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MIC2950/2951
Micrel
MIC2950/2951
150mA Low-Dropout Voltage Regulator
General Description
The MIC2950 and MIC2951 are "bulletproof" micropower voltage regulators with very low dropout voltage (typically 40mV at light loads and 250mV at 100mA), and very low quiescent current. Like their predecessors, the LP2950 and LP2951, the quiescent current of the MIC2950/MIC2951 increases only slightly in dropout, thus prolonging battery life. The MIC2950/MIC2951 are pin for pin compatible with the LP2950/LP2951, but offer lower dropout, lower quiescent current, reverse battery, and automotive load dump protection. The key additional features and protection offered include higher output current (150mA), positive transient protection for up to 60V (load dump), and the ability to survive an unregulated input voltage transient of -20V below ground (reverse battery). The plastic DIP and SOIC versions offer additional system functions such as programmable output voltage and logic controlled shutdown. The 3-pin TO-92 MIC2950 is pincompatible with the older 5V regulators. These system functions also include an error flag output that warns of a low output voltage, which is often due to failing batteries on the input. This may also be used as a power-on reset. A logic-compatible shutdown input is also available which enables the regulator to be switched on and off. This part may also be pin-strapped for a 5 V output, or programmed from 1.24 V to 29 V with the use of two external resistors.
Features
* * * * * * * * * * * * * * * * * * * High accuracy 3.3, 4.85, or 5V, guaranteed 150mA output Extremely low quiescent current Low-dropout voltage Extremely tight load and line regulation Very low temperature coefficient Use as regulator or reference Needs only 1.5F for stability Current and thermal limiting Unregulated DC input can withstand -20V reverse battery and +60V positive transients Error flag warns of output dropout (MIC2951) Logic-controlled electronic shutdown (MIC2951) Output programmable from 1.24V to 29V (MIC2951) Automotive Electronics Battery Powered Equipment Cellular Telephones SMPS Post-Regulator Voltage Reference Avionics High Efficiency Linear Power Supplies
Applications
3
Block Diagram
Unregulated DC Supply
FB
IN OUT Error Amp. 182k SNS TAP 330k 5V/150mA Output
SHDN
TTL/CMOS Control Logic Input
60mV
60k Error Detection Comparator
ERR 1.5F GND
TTL/CMOS Compatible Error Output
1.23V REF. MIC2951-0x
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The MIC2950 is available as either an -05 or -06 version. The -05 and -06 versions are guaranteed for junction temperatures from -40C to +125C; the -05 version has a tighter output and reference voltage specification range over temperature. The MIC2951 is available as an -02 or -03 version.
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The MIC2950 and MIC2951 have a tight initial tolerance (0.5% typical), a very low output voltage temperature coefficient which allows use as a low-power voltage reference, and extremely good load and line regulation (0.04% typical). This greatly reduces the error in the overall circuit, and is the result of careful design techniques and process control.
