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MC34063A: Operating Frequency

Part Number: MC34063A
Other Parts Discussed in Thread: MC33063A
Hi Team,
Good day!
I'm posting this to continue our support with our customer. Kindly please help to check
We are using MC34063AD in one our product and it was or is implemented with switching frequency of 22kHz at 7V output and 24V supply. Could we know what is the minimum frequency for this device, as it is stated 24kHz for 5V?

And I will also like to know if the minimum frequency is for all the output voltage or only for a define output voltage.
I also have a question about the 0°C temperature was, what will happen if the converter operate under 0°C for example by -10°C? what will be the impact of -10°C of the IC?

Concerning the lower frequency. I was also wondering how can I calculate the max. on time and determine also the off time of the device? I use the duty cycle to get the ratio ton/T =0,29. and using the formula for CT , how Can I get the max. on time of the IC?

Best regards,
  • Hello Jonathan,

    The frequency range given in the datasheet is +/- 30%. There will be some additional change over voltage and temperature, so I would recommend using +/- 50% for the frequency setting as conservative estimation.

    For operating at temperatures below 0C, please use MC33063A.

    The maximum duty cycle and lowest frequency define the max on time. The minimum duty cycle and minimum frequency define the max off time.

    Best regards,