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LM5021: Does LM5021 do OTP at high temperture

Ariel Peng
Prodigy 610 points
Part Number: LM5021

HI,

my customer  is using LM5021, they would like to know how the IC will behave when the IC case temp at 125C? will it do OTP , if no OTP, what is the failure mode? They do not use it with such high temperature at normal condition, this condition only happened at extreme condition or fault condition, but they would like to know what is the result come out. Thanks!

Ariel

  • 0
    TI__Genius 9130 points
    Ariel,

    The LM5021 does not have built-in internal over-temperature shutdown. If external over-temperature protection is required, and external circuit could be interfaced with an open-drain or open-collector pull-down on the SS pin - pulling down the SS pin will shut down the PWM, and keep it off as long as the pin is pulled low.

    If the ambient temperature reaches 125 C, the internal junction temperature needs to be estimated, it will be higher. This depends on the internal power dissipation of the IC, which in turns depends on the PWM frequency and size of the FET gate charge (which affect the amount of supply current consumed), and the voltage at the VIN pin (which affects the amount of dissipation in the internal LDO from VIN pin to VDD pin). You need to make sure that the max junction temperature stays below the Tjmax absolute maximum limit of 150 C.

    From the datasheet table of Absolute Maximum Ratings, note 1 states:

    Absolute Maximum Ratings are limits beyond which damage to the device may occur. Recommended Operation Conditions are
    conditions under which operation of the device is intended to be functional.

    So at Tj > 125 C, the device is not guaranteed to meet all electrical specs, and at Tj > 150 C, there is a risk of device damage.


    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    TI__Prodigy 610 points
    hI, Bernard
    thanks a lot for your feedback
    as customer found the LM5021 has no PWM output when the TC=125C( this is special condition that may have extreme or fault condition, at normal work status, the LM5021 does not has such high temperature ensure to be within recommendation temperature), customer want to know if such extreme condition happened, what will the LM5021 behave? if there is no OTP, then the IC may damaged, they would like to know what is the fail mode? do you have such related information? thanks!

    Ariel
  • 0 in reply to Ariel Peng
    TI__Prodigy 610 points
    hi,
    any comments? thanks!
    Ariel
  • 0 in reply to Ariel Peng
    TI__Genius 9130 points
    Ariel,

    Can you explain more clearly please?

    "as customer found the LM5021 has no PWM output when the TC=125C"

    - Are you saying that the PWM stopped when the Tc of the LM5021 reached 125 C?
    - If so, can you share the customer schematic so we can review it?


    As I said above, from the datasheet, if the device is operated above Tj = 125 C:

    Absolute Maximum Ratings are limits beyond which damage to the device may occur. Recommended Operation Conditions are
    conditions under which operation of the device is intended to be functional.

    So at Tj > 125 C, the device is not guaranteed to meet all electrical specs, and at Tj > 150 C, there is a risk of device damage.


    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    TI__Expert 7395 points
    Ariel,
    I reconfirmed with the design team: LM5021 does not have Over-temperature protection. Case temperature does not mean Tj so you could be exceeding the internal junction temperature depending on PCB, cooling, frequency, load at the gate, etc.
    Alternatively, I'm not sure what ambient temp you are running at but some other component may be changing drastically in the system if the ambient temp is high and the controller could be hitting current limit, hitting UVLO or some other condition at that point. It is critical to monitor the input signals that can trigger protections and see where they are at.
    Regards,
    John