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LSF0108: Vref_B / A power sequence

Kai Lai
Expert 8956 points
Part Number: LSF0108

Hi Team,

If the Vref_B and EN have the 3.3V first, and at this moment there is no 1.8V at Vref_A, then the 3.3V what at Vref_B will leakage to the Vref_A ?

If yes, how to prevent it? Pull low the EN pin when 1.8V is not ready when power on ?

Does the MOSFET what inside to connect Vref_A&B have a body diode ? Can you show the body diode direction for us ?

Thanks!

Kai

 

  • 0
    Guru 316690 points

    During normal operation, a current flows into Vref_B and out of Vref_A; it is limited by the 200 kΩ resistor. This current can (partially) power up your 1.8 V supply.

    Pulling EN low indeed disables all I/O and Vref pins. (Most other translators like TXU/SN74xxxT do not leak between their supplies.)

    The body of the MOSFETs is not connected to the source, but to ground (as shown above). So each MOSFET has two diodes, from ground to the A-side and B-side pins.