Ordering Information
Part Number MIC2950-05BZ MIC2950-06BZ MIC2951-02BM MIC2951-03BM MIC2951-02BN MIC2951-03BN MIC2951-03BMM MIC2951-3.3BM MIC2951-4.8BM
* junction temperature
Voltage 5.0V 5.0V 5.0V 5.0V 5.0V 5.0V 5.0V 3.3V 4.85V
Accuracy Temperature Range* 0.5% 1.0% 0.5% 1.0% 0.5% 1.0% 1.0% 1.0% 1.0% -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-92 TO-92 8-pin SOIC 8-pin SOIC 8-pin plastic DIP 8-pin plastic DIP 8-lead MM8TM 8-pin SOIC 8-pin SOIC
Pin Configuration
MIC2951-xx OUT 1
MIC2950-xx 3 2 1
8 7 6 5
IN FB TAP ERR
SNS 2 SHDN 3
IN
OUT GND
GND 4
TO-92 (Z) (Bottom View)
DIP (N), SOIC (M), MM8TM (MM) (Top View)
Pin Description
Pin # MIC2950 3 Pin # MIC2951 1 2 3 2 4 5 6 7 1 8 Pin Name OUT SNS SHDN GND ERR TAP FB IN Pin Function Regulated Output Sense (Input): Output-voltage sensing end of internal voltage divider for fixed 5V operation. Not used in adjustable configuration. Shutdown/Enable (Input): TTL compatible input. High = shutdown, low or open = enable. Ground Error Flag (Output): Active low, open-collector output (low = error, floating = normal). 3.3V/4.85/5V Tap: Output of internal voltage divider when the regulator is configured for fixed operation. Not used in adjustable configuration. Feedback (Input): 1.235V feedback from internal voltage divider's TAP (for fixed operation) or external resistor network (adjustable configuration). Unregulated Supply Input
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Absolute Maximum Ratings (Note 1)
Input Suppy Voltage (VIN) Note 5 ................. -20V to +60V Feedback Input Voltage (VFB) Note 6, 7 ...... -1.5V to +26V Shutdown Input Voltage (VSHDN) Note 6 ..... -0.3V to +30V Power Dissipation (PD) Note 4 ................ Internally Limited Storage Temperature .............................. -65C to + 150C Lead Temperature (soldering, 5 sec.) ....................... 260C ESD, Note 3
Operating Ratings (Note 2)
Input Supply Voltage (VIN) ........................... +2.0V to +30V Junction Temperature (TJ) ....................................... Note 4 MIC2950-05/MIC2950-06 ..................... -40C to +125C MIC2951-02/MIC2950-03 ..................... -40C to +125C
Electrical Characteristics
VIN = 6V; IL = 100A; CL = 1F; TJ = 25C, bold values indicate -40C TJ +125C; Note 8; unless noted. Parameter Output Voltage Condition MIC295x-02/-05 (0.5%), TJ = 25C MIC295x-03/-06 (1%), TJ = 25C MIC2951-3.3 (1%), TJ = 25C MIC2951-4.8 (1%), TJ = 25C Output Voltage MIC295x-02/-05 (0.5%), -25C TJ +85C MIC295x-03/-06 (1%), -25C TJ +85C MIC2951-3.3 (1%), -25C TJ +85C MIC2951-4.8 (1%), -25C TJ +85C Output Voltage Over Full Temperature Range MIC295x-02/-05 (0.5%), -40C to +125C MIC295x-03/-06 (1%), -40C to +125C MIC2951-3.3 (1%), -40C to +125C MIC2951-4.8 (1%), -40C to +125C Output Voltage Over Load Variation MIC295x-02/-05 (0.5%), 100A IL 150mA, TJ TJ(max) MIC295x-03/-06 (1%), 100A IL 150mA, TJ TJ(max) MIC2951-3.3 (1%), 100A IL 150mA, TJ TJ(max) MIC2951-4.8 (1%), 100A IL 150mA, TJ TJ(max) Output Voltage Temperature Coefficient MIC295x-02/-05 (0.5%), Note 9 MIC295x-03/-06 (1%), Note 9 MIC2951-3.3 (1%), Note 9 MIC2951-4.8 (1%), Note 9 Line Regulation MIC295x-02/-05 (0.5%), Note 10, 11 MIC295x-03/-06 (1%), Note 10, 11 MIC2951-3.3 (1%), Note 10, 11 MIC2951-4.8 (1%), Note 10, 11 Min 4.975 4.950 3.267 4.802 4.950 4.925 3.251 4.777 4.940 4.900 3.234 4.753 4.930 4.880 3.221 4.733 20 50 50 50 0.03 0.04 0.04 0.04 Typ 5.000 5.000 3.300 4.850 Max 5.025 5.050 3.333 4.899 5.050 5.075 3.350 4.872 5.060 5.100 3.366 4.947 5.070 5.120 3.379 4.967 100 150 150 150 0.10 0.20 0.20 0.40 0.20 0.40 0.20 0.40 Units V V V V V V V V V V V V V V V V ppm/C ppm/C ppm/C ppm/C % % % % % % % %
