LM5121: Is QD NMOSFET mandatory?

Kazuya Nakai59

Guru 21505 points

Part Number: LM5121
Other Parts Discussed in Thread: LM5122

Hello guys,

One of my customers is considering using LM5121 for their new products.

They have the following question. Could you please give my your answer or comment?

Q. Is QD NMOSFET which connects between current sense resistor (Rs) and inductor (Lin) mandatory?

In other words, can QD be removed if current flowing path from Vin to Vout is not needed to cut?

Your reply would be much appreciated.

Best regards,

Kazuya Nakai.

over 6 years ago

0 Youhao Xi over 6 years ago

TI__Guru* 78060 points

Hi Nakai-san,

Thank you for considering the LM5121. Yes the FET can be removed but my question is why not use the LM5122?

Thanks,
Youhao Xi, Applications Engineering

0 Kazuya Nakai59 over 6 years ago in reply to Youhao Xi

Guru 21505 points

Hi Youhao,

Thank you for your reply.
Could you tell me LM5122 advantage point compare to LM5121? It seems that price and package size are same.

Thank you again and best regards,
Kazuya Nakai.

0 Youhao Xi over 6 years ago in reply to Kazuya Nakai59

TI__Guru* 78060 points

Hi Nakai-san,

For the boost operation itself, they are basically the same. However, the LM5122 reuses the two pins taken by the LM5121 for the disconnect FET and you now get SYNCOUT and OPT function, able to configure multiple LM5122 in daisy chain to support higher power. You cannot use Lm5121 in multiphase.

Hope this clarifies.

Thanks,
Youhao

0 Kazuya Nakai59 over 6 years ago in reply to Youhao Xi

Guru 21505 points

Hi Youhao,

Thank you for your prompt reply. it is very helpful for the customer and me!

Best regards,
Kazuya Nakai.

Power management

Power management forum

LM5121: Is QD NMOSFET mandatory?