-xxBT) TO-220-5 Package (MIC29371/29372BT)
12 3 Front View
12345
The TAB is Ground on the TO-220 and TO-263 packages. 3-18 October 1999
MIC2937A/29371/29372
Micrel
Ordering Information
Part Number MIC2937A-3.3BU MIC2937A-3.3BT MIC2937A-5.0BU MIC2937A-5.0BT MIC2937A-12BU MIC2937A-12BT MIC29371-3.3BT MIC29371-3.3BU MIC29371-5.0BT MIC29371-5.0BU MIC29371-12BT MIC29371-12BU MIC29372BT MIC29372BU * Junction temperatures Voltage 3.3 3.3 5.0 5.0 12 12 3.3 3.3 5.0 5.0 12 12 Adj Adj Temperature Range* -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C Package TO-263-3 TO-220 TO-263-3 TO-220 TO-263-3 TO-220 TO-220-5 TO-263-5 TO-220-5 TO-263-5
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) ........ 260C Storage Temperature Range ............ -65C to +150C Operating Junction Temperature Range ................................................. -40C to +125C TO-220 JC ...................................................... 2.5C/W TO-263 JC ...................................................... 2.5C/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
TO-220-5 TO-263-5 TO-220-5 TO-263-5
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 25C.
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MIC2937A/29371/29372
MIC2937A/29371/29372
Micrel
Electrical Characteristics
Limits in standard typeface are for TJ = 25C and limits in boldface apply over the full operating temperature range. Unless otherwise specified, VIN = VOUT + 1V, IL = 5mA, CL = 10F. 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 IL = 5 to 500mA (Note 3) IL = 5mA IL = 100mA Output voltage > 10V IL = 500mA Output voltage > 10V IL = 750mA Min -1 -2 -2.5 -1.5 -3 -4 Typical Max 1 2 2.5 1.5 3 4 100 350 0.10 0.40 0.16 0.30 150 180 Units %
VO T VO VO VO VO VIN - VO
Output Voltage Temperature Coef. Line Regulation Load Regulation
20 80 0.03 0.04
ppm/C % %
Dropout Voltage (Note 4)
80 200 240 300 420 370
mV
600 750 250 300 2.5 3 13 16 25 500 A mA
IGND
Ground Pin Current (Note 5)
IL = 5mA IL = 100mA IL = 500mA IL = 750mA
160 1 8 15 200
IGNDDO
ILIMIT VO PD en
Ground Pin Current at Dropout (Note 5) Current Limit
VIN = 0.5V less than designed VOUT (VOUT 3.3V) IO = 5mA VOUT = 0V (Note 6) Thermal Regulation (Note 7) Output Noise Voltage (10Hz to 100kHz) IL = 100mA CL = 10F CL = 100F
A
1.1 0.05 400 260
1.5 2 0.2
A %/W V RMS
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Micrel
Electrical Characteristics (Continued)
MIC29372
Parameter Reference Voltage
Conditions
Min 1.223 1.210
Typical 1.235
Max 1.247 1.260 1.266
Units V V max V nA
Reference Voltage Adjust Pin Bias Current Reference Voltage Temperature Coefficient Adjust Pin Bias Current Temperature Coefficient Error Comparator Output Leakage Current Output Low Voltage Upper Threshold Voltage Lower Threshold Voltage Hysteresis Shutdown Input Input Logic Voltage Low (ON)
(Note 8)
1.204 20
40 60
(Note 7)
20
ppm/C
0.1
nA/C
MIC29371
VOH = 26V VIN = 4.5V IOL = 250A (Note 9) 40 25 0.01 1.00 2.00 250 400 A
150
mV
60
mV
(Note 9)
75
95 140
mV
(Note 9)
15
mV
MIC29371/MIC29372
1.3 0.7 High (OFF) 2.0 30 50 100 600 750 10 20 A V
Shutdown Pin Input Current
VSHUTDOWN = 2.4V
VSHUTDOWN = 26V Regulator Output Current in Shutdown (Note 10)
450
A A
3
