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TPSM846C23: EN accepts CMOS 3.3V input?

Kazuki Itoh
Genius 10660 points
Part Number: TPSM846C23
Other Parts Discussed in Thread: TPSM846C24, SN74LVC2G07

Hi team,

I just want to double check the input interface of EN-pin quickly.

Does EN pin accept 3.3V CMOS input?

Regards,

Itoh 

  • 0
    TI__Guru 56755 points

     

    The EN pin of the TPSM846C24 has a High to Low threshold greater than 0.8V, and an Low to High Threshold less than 1.3V with a typical hysteresis of 170mV, with a maximum voltage rating of 7V.   It is compatible with CMOS push-pull logic levels 1.8V, 2.5V, 3.3V, and 5V

  • 0 in reply to Peter James Miller
    TI__Genius 10660 points

    Hi Peter-san,

    I don't think TPSM846C24 is compatible with CMOS push-pull logic.

    In the thread below, you mentioned that EN pin has weak pull-up to BP6. 

    https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1011444/tpsm846c24-no-output-in-parallel-mode

    My customer tried to enable TPSM846C24 with 1.8V LDO output, then the LDO output rised to ~3.5V.

    I think open-collector/drain input is mandatory and CMOS logic is not accpeptable to control this device.

    My customer added a transistor to the LDO output for the workaround. The transistor is pulled up to BP3.

    Is this workaround OK?

    (The customer also tried to add the open collector buffer SN74LVC2G07, but it didn't meet the sequence requirement.)

    Best regards,

    Itoh

  • 0 in reply to Kazuki Itoh
    TI__Guru 56755 points

     

    I don't believe I am following your methodology here.

    You describe driving the EN pin with a 1.8V LDO output.  Are they directly connecting the 1.8V LDO to the Enable pin with no other loading on the 1.8V LDO other than the enable pin such that the 10μA pull-up on EN is driving the LDO into a negative-load condition?

    If the internal 10μA (max) enable pull-up is an issue for the driving logic, adding a 50-100kΩ EN to AGND loading resistor to the Enable pin will prevent the pull-up current on Enable from back-feeding the 1.8V supply.  This is generally not an issue since the 1.8V rail powering the Push-Pull drivers typically has more than 10μA of loading on it without the added EN to AGND resistor.