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MC33063A: pin 8 Driver Collector resistor calculation and thermal evaluation

Johnny Guo
Expert 4910 points
Part Number: MC33063A

Hi, team,

I have some questions about MC33063A pin 8 Driver Collector.

1. For pin 8, why should we put one resistor for Boost application , and no resistor for Buck application, shown as below?

2. And how to calculate the resistor value?

3. How to evaluate the power consumption of this resistor?

Thanks.

Johnny

  • 0
    TI__Guru 68495 points
    In boost configuration Pin 1 and Pin 8 are separated by the inductor. When the switch is turned on, the entire input voltage applies across the driver transistor (minus 3x Vbe), causing more power dissipation. In other configurations, the drive transistor sees much smaller voltage when turning on the switch. The resistor at Pin 1 relieves the IC driver from overheating in boost configuration.
  • 0 in reply to Youhao Xi
    TI__Expert 4910 points

    Youhao,

    Thanks for your reply on my first question. And for question 2 and 3, do you have some suggestion?

    2. And how to calculate the resistor value?

    3. How to evaluate the power consumption of this resistor?

    Thanks.

    Johnny