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TPS65105: TPS65105: About the possibility of typographical errors in data sheets(Part 3)

Guillermo Corrales
Intellectual 285 points
Part Number: TPS65105

Hi,

Please confirm if there is a typo mistake in VO2 output voltage equation:

VO2 = -1.213 * ( R3 / R4 ) does NOT match a resistor divider calculation, but VO1 and VO2 equation does. I think the correct equation should be VO2 = -1.213 * (( R3 / R4 ) + 1 )

Regards,

  • 0
    TI__Intellectual 1965 points

    Hi Guillermo,

    Thanks for your question. Let me contact the expert for this part. You can expect a response by 3/31/20.

    Best,

    Grant

  • 0
    TI__Mastermind 18550 points

    Hello Guillermo,

    Which resistor divider calculation does not match the VO2 voltage equation?

    I checked and negative charge pump voltage calculation of VO2=-1.213*((R3/R4) seems to be correct. For example, typical application circuit in figure 20 shows VO2=-7V, R3=750K and R4=130K. Using VO2=-1.213*((r3/r4) yields approx.-7V. So I believe it is correct.

    Kind Regards,

    Liaqat

  • 0 in reply to Liaqat Khan
    Intellectual 285 points

    Hello Liaqat,

    Thank you very much for your reply.

    I will try to explain me in a better way.:

    • Negative charge pump external resistor divider is composed of R3 (upper feedback resistor) and R4 (lower feedback resistor)
    • Expected voltage at FB2 is |Vref| = 1.213

    Assuming  that effectively the feedback resistors R3 and R4 are just a divider resistor like the one used in the VO1, VO3 and VCOMP calculations:

    • Vref = VO2 * ( R4 / (R3 + R4)) -> VO2 = Vref * ((R3 + R4) / R4) = Vref * (R3/R4 + 1)

    This is the reason that makes me wonder if the following equation for setting VO2  output voltage is correct:

    Best regards,

  • 0 in reply to Guillermo Corrales
    TI__Mastermind 18550 points

    Hello again Guillermo,

    Target voltage for negative charge pump regulation at FB2 is 0V not 1,213V. Please see electrical characteristics section of the datasheet.

    I believe the equation for VO2 is correct as is.

    Kind Regards,

    Liaqat

  • 0 in reply to Liaqat Khan
    Intellectual 285 points

    Hello Liaqat,

    My apologies! You are totally right: I get confused with Vref(FB2) = 0V and Vref(REF)=1.213V....

    Thank you very much for the clarification.

    Regards,