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UC2844: Thermal issue @86kHz

Joyce Gao
Intellectual 2870 points
Part Number: UC2844

Hi expert,

Customer is using UC2844 for Flyback (220Vac/340V-810Vdc input to 24Vdc output, 1A~4A output, 86kHz fsw) use case but met thermal issue. When ambient temperature around 20℃, UC2844 will reach ~90℃ with thermal risk, SCH and partial PCB as below:

Could you help give some comments and suggestions on this? Thanks!

Joyce

  • 0
    TI__Guru 73265 points

    Hi,

    Please find how much current on Vcc pin. That current x Vcc voltage is the device internal power to cause temperature rise. One possible reason is its OUTPUT driving a MOSFET with too large gate charge - if so you need to use external MOSFET driver or change to a MOSFET with smaller gate charge.

    So you need to check OUTPUT pin peak and average current and need to reduce that current.

    Also check COMP pin and Vref pin current.

    Vcc pin voltage and current have to be reduced to make the IC temperature lower.