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OPA454 status flag

Ryan Kriegsman
Prodigy 20 points

Other Parts Discussed in Thread: OPA454

I am hoping to read the status of the opa454 using a 0-5V ADC, if i have the E/D com wired to my digital ground, instead of wiring status flag to V+ through a pull up resistor, could i apply 5V, or around 7V to the status flag pin through the pull up resistor? This would be an attempt to have roughly a 5V output when there is an alarm, instead of have the alarm signal being around 90V? I would have done a simple voltage divider, but my V+ will be changing for my application, so instead of writing some software to work with an alert that will have a changing voltage level through a voltage divider, it would be great to just have a 5V output for the alarm.

-Ryan

  • 0
    TI__Guru* 93105 points

    Hi Ryan,

    When I study the OPA454 schematics, I find that the temperature/over-current Flag pin connects internally to the drain of a MOSFET and an ESD protection cell. The MOSFET source connects to the E/D com pin, which you intend to connect to ground; therefore, the low-level flag status would be referenced to ground. The MOSFET gate drive circuitry is referenced to the E/D com level as well. Having the Flag MOSFET connected in this manner the flag functionality should be maintained even when the drain pull-up is connected to a voltage much lower than the V+ pin level.

    I suspect the +50 V used for the flag pull-up voltage in the data sheet diagrams was selected because of the convenience of powering everything off that one positive level. The +5 to +7 volts you intend to use should be okay for the flag pull-up voltage. 

    It looks like most of the data sheet applications use a flag pull-down current of 50 uA. A 100 kΩ resistor would be a good value for a +5 V pull-up voltage.

    Regards, Thomas

    PA – Linear Applications Engineering