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DS90UB933-Q1: Pull down resistor value for PDB IO

Part Number: DS90UB933-Q1

Hello Team,

My customer design wrong schematic. it input 3.3V for PDB even VDDIO=1.8

but they have serial resistor on PDB signal line as below.

So I think they can use this serial resistor to change PDB level to 1.8V if I know Pull down resistor in PDB IO.

I understand it may have weak pull down resistor.

Can I know pull down resistor value in PDB IO??

Thank you.

  • Hello,

    I think what you are doing should be possible but the internal pull-down may very.  Allow me a couple days to find what the value of this pull-down might be.



  • Harry,

    I would not recommend this method because the PDB pulldown would be very large value meaning that to divide the voltage down you would need a very high series resistor looking into the part. That means that your effective bias current through the resistor divider would be extremely low and leave the PDB pin quite susceptible to noise coupling. Also, the pulldown current is not going to be well controlled so I doubt it would be possible to find a single value for the resistor that would work well across PVT. So please instruct the customer to revise the design to use the correct voltage straight away or use an external resistor for the pulldown with reasonably low value rather than relying on the weak internal pulldown 

    Best Regards,


  • Hello Casey,

    This problem is also same as on 953 side. it has 1Mohm pull down in IO in datasheet.

    With 953 , they also cannot use serial resistor to make 1.8V level for same reason?

    Thank you.

  • Hello Harry,

    Yes, same reason for 953 I would not recommend to do this

    Best Regards,