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Parameter Load Regulation Condition MIC295x-02/-05 (0.5%), 100A IL 150mA, Note 10 MIC295x-03/-06 (1%), 100A IL 150mA, Note 10 MIC2951-3.3 (1%), 100A IL 150mA, Note 10 MIC2951-4.8 (1%), 100A IL 150mA, Note 10 Dropout Voltage MIC295x-02/-03/-05/-06, IL = 100A, Note 12 MIC295x-02/-03/-05/-06, IL = 100mA, Note 12 MIC295x-02/-03/-05/-06, IL = 150mA, Note 12 MIC2951-3.3 (1%), IL = 100A, Note 12 MIC2951-3.3 (1%), IL = 100mA, Note 12 MIC2951-3.3 (1%), IL = 150mA, Note 12 MIC2951-4.8 (1%), IL = 100A, Note 12 MIC2951-4.8 (1%), IL = 100mA, Note 12 MIC2951-4.8 (1%), IL = 150mA, Note 12 Ground Current MIC295x-02/-03/-05/-06, IL = 100A MIC295x-02/-03/-05/-06, IL = 100mA MIC295x-02/-03/-05/-06, IL = 150mA MIC2951-3.3 (1%), IL = 100A MIC2951-3.3 (1%), IL = 100mA MIC2951-3.3 (1%), IL = 150mA MIC2951-4.8 (1%), IL = 100A MIC2951-4.8 (1%), IL = 100mA MIC2951-4.8 (1%), IL = 150mA Dropout Ground Current MIC295x-02/-03/-05/-06 (0.5%), VIN = 4.5V, IL = 100A MIC2951-3.3 (1%), VIN = 3.0V, IL = 100A MIC2951-4.8 (1%), VIN = 4.3V, IL = 100A Min Typ 0.04 0.10 0.10 0.10 40 250 300 40 250 320 40 250 300 120 1.7 4 100 1.7 4 120 1.7 4 280 150 280 Max 0.10 0.20 0.20 0.30 0.20 0.30 0.20 0.30 80 140 300 450 600 80 150 350 450 600 80 140 300 450 600 180 300 2.5 3.5 6 8 180 300 2.5 6 10 180 300 2.5 3.5 6 8 350 400 350 400 350 400
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Units % % % % % % % % mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV A A mA mA mA mA A A mA mA mA A A mA mA mA mA A A A A A A
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Parameter Current Limit Thermal Regulation Output Noise Condition VOUT = 0V Note 13 10Hz to 100kHz, CL = 1.5F 10Hz to 100kHz, CL = 200F 10Hz to 100kHz, CL = 3.3F, 0.01F bypass Feedback to Output Reference Voltage MIC295x-02/-05 (0.5%) MIC295x-03/-06 (1%) MIC2951-3.3 (1%) MIC2951-4.8 (1%) Reference Voltage MIC295x-02/-05 (0.5%), Note 14 MIC295x-03/-06 (1%), Note 14 MIC2951-3.3 (1%), Note 14 MIC2951-4.8 (1%), Note 14 Feedback Bias Current Reference Voltage Temperature Coefficient MIC295x-02/-05 (0.5%), Note 9 MIC295x-03/-06 (1%), Note 9 MIC2951-3.3 (1%), Note 9 MIC2951-4.8 (1%), Note 9 Feedback Bias Current Temperature Coefficient Error Comparator (Flag) Output Leakage Current Error Comparator (Flag) Output Low Voltage Error Comparator Upper Threshold Voltage Error Comparator Lower Threshold Voltage Error Comparator Hysteresis VOH = 30V VIN = 4.5V, IOL = 200A Note 15 Note 15 Note 15 40 25 1.220 1.200 1.210 1.200 1.210 1.200 1.210 1.200 1.190 1.185 1.185 1.185 20 20 50 50 50 0.1 0.01 150 60 75 15 95 140 1.00 2.00 250 400 Min Typ 300 0.05 430 160 100 1.235 1.235 1.235 1.235 1.250 1.260 1.260 1.270 1.260 1.270 1.260 1.270 1.270 1.285 1.285 1.285 40 60 Max 400 450 0.20
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Units mA mA %/W VRMS VRMS VRMS V V V V V V V V V V V V nA nA ppm/C ppm/C ppm/C ppm/C nA/C A A mV mV mV mV mV mV mV
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Parameter Shutdown Input Logic Voltage Condition MIC295x-02/-05 (0.5%) Low High MIC295x-03/-06 (1%) Low High MIC2951-3.3 (1%) Low High MIC2951-4.8 (1%) Low High Shutdown Input Current VSHUTDOWN = 2.4V VSHUTDOWN = 30V Regulator Output Current in Shutdown
Note 1. Note 2. Note 3. Note 4.
