May 2003
1
MIC811/812
MIC811/812
Micrel
MIC811/812
Microprocessor Reset Circuits
Final Information
General Description
The MIC811 and MIC812 are inexpensive microprocessor
supervisory circuit that monitors power supplies in micropro-
cessor based systems.
The function of this device 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 accommodate 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 V
CC
has risen above the designed reset threshold level.
The MIC811/812 comes in a 4-pin SOT-143 package.
Typical Application
VCC
RESET
P
RESET
VCC
MIC811
VCC
MR
Features
Precision voltage monitor for 3V, 3.3V or 5V power
supplies
/RESET remains valid with V
CC
as low as 1.4V
<15
A supply current
140ms minimum reset pulse width available
Manual reset input
Available in 4-pin SOT-143 package
Applications
Portable equipment
Intelligent instruments
Critical microprocessor power monitoring
Printers/computers
Embedded controllers
Micrel, Inc. 1849 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 http://www.micrel.com
Ordering Information
Threshold
Operating
Part Number
Marking
Voltage
Temp. Range
Package
MIC811LU
KL
4.63
40
C to +85C
4-lead SOT-143
MIC811MU
KM
4.38
40
C to +85C
4-lead SOT-143
MIC811JU
KJ
4.00
40
C to +85C
4-lead SOT-143
MIC811TU
KT
3.08
40
C to +85C
4-lead SOT-143
MIC811SU
KS
2.93
40
C to +85C
4-lead SOT-143
MIC811RU
KR
2.63
40
C to +85C
4-lead SOT-143
MIC812LU
LL
4.63
40
C to +85C
4-lead SOT-143
MIC812MU
LM
4.38
40
C to +85C
4-lead SOT-143
MIC812JU
LJ
4.00
40
C to +85C
4-lead SOT-143
MIC812TU
LT
3.08
40
C to +85C
4-lead SOT-143
MIC812SU
LS
2.93
40
C to +85C
4-lead SOT-143
MIC812RU
LR
2.63
40
C to +85C
4-lead SOT-143
MIC811/812
Micrel
MIC811/812
2
May 2003
Pin Description
Pin Number
Pin Number
MIC811
MIC812
Pin Name
Pin Function
1
1
GND
IC Ground Pin
2
N/A
/RESET
/RESET goes low if V
CC
falls below the reset threshold and remains
asserted for one reset timeout period (140ms min.) after V
CC
exceeds the
reset threshold
N/A
2
RESET
RESET goes high if V
CC
falls below the reset threshold and remains
asserted for one reset timeout period (140ms min.) after V
CC
exceeds the
reset threshold
3
3
/MR
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.
4
4
VCC
Power Supply Input.
Pin Configuration
1
2
4 V
CC
GND
MIC812
RESET
3
MR
1
2
4 V
CC
GND
MIC811
RESET
3
MR
MIC811 4-Lead SOT-143
MIC812 4-Lead SOT-143
May 2003
3
MIC811/812
MIC811/812
Micrel
Absolute Maximum Ratings
(Note 1)
Terminal Voltage (V
CC
) ............................... 0.3V to +6.0V
Input Current (V
CC
, /MR) ............................................ 20mA
Output Current (/RESET, RESET) ............................. 20mA
Lead Temperature (soldering, 10 sec.) ..................... 300
C
Storage Temperature (T
S
) ......................... 65
C to 150C
Rate of Rise (V
CC
) ................................................. 100V/
s
ESD Rating, Note 3
Operating Ratings
(Note 2)
Operating Temperature Range
MIC811 ..................................................... 40
C to 85C
MIC812 ..................................................... 40
C to 85C
Power Dissipation (T
A
= +70
C) .............................. 320mW
Electrical Characteristics
