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OPA549 E/S state

Mahmoud Mohammed
Intellectual 315 points

Other Parts Discussed in Thread: OPA549

Hi Bruce,

I need to ask you about the E/S internal structure as i have connected it to Open collector circuit {to Disable Output} and Gate of N-channel MOSFET to get thermal shut down state as per Figure(5) i'm not used HCT TTL instead i used MOSFET connected to the E/S through 1Kohm resistor to MOSFET gate.

my question is that OPA549 can't give me 3.4V {with no load and mosfet connected to it i got Max. Volt 1.8Vdc} also when i remove MOSFET i got 3.4V, should i use Pullup resistor to get 3.4V in case of using mosfet or must i use HTC chip?

what is the best solution?

please help me regards,

Mahmoud

  • 0
    Guru 21975 points

    Mahmoud,

    It seems that your MOSFET may possibly be damaged if it is able to load this pin. What type of MOSFET are you using?

    It would be okay to provide a pull-up resistor to a voltage that is 5V above the Ref pin. Note that the Ref pin voltage must be 8V below the positive rail voltage.

    Regards, Bruce

  • 0 in reply to Bruce Trump
    Intellectual 315 points

    MOSFET type 2N7000. if not working properly please recommend another one or just specs.

    also can OPA549 pull E/S pin LOW to 200mV in case of thermal indication in spite of Pullup resistor that will feed current into E/S Pin, if so what is the Min. value that i can add?

    what happen if control VOLTAGE (VSET) to Ilim Pin exceeds (Ref) + 4.75V?

    also i have configured OPA549 to voltage follower topology but i get Output offset of 630mV when input voltage is 0Vdc is that OK? if not how can i minimize that offset?

    regards,

    Mahmoud

  • 0 in reply to Mahmoud Mohammed
    Guru 21975 points

    Mahmoud,

    2N7000 is a good choice. It is okay to pull the E/S pin up to 5V above the Ref pin voltage with a 10k resistor.

    It appears that you do not have a negative power supply and are operating with a single positive power supply. The OPA549 does not have a rail-to-rail output stage. Depending on load current conditions, the output voltage may not be about to swing closer to ground. What is the load current under this condition?

    Please provide a schematic showing circuit configuration including power supply voltages and details on the load.

    Regards, Bruce