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Min Typ 1.3 0.7 2.0 1.3 0.7 2.0 1.3 0.7 2.0 1.3 0.7 2.0 30 450 3 50 100 600 750 10 20 Max Units V V V V V V V V V V V V A A A A A A
Note 7
Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions are recommended. The junction-to-ambient thermal resistance of the TO-92 package is 180C/W with 0.4" leads and 160C/W with 0.25" leads to a PC board. The thermal resistance of the 8-pin DIP package is 105C/W junction-to-ambient when soldered directly to a PC board. Junction-to-ambient thermal resistance for the SOIC (M) package is 160C/W. Junction-to-ambient thermal resistance for the MM8TM (MM) is 250C/W. The maximum positive supply voltage of 60V must be of limited duration (100ms) and duty cycle (1%). The maximum continuous supply voltage is 30V. When used in dual-supply systems where the output terminal sees loads returned to a negative supply, the output voltage should be diodeclamped to ground. VSHDN 2V, VIN 30 V, VOUT = 0, with the FB pin connected to TAP. Additional conditions for 8-pin devices are VFB = 5V, TAP and OUT connected to SNS (VOUT = 5V) and VSHDN 0.8V. Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.
Note 5. Note 6. Note 7. Note 8. Note 9.
Note 10. Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are covered in the specification for thermal regulation. Note 11. Line regulation for the MIC2951 is tested at 150C for IL = 1mA. For IL = 100A and TJ = 125C, line regulation is guaranteed by design to 0.2%. See Typical Performance Characteristics for line regulation versus temperature and load current. Note 12. Dropout voltage is defined as the input to output differential at which the output voltage drops 100mV below its nominal value measured at 1V differential. At very low values of programmed output voltage, the minimum input supply voltage of 2V (2.3V over temperature) must be taken into account. Note 13. 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 50mA load pulse at VIN = 30V (1.25W pulse) for t = 10ms. Note 14. VREF VOUT (VIN - 1 V), 2.3V VIN 30V, 100A < IL 150mA, TJ TJMAX. Note 15. Comparator thresholds are expressed in terms of a voltage differential at the FB terminal below the nominal reference voltage measured at 6V input. 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 95mV x 5V/1.235V = 384mV. Thresholds remain constant as a percent of VOUT as VOUT is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed.
