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TPS65131-Q1 - About parts-choice and VREF-terminal

Dice-K
Mastermind 7540 points
Other Parts Discussed in Thread: TPS65131-Q1

Hello,

I have six questions about TPS65131-Q1.

I am reading "SLVSBB2D".

 

1:Inductor Selection.

SLVSBB2D describes "In typical applications, the recommendation is to choose a 4.7-uH inductor" in the page-14.

When I calculate equation-3-7, L-value is larger than 4.7uH.

Which should I follow?

 

2:Equation-3-4 in the page-13.

Please teach me the origin of "0.64".

 

3:Equation-11-12 in the page-15.

Please teach me the meaning of "6.8us" and "7.5us".

 

4:The capacitors of CP and CN.

Please teach me the choice method of C6=10nF and C7=4.7nF in the page-12.

 

5:R7 in the page-12.

Please teach me the purpose of R7.

I want to know the reason that I cannot connect Vi and VIN-terminal directly.

 

6:The Absolute Maximum Rating of VREF-terminal.

Please teach me the Absolute Maximum Rating of VREF-terminal.

 

Regards,

Daisuke

  • 0
    TI__Expert 8010 points

    Hello Daisuke,

    Q1: We are recommending to use 4.7uH, but it is highly dependent of the application. What output current do you draw?

    Q2: The origin of 0.64 comes from the law of conservation of energy, which leads to this formula (ideallized)
           As in the d/s given, the output voltage ripple is defined of 20% of IIN_AVG, therefore you can rearrange by saying that IIN_PEAK=IIN_AVG/0.8.
           Additionally the efficieny is set to 80%. Rearranging this formula to IIN_PEAK, IOUT=IPOS, VOUT=VPOS you will get the formula as in the d/s.

    Q3/Q4: These are values, which have been analyzed by simulation and been encountered to work on the optimal operating point.

    Q5: As described in 9.2.1.2.3.1 this small input circuit will improve transient behavior, the resistance is added to damp the input current. There is no critical reason why not to connect VI- VIN directly except performence reasons.

    Q6: Why would you need to know this, this pin is regulated internally.

    Regards,

    ilona