July 2005 1 MIC1815
MIC1815 Micrel
MIC1815
Microprocessor Reset Circuit
General Description
The MIC1815 is an inexpensive microprocessor supervisory
circuit that monitors power supplies in microprocessor based
systems.
The function of these devices is to assert a reset if the power
supply drops below a designated reset threshold level. Several
different reset threshold levels are available to accommodate
10% or 20% drop in 3.3V powered systems.
The MIC1815 has an active low /RESET output. The reset
output is guaranteed to remain asserted for a minimum of
100ms after VCChas risen above the designated reset thresh-
old level. The MIC1815 comes in a 3-pin SOT-23 package.
Typical Application
VCC
RESET
µP
RESET
VCC
MIC1815
VCC
Features
• Precision voltage monitor for 10% or 20% drop in 3.3V
power supplies
• /RESET remains valid with VCC as low as 1V
• 5µA supply current
• 100ms minimum reset pulse width
• No external components required
• Available in 3-pin SOT-23 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) 474-1000 • fax + 1 (408) 944-0970 • http://www.micrel.com
Ordering Information
Threshold
Part Number Marking Voltage Operating Temp. Range Package Pb-Free
MIC1815-10U ND 2.88V –40°C to +85°C SOT-23 No
MIC1815-20U NE 2.55V –40°C to +85°C SOT-23 No
MIC1815-10UY ND 2.88V –40°C to +85°C SOT-23 Yes
MIC1815-20UY NE 2.55V –40°C to +85°C SOT-23 Yes
MIC1815 Micrel
MIC1815 2 July 2005
Pin Description
Pin Number Pin Name Pin Function
1 /RESET /RESET goes low if VCC falls below the reset threshold and remains as-
serted for one reset timeout period (100ms min) after VCC exceeds the reset
threshold.
2 VCC Power supply input.
3 GND IC ground pin
Pin Configuration
1
2
3
V
CC
GND
MIC1815
RESET
3-Lead SOT23
July 2005 3 MIC1815
MIC1815 Micrel
Absolute Maximum Ratings(Note 1)
Terminal Voltage (VCC) ....................................–0.3V to +6V
Input Current (VCC) ..................................................... 20mA
Output Current (/RESET) ........................................... 20mA
Rate of Rise (VCC) .................................................. 100V/µs
Lead Temperature (soldering, 10 sec.) ...................... 300°C
Storage Temperature (TS) .......................... –65°C to 150°C
ESD Rating, Note 3 ....................................................... 3kV
Operating Ratings(Note 2)
Operating Temperature Range
MIC1815-10U ......................................... –40°C to +85°C
MIC1815-20U ......................................... –40°C to +85°C
Power Dissipation (TA = +70°C) .............................. 320mW
Electrical Characteristics
For typical values, VCC = 3.3V, TA = 25°C; bold values indicate –40°C ≤ TA ≤ +85°C; unless noted
Symbol Parameter Condition Min Typ Max Units
VCC Operating Temperature Range TA = –40°C to +85°C 1 5.5 V
ICC Supply Current 5 20 µA
VTH Reset Voltage Threshold MIC1815-10U 2.80 2.88 2.97 V
MIC1815-20U 2.47 2.55 2.64 V
tRST Reset Timeout Period 100 150 250 ms
VOH /RESET Output Voltage ISOURCE = 800µA 1.5 V
VOL /RESET Output Voltage VCC = VTH min., ISINK = 10mA 0.4 V
VCC > 1V, ISINK = 50µA 0.3 V
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.
Timing Diagram
/RESET
VCC
tRST tRST
VTH VTH
Reset Timing Diagram
MIC1815 Micrel
MIC1815 4 July 2005
Functional Diagram
VCC(2)
GND (3)
RESET (1)
Reset
Threshold (VTH)
RESET
GENERATOR
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MIC1815 Micrel
Applications Information
Microprocessor Reset
The /RESET pin is asserted whenever VCC falls below the
reset threshold voltage. The reset pin remains asserted for a
period of tRST after VCC has risen above the reset threshold
voltage. 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 1V.
VCC Transients
The MIC1815 is 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 an unwanted reset.
/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 /RESET-to-ground is
recommended. The resistor should be large enough not to
load the /RESET output and small enough to pull-down any
stray leakage currents. See Figure below.
VCC
RESET
µP
RESET
VCC
MIC1815
VCC
100K
/RESET Valid to VCC = 0V
MIC1815 Micrel
MIC1815 6 July 2005
Package Information
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3-Pin SOT-23 Small Outline Transistor
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.
