LM5145: Could you please tell me how to measure external FET drain current?

Kazuya Nakai59

Part Number: LM5145

Hello guys,

One of my customers is evaluating LM5145 with their own PCB.

Now they are going to check whether external high/low side MOSFETs are working in area of Safety Operation(ASO) of the MOSFET. For that, they tried to measure the MOSFET drain current with a current probe of oscllioscope. But because they add a jumper wire for the current measurement, big spike noise was observed.

Do you have any idea to measure the drain current with smaller spike noise?

Or is the spike noise not impact to measure ASO? Is it good way to use a lowpass filter?

Your reply would be much appreciated?

Best regards,

Kazuya Nakai.

over 6 years ago

0 Katelyn Wiggenhorn over 6 years ago

TI__Genius 11040 points

Hello,

It is important to make sure the loop is as small as possible as you are pointing out as to not add more inductance. Would you be able to share a waveform of the FET current with the noise that you are referring to?

I am also going to reach out to the product expert for his comments as well.

Best Regards,
Katelyn

0 Timothy Hegarty over 6 years ago

TI__Guru 73752 points

Nakai-san,

It's easiest to meaure the inductor current and infer the MOSFET current from that. Measuring the MOSFET current typically adds inductance to the switching loop, disturbing the actual switch current waveform.

Regards,
Tim

0 Kazuya Nakai59 over 6 years ago in reply to Timothy Hegarty

Guru 21595 points

Hi Tim,

Thank you very much for the reply. I told the measurement method to the customer.

Thank you again and best regards,
Kazuya Nakai.

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LM5145: Could you please tell me how to measure external FET drain current?