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Typical Characteristics
Ground Pin Current
6
OUTPUT VOLTAGE (V) INPUT CURRENT (A)
10
QUIESCENT CURRENT
Dropout Characteristics
5 4 3 2 1 0 0 1 2 3 4 5 6 R L = 33 R L = 50k
400 350 300 250 200 150 100 50 0
Input Current
1
R L = 50k RL =
0.1
0.01 0.1
1
10
150
01234
5 6 7 8 9 10
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Input Current
160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0
Output Voltage vs. Temperature of 3 Representative Units
5.06
QUIESCENT CURRENT (A) OUTPUT VOLTAGE (V)
Ground Pin Current
180 140 120 100 80 60 40 20 0 0 1 2 3 4 5 6 7 8 INPUT VOLTAGE (V) IL = 1 mA IL = 0
INPUT CURRENT (mA)
R L = 50
5.04 5.02 5.0 4.98 4.96 0.2%
3
01
234
5
67
8 9 10
4.94 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
INPUT VOLTAGE (V)
Ground Pin Current
QUIESCENT CURRENT (mA)
Ground Pin Current
7
QUIESCENT CURRENT (mA)
Ground Pin Current
9
350
QUIESCENT CURRENT (A)
300 250 200 150 100 50 0 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C) VIN = 6V IL = 100 A
7
6 VIN = 6V IL = 150 mA 5
5 IL = 150 mA 3
4 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
0 0 1 2 3 4 5 6 7 8 INPUT VOLTAGE (V)
Short Circuit Current
SHORT CIRCUIT CURRENT (mA)
Dropout Voltage
600
DROPOUT VOLTAGE (mV)
Dropout Voltage
500
DROPOUT VOLTAGE (mV)
450 400 350 300 250 200 150 100 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
500 400 300 100 50
IL = 150 mA
400 300 200 100 0
IL = 100 A
TJ = 25 C 150 0.1 1 10 100
0 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
OUTPUT CURRENT (mA)
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MINIMUM OPERATING VOLTAGE (V)
2.2 2.1 2.0 1.9 1.8 1.7
MIC2951 Minimum Operating Voltage
BIAS CURRENT (nA)
20 10 0 -10 -20
MIC2951 Feedback Bias Current
FEEDBACK CURRENT (A)
50 0 -50 -100 -150
MIC2951 Feedback Pin Current
PIN 7 DRIVEN BY EXTERNAL SOURCE (REGULATOR RUN OPEN LOOP)
TA = 125C
TA = 25C -200 TA = -55C -250 -2.0 -1.5 -1.0 -0.5 0 0.5 1.0
1.6 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
-30 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
FEEDBACK VOLTAGE (V)
8
COMPARATOR OUTPUT (V)
2.5
SINK CURRENT (mA)
VOUT = 5V 6 4 HYSTERESIS 2 0 -2 0
PULLUP RESISTOR TO SEPARATE 5V SUPPLY
2.0 1.5 1.0
TA = 125C
OUTPUT VOLTAGE CHANGE
MIC2951 Error Comparator Output
MIC2951 Comparator Sink Current
400 mV 200 mV 0 -50 mV 8V 6V 4V
Line Transient Response
TA = 25C
0.5 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 OUTPUT LOW VOLTAGE (V)
1
2
3
4
5
6
INPUT VOLTAGE
TA = -55C
C L = 4.7F IL = 1 mA VOUT = 5V
0
200
400
600
800
INPUT VOLTAGE (V)
TIME (S)
Load Transient Response
OUTPUT VOLTAGE LOAD CHANGE (mV) CURRENT
Load Transient Response
SHUTDOWN OUTPUT PIN VOLTAGE (V) VOLTAGE (V)
MIC2951 Enable Transient
7 6 5 4 3 2 1 0 2 0 -2 CL = 1.5 F
125 100 75 50 25 0 -25 -50 100 mA 100 A 0 2 4
LOAD CURRENT
C L = 4.7 F VOUT = 5V
80 60 40 20 0 -20 -40 -60 100 mA 100 A 0 4 8
OUTPUT VOLTAGE CHANGE (mV)
C L = 15 F VOUT = 5V
IL = 10 mA VIN = 8V CL = 10 F VOUT = 5V
6
8
10
12
16
20
-100 0 100 200 300 400 500 600 700 TIME (S)
TIME (mS)
TIME (mS)
Output Impedance
OUTPUT IMPEDANCE (OHMS)
Ripple Rejection
90
RIPPLE REJECTION (dB)
Ripple Rejection
90
RIPPLE REJECTION (dB)
10 5 2 1 0.5 0.2 0.1 0.05 0.02 0.01
I0 = 100 A I0 = 1 mA I0 = 100 mA VOUT = 5V C L = 4.7 F
80 70 60 50 40 30 20 CL = 1.5 F VIN = 6V VOUT = 5V 101 10 2 10 3 IL = 100 A IL = 0
80 70 I = 1 mA L 60 50 40 30 20 101
CL = 1.5 F VIN = 6V VOUT = 5V
IL = 10 mA 102 10 3 10 4 10 5 106 FREQUENCY (Hz)
10
100
1K
10K 100K 1M
10 4
10
106
FREQUENCY (Hz)
FREQUENCY (Hz)
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RIPPLE REJECTION (dB)
70 60 50 40
IL = 50 A
VOLTAGE NOISE SPECTRAL DENSITY (V/ Hz)
80
3.5 3.0 2.5 2.0 1.5 1.0 0.5
PIN 2 TO PIN 4 RESISTANCE (k )
Ripple Rejection
Output Noise
