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UA78M: UA78M05ICD

RUFINO GONZALEZ
Prodigy 20 points
Part Number: UA78M

Tool/software:

En nuestro nuevo diseño vamos a utilizar el circuito UA78M05ICD. La fuente de alimentación que tenemos es de 24Vdc, según la ficha técnica se puede utilizar hasta 35Vdc. La pregunta es: ¿Hay algún problema con que la entrada de 24Vdc funcione continuamente?

*******************************

En nuestro nuevo diseño vamos a emplear el circuito UA78M05ICD. La alimentación que tenemos es de 24Vdc, según el datasheet se puede emplear hasta 35Vdc. La pregunta es: Hay algún problema en que esté continuamente trabajadora los 24Vdc de entrada?

  • 0
    TI__Expert 4660 points

    Hi Rufino,

    This device can operate continuously on 24V input voltage, given the Junction temperature does not exceed the recommended temperature in the datasheet.

    If you can give me your output current and output voltage (5V?) and the package that you are using, I can calculate it for you.

    Let me know if you have any questions.

    Regards,

    Bobby

  • 0 in reply to Bobby
    Prodigy 20 points

    Thank you for your reply. The input power will be 24V and the output 5V with a current of about 250mA and peaks of 350mA.

    Thanks again

    *****************************************************

    Gracias por su respuesta. La alimentación de entrada será de 24V y la de salida 5V con una corriente de unos 250mA y picos de 350mA.

    Gracias de nuevo

  • 0 in reply to RUFINO GONZALEZ
    TI__Expert 4660 points

    Hi Rufino,

    Here, your Vin= 24V, Vout= 5V, and Iout= 0.25A

    It gives Power Dissipated (Pd) = (24-5)* 0.25 = 4.75W.

    Max Junction temperature allowed for the device is 125C.

    Now calculating Junction Temperature (Tj) = Ambient Temp (Ta) + Pd * RθJA

    ⇒ RθJA ≤ (Tj - Ta)/Pd = (125-25)/4.75 = 21.05 °C/W

    From datasheet, RθJA (for KVU)= 30.3 °C/W, RθJA (for KCS)= 19 °C/W, RθJA (for DCY)= 77.7 °C/W

    From this, the only package that you can use will be KCS, and the part number will be UA78M05IKCS

    But, when your load becomes 0.35A, for KCS package

    Tj = 25 + 19*((24-5)*0.35) = 151.35 °C

    This is not recommended for the device, and device might go into thermal shutdown. So this part is not recommended for your application.

    Regards,

    Bobby