MC34063A: The output frequency of the circuit does not match the calculated value.

user5916026

Part Number: MC34063A

Dears

The measured output voltage frequency of the following circuit is 177khz, but according to the theoretical calculation, this value should be 96k.

I'd like to know what might be wrong with this circuit?

over 6 years ago

0 Garrett Roecker over 6 years ago

TI__Mastermind 21720 points

Hello,

Thanks for reaching out with your question.

Can you please let me know the value of the timing capacitor that is populated on your board?
Also how is the switching frequency measured?

Thanks,

Garrett

0 user5916026 over 6 years ago in reply to Garrett Roecker

Prodigy 20 points

Attach the schematics, the capacitor is 68pf. We use an oscilloscope to test the frequency. the frequency of pin 3 is about 177k ,and the frequency of pin 7 without load is about 1k.

Sometimes the chip will burn out , is it because the capacitor is selected improperly? thanks

0 Garrett Roecker over 6 years ago in reply to user5916026

TI__Mastermind 21720 points

Hello,

What is the calculated on time? 69pF seems small for this design.

Thanks,

Garrett

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MC34063A: The output frequency of the circuit does not match the calculated value.