IL = 100 mA CL = 4.7 F CL = 220 F CL = 3.3 F
0.01 F BYPASS PIN 1 TO PIN 7
MIC2951 Divider Resistance
400
300
IL = 100 mA
200
CL = 1.5 F 30 VIN = 6V VOUT = 5V 20 10 101 102 10 3 10 4 10 5 106
100
0.0 102
10 3
10 4
10 5
0 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
FREQUENCY (Hz)
FREQUENCY (Hz)
SHUTDOWN THRESHOLD VOLTAGE (V)
1.8 1.6 1.4 1.2 1.0 0.8 0.6 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
OUTPUT VOLTAGE CHANGE (mV)
Shutdown Threshold Voltage
Line Regulation
OUTPUT CURRENT (mA) 30 25 20 15 T = 150C 10 J 5 0 10 5 TJ = 125C 0 -5 -10 5 10 15 150 IL = 100 A IL = 1 mA 140 130 120 100 80
MIC2951 Maximum Rated Output Current
8-PIN SOIC SOLDERED TO PC BOARD
T J
MAX
= 125C
VOUT = 5V TA = 25C
3
IL = 100 A
60 TA = 50C 40 TA = 85C 20 0 0 5 10 15 20 25 INPUT VOLTAGE (V) 30
20
25
30
INPUT VOLTAGE (V)
POWER OUTPUT VOLTAGE DISSIPATION (W) CHANGE (mV)
150 OUTPUT CURRENT (mA) 140 130 120 100 80 60 40 20 0
MIC2950 Maximum Rated Output
TO-92 PACKAGE .25" LEADS SOLDERED TO PC BOARD
Thermal Response
4 2 0 -2 1 0 -1 0 10 20 30 40 50 TIME (S) 1.25W OUTPUT CURRENT (mA) 5
600 500 400 300 200 100
Fold-Back Current Limiting
T J
MAX
= 125C
TA = 25C T = 85C 0 5 10 15 20 25
A
30
0
1
2
3
4
5
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
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Applications Information
Automotive Applications
The MIC2950/2951 are ideally suited for automotive applications for a variety of reasons. They will operate over a wide range of input voltages, have very low dropout voltages (40mV at light loads), and very low quiescent currents. These features are necessary for use in battery powered systems, such as automobiles. They are also "bulletproof" devices; 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. offset of about 60mV 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 MIC2951. 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, current limiting, thermal limiting, or overvoltage on input (over 40V). Figure 1 is a timing diagram depicting the ERROR signal and the regulated output voltage as the MIC2951 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--for 5.0V applications). Since the MIC2951'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 does not vary with load. The error comparator has an open-collector output which requires an external pull-up resistor. Depending on system requirements, this resistor may be returned to the output or some other supply voltage. In determining a value for this resistor, note that while the output is rated to sink 200A, 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.
External Capacitors
A 1.5 F (or greater) capacitor is required between the MIC2950/MIC2951 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. Using the 8-pin versions at voltages below 5V runs the error amplifier at lower gains so that more output capacitance is needed. For the worst-case situation of a 150mA load at 1.23V output (Output shorted to Feedback) a 5F (or greater) capacitor should be used. The MIC2950 will remain stable and in regulation with no load in addition to the internal voltage divider, unlike many other voltage regulators. This is especially important in CMOS RAM keep-alive applications. When setting the output voltage of the MIC2951 version with external resistors, a minimum load of 1A is recommended. A 0.1F capacitor should be placed from the MIC2950/ MIC2951 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. Stray capacitance to the MIC2951 Feedback terminal (pin 7) can cause instability. This may especially be a problem when using high value external resistors to set the output voltage. Adding a 100pF capacitor between Output and Feedback and increasing the output capacitor to at least 3.3F will remedy this.