For typical values, V
CC
= 5V for MIC8_L/M/J, V
CC
= 3.3V for MIC8_S/T, V
CC
= 3V for MIC8_R; T
A
= 25
C, bold values indicate 40C
T
A
+85C; unless noted
Symbol
Parameter
Condition
Min
Typ
Max
Units
V
CC
Operating Voltage Range
T
A
= 0
C to 70C
1.4
5.5
V
T
A
= 40
C to 85C
1.6
5.5
V
I
CC
Supply Current
MIC811L/M/J, MIC812L/M/J
9
15
A
V
CC
< 3.6V, MIC811R/S/T, MIC812R/S/T
6
10
A
V
TH
Reset Voltage Threshold
MIC811L, MIC812L
4.50
4.63
4.75
V
MIC811M, MIC812M
4.25
4.38
4.50
V
MIC811J, MIC812J
3.89
4.00
4.10
V
MIC811T, MIC812T
3.00
3.08
3.15
V
MIC811S, MIC812S
2.85
2.93
3.00
V
MIC811R, MIC812R
2.55
2.63
2.70
V
t
RST
Reset Timeout Period
140
240
560
ms
V
OH
/RESET Output Voltage
I
SOURCE
= 800
A, MIC811L/M/J
V
CC
1.5V
V
I
SOURCE
= 500
A, MIC811R/S/T
0.8
V
CC
V
V
OL
/RESET Output Voltage
V
CC
= V
TH
min., I
SINK
= 3.2mA, MIC811L/M/J
0.4
V
V
CC
= V
TH
min., I
SINK
= 1.2mA, MIC811R/S/T
0.3
V
V
CC
> 1.4V, I
SINK
= 50
A, T
A
= 0
C to +70C
0.3
V
V
CC
> 1.6V, I
SINK
= 50
A, T
A
= 40
to +85C
0.3
V
V
OH
RESET Output Voltage
1.8V < V
CC
< V
TH
min., I
SOURCE
= 150
A
0.8
V
CC
V
V
OL
RESET Output Voltage
I
SINK
= 3.2mA, MIC812L/M/J
0.4
V
I
SINK
= 1.2mA, MIC812R/S/T
0.3
V
/MR Minimum Pulse Width
10
s
/MR to Reset Delay
0.5
s
V
IH
/MR Input Threshold
V
CC
> V
TH
max., MIC81_L/M/J
2.3
V
MIC81_R/S/T
0.7
V
CC
V
V
IL
/MR Input Threshold
V
CC
. V
TH
max., MIC81-L/M/_
0.8
V
MIC81_R/S/T
0.25
V
CC
/MR Pull-Up Resistance
10
20
30
k
/MR Glitch Immunity
100
ns
Note 1.
Exceeding the absolute maximum rating may damage the device.
Note 2.
The device is not guaranteed to function outside its operating rating.
Note 3.
Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
MIC811/812
Micrel
MIC811/812
4
May 2003
Functional Diagram
+
-
Reset
Threshold (V)
VCC (4)
RESET (2)
RESET (MIC812)
GND (1)
RESET
GENERATOR
MR (3)
Timing Diagram
/MR
/RESET
V
CC
V
TH
t
RST
t
RST
Reset Timing Diagram
May 2003
5
MIC811/812
MIC811/812
Micrel
Applications Information
Microprocessor Reset
The /RESET (or RESET) pin is asserted whenever V
CC
falls
below the reset threshold voltage. The /RESET pin remains
asserted for a period of 140ms after V
CC
has risen above the
reset threshold voltage. The reset function ensures the
microprocessor is properly reset and powers up in a known
condition after a power failure. /RESET will remain valid with
V
CC
as low as 1.4V.
V
CC
Transients
The MIC811/812 are relatively immune to negative-going
V
CC
glitches below the reset threshold. Typically, a negative-
going transient 125mV below the reset threshold with a
duration of 50
s (25s for MIC8_R/S/T) or less will not cause
a reset.
Interfacing to Bidirectional Reset Pins
The MIC811/812 can interface with
Ps with bidirectional
reset pins by connecting a 4.7k
resistor in series with the
MIC811/812 output and the
P reset pin.
/RESET Valid at Low Voltage
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 the /RESET to ground is
recommended. The size of the resistor should be large
enough not to load the output excessively and small enough
to pull-down any stray leakage currents.
VCC
RESET
P
RESET
VCC
MIC811
VCC
100K
Reset Valid to V
CC
= 0V
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