LM567C: The output pin of LM567C can't be drop down

user4702864

Part Number: LM567C

Hi, I'm trying to use LM567 to recognize the specific frequency signal. But I can't make the output low. For excample, I set the capacity and resistor to make VCO oscillate at 100kHz which I can detect at the pin 6. But no matter what's frequceny of the signal I input to pin3(from 1Hz to 1Mhz), the output always high. I use the signal generator as the input source. And I also tried different phase (from 0 to 359) and amptitude (from 50mVrms to 500mVrms). Could you kindly help to give me some hint about it? Cheers.

over 7 years ago

0 Alan O over 7 years ago

TI__Mastermind 32575 points

Try an input with Vrms > 200mV and frequency of 177 kHz (Fo) +/- 14 kHz (BW of 8%). Does the output go low for such an input condition?

Alan

0 user4702864 over 7 years ago in reply to Alan O

Prodigy 20 points

Hi Alan, thank you very much for your help. It still doesn't work. I re-set the cap and resistor to make the f0=1kHz. And erase the output filer cap(C65).

Here is the capture from oscilloscope. The blue line is the signal from pin6. The green line is the input signal from signal generator, and the amptitude is 300mVrms. the pink one is output signal without cap.

The frequency of blue one and green one are almost the same.

And a use a different frequency. The output signal has same behavior.

0 Alan O over 7 years ago in reply to user4702864

TI__Mastermind 32575 points

I suggest to take a look at a couple related posts:
e2e.ti.com/.../701382
e2e.ti.com/.../2184331

Alan

Logic

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LM567C: The output pin of LM567C can't be drop down