LM5117 / to use smaller sense resistor

K.Yaita

Guru 29710 points

Other Parts Discussed in Thread: LM5117

Hi Team,

I'd like to ask about LM5117.

My customer considers to use LM5117 for following condition.

*Vin:30-65V, Vout:14V, Iout:200A, schematic:following

Accroding to equation(24) in datasheet P.28, the value of current sense resistor(Rs) is calculated 0.5mΩ under this condition.

However, my customer would like to use smaller sense resistor to reduce power dissipation, so he consider to use 0.05mΩ and add external OPAMP(gain:x10).

Is it possible to use extrernal OPAMP to reduce the value of Rs?

If it is practical method, I would also like to know the required specifications of this OPAMP.

Could you advise me please?

Best Regards,

Yaita / Japan disty

over 10 years ago

0 EricLee over 10 years ago

TI__Guru 50501 points

I doubt the accuracy (signal-to-noise ratio) of your current sense. Assuming 1A current flows, OPAMP input will be only 0.05mV and the output will be only 0.5mV.

Usually, there is a big switching noise in such a high power system (2.8kWatt)

Regards,

0 K.Yaita over 10 years ago in reply to EricLee

Guru 29710 points

Hi Eric-san,

I also go along with your comment.

I appreciate for your support.

Best Regards,

Yaita

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LM5117 / to use smaller sense resistor