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TPS23754: Can not power on if temp. low than 0degreeC

chentsu chung
Mastermind 6180 points
Part Number: TPS23754
Other Parts Discussed in Thread: TL431

Hi Team,

TPS23754 work well in normal temp. condition, but IC can not power on if temp. lower than 0 degreeC,

Then we measure the voltage of Aux. widing:

CH1: Vc CH2: PWM CH3: Aux.Widing

Room temp.

Low temp.

After these testing, we use Cold Spray to check what component can make this issue(IC, cap, diode, resistor, opto-coupler, TL431...), and we found this issue result from TPS23754.

And the issue can be improving by add Vc cap and reduce Aux.widing series resistor.

Could TI help to check that why low temp. makes TPS23754's Vc hard to establish?

Thank you.

C.T.

  • 0
    TI__Mastermind 41770 points

    Hi CT,

    Do you have the waveform of VDD-RTN with the waveforms above? It looks like the PSE is removing power. If so, it may be that the colder temperatures will have a weaker startup source (per the datasheet EC table) and it might be enough for the PSE to remove power. If so, you can add a small 10mA load between VDD-RTN to keep the PSE connected while the DCDC tries to startup.

    Also, do you have a load connected to the DCDC output when you plug into the PSE? If so, how much power?

    Thanks!

  • 0 in reply to Darwin Fernandez
    Mastermind 6180 points
    Hi Darwin,

    Thanks for yuor help, this testing done by 48V adapter at PD input, so this issue should not about PSE, and the issue happened not only no load but also 1A output.

    Thank you so mch!
    C.T.
  • 0 in reply to chentsu chung
    TI__Mastermind 41770 points
    Hi CT,

    Looking at the first waveform, the VC signal crashes as soon as the FET starts switching. Given this, and that it improves with increasing the cap and decreasing the series resistor, it leads me to believe it might be how Vc is driving that specific primary FET. I have not used that particular FET has we use FDMS86242 in our newer reference designs for this power level. This has 3x less gate charge and 2x less input/output capacitance. I would continue increasing the VC cap if necessary for that particular FET. Thanks!