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TPL0401A-10: TPL0401A power down concern

user6049718
Prodigy 95 points
Part Number: TPL0401A-10
Other Parts Discussed in Thread: TPS82130

TPL0401A Power Sequence as below: 

Protection diodes limit the voltage compliance at SDA, SCL, terminal H, and terminal W, making it important to
power up VDD first before applying any voltage to SDA, SCL, terminal H, and terminal W. The diodes are forwardbiasing,
meaning VDD can be powered unintentionally if VDD is not powered first.

TPS82130 Vin and TPL0401A VDD use the same 5V power. 

I have some concern with power down.  If the 5V_Vin voltage discharge faster than Vout(5V_Vin is lower than Vout during power down) , will it cause a damage to TPL0401A?

 If the 5V_Vin supply voltage goes to 0V eventually, will it cause a damage to TPL0401A?  How can I protect TPL0401A in these situation?

  • 0
    TI__Genius 14220 points

    Hello,

    Thank you for your query. Let's consider the worst case scenario. VDD = 0 momentarily while VOUT is still ON due to the output capacitor. I am assuming VOUT to be 3.3V. When VIN is smaller than VOUT, the parasitic diodes in the MOSFETs inside TPS82130 will provide a path from VOUT to VIN. So, VIN will be VOUT - diode drop. Hence, TPL0401 will not see a significant violation of the ABS max limits. When there is the availability of VIN, VFB might be at its proper value of 800mV or lower. That means the worst case is if VFB supplies current through the "H" pin of TPL0401.

    The resistance of the DPOT is 10k. So, the effective voltage at the "H" pin will be around 400mV. This will turn on the ESD diode at this pin and there will be a current (400mV/19k) = 21uA. This current will be there till the output capacitor discharges, which may be for a few minutes in case of a no-load condition.

    In any case, a 21uA current is not big enough value to cause any damage.

    Hope that answers your question.

    Regards,

    Uttam Sahu

    Applications Engineer, Precision DACs