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TPS4811-Q1: the external circuit of reverse polarity protection.

Hank Lin
Intellectual 1675 points
Part Number: TPS4811-Q1

Tool/software:

Dear team,

I heard that TPS48111-Q1 can applied the circuitry mentioned in PS1211-Q1 datasheet to provide the RPP feature. I have following two questions:

Q1

in the datasheet we demonstrate the system design with DMN601WKQ-7 and SZMM3Z12VST1G for RPP, but what is the Rbias resistance and the package suggestion?

Q2

is the same components of RPP circuitry recommended for TPS48111-Q1? how much negative voltage that the whole circuitry (TPS48111-Q1 + RPP circuit) can withstand?

how to determine the negative voltage rating?

Best regards,

Hank Lin

  • 0
    TI__Intellectual 1675 points

    Dear team,

    is there any update?

    best regards,

    Hank Lin

  • +1 in reply to Hank Lin
    TI__Mastermind 34935 points

    Hank,

    1. For RBIAS you want to ensure that it has enough VGS to fully enhance Q1 while limiting current through D1 to avoid overheating and stabilizing the gate voltage. The D1 Zener clamps at 12V and the gate will be 12V minus any voltage drop. Q4 is a logic level FET fully enhanced at Vgs = 4.5V to 10V... so 12V is good. The SZMM3Z12VST1G's minimum knee current is ~5mA for safe operation and the abs max is 50mA. .. a good buffer here would be to have 5mA to 20mA.  In reality you shouldn't choose the absolute minimum knee voltage as transients can cause undershoot, so 10mA nominal would be a safe bet. You would be able to calculate an appropriate BIAS resistor by:

    RBIAS = (VBAT - VZener) / IZener

    So if we picked a higher range for the nominal 12 battery range (which is 18V) you would get:

    (18 -12) / 10mA = ~600Ohm

    2. Yes it would be also relevant for TPS4811-Q1, you would just use 48V to size accordingly... so (48 -12) / 10mA = 3.6k.

    Best Regards,
    Tim 

  • 0 in reply to Timothy Logan
    TI__Intellectual 1675 points

    Dear Timothy,

    I updated the review request with the customer's schematic and layout over the mail.

    I've shortly go through the schematic guideline on datasheet, but still want to double check if anything was missed.

    Sincerely thanks!!!

    Best regards,

    Hank Lin