LM5122: IRIPPLE_MAX(COUT)

Kuramochi Tadahiko

Guru 28715 points

Part Number: LM5122

Hi,

My customer is considering using LM5122 and calculating Cout.

Does IRIPPLE_MAX(COUT) mean the peak to peak current from COUT by charging and discharging?

If yes, why can it be calculated by equation(32)?

Best Regards,

Kuramochi

over 4 years ago

0 Yinsong Cai1 over 4 years ago

TI__Expert 7450 points

Hi Kuramochi,

It is supposed to. Maybe it uses some kind of simplification based on its inductor selection method.

But the inductor current ripple can be calculated as follows.

I_ripple = Vin*D/(L*fs)

Please let me know if you have any questions.

Thanks,

Yinsong

0 Kuramochi Tadahiko over 4 years ago in reply to Yinsong Cai1

Guru 28715 points

Yinsong-san,

Thank you for your support.

However, the shown equation seems to not matched with (32) as below.

Vin*D/(L*fs)=9V*(1-9/24)/(10uH*250kHz)=2.25A

Could you check again?

Best Regards,

Kuramochi

0 Yinsong Cai1 over 4 years ago in reply to Kuramochi Tadahiko

TI__Expert 7450 points

Hi Kuramochi,

Thank you for pointing this out. I'm not sure about it but let me ask engineers in our team and I'll let you know.

Thanks,

Yinsong

0 Kuramochi Tadahiko over 4 years ago in reply to Yinsong Cai1

Guru 28715 points

Yinsong-san,

Thank you for your reply.

How is this situation?

Best Regards,

Kuramochi

0 Yinsong Cai1 over 4 years ago in reply to Kuramochi Tadahiko

TI__Expert 7450 points

Hi Kuramochi,

Sorry I ignored the context. It calculates the output ripple instead of the inductor current ripple.

The output ripple is just the the inductor current divide by two.

The inductor current equals the input current so

I_output_ripple = Iin/2 = Vout*Iout/Vin/2

Please let me know if you have any questions.

Thanks,

Yinsong

0 Kuramochi Tadahiko over 4 years ago in reply to Yinsong Cai1

Guru 28715 points

Yinsong-san,

Thank you for your reply.

>The output ripple is just the inductor current divide by two.

Is this because of VIN(NOM)=12V and VOUT=24V?

Best Regards,

Kuramochi

0 Yinsong Cai1 over 4 years ago in reply to Kuramochi Tadahiko

TI__Expert 7450 points

Kuramochi-san,

Yes I think it is the simplification it makes here.

Thanks,

Yinsong

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LM5122: IRIPPLE_MAX(COUT)