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MIC811/MIC812 Microprocessor Reset Circuits
MIC811/MIC812
Microprocessor Reset Circuits
Description
The MIC811/MIC812 are inexpensive microprocessor supervisory circuits that monitor power supplies in microprocessor based systems. The function of these devices is to assert a reset if either the power supply drops below a designated reset threshold level or MR is forced low. Several different reset threshold levels are available to accomodate 3V, 3.3V or 5V powered systems. The MIC811 has an active low RESET output, while the MIC812 offers an active high RESET output. The reset output is guaranteed to remain asserted for a minimum of 140ms after VCC has risen above the designated reset threshold level. The MIC811/MIC812 come in a 4pin SOT-143 package.
Pin Configuration
Top View
GND 1 4 VCC
MIC811
RESET 2 3 MR
GND 1
4 VCC
MIC812
RESET 2 3 MR
Typical Applications
Features
RESET * as 1.4V Remains Valid with VCC as Low * Precision Voltage Monitor for 3V, 3.3V or 5V Power Supplies * Available in 4-Pin SOT-143 Package * <15A Supply Current * 140ms Minimum Reset Pulse Width * Manual Reset Input
* Portable Equipment * Intelligent Instruments * Critical Microprocessor Power Monitoring * Printers/Computers * Controllers
Reset Threshold Voltage (V) 4.63 4.38 4.00 3.08 2.93 2.63 Device Suffix L M J T S R
Typical Operating Circuit
VCC VCC
MIC811
Ordering Information
Part MIC811_U MIC812_U Package 4-Lead SOT-143 4-Lead SOT-143 Temp. Range -40C to +85C -40C to +85C
VCC
P
Place the device suffix of desired reset threshold voltage from table above in blank to complete the part number.
MR
RESET
RESET
1
MIC811/MIC812 Microprocessor Reset Circuits
Absolute Maximum Ratings
Terminal Voltage VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6.0V MR . . . . . . . . . . . . . . . . . . . . . -0.3V to (VCC + 0.3V) Input Current, VCC, MR . . . . . . . . . . . . . . . . . . . . 20mA Output Current, RESET, RESET . . . . . . . . . . . . . .20mA Rate of Rise, VCC . . . . . . . . . . . . . . . . . . . . . . 100V/s Operating Temperature Range MIC81--U . . . . . . . . . . . . . . . . . . . . . . . . -40C to 85C Storage Temperature Range . . . . . . . . . . . . .-65C to 150C Lead Temperature (Soldering - 10 sec.) . . . . . . . . . . . 300C Power Dissipation (TA = +70C) . . . . . . . . . . . . . . . . 320mW
Stresses above those listed under ABSOLUTE MAXIMUM RATINGS may cause permanent device failure. Functionality at or above these limits is not implied. Exposure to absolute maximum ratings for extended periods may affect device reliability. Operating ranges define those limits between which the functionality of the device is guaranteed.
Electrical Characteristics
VCC = 5V for MIC81-L/M/J, VCC = 3.3V for MIC81-S/T, VCC = 3V for MIC81-R, TA = Operating Temperature Range, unless otherwise noted. Parameter Operating Voltage Range, VCC Supply Current, ICC Reset Voltage Threshold, VTH Conditions TA = 0C to 70C TA = -40C to 85C MIC811L/M/J, MIC812L/M/J VCC < 3.6V, MIC811R/S/T, MIC812R/S/T MIC811L, MIC812L MIC811M, MIC812M MIC811J, MIC812J MIC811T, MIC812T MIC811S, MIC812S MIC811R, MIC812R 4.50 4.25 3.89 3.00 2.85 2.55 140 ISource = 800A, MIC811L/M/J ISource = 500A, MIC811R/S/T VCC=VTH Min., ISink=3.2mA, MIC811L/M/J VCC=VTH Min., ISink =1.2mA, MIC811R/S/T VCC>1.4V, ISink =50A, TA = 0C to 70C VCC>1.6V, ISink =50A, TA = -40C to 85C 1.8V < VCC < VTH Min., ISource = 150A ISink=3.2mA, MIC812L/M/J ISink=1.2mA, MIC812R/S/T 10 0.5 VCC > VTH Max., MIC81_L/M/J MIC81_R/S/T VCC > VTH Max., MIC81_L/M_ MIC81_R/S/T 10 20 100 2.3 0.7 X VCC 0.8 0.25 X VCC 30 0.8 X VCC 0.4 0.3 VCC - 1.5V 0.8 X VCC 0.4 0.3 0.3 0.3 Min 1.4 1.6 9 6 4.63 4.38 4.00 3.08 2.93 2.63 240 Typ Max 5.5 5.5 15 10 4.75 4.50 4.10 3.15 3.00 2.70 560 Units V A V
Reset Timeout Period RESET Output Voltage, VOH RESET Output Voltage, VOL
ms V
V
RESET Output Voltage, VOH RESET Output Voltage, VOL MR Minimum Pulse Width MR to Reset Delay MR Input Threshold, VIH MR Input Threshold, VIL MR Pull-Up Resistance MR Glitch Immunity
V
V s s V V k ns
2
MIC811/MIC812 Microprocessor Reset Circuits
Pin Functions
Pin No.
