MC34064, MC33064, NCV33064
80
I F , FORWARD CURRENT (mA)
V
in
= 0 V
T
A
= 25°C
60
40
20
0
0
0.4
0.8
1.2
V
F
, FORWARD VOLTAGE (V)
1.6
Figure 8. Clamp Diode Forward Current versus Voltage
+
Power
Supply
2 (2)
1 (1)
R
Reset
Microprocessor
Circuit
−
−
+
1.2 V
ref
C
DLY
A time delayed reset can be accomplished with the
addition of C
DLY
. For systems with extremely fast
power supply rise times (<500 ns) it is recommended
that the RC
DLY
time constant be greater than 5.0
ms.
V
th(MPU)
is the microprocessor reset input threshold.
1
t
DLY
= RC
DLY
In
1−
V
th(MPU)
V
in
3 (4)
Figure 9. Low Voltage Microprocessor Reset
TEST DATA
R
H
+
Power
Supply
1 (1)
−
−
+
1.2V
ref
V
H
≈
4.6 R
H
+ 0.02
R
L
I
in
2 (2)
R
L
Reset
V
H
(mV)
20
51
40
81
71
112
100
164
190
327
276
480
DV
th
(mV)
0
3.4
6.8
6.8
10
10
16
16
34
34
51
51
R
H
(W)
0
10
20
20
30
30
47
47
100
100
150
150
R
L
(kW)
0
1.5
4.7
1.5
2.7
1.5
2.7
1.5
2.7
1.5
2.7
1.5
Microprocessor
Circuit
DV
th(lower)
≈
340 R
H
x 10
−6
Where: R
H
≤
150
W
Where:
R
L
≥
1.5
W,
≤
10 kW
3 (4)
Comparator hysteresis can be increased with the addition of resistor R
H
. The hysteresis equation has been
simplified and does not account for the change of input current I
in
as V
CC
crosses the comparator threshold
(Figure 4). An increase of the lower threshold
DV
th(lower)
will be observed due to I
in
which is typically 340
mA
at
4.59 V. The equations are accurate to
±10%
with R
H
less than 150
W
and R
L
between 1.5 kW and 10 kW
.
Figure 10. Low Voltage Microprocessor Reset with Additional Hysteresis
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