Programming the Output Voltage (MIC2951)
The MIC2951 may be pin-strapped for 5V (or 3.3V or 4.85V) using its internal voltage divider by tying Pin 1 (output) to Pin 2 (sense) and Pin 7 (feedback) to Pin 6 (5V Tap). Alternatively, it may be programmed for any output voltage between its 1.235V reference and its 30V maximum rating. An external pair of resistors is required, as shown in Figure 2. 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 feedback pin bias current, nominally -20nA. The minimum recommended load current of 1 A 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 12 A.
Reducing Output Noise
In some 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 the only method by which noise can be reduced on the 3 lead MIC2950 and is relatively inefficient, as increasing the capacitor from 1F to 220F only decreases the noise from 430V to 160V rms for a 100kHz bandwidth at 5V output. February 1999
Error Detection Comparator Output
A logic low output will be produced by the comparator whenever the MIC2951 output falls out of regulation by more than approximately 5%. This figure is the comparator's built-in
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Noise can be reduced fourfold by a bypass capacitor across R1, since it reduces the high frequency gain from 4 to unity. Pick:
CBYPASS 1 2 R1 * 200 Hz
Micrel
or about 0.01 F. When doing this, the output capacitor must be increased to 3.3 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.
4.75V OUTPUT VOLTAGE
100k
+VIN 8 VIN VOUT 1
ERROR
NOT * VALID
NOT * VALID
ERROR OUTPUT
5 ERROR MIC2951
VOUT = V REF R1 x (1 + ) R2 VOUT 1.2 30V
INPUT VOLTAGE 1.3V
5V
ON
SHUTDOWN 3 SD INPUT
OFF
3.3F GND 4 FB 7 R1 100 pF 1.23V R2
3
V REF
* SEE APPLICATIONS INFORMATION
NOTE: PINS 2 AND 6 ARE LEFT OPEN
*SEE APPLICATIONS INFORMATION
Figure 1. ERROR Output Timing
Figure 2. Adjustable Regulator
870 23
Typical Applications
+V IN *SLEEP INPUT 47k 8 +V IN V OUT 1 C-MOS GATE
+VIN 8 +VIN ERROR OUTPUT
+V OUT
470 k
5 ERROR 3
OFF
*VOUT VIN VOUT 1
870 25
MIC2951 SHUTDOWN INPUT SD GND 4 FB 7
ERROR OUTPUT
5
ERROR MIC2951
SHUTDOWN 3 SD INPUT OFF GND ON 4
FB 7
200k + 2N3906 1% 100k 100pF
3.3F
ON
1% 100k
*HIGH INPUT LOWERS VOUT TO 2.5V
*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV, DEPENDING ON LOAD CURRENT.
5V Regulator with 2.5V Sleep Function
Wide Input Voltage Range Current Limiter
February 1999
3-59
MIC2950/2951
+V = 2 30V I L LOAD 1.23V I L= R
Micrel
5V BUS +V IN
8 VIN VOUT 1 MIC2951
V OUT MIC2950Z
*V OUT5V
+ GND
1F
SHUTDOWN 3 SD INPUT
OFF ON
0.1F FB 7 R 1% 1F
GND 4
870 27
5-Volt Current Limiter
* MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV, DEPENDING ON LOAD CURRENT.