Pin Name GND RESET MIC811 1 2 MIC812 1 N/A Description IC Ground Pin. RESET goes low if VCC falls below the reset threshold and remains asserted for one reset timeout period (140ms min.) after VCC exceeds the reset threshold. RESET goes high if VCC falls below the reset threshold and remains asserted for one reset timeout period (140ms min.) after VCC exceeds the reset threshold. Manual reset input. A logic low on MR forces a reset. The reset will remain asserted as long as MR is held low and for one reset timeout period (140ms min.) after MR goes high. This input can be shorted to ground via a switch or driven from CMOS or TTL logic. Float if unused. Power supply input, 3V, 3.3V or 5V.
RESET
N/A
2
MR
3
3
VCC
4
4
3
MIC811/MIC812 Microprocessor Reset Circuits
Block Diagram
VCC (4) Reset Threshold (V)
+ RESET GENERATOR RESET (2) RESET (MIC812)
MR (3)
GND (1)
Figure 1. MIC811/812 Block Diagram
4
MIC811/MIC812 Microprocessor Reset Circuits
Circuit Description
Microprocessor Reset The RESET pin is asserted whenever VCC falls below the reset threshold voltage or if MR (manual reset) is forced low. The reset pin remains asserted for a period of 240ms after VCC has risen above the reset threshold voltage or MR has returned high. The reset function ensures the microprocessor is properly reset and powers up into a known condition after a power failure. RESET will remain valid with VCC as low as 1.4V. VCC Transients The MIC811/MIC812 are relatively immune to negativegoing VCC glitches below the reset threshold. Typically, a negative-going transient 125mV below the reset threshold with a duration of 50s (25s for MIC81_R/S/T) or less will not cause an unwanted reset. Interfacing to Bidirectional Reset Pins The MIC811/MIC812 can interface with Ps with bidirectional reset pins by connecting a 4.7K resistor in series with the MIC811/MIC812 output and the P reset pin.
VCC
Vthr
MR t1 RESET t1
Figure 2. Reset Timing Diagram
VCC VCC VCC P RESET
100K
MIC811
RESET
RESET Valid to 0V A resistor can be added from the RESET pin to ground to ensure the RESET output remains low with V CC down to 0V. A 100K resistor connected from RESET to ground is recommended. The size of the resistor should be large enough to not load the RESET output and small enough to pull-down any stray leakage currents.
Figure 3. RESET Valid to VCC = 0V.
5
MIC811/MIC812 Microprocessor Reset Circuits
Alternate Source Cross Reference Guide
Industry P/N
MAX811JEUS-T MAX811LEUS-T MAX811MEUS-T MAX811REUS-T MAX811SEUS-T MAX811TEUS-T MAX812JEUS-T MAX812LEUS-T MAX812MEUS-T MAX812REUS-T MAX812SEUS-T MAX812TEUS-T
MIC Direct Replacement
MIC811JU MIC811LU MIC811MU MIC811RU MIC811SU MIC811TU MIC812JU MIC812LU MIC812MU MIC812RU MIC812SU MIC812TU
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MIC811/MIC812 Microprocessor Reset Circuits
Packaging Information
U Package, 4-Pin SOT-143 Small-Outline Transistor Package
0.079 0.071
0.055 0.047
0.098 0.083
0.037 0.030
0.021 0.015
0.120 0.105 0.0059 0.0035 0-81/4
0.040 0.031
0.080 0.070
0.004 0.001
0.010 0.005
Dimensions are in inches.
Device Marking Information
Lot Code
KJXX KLXX KMXX KRXX KSXX KTXX LJXX LLXX LMXX LRXX LSXX LTXX
= = = = = = = = = = = =
MIC811J MIC811L MIC811M MIC811R MIC811S MIC811T MIC812J MIC812L MIC812M MIC812R MIC812S MIC812T
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MIC811/MIC812 Microprocessor Reset Circuits
Packaging Information
Tape and Reel Information
4.0-0.1 2.0-0.05
fl1.5-0.1
1.75-0.1
3.5-0.05 8.0-0.3
4.0-0.1
fl1.1-0.1
2.7-0.1
1.2-0.1
3.1-0.1
Dimensions are in millimeters.
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