Preliminary Datasheet
3-PIN MICROPROCESSOR RESET CIRCUIT
Application Information (Continued)
Negative Going V
CC
Transient
The AZ809A is optimized to immune fast negative-
going transients or glitches on the V
CC
line, and the
sensitivity depends on the duration of the transient and
the magnitude of the undershoot below the reset
threshold (reset comparator overdrive). Figure 13
shows the maximum pulse width of a negative-going
V
CC
transient that will not cause a reset pulse. As the
magnitude of the transient increases (goes farther
below the reset threshold), the maximum allowable
pulse width decreases. Any combination of duration
and overdrive that lies under the curve will not
generate a reset signal, typically, a V
CC
transient that
goes 100mV below the reset threshold and lasts about
20
µ
s or less will not cause a reset pulse.
A 0.1
µ
F bypass capacitor mounted as close as possible
to the V
CC
pin will provide additional transient
rejection.
400
AZ809A
VCC
360
Maximum Transient Duration (
µ
s)
V
TH
320
280
240
200
160
120
80
40
0
2
Duration
Overdrive
Reset Occurs
above the Curve
10
100
1000
Reset Comparator Overdrive V
TH
-V
CC
(mV)
Figure 13. Maximum Transient Duration NOT Causing
a Reset Pulse vs. Reset Comparator Overdrive
Typical Application
V
CC
VCC
VCC
AZ809A
Microprocessor
RESET
RESET
GND
GND
Figure 14. Typical Application of AZ809A
Jan. 2008 Rev. 1. 0
9
BCD Semiconductor Manufacturing Limited
BCDSEMI [ BCD SEMICONDUCTOR MANUFACTURING LIMITED ]
