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LTM4625 Power Good Indicator

Page 2 of the LTM4625 datasheet, Rev. D, states that the Absolute Maximum Rating of the PGOOD signal is -0.3V to INTVcc.  Because the PGOOD signal is an open-drain output , as described on page 6, it seems to me that the Absolute Maximum Rating for the PGOOD output is not correctly specified.  How can the Absolute Maximum Rating for an output depend on a voltage generated inside the device?  Note that page 3 of the datasheet states that VINTVCC is some voltage between 3.1V and 3.3V. 

In any case, I have a design with 4 of these devices.  I would like to tie all 4 PGOOD outputs together, and then pull them up using a single 10K ohm pull-up resistor to some voltage (called Vpull-up).  Can Vpull-up originate from a +3.3V source that is independent from the 4 LTM4625 devices?

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  • It is not advisable to use the absolute maximum of a pin unless it is an internal LDO. This is because the variation from outside sources(ripple/voltage drop/overvoltage) is not ensured to be within the limit as compared to an internal LDO. Theoretically, you can use an outside source for Vpull-up from a 3.3V source, if it is stable.

    Regards,

    Jhun

  • Hello, 

    I have also a question about the Power Good output of LTM4625, so I did not create a new title, I think that I can put my question here; 

    I want to connect the Power Good output of LTM4625 to the RUN input of a LTM4622.

    Could I pull the Power Good output of LTM4625 up to a VIN of LTM4622 via 4.7Kohm? VIN of LTM4622=5V. 

    Or should I pull Power Good output up to INTVCC of LTM4625? 

    Best Regards,

  • Hello,

    Could I pull the Power Good output of LTM4625 up to a VIN of LTM4622 via 4.7Kohm? VIN of LTM4622=5V. 

    The answer is no. PGOOD of LTM4625 has an abs max of INTVCC(3.3V) which means the 5V input is over the limit.

    Or should I pull Power Good output up to INTVCC of LTM4625? 

    This would be the most optimal thing to do.

    Regards,

    Jhun

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