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LM460002 inverting application - Enable pin to start regulation

Roberto Torres
Prodigy 120 points
Other Parts Discussed in Thread: LM46002, LMZ14203

Hi,

I am looking at the LM46002 device and there is a good quantity of notes about how to use this device to generate a negative voltage. But unfortunately, on all of them, the ENABLE pin is just tied to VIN by a 100kΩ resistor. Also, the PGOOD pin is not used (floating).

On the applications notes I saw from TI, AGND, PGND and EP is always tied to the negative voltage, and I would like to guarantee that if I use an external positive signal in the ENABLE pin (e.g. 5V signal from a micro) there will be no issue.

Ont he other hand, if I use a voltage divider to set up the start and stop voltages for the LM46002 to regulate the negative output, should I have the voltage divider referenced to GND or to the negative voltage generated by the LM46002?

Thank you very much in advance,

Kind Regards,

  • 0
    TI__Genius 15810 points
    Hello,
    Please refer to the section "External Enable Logic Level Shifters" in this app note: www.ti.com/.../snva425a.pdf

    You cannot use the ground referenced signal directly and will have to level shift it.

    Regards,
    Akshay
  • 0 in reply to Akshay Mehta
    Prodigy 120 points

    Hi Akshay,

    Thank you very much for your replay.

    I would like to test two scenarios: one when I have an external signal open/drain signal (5V pulled up) and another one when I have the voltage divider with Rent and Renb and pop and depop each option as required.

    Looking at the app note, I have a question. The app note you sent me, a CMOS logic enable signal passing through a P-Ch MOSFET or a PNP BJT and from then, the voltage divider is placed with Rent and Renb and the app note put Rent and Renb to 10kΩ both. Should I recalculate the Rent and Renb for the LM46002?

    On the other hand, if I put the voltage divider (Rent and Renb) directly attached to the ENABLE pin, with Rent attached tot eh Vin, Renb attached to -Vout, are the formulas specified on the datasheet still valid (datasheet formula are referred to a positive Vout application)?

    Thank you very much in advance, Akshay!

    Kind Regards,

  • 0 in reply to Roberto Torres
    TI__Genius 15810 points
    Hello,
    The two 10 kohm resistors are used for that particular device. You would need to re-calculate them for your required turn on/off thresholds. The internal threshold values for the LM46002 would be different from the LMZ14203 that is used for the demonstration purpose in the app note.

    The RENB resistor is connected from EN to -VOUT. The IC has its ground also referenced to -VOUT. Therefore the equations should remain the same.

    Regards,
    Akshay
  • 0 in reply to Akshay Mehta
    Prodigy 120 points

    Hi Akshay,

    I hope you are just fine.

    Your answered my question. Thank you very much for it!

    Kind Regards,