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TPL5111: Using Potentiometer for time setting resistor

Chip
Prodigy 20 points

Part Number: TPL5111

I am using this part as timer. The operator of the equipment selects a time interval by rotating a potentiometer on a control panel and actuates a push button switch to cause the input power to be cycled to the TPL5111, so it will read the new resistor value. I see the data sheet warns about capacitance effecting the reading of the resistance. It does not say how much capacitance is allowed. My plan is to use a PC mountable potentiometer so it has minimum distance to the circuit board. I am not sure how much capacitance the potentiometer has. Will I have any issues?

Also, can I add and ESD diode to the Delay/M_DRV pin to ground? e.g. more capacitance

It would be helpful to know relationship of timing error versus capacitance.

Thank you

Chip

  • 0
    TI__Genius 16845 points
    Hi Chip,

    I wouldn't expect an issue using a surface mount potentiometer located near the device. This is also done on TPL5111EVM.

    After the device powers up, it executes the resistance reading by measuring the current through R_ext on the DELAY/M_DRV pin. During this time, constant current is flowing into R_ext. Capacitance can impact the current and voltage on the pin, especially immediately after startup, which would affect the resistance reading (as the pin is expecting a nonreactive impedance).

    By the same principle, adding an ESD diode can impact the resistance reading. I haven't tried it before, but it is not recommended.

    I hope this information helps!

    Kind regards,
    Lane
  • 0 in reply to Lane Boyd
    Prodigy 20 points
    Thank you for your insight. Knowing a potentiometer has been used in the evaluation board is helpful. I have a panel mount potentiometer with PC tails for direct circuit board connection. I think I will purchase an evaluation board and do some testing. Thanks again.