Low Drift Current Source
+V IN 8 +V IN 2 SENSE
D1
VOUT
1
D2
MEMORY V+ 20
MIC2951 #1 5 ERROR GND 4 27k
1F
3.6V NICAD
870 29
2.7M Q1
D4
D3
EARLY WARNING RESET
8 +V IN
2 SENSE VOUT 1
330k MAIN OUTPUT
P VDO
MIC2951 #2 5 3 SD ERROR GND 4
+
1f
Regulator with Early Warning and Auxiliary Output
* EARLY WARNING FLAG ON LOW INPUT VOLTAGE * MAIN OUTPUT LATCHES OFF AT LOWER INPUT VOLTAGES * BATTERY BACKUP ON AUXILIARY OUTPUT OPERATION: REG. #1'S VOUT IS PROGRAMMED ONE DIODE DROP ABOVE 5 V. ITS ERROR FLAG BECOMES ACTIVE WHEN VIN 5.7 V. WHEN VIN DROPS BELOW 5.3 V, THE ERROR FLAG OF REG. #2 BECOMES ACTIVE AND VIA Q1 LATCHES THE MAIN OUTPUT OFF. WHEN VIN AGAIN EXCEEDS 5.7 V REG. #1 IS BACK IN REGULATION AND THE EARLY WARNING SIGNAL RISES, UNLATCHING REG. #2 VIA D3.
3-60
February 1999
MIC2950/2951
+V IN
4 20mA 8 +5V 4.7mA 1 V OUT MIC2951 7 FB GND 4 1N457 4V 2 360 1 4
Micrel
470k 5 470k 3 RESET
8 +V IN ERROR VOUT 1 7 R2 VOUT R1 FB GND 4 + 1F
1N 4001 0.1F
V IN
OUTPUT* 5
MIC2951 SD
* HIGH FOR IL < 3.5mA
Latch Off When Error Flag Occurs
MIN. VOLTAGE
Open Circuit Detector for 4mA to 20mA Current Loop
39k 5 RESET
8 +V IN ERROR
2 SENSE VOUT 1 7 +V OUT = 5V + 1F
3
MIC2951
- +
C4
3
SD GND 4 TAP 6
FB
39k
+
6V 1% LEADACID BATTERY 1% C1-C4 LP339
100 k 1 k 1 k 10k 20k
- + - +
100k <5.8V** 100k <6.0V** 100k <6.2V**
C1
C2
1%
- +
C3
R3 1%
870 33
C1 TO C4 ARE COMPARATORS (LP339 OR EQUIVALENT) *OPTIONAL LATCH OFF WHEN DROP OUT OCCURS. ADJUST R3 FOR C2 SWITCHING WHEN VIN IS 6.0V **OUTPUTS GO LOW WHEN VIN DROPS BELOW DESIGNATED THRESHOLDS.
Regulator with State-of-Charge Indicator
February 1999
3-61
MIC2950/2951
+ 6V 120k 1.5k** SEALED 1N457 LEADACID BATTERY FB LM385 SOURCE - 400k* FOR 5.5V 100k 3 SD
Micrel
8 +V IN VOUT 1 MIC2951 SENSE GND 4 2 1F +
* Sets disconnect voltage ** Sets disconnect hysteresis
Low-Battery Disconnect
For values shown, Regulator shuts down when VIN < 5.5 V and turns on again at 6.0 V. Current drain in disconnected mode is 150A.
+VIN
8 +VIN AUX. SHUTDOWN INPUT
OFF ON
10k 5 5 PRE-SHUTDOWN FLAG
3
SD
ERROR MIC2951
1 V OUT GND 4 FB 7 EXTERNAL CIRCUIT PROTECTED FROM OVER TEMPERATURE (V+ GOES OFF WHEN TEMP.> 125) OR RELAY
+ TEMP. LM34 OR SENSOR LM35 -
8.2k
LM34 for 125F Shutdown LM35 for 125C Shutdown
System Overtemperature Protection Circuit
Schematic Diagram
IN FEEDBACK
R18 20k
Q15A Q15B
100 x 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 182 k
5V TAP
R28 60 k
Q22 Q21
C2 40 pF
Q42
R8 31.4 k
R10 150 k
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 DENOTES CONNECTION ON MIC2950 ONLY
R25 2.8 k
Q39
GND
3-62
February 1999

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