ILC811 Datasheet, PDF (3/5 Pages) Impala Linear Corporation – MICROPROCESSOR RESET CIRCUITS

Microprocessor Reset Circuits
Preliminary
Pin Functions
Pin Name
GND
RESET
RESET
MR
V_CC
Pin Number
ILC811 ILC812
1
1
2
N/A
N/A
2
3
3
4
4
Description
Ground Pin.
RESET goes low if V_CC falls below the reset threshold and
remains asserted for one reset timeout period (140ms min.)
after V_CC exceeds the reset threshold.
RESET goes high if V_CC falls below the reset threshold and
remains asserted for one reset timeout period (140ms min.)
after V_CC exceeds the reset threshold.
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 (140ms 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.
Power supply input, 3V, 3.3V or 5V.
Circuit Description
Microprocessor Reset
The RESET pin is asserted whenever V_CC falls below the
reset threshold voltage or if MR (manual reset) is forced
low. The reset pin remains asserted for a period of 240ms
after V_CC has risen above the reset threshold voltage or MR
has returned high. The reset function ensures the micro-
processor 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.
VCC
VTH
MR
tR
tR
RESET
VCC 4
+
Reset
-
Threshold (V)
MR 3
Reset
Generator
RESET (ILC811)
2
RESET (ILC812)
1
GND
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 100kW 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.
VCC Transients
The ILC811/ILC812 are relatively immune to negative-going
V_CC glitches below the reset threshold. Typically, a nega-
tive-going transient 125µV below the reset threshold with a
duration of 50ms (25µs for ILC81_R/S/T) or less will not
cause an unwanted reset.
Interfacing to Bidirectional Reset Pins
The ILC811/ILC812 can interface with µPs with bidirection-
al reset pins by connecting a 4.7kΩ resistor in series with
the ILC811/ILC812 output and the µP reset pin.
VCC
ILC811
RESET
Reset Valid to V_CC =0V
VCC
VCC
µP
RESET
100
K
Impala Linear Corporation
ILC811/812 1.3
[phone] www.impalalinear.com
Sept 1999 3