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LM5169: some questions about equations

Noriyuki Takahashi
Genius 10980 points
Part Number: LM5169

Tool/software:

Hi team,

There are questions about equations in datasheet.

1. In order to decide the RA, we can use the equation for type 3 in the table 7-1 and equation 31. But it seems the sign of inequality is not same. Could you confirm this difference and tell which equation they should follow?

2. In table 7-1, there are two equations to get the RESR for type 1 and type 2. As you can see below, the above equations are different between type 1 and type 2, while the below equations  are same in type 1 and type 2. Could you explain these differeneces and accordance? And which equations they should follow?

Regards,

Noriyuki Takahashi

  • 0
    TI__Expert 5490 points

    Hi Noriyuki,

    1. Equation mentioned in the table 7-1 is correct. This will be updated in the next revision of the datasheet. Thanks for highlighting. 

    2.

    • First equation(R_ESR >= 20mV*Vout/VFB*DeltaIL) on the type-1 represents the minimum R_ESR that ensures a 20-mV resistive ripple component is present at the feedback node. And second equation ensures that the generated ripple on the feedback node is in phase with the inductor current. 
    • For Type-2 ripple generation method, As the output voltage ripple is AC-coupled by CFF to the feedback node, the R_ESR value and ultimately the output voltage ripple are reduced by a factor of VOUT / VFB.

    For more info. about the COT mode control ripple generation circuit refer SNVA776A App note.

    Hope this helps. 

    Thanks,

    Nitya