ILC811/ILC812 Microprocessor Reset Circuits
October 1999
Pin Functions
Pin Number
Pin Name
Description
Ground Pin.
ILC811 ILC812
GND
1
1
RESET goes low if V falls below the reset threshold and remains asserted for one reset timeout
CC
RESET
2
N/A
period (140 ms min.) after V exceeds the reset threshold.
CC
RESET goes high if V falls below the reset threshold and remains asserted for one reset timeout
CC
RESET
MR
N/A
2
period (140ms min.) after V exceeds the reset threshold.
CC
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 (140 ms 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.
3
4
3
4
V
Power supply input, 3 V, 3.3 V or 5 V.
CC
Circuit Description
Microprocessor Reset
The RESET pin is asserted whenever VCC falls below the
reset threshold voltage or if MR (manual reset) is forced low.
The reset pin remains asserted for a period of 240 ms after
VCC has risen above the reset threshold voltage or MR has
returned high. 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
1.4V.
V
4
3
CC
+
-
Reset
Threshold (V)
RESET
(ILC811)
Reset
Generator
2
RESET
(ILC812)
MR
1
GND
V
CC
V
TH
RESET Valid to 0V
A resistor can be added from the RESET pin to ground to
ensure the RESET output remains low with VCC down to 0V.
A 100 kΩ resistor connected from RESET to ground is
recommended. The size of the resistor should be large
enough to not load the RESET output and small enough to
pull-down any stray leakage currents.
MR
t
t
R
R
RESET
V
Transients
V
CC
CC
The ILC811/ILC812 are relatively immune to negative-going
V
CC glitches below the reset threshold. Typically, a negative-
going transient 125 mV below the reset threshold with a
duration of 50 µs (25 µs for ILC81_R/S/T) or less will not
cause an unwanted reset.
V
V
CC
CC
ILC811
RESET
µP
Interfacing to Bidirectional Reset Pins
The ILC811/ILC812 can interface with µPs with bidirectional
reset pins by connecting a 4.7 kΩ resistor in series with the
ILC811/ILC812 output and the µP reset pin.
RESET
100K
Figure 3: RESET Valid to V = 0 V
CC
3
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