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TPSM5D1806: RENB formula for EN

Steve Widener
Genius 9585 points
Part Number: TPSM5D1806

In section 7.3.10. the formula for RENB yields unusual values for RENB.

For instance, when Vin is 12V, the formula is RENB = 110 / (12V - 1.1V) = 10.1kohms.

When working this into the 1.2V EN threshold & the 100kohm "top" resistor I estimate a typical start voltage of (1.2V/10.1K - 1.4uA)*100K + 1.2V =~ 13V

The formula doesn't appear to work - please advise. This also contradicts the recommend RENB values from table 7-3

  • +1
    TI__Genius 16670 points

    I think the offset voltage from the internal pullup is RenB//RenT*1.4uA.     

    Using the equation 2, will give the stop voltage or uvlo threshold.   The enable pin has 100mV of hystersis

    Using 1.1V will give the stop threshold and 1.2V will be the start threshold.

    So, calculating 10.1kOhm with 12V means when the voltage falls the device will turn off at 12V. 

    13V is the start voltage 

  • 0 in reply to David_Daniels
    TI__Genius 9585 points

    I think I understand - the Vin is not the nominal supply voltage, it is the UVLO point, such as 6V or so given a 12V nominal supply.