HA17901 Datasheet, PDF (11/16 Pages) Hitachi Semiconductor – Quadruple Comparators

HA17901, HA17339 Series
2. Pulse Generator
The charge and discharge circuits in the circuit from figure 1 are separated by diodes in this circuit. (See
figure 3.) This allows the pulse width and the duty cycle to be set independently. Figure 4 shows the
waveforms generated by this circuit.
V_CC
R₁ 1M D₁ IS2076
R₂ 100k D₂ IS2076
C
80pF
V_CC
–
HA17901
V_CC
+
1M
1M ^1M
Vout
Figure 3 Pulse Generator
Horizontal: 2 V/div, Vertical: 20 µs/div, V_CC = 5 V Horizontal: 5 V/div, Vertical: 20 µs/div, V_CC = 15 V
Figure 4 Operating Waveforms
3. Voltage Controlled Oscillator
In the circuit in figure 5, comparator A₁ operates as an integrator, A₂ operates as a comparator with
hysteresis, and A₃ operates as the switch that controls the oscillator frequency. If the output Vout1 is at
the low level, the A₃ output will go to the low level and the A1 inverting input will become a lower
level than the A1 noninverting input. The A1 output will integrate this state and its output will increase
towards the high level. When the output of the integrator A₁ exceeds the level on the comparator A₂
inverting input, A₂ inverts to the high level and both the output Vout1 and the A₃ output go to the high
level. This causes the integrator to integrate a negative state, resulting in its output decreasing towards
the low level. Then, when the A₁ output level becomes lower than the level on the A₂ noninverting
input, the output Vout1 is once again inverted to the low level. This operation generates a square wave
on Vout1 and a triangular wave on Vout2.
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