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ADM2653E power-up problem

I'm a DFAE in Japan.

My customer reported me that VISO output does NOT power up correctly, when he set VISO output to 3.3V and supply 5V to VCC.

he said VISO output power up correctly in the case that he set VISO output to 3.3V and supply 3.3V to VCC and in the case that

he set VISO output to 5V and supply 5V to VCC.

I attached scope shot when VISO output does NOT power up.

the circuit is the identical to the evaluation board.

What is the cause of the problem?

ADM2563E

  • Thank you for your query,

    This start up behavior can occur in the VCC = 5V, VISO = 3.3V condition, if there is too much inductance between the VISOOUT/GNDISO pins and the 100nF decoupling capacitor. This can happen if the 100nF decoupling capacitor is connected using vias to the opposite side of the PCB to the ADM2563E. 

    To avoid unwanted start up behaviour, the layout guidelines on Figure 53 of the ADM2563E datasheet should be followed. You can contact me directly via email if the customer would like support when reviewing the PCB layout. 

    I'd recommend increasing the 100nF capacitor between VISOOUT and GNDISO  to 220nF, to compensate for the larger trace/via inductance. This may avoid a respin of the PCB layout. 

    Regards,

    Neil