ADG3308: a solution for VCCA before VCCY?

Happy New Year!

I need to do some logic level translation, and normally ADG3308 fits, but in this particular case VCCA and signals on the 'A' side arrive before VCCY. Can I use something like an ADG1421 (it seems to handle 200+mA current),  or an N-MOSFET to switch power on on both sides simultaneously, upon arrival of Power Good for VCCY?

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  • Hi Nick,

    I was confused with the lines "VCCIO is coming from processor board, VDD is derived on my board from VCCIO, with some delay due to overvoltage protection (about 40 msecs) and soft start, 800 msecs total." and "VDD can't be made independent of VCCIO here." mentioned earlier that is why I suggested to switch connections of VCCIO and VDD.

    Can you clarify if VDD was derived from VCCIO? Did you used a boost circuit to level up the voltage from 3.3V to 5V? I'm asking this to confirm the delay time from VCCIO to reach VDD.

    For your second configuration, you need not use a dual SPST switch (ADG1421). If so, Vccy and Vcca will have same power-up time since both IN1 and IN2 are connected to the line READY and is toggled at the same time.

    However, you may tie VDD directly to Vccy and use ADG601 for the delay of VCCIO to Vcca. Check if the VDD pin of the ADG601 is connected to VDD line, this way we can ensure that VDD reaches 5V first before turning ON ADG601 for VCCIO and Vcca.

    Using ADG1419 for the RUN line would be fine.

    Best Regards,

    May

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  • Hi Nick,

    I was confused with the lines "VCCIO is coming from processor board, VDD is derived on my board from VCCIO, with some delay due to overvoltage protection (about 40 msecs) and soft start, 800 msecs total." and "VDD can't be made independent of VCCIO here." mentioned earlier that is why I suggested to switch connections of VCCIO and VDD.

    Can you clarify if VDD was derived from VCCIO? Did you used a boost circuit to level up the voltage from 3.3V to 5V? I'm asking this to confirm the delay time from VCCIO to reach VDD.

    For your second configuration, you need not use a dual SPST switch (ADG1421). If so, Vccy and Vcca will have same power-up time since both IN1 and IN2 are connected to the line READY and is toggled at the same time.

    However, you may tie VDD directly to Vccy and use ADG601 for the delay of VCCIO to Vcca. Check if the VDD pin of the ADG601 is connected to VDD line, this way we can ensure that VDD reaches 5V first before turning ON ADG601 for VCCIO and Vcca.

    Using ADG1419 for the RUN line would be fine.

    Best Regards,

    May

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