MIC8115
Micrel
MIC8115
Microprocessor Reset Circuit
General Description
The MIC8115 is an inexpensive microprocessor supervisory
circuit that monitors power supplies in microprocessor based
systems.
The function of this device is to assert a reset if the power
supply drops below a designated reset threshold level or
/MR is forced low.
The MIC8115 has an active low /RESET output. The reset
output is guaranteed to remain asserted for a minimum of
1100ms after V
CC
has risen above the designated reset
threshold level. The MIC8115 comes in a 4-pin SOT-143
package.
Features
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Precision voltage monitor for 3.3V power supplies
Specifically tailored to the
AMD Elan SC500
Series
/RESET remains valid with V
CC
as low as 1V
5µA typical supply current
1100ms minimum reset pulse width
Manual reset input
Available in 4-Pin SOT-143 Package
Portable equipment
Intelligent instruments
Critical microprocessor power monitoring
Printers/computers
Embedded controllers
Applications
Ordering Information
Part Number
MIC8115TU
MIC8115TUY
Marking
NT
NT
Operating Temp. Range
–40°C to +85°C
–40°C to +85°C
Package
4-lead SOT-143
4-lead SOT-143
Pb-Free
No
Yes
Typical Application
VCC
VCC
VCC
MIC8115
MR
µP
RESET
RESET
MIC8115 Typical Application
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
July 2005
1
MIC8115
MIC8115
Micrel
Pin Configuration
GND
1
4
V
CC
MIC8115
RESET
2
3
MR
4-Lead SOT-143
Pin Description
Pin Number
1
2
Pin Name
GND
/RESET
Pin Function
IC Ground Pin
/RESET goes low if either V
CC
falls below the supply reset threshold voltage
or if /MR is asserted. /RESET remains asserted for one reset timeout period
1100ms min. After both V
CC
exceeds the supply reset threshold voltage and
/MR is deasserted.
Manual Reset Input. A logic low on /MR forces a reset. The reset will re-
main asserted as long as /MR is held low and for one reset timeout period
(1100ms min.) after /MR goes high. This input can be shorted to ground via
a switch or driven from CMOS or TTL logic. Pulled high internally through a
20kΩ resistor. Float if unused.
Power supply Input.
3
/MR
4
V
CC
MIC8115
2
July 2005
MIC8115
Micrel
Absolute Maximum Ratings
(Note 1)
Terminal Voltage
(V
CC
) ...........................................................–0.3V to 6.0V
(/MR) ..................................................–0.3V (V
CC
+ 0.3V)
Input Current (V
CC
, /MR) ............................................ 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 .................................................................... 3kV
Operating Ratings
(Note 2)
Operating Temperature Range
MIC8115TU ............................................ –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
Parameter
Condition
Operating Voltage Range
Supply Current
Reset Voltage Threshold
Reset Timeout Period
/RESET Output Voltage
/RESET Output Voltage
/MR Minimum Pulse Width
/MR to Reset Delay
/MR Input Threshold, V
IH
/MR Input Threshold, V
IL
/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
Typ
5
Max
5.5
15
3.15
2500
0.3
0.3
Units
V
µA
V
ms
V
V
V
µs
µs
V
T
A
= –40°C to 85°C
3.00
1100
I
SOURCE
= 500µA
V
CC
= V
TH
min, I
SINK
= 1.2mA
0.8×V
CC
3.08
1700
t
RST
V
OH
V
OL
V
CC
= 1V, I
SINK
= 50µA, T
A
= –40°C to +85°C
10
0.5
0.7×V
CC
10
20
100
0.25×V
CC
30
kΩ
ns
Timing Diagram
V
CC
/MR
V
TH
/RESET
t
RST
t
RST
July 2005
3
MIC8115
MIC8115
Micrel
Functional Diagram
VCC
MR (3)
RESET
GENERATOR
RESET (2)
VCC (4)
+
Reset
Threshold (V)
-
GND (1)
MIC8115
4
July 2005
MIC8115
Micrel
/RESET Valid at Low Voltage
A resistor can be added from the /RESET pin-to-the 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.
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 1100ms after V
CC
has risen above the reset thresh-
old 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 MIC8115 is relatively immune to the 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 a reset.
VCC
VCC
MIC81 15
RESET
100K
µP
RESET
/RESET Valid to V
CC
= 0V
July 2005
5
MIC8115
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