MC34064 MC33064
Figure 7. Clamp Diode Forward Current
versus Voltage
80
Vin = 0 V
TA = 25°C
60
40
20
0
0
0.4
0.8
1.2
1.6
VF , FORWARD VOLTAGE (V)
Figure 8. Low Voltage Microprocessor Reset
+
Power
Supply
–
2 (2)
–
+
1.2 Vref
3 (4)
R
Reset
1 (1)
CDLY
Microprocessor
Circuit
A time delayed reset can be accomplished with the
addition of CDLY. For systems with extremely fast
power supply rise times (<500 ns) it is recommended
that the RCDLY time constant be greater than 5.0 µs.
Vth(MPU) is the microprocessor reset input threshold.
1
tDLY = RCDLY In
1–
Vth(MPU)
Vin
Figure 9. Low Voltage Microprocessor Reset with Additional Hysteresis
+
Power
Supply
–
RH
Iin 2 (2)
–
+
1.2Vref
3 (4)
RL
1 (1)
Reset
Microprocessor
Circuit
VH
≈
4.6 RH
RL
+ 0.02
∆Vth(lower) ≈ 340 RH x 10–6
Where: RH ≤ 150 Ω
Where: RL ≥ 1.5 Ω, ≤ 10 kΩ
Comparator hysteresis can be increased with the addition of resistor RH. The hysteresis equation has been
simplified and does not account for the change of input current Iin as VCC crosses the comparator threshold
(Figure 4). An increase of the lower threshold ∆Vth(lower) will be observed due to Iin which is typically 340 µA at
4.59 V. The equations are accurate to ±10% with RH less than 150 Ω and RL between 1.5 kΩ and 10 kΩ .
Test Data
VH
∆Vth
RH
RL
(mV) (mV)
(Ω)
(kΩ)
20
0
0
0
51
3.4
10
1.5
40
6.8
20
4.7
81
6.8
20
1.5
71
10
30
2.7
112
10
30
1.5
100
16
47
2.7
164
16
47
1.5
190
34
100
2.7
327
34
100
1.5
276
51
150
2.7
480
51
150
1.5
4
MOTOROLA ANALOG IC DEVICE DATA