AD654 erroneous pulse output

Hi All,

 

One of my customer has trouble with AD654 V/F Converter in his renewal design.

The current design circuit is shown in attached document.

As shown in the attached sheet, the output terminal of AD654 (FOUT) is connected to photo-coupler input and is pulled up to +15 supply through 1.5kohm and LED in the photo-coupler.

In this configuration, the problem is the current at FOUT terminal at logic 1 state.

The output voltage scope shot is also attached the same sheet.

As shown in the scope shot, FOUT waveform is not stable at logic 1 state thus the pin5 of photo-coupler shows erroneous pulse output.

Could you advise us what is cause this problem?

 

Best Regards,

Ricky

AD654ShematicandScopeshot.docx
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