LM25117: LM25117 CM calculation

Yangbo

Part Number: LM25117

Hi Team,

I have two questions regarding LM25117:

1.What is the Sample and Hold DC value? As far as I understand, this DC level is the inductor valley current.

2. If the DC level is the inductor valley current, then equation 14 is not correct. According to equation 14, we can get the average inductor value. But what sampled and hold in CM is the inductor valley current.

over 7 years ago

0 David Baba over 7 years ago

TI__Mastermind 40060 points

Hello Yanbo,

The Sample an hold is the DC level is the valley. But superimposed on top of this is the voltage generated by Cramp as depicted in Fig 20. The peak (Generated by Cramp) and the valley (DC sample and hold) is then conditioned and delivered to the CM pin.

Hope this helps?

David.

0 Yangbo over 7 years ago in reply to David Baba

TI__Intellectual 1690 points

Hi David,

Thank you for your reply.

But in the datasheet's block diagram, I am seeing CM is coming from Rs which does not include the ramp.

0 David Baba over 7 years ago in reply to Yangbo

TI__Mastermind 40060 points

Hello Yanbo,

You are right. The CM is made up of its own dedicated sample and hold circuits not depicted in the block diagram. But these circuits are in the conditioner block

I hope this helps?

David.

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LM25117: LM25117 CM calculation