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SN65HVDA100-Q1: INH Pin low output

Part Number: SN65HVDA100-Q1

Hi,

I am a bit confused by the INH pin of the device. Every diagram I see with SN65 shows INH directly connected to the EN of the LDO but the block diagram makes it look like that wouldn't work to disable the LDO unless there is an external pulldown. The language in the datasheet also says it goes into a Hi-z state which doesnt mean it is pulled low necessarily. Any help clarifying this?

Regards,

Kevin

  • Hi Kevin,

    You are right that in many cases a pull-down is needed on INH to properly disable a regulator, since the HVDA100 will not drive a low signal (INH is either pulled to VSUP or made high impedance).

    Max
  • Okay, thanks for confirming.

    Any recommendation on pull-down resistor sizing? 10k, 100k? Bigger would be better for current consumption but wanted to see how big they can go.
  • Kevin,

    On the low end you would be limited by the current-sourcing ability of the INH pin, which is designed to be 2 mA. You could use this value to compute a minimum resistance based on the maximum battery voltage in the system.

    On the high end, you need to make sure that the "EN" pin's low-level threshold is not exceeded even when accounting for some leakage current. The leakage into INH will be at worst 5 uA. If you had a good estimate for the leakage current of the regulator as well, you could add those together and multiply them by the resistance value and make sure the resulting voltage is still low enough.

    Typically I've seen ~100 kOhm work out to be a reasonable value after considering these constraints.

    Max