MIC811/812
Micrel, Inc.
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.
Having a push-pull output stage, MIC811/812 does not
require a pull-up resistor at the output. The MIC811/812
comes in a 4-pin SOT-143 package.
If a microprocessor voltage supervisor with an open-drain
output stage is needed, see MIC6315.
Features
• Precision voltage monitor for 3V, 3.3V or 5V power
supplies
• /RESET remains valid with V
CC
as low as 1.4V
• <15µA 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
Ordering Information
Standard
Part Number
Marking
MIC811LU
MIC811MU
MIC811JU
MIC811UU
MIC811TU
MIC811SU
MIC811RU
MIC812LU
MIC812MU
MIC812JU
MIC812UU
MIC812TU
MIC812SU
MIC812RU
KL
KM
KJ
KU
KT
KS
KR
LL
LM
LJ
LU
LT
LS
LR
Pb-Free
Part Number Marking
MIC811LUY
MIC811MUY
MIC811JUY
MIC811UUY
MIC811TUY
MIC811SUY
MIC811RUY
MIC812LUY
MIC812MUY
MIC812JUY
MIC812UUY
MIC812TUY
MIC812SUY
MIC812RUY
KL
KM
KJ
KU
KT
KS
KR
LL
LM
LJ
LU
LT
LS
LR
Threshold
Voltage
4.63
4.38
4.00
3.00
3.08
2.93
2.63
4.63
4.38
4.00
3.00
3.08
2.93
2.63
Operating
Temp. Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
4-lead SOT-143
*Under bar symbol (_) may not be to scale.
Typical Application
VCC
VCC
MIC811
VCC
µP
MR
RESET
RESET
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
February 2005
1
MIC811/812
MIC811/812
Micrel, Inc.
Pin Configuration
GND 1
4 V
CC
MIC811
RESET 2
3 MR
GND 1
4 V
CC
MIC812
RESET 2
3 MR
MIC811 4-Lead SOT-143
MIC812 4-Lead SOT-143
Pin Description
Pin Number
MIC811
1
2
Pin Number
MIC812
1
N/A
Pin Name
GND
/RESET
Pin Function
IC Ground Pin
/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
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
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.
N/A
2
RESET
3
3
/MR
4
4
VCC
MIC811/812
2
February 2005
MIC811/812
Micrel, Inc.
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 150°C
Rate of Rise (V
CC
) ................................................. 100V/µs
ESD Rating,
Note 3
Operating Ratings
(Note 2)
Operating Temperature Range
MIC811 ..................................................... –40°C to 85°C
MIC812 ..................................................... –40°C to 85°C
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 –40°C
≤
T
A
≤
+85°C; unless noted
Symbol
V
CC
I
CC
Parameter
Operating Voltage Range
Condition
T
A
= 0°C to 70°C
T
A
= –40°C to 85°C
Supply Current
MIC811L/M/J, MIC812L/M/J:
V
CC
= 5.0V, no load
MIC811S/T, MIC812S/T
V
CC
= 3.3V, no load
V
TH
Reset Voltage Threshold
MIC811R, MIC812R: V
CC
= 3.0V, no load
MIC811L, MIC812L
MIC811M, MIC812M
MIC811J, MIC812J
MIC811T, MIC812T
MIC811S, MIC812S
MIC811R, MIC812R
t
RST
V
OH
V
OL
Reset Timeout Period
/RESET Output Voltage
I
SOURCE
= 800µA, MIC811L/M/J
I
SOURCE
= 500µA, MIC811R/S/T
/RESET Output Voltage
V
CC
= V
TH
min., I
SINK
= 3.2mA, MIC811L/M/J
V
CC
= V
TH
min., I
SINK
= 1.2mA, MIC811R/S/T
V
CC
> 1.4V, I
SINK
= 50µA, T
A
= 0°C to +70°C
V
CC
> 1.6V, I
SINK
= 50µA, T
A
= –40° to +85°C
V
OH
V
OL
RESET Output Voltage
RESET Output Voltage
1.8V < V
CC
< V
TH
min., I
SOURCE
= 150µA
I
SINK
= 3.2mA, MIC812L/M/J
I
SINK
= 1.2mA, MIC812R/S/T
/MR Minimum Pulse Width
/MR to Reset Delay
V
IH
V
IL
/MR Input Threshold
V
CC
> V
TH
max., MIC81_L/M/J
MIC81_R/S/T
/MR Input Threshold
V
CC
. V
TH
max., MIC81-L/M/_
MIC81_R/S/T
/MR Pull-Up Resistance
/MR Glitch Immunity
Note 1.
Note 2.
Note 3.
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 recommended. Human body model, 1.5k in series with 100pF.
Min
1.4
1.6
Typ
Max
5.5
5.5
Units
V
V
µA
µA
µA
V
V
V
V
V
V
ms
V
V
9
6
6
4.50
4.25
3.89
3.00
2.85
2.55
140
V
CC
–1.5V
0.8×V
CC
×
4.63
4.38
4.00
3.08
2.93
2.63
240
15
10
10
4.75
4.50
4.10
3.15
3.00
2.70
560
0.4
0.3
0.3
0.3
0.8×V
CC
×
0.4
0.3
10
0.5
2.3
0.7×V
CC
×
0.8
0.25×V
CC
×
10
20
100
30
V
V
V
V
V
V
V
µs
µs
V
V
V
kΩ
ns
February 2005
3
MIC811/812
MIC811/812
Micrel, Inc.
Timing Diagram
V
CC
V
TH
/MR
t
RST
t
RST
/RESET
Reset Timing Diagram
Functional Diagram
VCC (4)
Reset
Threshold (V)
MR (3)
+
-
RESET
GENERATOR
RESET (2)
RESET (MIC812)
GND (1)
MIC811/812
4
February 2005
MIC811/812
Micrel, Inc.
/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 100kΩ 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.
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 50µs (25µs for MIC8_R/S/T) or less will not cause
a reset.
Interfacing to Bidirectional Reset Pins
The MIC811/812 can interface with
µPs
with bidirectional
reset pins by connecting a 4.7kΩ resistor in series with the
MIC811/812 output and the
µP
reset pin.
VCC
VCC
MIC811
VCC
µP
RESET
100K
RESET
Reset Valid to V
CC
= 0V
February 2005
5
MIC811/812
Microcontroller MCU
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