September 2005 1 MIC811/812
MIC811/812 Micrel
MIC811/812
Microprocessor Reset Circuits
General Description
The MIC811 and MIC812 are inexpensive microprocessor
supervisory circuits that monitor 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 VCC has risen above the designed reset threshold level.
Having a push-pull output stage, the 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 sup-
plies
• /RESET remains valid with VCC as low as 1V
• 5µA typical 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. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
Typical Application
VCC
RESET
µP
RESET
VCC
MIC811
VCC
MR
MIC811/812 Micrel
MIC811/812 2 September 2005
Ordering Information
Part Number Marking Threshold
Voltage
Operating Temp.
Range
Package
Standard Pb-Free Standard Pb-Free
MIC811LU MIC811LUY KL KL 4.63 –40°C to +85°C 4-lead SOT-143
MIC811MU MIC811MUY KM KM 4.38 –40°C to +85°C 4-lead SOT-143
MIC811JU MIC811JUY KJ KJ 4.00 –40°C to +85°C 4-lead SOT-143
MIC811TU MIC811TUY KT KT 3.08 –40°C to +85°C 4-lead SOT-143
MIC811SU MIC811SUY KS KS 2.93 –40°C to +85°C 4-lead SOT-143
MIC811RU MIC811RUY KR KR 2.63 –40°C to +85°C 4-lead SOT-143
MIC812LU MIC812LUY LL LL 4.63 –40°C to +85°C 4-lead SOT-143
MIC812MU MIC812MUY LM LM 4.38 –40°C to +85°C 4-lead SOT-143
MIC812JU MIC812JUY LJ LJ 4.00 –40°C to +85°C 4-lead SOT-143
MIC812TU MIC812TUY LT LT 3.08 –40°C to +85°C 4-lead SOT-143
MIC812SU MIC812SUY LS LS 2.93 –40°C to +85°C 4-lead SOT-143
MIC812RU MIC812RUY LR LR 2.63 –40°C to +85°C 4-lead SOT-143
September 2005 3 MIC811/812
MIC811/812 Micrel
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 VCC falls below the reset threshold and remains as-
serted for one reset timeout period (140ms min.) after VCC exceeds the reset
threshold
N/A 2 RESET RESET goes high if VCC falls below the reset threshold and remains as-
serted for one reset timeout period (140ms min.) after VCC 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
VCC
GND
MIC811
RESET
3
MR
MIC811 4-Lead SOT-143
MIC812 4-Lead SOT-143
MIC811/812 Micrel
MIC811/812 4 September 2005
Absolute Maximum Ratings(Note 1)
Terminal Voltage (VCC) .................................–0.3V to +6.0V
Input Current (VCC, /MR) ............................................ 20mA
Output Current (/RESET, RESET) .............................. 20mA
Lead Temperature (soldering, 10 sec.) ...................... 300°C
Storage Temperature (TS) .......................... –65°C to 150°C
Rate of Rise (VCC) .................................................. 100V/µs
ESD Rating, Note 3 ....................................................... 3kV
Operating Ratings(Note 2)
Operating Temperature Range
MIC811 ..................................................... –40°C to 85°C
MIC812 ..................................................... –40°C to 85°C
Power Dissipation (TA = +70°C) .............................. 320mW
Electrical Characteristics
For typical values, VCC = 5V for MIC8_L/M/J, VCC = 3.3V for MIC8_S/T, VCC = 3V for MIC8_R; TA = 25°C, bold values indicate –40°C
≤ TA ≤ +85°C; unless noted
Symbol Parameter Condition Min Typ Max Units
VCC Operating Voltage Range TA = –40°C to 85°C 1 5.5 V
ICC Supply Current MIC811L/M/J, MIC812L/M/J: 5 15 µA
VCC = 5.0V, no load
MIC811S/T, MIC812S/T 5 10 µA
VCC = 3.3V, no load
MIC811R, MIC812R: VCC = 3.0V, no load 5 10 µA
VTH 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
tRST Reset Timeout Period 140 240 560 ms
VOH /RESET Output Voltage ISOURCE = 800µA, MIC811L/M/J VCC–1.5V V
ISOURCE = 500µA, MIC811R/S/T 0.8×VCC V
VOL /RESET Output Voltage VCC = VTH min., ISINK = 3.2mA, MIC811L/M/J 0.4 V
VCC = VTH min., ISINK = 1.2mA, MIC811R/S/T 0.3 V
VCC > 1V, ISINK = 50µA, TA = –40° to +85°C 0.3 V
VOH RESET Output Voltage 1.8V < VCC < VTH min., ISOURCE = 150µA 0.8×VCC V
VOL RESET Output Voltage ISINK = 3.2mA, MIC812L/M/J 0.4 V
ISINK = 1.2mA, MIC812R/S/T 0.3 V
/MR Minimum Pulse Width 10 µs
/MR to Reset Delay 0.5 µs
VIH /MR Input Threshold VCC > VTH max., MIC81_L/M/J 2.3 V
MIC81_R/S/T 0.7×VCC V
VIL /MR Input Threshold VCC . VTH max., MIC81-L/M/J 0.8 V
MIC81-R/S/T
0.25
×
VCC
/MR Pull-Up Resistance 10 20 30 kΩ
/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.
September 2005 5 MIC811/812
MIC811/812 Micrel
Functional Diagram
+
-
Reset
Threshold (V)
VCC (4)
RESET (2)
RESET (MIC812)
GND (1)
RESET
GENERATOR
MR (3)
Timing Diagram
/MR
/RESET
VCC VTH
tRST tRST
Reset Timing Diagram
MIC811/812 Micrel
MIC811/812 6 September 2005
Applications Information
Microprocessor Reset
The /RESET (or RESET) pin is asserted whenever VCC falls
below the reset threshold voltage. The /RESET pin remains
asserted for a period of 140ms after VCC has risen above the
reset threshold voltage. The reset function ensures that the
microprocessor is properly reset and powers up in a known
condition after a power failure. /RESET will remain valid with
VCC as low as 1V.
VCC Transients
The MIC811/812 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
20µs 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.
/RESET Valid at Low Voltage
A resistor can be added from the /RESET pin to ground to
ensure the /RESET output remains low with VCC 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.
VCC
RESET
µP
RESET
VCC
MIC811
VCC
100K
Reset Valid to VCC = 0V
September 2005 7 MIC811/812
MIC811/812 Micrel
Package Information
0.150 (0.0059)
0.089 (0.0035)
8
0
0.400 (0.016) TYP 3 PLACES
2.50 (0.098)
2.10 (0.083)
1.40 (0.055)
1.20 (0.047)
0.950 (0.0374) TYP
3.05 (0.120)
2.67 (0.105)
0.800 (0.031) TYP
1.12 (0.044)
0.81 (0.032)
0.10 (0.004)
0.013 (0.0005)
DIMENSIONS:
MM (INCH)
0.41 (0.016)
0.13 (0.005)
C
L
C
L
4-lead SOT-143 (M3)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this datasheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not�
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into
the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s
use or sale of Micrel Products for use in life support appliances, devices or systems is at Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2005 Micrel, Incorporated.
