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UC2844: uc2844 junction temperature calculation

Sammi Shang
Expert 4450 points
Part Number: UC2844

Dear team,

I want to confirm when calculate the junction temperature of uc2844, how to calculate the PD, power loss?

I am not sure if it is easier for UC2844 to calculate the Pin and Pout, customer think if they could use standby power (standby current could be found in datasheet) add driver power(fs*Qg*Vcc*Rc/(Ro+Rg+Rgint)) as the total power loss?

Thanks.

Best regards,

Sammi

  • 0
    TI__Intellectual 2640 points

    Hi Sammi! 

    Thanks for reaching out to us! The junction temperature of the device is not affected by the power dissipated in the switching elements since they're not integrated into the UC2844. This means that a worst case power value for the UC2844 device can be obtained from multiplying the highest possible Vcc in the customer system by the device's maximum operating current of 17mA (found in the datasheet in Section 7.5). The thermal resistance from junction to ambient is also available in the datasheet in Section 7.4. Other thermal information is also available in the datasheet and some great tips for designing with thermal considerations can be found here. 

    Thanks for getting in touch with us! I hope this information helps your design process! 

    Aidan Davidson

  • 0 in reply to Aidan Davidson1
    TI__Intellectual 2640 points

    Hi Sammi! 

    To add a bit more to my previous answer, you definitely do want to also include driver power, that was a mistake in my original post. We generally recommend using the equation found in the pin function description for the VCC pin: average Ioutput = Qg * fsw where Ioutput is the current that is driving the external switching element and then multiplying that by the output voltage to obtain the average driver power used. This added to the Iccmax * Vccmax equation above that is used to find the IC power should give you a reasonable estimate of the average power dissipated as needed for your thermal considerations. 

    Thanks for getting in touch, hope this additional information gives you more insight! 

    Aidan Davidson