HA17901AFP datasheet(11/16 Pages) RENESAS

11 / 16 page

HA17901A Series

Rev.1.00 Mar 10, 2006 page 11 of 15

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.

VCC

−

VCC

+VC

VCC/2

VCC

50 k

Frequency

control

voltage

input

VCC = 30 V

+250 mV

< +V

C < +50 V

700 Hz

< / < 100 kHz

Output 2

Output 1

100 k

20 k

5.1 k

3 k

VCC

3 k

100 k

20 k

0.1

HA17901A

−

HA17901A

0.01

500 p

HA17901A

−

Figure 5 Voltage Controlled Oscillator

4. Basic Comparator

The circuit shown in figure 6 is a basic comparator. When the input voltage VIN exceeds the reference voltage VREF,

the output goes to the high level.

−

VCC

3 k

Ω

Vin

VREF

HA17901A

Figure 6 Basic Comparator

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