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Original question:

LM5175: Excessive temperature

LM5175: LM5175: Excessive temperature

Fotis Panagiotopoulos
Prodigy 70 points
Part Number: LM5175

I face some problems with an existing design using the LM5175 regulator.

For some reason this chip gets really hot, some times 85oC or more. I also had a case of a product returning for service where this chip was completely inoperational (needed replacement).

As discussed previously here, changing the output capacitors initially seemed to have solved the problem, but unfortunately it still persists.

Also as discussed here, in my implementation I have set the regulator in DCM, but it does not solve my issue.

In most cases the regulator operates normally within 15oC of the ambient temperature. Then, for some reason it gets to a state where its temperature is increased a lot. Some times it stabilizes to 60oC, while in other cases it may reach up to 85-95oC. The temperature issue seems unrelated to the voltage input (I have tried from 12V up to 30V), and it is not affected by the load (I tried from no load, up to several amps).

What can be the cause of this?

Since it is not happening in all cases, can it be a component tolerance issue?

  • 0
    TI__Guru* 78240 points
    Hi Fotis,

    It should not be a component tolerance issue. The device has been used by other customers in mass production (very high volume) and there is no such issue.

    Hope you not to mistake me here (no insulting but just a question to ask): could you check if there is any part misplaced or soldered improperly to put the IC to be programmed in a wrong state?

    Thanks,
    Youhao Xi
  • 0 in reply to Youhao Xi
    Prodigy 70 points

    Hi,

    Soldering has been checked very carefully. I face the same issue on lots of boards, assembled by different PCBA houses. I have also checked whether the chip gets in the correct mode, and I can acknowledge that it operates in DCM mode. I believe that a manufacturing issue is very unlikely, if not impossible.

    While talking about tolerances. I am not referring to the chip itself, but any of the peripheral components used, that if out of spec may cause such an issue.

    In other words, can you advise my on how should I start looking for the issue? Shall I suspect any other component? Or maybe, is there any possible problem with the implementation as I have attached it on the other issue?

  • 0 in reply to Fotis Panagiotopoulos
    Prodigy 70 points

    Hi,

    So what can we do about this issue?

    Can you propose us what to look for to solve this issue?

  • 0 in reply to Fotis Panagiotopoulos
    TI__Guru* 78240 points
    Hi Fotis,

    The IC is usually get hot owing to power dissipation in side, which is mainly caused by the internal LDO. The gate drive is the main load of the LDO, if you do not have other external circuit to pull current from the VCC pin. The each driver takes the current of about (Qg x Fsw), where Qg is the MOSFET gate charge, and Fsw is the switching losses. there are four drivers and they all draw current from VCC.

    Because it is an LDO, and VCC is regulated, under higher VIN the voltage difference to VCC will be across the LDO. Please check if there is any external circuit loading the VCC, and check if the switching frequency is correct.

    Thanks,
    Youhao