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TPS25923: Vout = 3.3V (instantaneous)

Roy Chou1
Genius 12535 points
Part Number: TPS25923
Other Parts Discussed in Thread: TPS25982, TPS25910

Hi Team,

I have a question about the output voltage of efuse. My customer is using an DC/DC (12V to 5V) in front of efuse. The Vin suddenly occur noise and then it will cause output voltage from 5V to 3.3V in flash and then it will recover to 5V like a pulse. I have no idea why our efuse output voltage will occur 3.3V in output and then recover because I see the UVLO is 4.3V, the IC must be shutdown(TPS259230-latch off). Do you have any idea why IC generate 3.3V in output side. Below is the schematic of efuse

And what is the minimum time value of IC could detect the UVLO, I mean because the UVLO value may caused by noise instantaneously. The IC UVLO function wouldn't work due to short time. And what is the value of minimum time ? 

Regards,

Roy

  • 0
    TI__Guru 57737 points

    Hi Roy,

    The device output voltage can droop when the device is actively current limiting or clamping the over voltage. This could be a case of current limiting.

    UVLO operation is based on VIN and not VOUT.

    Can you please share waveform capture (Vin. Vout, Iout) related to the IC behavior that you are describing. 

    The value of ILIM resistor is 170 kohms in the schematics. It is not recommended to use this resistor greater than 150 kohms as higher current value is not characterized and the current limit variation for this setting is unknown. 

  • 0 in reply to Praveen GD
    TI__Genius 12535 points

    Hi Praveen,

    Customer will measure the input voltage and output voltage waveform.

    You means that current might be large in short time and cause the efuse detect the limitation current, right?

    So if it occurred, Vin-Vout=1V, Vout=3.3V, So if we measure the input voltage is around 4.3V and then we could say that is detecting current limitation, right?

    ps. it's hard to measure the current so I would like to measure the voltage to verify the issue.

    Roy

  • 0 in reply to Roy Chou1
    TI__Genius 12535 points

    Hi Praveen,

    Rlin that customer used is 160kohm. I know it's greater than 150kohm.

    Do you know what happened when we use Rlim greater than 150k?

    Roy

  • 0 in reply to Roy Chou1
    TI__Genius 12535 points

    Hi Praveen,

    I measure the EVM board of TPS259250 and I set the Rlim - 170k and the datasheet recommend maximum value is 160k.

    I try to measure the Ilimit when Rlim=170k and the value=6.24A. I use the formula of Rlim=(Ilim-0.7)/(3*10^-5) and Rlim is 180k and this value is near to 170k.

    So I think it may not cause big influence when Rlim set 160k in TPS259230, only I limit will cause little higher, right?

    Roy

  • 0 in reply to Roy Chou1
    TI__Guru 57737 points

    Hi Roy,

    Using a Rlim >150k can set the current limit value to greater than 5A. Below are the two reasons because of which we do not recommend  this setting,

    • As the device has not been characterized for Rlim >150k , we do know the variation in current limit setting. The variation in current limit setting can be high.
    • The device package is not rated to carry load current greater than 5A continously.

    Hence, we highly recommend not to use this device for high current values.

    You can consider using TPS25910 or TPS25982 for your application.