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TPS2557: Fault pin impedance with pull up supply

Part Number: TPS2557

hi,

im using TPS2557 in one my application.

the device was working fine in the begining, we did some rework @ regulator side since the out put was not constant and is dipping @ regular interval.

same regulator output is give as input to tps2557 switch. Now im seeing fault asserted ! FAULT# = 0'. suprisingly still im getting output voltage.

and when i measured the impedance of the FAULT pin to the PULL UP supply, it is showing 3.332K, even there is a pull up to this pin with 100K. 

i removed 100K then verified the impedance b/w FAULT pin to PULL up supply but still im getting 3.3K only. 

Can you explain me why it is seeing such low impedance ?

thank you,

Praveenkumar

  • Hi Sir,

    I am not clear about you description.

    What do you mean the output not constant?

    Current limit or any other fault?

    What do you mean the impedance from fault pin to power supply?

    I think you mean the fault pin to GND, correct?

    It should be infinity value.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • Hi Zhang,

    What do you mean the output not constant? 

    -- Its a DC-DC converter output, for TPS2557 input supply is given from DC-DC converter. and for some reason this voltage was not constant.

    Current limit or any other fault?

    -- Current limit looks ok since it was working fine earlier, and i suspect input supply implications since it was toggling earlier.

    What do you mean the impedance from fault pin to power supply?

    -- Its a impedence measured between fault pin to input supply (pull up VCC).

    I think you mean the fault pin to GND, correct?

    -- No, I measured fault pin to pull up VCC, fault pin recommends 100K pull up, im seeing 3.3K instead of 100K.

    thank you,

    Praveenkumar 

  • Hi Praveenkumar,

    1. try to offer input power by power supply instead of DC-DC regulator and to see whether still fault assert.

    2. Change to another new IC to confirm whether the IC has been damaged.

    3. transfer the schematic to me and I want to have a check of the configuration.

    4. If still not resolved, capture the input voltage dipping waveform and send it to me.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.