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What resistor value should i use for EN pin pull up?

Poh Kok Keng
Genius 5262 points
Part Number: TPS2557

Dear Sir/Madam,

I would like to check with you on resister value using at EN pin and FAULT pin.

  • Based on IC specification is using 100Kohm but EVM using 10Kohm

  • Circuit from IC specification.(using 100Kohm)

　

  • Circuit from EVM. (using 10Kohm resistor)

If I do not used Fault pin and i isolated the resistor value for fault and EN pin. what value of R1 should i use for to pull up EN pin?

Any internal pull up for EN pin for TPS2557? if yes, what is the value?

I saw in datasheet that the Ien is max at 5uA. it my input is 5V, does that means I should put a < (5/5uA) = 1Mohm on EN pin?

Best regards,

kpk

  • 0
    TI__Expert 8980 points
    Hi, Kpk,

    If you do not use Fault pin, you can leave it floating or connect it to GND.

    There's no pull up internal for EN pin in TPS2557, so you need to pull up this pin to Vin to enable the part. You can tie EN to Vin directly, you can also pull up this pin with a 10k-100k resistor.

    In datasheet, max Ien is 5uA, it means EN pin max leakage current will be 5uA. According to Ien<5uA, we can take the input impedance of this pin should >(6.5V/5uA)=1.3Mohm. EN threshold range is from 0.66V to 1.1V. So when Vin=5V, and pull up resistor is Rp, to Enable the part: Vin*(1.3M/(Rp+1.3M))>1.1V, we get Rp<4.61Mohm.

    Anyway, we suggest you use pull up resistor from 10K to 100K resistor. You can also tie EN to Vin directly.

    Regards,
    Bob