• Resolved

TPS7B7702-Q1: Concept of Absolute Max's Tj&TA, TSD in TPS7B7702

Part Number: TPS7B7702-Q1

Hello.

I'm trying to sale of TPS7B7702, now.

And I have a question about this product.

(I'm asked by this customer for this thing.)

So, please teach me about this thing.

<Question>

Junction temperature (Tj) of absolute maximum rating: - 40 to 150 ° C and ambient temperature (TA): - 40 to 125 ° C.

However, Thermal shutdown detection temperature of this product is 175 ° C @ TYP (Junction).

In such a condition, I think that the detection temperature of Thermal shutdown is 150 ° C @ TYP and it is necessary to have hysteresis of about 15 ° C.

(This is because there is concern that "If the ambient temperature has reached near the rated rating, it is not reset if the IC is detected at 175 ° C.")

Is my consider a mistake?

Could you help us?

Best Regards,

Masumi Sekiguchi

  • Hi Sekiguchi-san,

    Thermal shutdown junction temperature(Tj) of TPS7B770x-Q1 is 175° C, this means device would be OFF at this junction temperature.
    Thermal shutdown hysteresis is 15° C, this means when the junction temperature is 15° C lower than thermal shutdown junction temperature, device would be ON again.

    If the ambient temperature(Ta) is 125° C, the device working status is depended on the power dissipation (Pd).
    Junction temperature Tj=Ta+Pd*thetaJA, thetaJA is the thermal resistance, could be found in the datasheet. only if the Tj is around 175° C could trigger the thermal shutdown.

    Best regards,
    Jason Liu

    PSIL-LED // Sys/Apps Engineer // jason-liu@ti.com

  • In reply to Jason. Liu:

    Hi Liu-san,

    Thank you very much for the answer.
    In addition, please teach me more one question about this thing.

    <Question>
    Since thermal shutdown is a protection function of IC, I am thinking as follows.

    It's necessary to shut down the IC operation where it is likely to exceed the junction rated temperature.
    (Since it is also worried to shut down within the recommended operating temperature range, it is also premised that it will not be reset in this range.)

    Is this consider correct?

    If this answer is yes (correct), that how is it to beteer answer to similar inquiries from customers?

    Please help.

    Best Regards,
    Masumi Sekiguchi
  • In reply to MASUMI SEKIGUCHI:

    Hi Sekiguchi-san,

    When device working under junction temperature range from - 40 to 150 °C, there is no influence for device operating well. When device working under junction temperature range from 150 °C to TSD, device could still work, but the device lifetime would be shorten very much.

    For LDO products, power dissipation and thermal is always the big problem for every device. Customer need to consider the actual junction temperature during device operating, and calculate the proper power dissipation across the device.

    Best regards,
    Jason Liu

    PSIL-LED // Sys/Apps Engineer // jason-liu@ti.com

  • In reply to Jason. Liu:

    Hi Jason Liu-san,

    Thank you very much answering.

    >When device working under junction temperature range from 150 °C to TSD, device could still work, but the device lifetime would be shorten very much.

    Therefore, I think that it is necessary to apply thermal shutdown so that the junction temperature does not exceed the rating (150℃).

    I asked the meaning, but is my considering a mistake?

    Best regards,

    Masumi Sekiguchi

  • In reply to MASUMI SEKIGUCHI:

    Hi Sekiguchi-san,

    Your understanding is right. But we need to left some margin of the transient voltage or current pulse, and LDO should not be shutoff during the transient. So we set about 25 °C junction temperature margin for that.

    Best regards,
    Jason Liu

    PSIL-LED // Sys/Apps Engineer // jason-liu@ti.com

  • In reply to Jason. Liu:

    Hi Jason Liu-san,
    Thank you very much for giving a detailed explanation.

    I could understand by this answer.
    I understood that the thermal shutdown detection temperature was having any margins in consideration of sudden heat generation due to transient fluctuations.
    (If that's not an mistake ....)

    Best regards,
    Masumi Sekiguchi