LM76005: Equation 20 ( Cout min)

d_zero

Genius 4795 points

Part Number: LM76005

Dear Team,

i'm using your example numbers for EQ 20 , LM76005 DS page 26 and getting that Cout > 1.4mF

Vin=24V

Vout=5V

Iout=5A

dVout=30mV

fsw=400kHz

D'=1-D=0.7916667

r=0.291

L=6.8uH

Is there an error in the equation? because when i use simplified equation for cout_min form SLVA477B EQ12

Coutmin=(diL)/(8*fsw*dVout) = 15uF

Best Regards,

over 1 year ago

0 Rahil Ajani over 1 year ago

TI__Genius 9460 points

Hi,

It looks like the issue is the order of magnitude, probably due to units. If you look at equation 19 on the datasheet, it rearranges to give equation 12 from the App Note. Based on experience 15uF seems more normal for output caps. Note that that is the minimum and that the capacitors will derate so I would recommend using 22uF.

Regards,

Rahil

0 d_zero over 1 year ago in reply to Rahil Ajani

Genius 4795 points

Hi Rahil,

i can't figure out which part has the wrong units in EQ20 in LM76005 datasheet.

Best Regards,

0 David Baba over 1 year ago in reply to d_zero

TI__Mastermind 40040 points

Hello D_Zero,

there appears to be an error in the calculation, we will fix in due course, thanks for the feedback.

David.

0 d_zero over 1 year ago in reply to David Baba

Genius 4795 points

Hi David,

can you tell what is the error?

Best Regards,

0 David Baba over 1 year ago in reply to d_zero

TI__Mastermind 40040 points

Hello Dzero

first part of the formula should read:

This is Equation 19 transposed for COUT.

Hope this helps.

David.

0 d_zero over 1 year ago in reply to David Baba

Genius 4795 points

Hi David,

please let me know when the fix is reflected in datasheet.

so the equation should be as following?

Can you tell in table 8-1 Typical component selection

What is the Vin for the red marked case?

Is this value of 180uF the de-rated value?

Can this 180uF be only ceramic, only electrolytic, or a combination of ceramic + electrolytic in any capacitance percentage?

Would you recommend small ceramic for ESR + hybrid polymer capacitor?

Best Regards,

0 David Baba over 1 year ago in reply to d_zero

TI__Mastermind 40040 points

Hello D,

Typical values for 48V in

I cannot say for sure when this will be modified, but it is marked for revision sometime in the future.

You can follow the Cout calculation as you stated in your previous thread, correct.

hope this helps,

David.

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LM76005: Equation 20 ( Cout min)