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 V
CC
has risen above the designated reset thresh-
old level. The MIC1815 comes in a 3-pin SOT-23 package.
Features
• Precision voltage monitor for 10% or 20% drop in 3.3V
power supplies
• /RESET remains valid with V
CC
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
Ordering Information
Part Number
MIC1815-10U
MIC1815-20U
MIC1815-10UY
MIC1815-20UY
Marking
ND
NE
ND
NE
Threshold
Voltage
2.88V
2.55V
2.88V
2.55V
Operating Temp. Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package
SOT-23
SOT-23
SOT-23
SOT-23
Pb-Free
No
No
Yes
Yes
Typical Application
VCC
VCC
VCC
MIC1815
RESET
µP
RESET
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 474-1000 • fax + 1 (408) 944-0970 • http://www.micrel.com
July 2005
1
MIC1815
MIC1815
Micrel
Pin Configuration
RESET
1
MIC1815
V
CC
2
3
GND
3-Lead SOT23
Pin Description
Pin Number
1
Pin Name
/RESET
Pin Function
/RESET goes low if V
CC
falls below the reset threshold and remains as-
serted for one reset timeout period (100ms min) after V
CC
exceeds the reset
threshold.
Power supply input.
IC ground pin
2
3
VCC
GND
MIC1815
2
July 2005
MIC1815
Micrel
Absolute Maximum Ratings
(Note 1)
Terminal Voltage (V
CC
) ....................................–0.3V to +6V
Input Current (V
CC
)..................................................... 20mA
Output Current (/RESET) ........................................... 20mA
Rate of Rise (V
CC
) .................................................. 100V/µs
Lead Temperature (soldering, 10 sec.) ...................... 300°C
Storage Temperature (T
S
) .......................... –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 (T
A
= +70°C) .............................. 320mW
Electrical Characteristics
For typical values, V
CC
= 3.3V, T
A
= 25°C;
bold
values indicate –40°C ≤ T
A
≤ +85°C; unless noted
Symbol
V
CC
I
CC
V
TH
t
RST
V
OH
V
OL
Parameter
Condition
Operating Temperature Range
Supply Current
Reset Voltage Threshold
Reset Timeout Period
/RESET Output Voltage
/RESET Output Voltage
V
CC
= V
TH
min., I
SINK
= 10mA
V
CC
> 1V, I
SINK
= 50µA
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
Typ
5
Max
5.5
20
2.97
2.64
250
0.4
0.3
Units
V
µA
V
V
ms
V
V
V
T
A
= –40°C to +85°C
MIC1815-10U
MIC1815-20U
I
SOURCE
= 800µA
2.80
2.47
100
1.5
2.88
2.55
150
Note 1.
Note 2.
Note 3.
Timing Diagram
V
CC
V
TH
t
RST
/RESET
V
TH
t
RST
Reset Timing Diagram
July 2005
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MIC1815
MIC1815
Micrel
Functional Diagram
V
CC
(2)
Reset
Threshold (V
TH
)
RESET
GENERATOR
RESET (1)
GND (3)
MIC1815
4
July 2005
MIC1815
Micrel
/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 /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
Applications Information
Microprocessor Reset
The /RESET pin is asserted whenever V
CC
falls below the
reset threshold voltage. The reset pin remains asserted for a
period of t
RST
after V
CC
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 V
CC
as low
as 1V.
V
CC
Transients
The MIC1815 is 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
20µs or less will not cause an unwanted reset.
VCC
VCC
MIC1815
RESET
100K
µP
RESET
/RESET Valid to V
CC
= 0V
July 2005
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MIC1815
