1
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 4-
pin SOT-143 package.
1
2
4 V
CC
GND
MIC812
RESET
3
MR
1
2
4 V
CC
GND
MIC811
RESET
3
MR
Top View
Part
Package
Temp. Range
MIC811_U
4-Lead SOT-143
-40C to +85C
MIC812_U
4-Lead SOT-143
-40C to +85C
Place the device suffix of desired reset threshold voltage from table above in
blank to complete the part number.
Portable Equipment
Intelligent Instruments
Critical Microprocessor Power Monitoring
Printers/Computers
Controllers
RESET Remains Valid with VCC as Low
as 1.4V
Precision Voltage Monitor for 3V, 3.3V
or 5V Power Supplies
Available in 4-Pin SOT-143 Package
<15
A Supply Current
140ms Minimum Reset Pulse Width
Manual Reset Input
VCC
RESET
P
RESET
VCC
MIC811
VCC
MR
Typical Operating Circuit
Features
Description
Pin Configuration
Ordering Information
Typical Applications
Reset Threshold
Device
Voltage (V)
Suffix
4.63
L
4.38
M
4.00
J
3.08
T
2.93
S
2.63
R
MIC811/MIC812 Microprocessor Reset Circuits
MIC811/MIC812
Microprocessor Reset Circuits
MIC811/MIC812 Microprocessor Reset Circuits
2
Electrical Characteristics
VCC = 5V for MIC81-L/M/J, VCC = 3.3V for MIC81-S/T, VCC = 3V for MIC81-R, T
A
= Operating Temperature Range, unless
otherwise noted.
Parameter
Conditions
Min
Typ
Max
Units
Operating Voltage Range, VCC TA = 0C to 70C
1.4
5.5
V
TA = -40C to 85C
1.6
5.5
Supply Current, ICC
MIC811L/M/J, MIC812L/M/J
9
15
A
VCC < 3.6V, MIC811R/S/T, MIC812R/S/T
6
10
Reset Voltage Threshold, VTH
MIC811L, MIC812L
4.50
4.63
4.75
V
MIC811M, MIC812M
4.25
4.38
4.50
MIC811J, MIC812J
3.89
4.00
4.10
MIC811T, MIC812T
3.00
3.08
3.15
MIC811S, MIC812S
2.85
2.93
3.00
MIC811R, MIC812R
2.55
2.63
2.70
Reset Timeout Period
140
240
560
ms
RESET Output Voltage, VOH
ISource = 800
A, MIC811L/M/J
VCC - 1.5V
V
ISource = 500
A, MIC811R/S/T
0.8 X VCC
RESET Output Voltage, VOL
VCC=VTH Min., ISink=3.2mA, MIC811L/M/J
0.4
V
VCC=VTH Min., ISink =1.2mA, MIC811R/S/T
0.3
VCC>1.4V, ISink =50
A, TA = 0C to 70C
0.3
VCC>1.6V, ISink =50
A, TA = -40C to 85C
0.3
RESET Output Voltage, VOH
1.8V < VCC < VTH Min., 0.8
X
VCC
V
ISource = 150
A
RESET Output Voltage, VOL
ISink=3.2mA, MIC812L/M/J
0.4
V
ISink=1.2mA, MIC812R/S/T
0.3
MR Minimum Pulse Width
10
s
MR to Reset Delay
0.5
s
MR Input Threshold, VIH
VCC > VTH Max., MIC81_L/M/J
2.3
V
MIC81_R/S/T
0.7 X VCC
MR Input Threshold, VIL
VCC > VTH Max., MIC81_L/M_
0.8
V
MIC81_R/S/T
0.25 X VCC
MR Pull-Up Resistance
10
20
30
k
MR Glitch Immunity
100
ns
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.
Pin Functions
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.
Pin No.
Pin Name
MIC811
MIC812
GND
1
1
RESET
2
N/A
RESET
N/A
2
MR
3
3
VCC
4
4
MIC811/MIC812 Microprocessor Reset Circuits
3
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 negative-
going VCC glitches below the reset threshold. Typically,
a negative-going transient 125mV below the reset
threshold with a duration of 50
s (25
s 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.
RESET Valid to 0V
A resistor can be added from the RESET pin to ground
to ensure the RESET output remains low with VCC
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.
Circuit Description
Figure 2. Reset Timing Diagram
Figure 3. RESET Valid to VCC = 0V.
VCC
MR
RESET
t1
t1
Vthr
MIC811/MIC812 Microprocessor Reset Circuits
5
VCC
RESET
P
RESET
VCC
MIC811
VCC
100K
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