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LMZ34202: Driving INH/UVLO pin to turn ON and turn OFF the device

Part Number: LMZ34202

Hi,

Q1. From the datasheet I understood that LMZ34202 will be turned ON if 'INH/UVLO pin' voltage is greater than 2.1V(typically). Is it right?
        What happen if this pin is left floating? Do this pin have any internal pull-up?

Q2. I am planning to drive the 'INH/UVLO pin' from a GPIO of uC/FPGA. The GPIO is not an Open-Drain pin. Is it OK to drive INH/UVLO with normal GPIO pin?
       I can't ensure that this GPIO will be at Ground during initial Power-ON or during reset.
       Please find the attached image for sequencing control of LMZ34202.Do the setting shown in image enough to perfom the ON-sequencing and OFF-sequencing of LMZ34202?


 


Thanks in Advance
DEEPAK V

  • Hi Deepak,

    The INH/UVLO is not internally tied to anything. Because of this, the INH/UVLO pin should not be left floating  to prevent from being in an undefined state. Generally the INH/UVLO pin is tied to the power supply when not used. Otherwise a resistor divider is placed between this pin, AGND and PVIN to adjust the UVLO voltage.  The datasheet specs the inhibit high threshold at a typical value of 2.1V. Any voltage at or beyond that will turn the device on.

    The INH/UVLO pin must be driven by an open drain device. Figure 30 in Section 8.1.2 in the datasheet provides an example of how to use the INH/UVLO pin.

    Regards,

    Jimmy Hua 

  • Hi Jimmy Hua,

    Thank you for replaying the queries.

    Based on your suggestions I understood the following

    1. INH/UVLO pin should not be left floating.

    2. The figure:30 you have attached shows that the state of 'INH/UVLO pin' is determined by the MOSFET Q1.

        When the gate of MOSFET is at a logic high the 'INH/UVLO pin' will be at Ground potential, thus LMZ34202 will be turned-OFF.

        When the gate of MOSFET is at the ground or floating the 'INH/UVLO pin' will be at PVIN voltage, thus LMZ34202 will be turned-ON.

        So to turn ON/OFF LMZ34202 we have to properly drive the gate of MOSFET Q1.

        In our project, the gate of MOSFET is controlled from GPIO of uc/FPGA . Here during initial power-ON, the Gate of MOSFET that is being controlled from GPIO of uc/FPGA may be at high impedance or ground.

        That will result in turning-ON the LMZ34202 before the actual Power ON Sequencing start. So this situation has to be avoided.

    Solution to avoid the above problems
    So for avoiding the floating of INH/UVLO pin and to make sure LMZ34202 will be turned ON only when GPIO of uC/FPGA is at high the circuit arrangement shown in the attached image is performed.
    Please find the attached image.

    When the jumper is at position 1&2, the resistor R1 ensures that INH/UVLO pin is not floating even if the GPIO of uC/FPFA at high-impedance during power-ON.
    LMZ34202 will start switching only when GPIO is made at logic high(3.3V).
    But here the GPIO is not an open-drain pin, it is a normal logic pin.

    Question1: Do the circuit attached to the image is sufficient to perform the sequencing ON and OFF for LMZ34202?

    Question2: I think it is acceptable to drive INH/UVLO with normal GPIO. Not mandatory to have an open-drain pin.
                         Page-17, paragraph-2 of the datasheet says INH/UVLO pin can be driven by a logic pin not necessarily open-drain. Please find the attached image.
                         So is it okay to drive INH/UVLO with a normal GPIO pin?

     


     


    Thank you for continuing support.

    Thanks and regards
    DEEPAK V




    Thanks and regards
    DEEPAK V

  • Hi Jimmy Hua,
    Please have a look at queries in the previous post.
    I am waiting for your reply!!!

    Thanks and regards
    DEEPAK V
  • HI Deepak,

    Sorry that I missed this reply. This must have slipped through my email filter.

    To answer your two concerns:
    1. Yes the R1(82k) resistor will ensure that the LMZ34202 will not be floating if the GPIO doesn't send a logic input.
    2. Yes the INH/UVLO pin can take logic input directly. In your case it will be the logic input from the uC GPIO.

    Regards,
    Jimmy

  • Hi Jimmy,
    Thank you for continuing support and resolving my query.
    Now I am pretty clear about enabling the LMZ34202.

    Thanks and Regards
    DEEPAK V