May 2003
1
MIC1815
MIC1815
Micrel
MIC1815
Microprocessor Reset Circuit
Final Information
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. Sev-
eral different reset threshold levels are available to accom-
modate 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.
Typical Application
8++
4-5-6
P
4-5-6
8++
MIC1815
8++
Features
Precision voltage monitor for 10% or 20% drop in 3.3V
power supplies
/RESET remains valid with V
CC
as low as 1.4V
9
A 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. 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
Part Number
Marking
Voltage
Operating Temp. Range
Package
MIC1815-10U
ND
2.88V
40
C to +85C
SOT-23
MIC1815-20U
NE
2.55V
40
C to +85C
SOT-23
MIC1815
Micrel
MIC1815
2
May 2003
Pin Description
Pin Number
Pin Name
Pin Function
1
/RESET
/RESET goes low if V
CC
falls below the reset threshold and remains
asserted for one reset timeout period (100ms min) after V
CC
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
May 2003
3
MIC1815
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/
s
Lead Temperature (soldering, 10 sec.) ..................... 300
C
Storage Temperature (T
S
) ......................... 65
C to 150C
ESD Rating, Note 3
Operating Ratings
(Note 2)
Operating Temperature Range
MIC1815-10U ......................................... 40
C to +85C
MIC1815-20U ......................................... 40
C to +85C
Power Dissipation (T
A
= +70
C) .............................. 320mW
Electrical Characteristics
For typical values, V
CC
= 3.3V, T
A
= 25
C; bold values indicate 40C T
A
+85C; unless noted
Symbol
Parameter
Condition
Min
Typ
Max
Units
Operating Temperature Range
T
A
= 0
C to +70C
1.4
5.5
V
T
A
= 40
C to +85C
1.5
5.5
V
I
CC
Supply Current
9
20
A
V
TH
Reset Voltage Threshold
MIC1815-10U
2.80
2.88
2.97
V
MIC1815-20U
2.47
2.55
2.64
V
t
RST
Reset Timeout Period
100
150
250
ms
V
OH
/RESET Output Voltage
I
SOURC$
= 800
A
1.5
V
V
OL
/RESET Output Voltage
V
CC
= V
TH
min., I
SINK
= 3.2ma
0.4
V
V
CC
> 1.4V, I
SINK
= 50
A
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
V
CC
t
RST
t
RST
V
TH
V
TH
Reset Timing Diagram
MIC1815
Micrel
MIC1815
4
May 2003
Functional Diagram
+
-
Reset
Threshold (VTH)
VCC (2)
RESET (1)
GND (3)
RESET
GENERATOR
May 2003
5
MIC1815
MIC1815
Micrel
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
1.4V.
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 50
s 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 V
CC
down to 0V.
A 100k
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
P
RESET
VCC
MIC1815
VCC
100K
/RESET Valid to V
CC
= 0V
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