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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, JA, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated using: P(MAX) = (TJ(MAX) - TA) / 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. The MIC2937A operates down to 2V of input at reduced output current at 25C. 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 150k. 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
IN FEEDBACK
R18 20k
Q15A Q15B
Q24 Q26 Q25 Q9 Q3
OUT
R11 18 k
Q4
Q7 Q5 Q8
SENSE Q14
Q6 Q1 10
R1 20 k
C1 20 pF
R11 20.6 k
Q2
Q20
Q16
Q17
R17 12 k
R27 V TAP R28
Q42
R8 31.4 k
R10 150 k
Q22 Q21
C2 40 pF
Q23
R2 50 k
R5 180 k
Q13
R6 140 k
Q12
R9 27.8 k
R15 100 k
Q40 Q41
R12 110 k
Q11
R13 100 k
R14 350 k
Q29
R16 30 k
R17 10
R30 30 k
Q18
Q19 Q28
R3 50 k
R4 13 k
R21 8
50 k
Q37 Q36
Q30 Q31
SHDN
R22 150 k
R24 50 k
R23 60 k
10 k
ERROR Q38
R26 60 k
Q34
R25 2.8 k
DENOTES CONNECTION ON MIC2937A-xx AND MIC29371-xx VERSIONS ONLY
Q39
GND
MIC2937A/29371/29372
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MIC2937A/29371/29372
Micrel
Typical Characteristics
Dropout Voltage vs. Output Current
500 DROPOUT VOLTAGE (mV)
DROPOUT VOLTAGE (mV)
Dropout Voltage vs. Temperature
700
Dropout Characteristics
6 OUTPUT VOLTAGE (V) 5 4 3 2 ILOAD = 750mA 1 0 0 1 2 3 4 5 INPUT VOLTAGE (V) 6 ILOAD = 5mA
400 300 200 100 0
600 500 400 300 200 100 0 -60 -30 0 30 60 90 120 150 TEMPERATURE (C) ILOAD = 750mA
0
200 400 600 800 OUTPUT CURRENT (mA)
Ground Current vs. Output Current
30 GROUND CURRENT (mA) GROUND CURRENT (A) 10 200
Ground Current vs. Supply Voltage
30 GROUND CURRENT (mA) 25 20 15 10 5 0 0
Ground Current vs. Supply Voltage
150
100 FIXED 5V VERSION ILOAD = 5mA
1
50
FIXED 5V ILOAD = 750mA 2 4 6 8 INPUT VOLTAGE (V) 10
0.1
1
10 100 1000 OUTPUT CURRENT (mA)
0
0
1
234567 SUPPLY VOLTAGE (V)
8
Ground Current vs. Temperature
0.25
Ground Current vs. Temperature
2.0 GROUND CURRENT (mA)
GROUND CURRENT (mA) 30 25 20 15 10 5
Ground Current vs. Temperature
ILOAD = 750mA
GROUND CURRENT (mA)
0.20 0.15 0.10 0.05 ILOAD = 5mA
1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -60 -30 0 30 60 90 120 150 TEMPERATURE (C) ILOAD = 100mA
0.00 -60 -30 0 30 60 90 120 150 TEMPERATURE (C)
0 -60 -30 0 30 60 90 120 150 TEMPERATURE (C)
Fixed 3.3V Output Voltage vs. Temperature
3.40 OUTPUT VOLTAGE (V) 3.38 3.36 CURRENT (A) 3.34 3.32 3.30 3.28 3.26 3.24 3.22 3.20 -60 -30 0 30 60 90 120 150 TEMPERATURE (C) 1.4 1.2 1.0 0.8 0.6 0.4 0.2
Short Circuit and Maximum Current vs. Temperature
500 GROUND CURRENT (A)
VOUT = VNOMINAL - 0.5V
Ground Current vs. Input Voltage
400 300 200 100 0 -100 -30 -20 -10 0 10 20 INPUT VOLTAGE (V) 30 RLOAD = 100
VOUT = 0V
FIXED 5V VERSION
0.0 -60 -30 0 30 60 90 120 150 TEMPERATURE (C)
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MIC2937A/29371/29372
MIC2937A/29371/29372
Micrel
MIC29371/2 Shutdown Current vs. Temperaure
OUTPUT (mA) OUTPUT (mV)
125 ENABLE CURRENT (A) 100 VEN = 5V 75 50 VEN = 2V 25 0 -60 -30 0 30 60 90 120 150 TEMPERATURE (C)
Load Transient
150 0 -150 1000 -300 750 500 250 0 -250 -5 5mA C
OUT
Load Transeint
OUTPUT (mV) 200 100 0 -100 1000 -200 750 500 250 0 -250 -5 5mA COUT = 100 F
300 = 10 F
0 5 TIME (ms)
10
OUTPUT (mA)
0 5 TIME (ms)
10
