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External pars of TPS54308 and TPS54202

Takahiro Nishizawa
Genius 5575 points
Other Parts Discussed in Thread: TPS54202, TPS54308, TPS5402

I have questions about TPS54308 and TPS54202

Question 1. Output voltage Set Point 

TPS54308 : datasheet p.15

 TPS54202 : datasheet p.14

                                   

 (In datasheet)

The 49.9-Ω resistor, R1, is provided as a convenient location to break the control loop for stability testing.

Must we use R1?

We want to reduce external parts.

Are there any concerns if we do not use R1.

Question 2. Feed-Forward Capacitor

TPS54202 : datasheet p.17

(In datasheet)

C6 is not needed when COUT has high ESR, and C6 calculated from Equation 16 should be reduced with medium ESR.

Please tell us the specific numerical value about high ESR and midium ESR.

What value is High ESR?

Whats value is midium ESR?

Question 3.  Feed-Forward Capacitor

PS54308  and TPS5402

Must we use C6?

We want to reduce external parts.

We think C6 does not need if we use electrolytic capacitor in output capacitor.

Best regards,

Takahiro Nishizawa

  • 0
    TI__Genius 9550 points
    Hi, I am looking into this case and will give feedback tomorow.
  • 0
    TI__Expert 4035 points

    Hi Takahiro,

    Below inputs for your questions.

    A1: The function of R1 is just what you said, R1 is not a must, no influence to your application.

    A2: Usually, Electrolytic capacitor means high ESR, ceramic capacitor means low ESR.

    A3: C6 is not a must, just used to get a higher phase margin and a slight boosted crossing frequency, but even without the feed-forward cap, the phase margin and crossing frequency would be ok under normal use.

    BRs,

    Ryan