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LM25149: Pulldown resistor value for CNFG pin on disable Active EMI Filter

Satoshi
Guru 19485 points
Part Number: LM25149

Datasheet is described "Disable active EMI filter is by pulling the CNFG pin below 0.8 V", is there recommend pulldown resistor value?

I couldn't confirm about internal circuit, Vcc, resistor value, etc on the datasheet.

I want know the range of pulldown resistor certainly set below 0.8V. 

Best regards,

Satoshi

  • 0
    TI__Mastermind 22299 points

    Hi Satoshi,

    The CNFG pin is dual-function.

    It is also used to configure spread spectrum and dual-phase modes before startup.

    The CNFG resistance to GND is measured at startup, based on table 8-2.

    Then CNFG becomes Active EMI filter EN control.

    Technically, you should have to wait until after the configuration time and soft-start to start, and then actively pull down CNFG to disable AEF.

    However for a quick check you can just tie CNFG to GND and the controller will operate single-phase, no spread spectrum, and AEF disabled.

    Otherwise, you can unpower AEF by remove CAEFVDDA, and RAEFVDDA to disconnect AEFVDDA from VCC.

    Hope this helps,

    -Orlando

  • 0 in reply to Orlando Murray
    Guru 19485 points

    Hi Orland

    Thank you for reply,

    For example I consider to set dual phase condition, Rcnfg: 71.5kΩ by Table 8-2.

    I think that in this case CNFG pin need to set pulldown after CNFG pin latched, is there recommend pulldown range?

    I want to consider in both cases of CNFG pin set direct to GND and pulldown.

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Mastermind 22299 points

    Hi Satoshi,

    Section 7.6 of the EC table shows 0.8V as the low threshold, it must go below 0.8V, and the rising threshold is 2V.

    I'm not sure the strength of the pullup or pulldown resistance necessary, I recommend trying different values.

    -Orlando

  • 0 in reply to Orlando Murray
    Guru 19485 points

    Hi Orlando

    I understood pullup/down range.

    Sorry for additional question, since the CNFG pin has two roles, it is impossible to connect to GND when setting Active EMI Filter: OFF and Dual-Phase, correct?

    I think there are cases where it is okay to connect to GND from the beginning and cases where it is not.

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Mastermind 22299 points

    Hi Satoshi,

    Correct. It's possible to tie CNFG to GND before startup for single phase. (This also disables DRSS)

    It's not possible to tie CNFG to GND before startup for dual-phase. The resistance must be read to configure dual-phase.

    After startup then it is possible.

    Hope this helps,

    -Orlando