MIC29372/3 Adjust Pin Current vs. Temperature
OUTPUT (mV)
50 ADJUST PIN CURRENT (nA) 40 30 20 10 ILOAD = 1mA
Line Transient
20 0 -20 10 -40 8 6 4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 TIME (ms) COUT = 10 F IL = 5mA OUTPUT (mV) 40 20 10 0 10 -10 8 6
Line Transient
COUT = 100 F IL = 5mA
INPUT (V)
0 -60 -30 0 30 60 90 120 150 TEMPERATURE (C)
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 vs. Frequency
10
OUTPUT IMPEDANCE ()
1
0.1 ILOAD = 10mA 0.01
1x100
10x100
100x100
1x103
10x103
100x103
FREQUENCY (Hz)
MIC2937A/29371/29372
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MIC2937A/29371/29372
Micrel
Applications Information
External Capacitors
A 10F (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 -30C, so solid tantalums are recommended for operation below -25C. 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 0.5F for current below 10mA or 0.15F 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 22F (or greater) capacitor should be used. 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 0.1F 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. 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 250A, this sink current adds to battery drain in a low battery condition. Suggested values range from 100k to 1M. The resistor is not required if this output is unused.
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. 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 1A forces an upper limit of 1.2M 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 12A. Since the MIC29372 typically draws 100A at no load with SHUTDOWN opencircuited, this is a negligible addition.
Error Detection Comparator Output (MIC29371)
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. 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.
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 1F to 220F only decreases the noise from 430V to 160VRMS for a 100kHz bandwidth at 5V output. Noise can be reduced by a factor of four with the adjustable
4.75V OUTPUT VOLTAGE
ERROR
NOT * VALID
NOT * VALID
INPUT VOLTAGE 1.3V
5V
* SEE APPLICATIONS INFORMATION
Figure 1. ERROR Output Timing
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MIC2937A/29371/29372
MIC2937A/29371/29372
regulators with a bypass capacitor across R1, since it reduces the high frequency gain from 4 to unity. Pick
CBYPASS 1 2 R1 * 200 Hz
Micrel
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 (100A 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.
or about 0.01F. When doing this, the output capacitor must be increased to 10F to maintain stability. These changes reduce the output noise from 430V to 100VRMS 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 VOUT + GND
ON
*V OUT 5V
VIN
VOUT = 5V
10F
VOUT SHUTDOWN INPUT
OFF
VOUT 1.2V
26V
SHUTDOWN GND ADJUST 1.23V R1 .01 F
10F
R1 VOUT = VREF x (1 + ) R2
V REF
R2
Figure 2. MIC2937A-5.0 Fixed +5V Regulator
Figure 3. MIC29372 Adjustable Regulator
+5V to +7V
+VIN
VIN VOUT
VOUT VIN
+VIN
SHUTDOWN INPUT OFF ON
VCC OUT VOUT
SHUTDOWN + 100pF GND ADJUST 300k 1% 10F
GND
ADJUST
470 k 220k 1% 2N2222
Input 0 1 Output 3.3V 5.0V
5V 3.3V
180k 1%
*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
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