LM5148: NC pin connectivity

KB Shah

Part Number: LM5148
Other Parts Discussed in Thread: LM5149, LM25149-Q1EVM-2100

While datasheet mentions that for all NC (No connect) pins - Connect to GND at exposed pad to improve heat spreading , not a single reference design example follows that guideline. Is there a specific reason ?

Also I am using LM5148 in IBB(inverted buck boost) configuration to generate negative voltage from positive input supply. My exposed pads are connected to negative supply (Not GND). can I connect all NC (No connect) pints to exposed pad that is connected to negative output supply

over 1 year ago

0 Orlando Murray over 1 year ago

TI__Mastermind 22301 points

Hi KB,

The NC pins are unbonded, there is no electrical connection for them.

You can leave them floating or connect them to your negative VOUT yes.

Hope this helps,

-Orlando

+1 KB Shah over 1 year ago in reply to Orlando Murray

Prodigy 30 points

Thanks Orlando.

Is there any reason TI reference design is not connecting them to exposed pads while recommended in datasheet ?

I am inferring that since NC pins are not connected with any wire bond I can connect them to negative VOU that can be as high as -50V. The device has input-output 80V rating so I can have input supply as high as 28V

0 Orlando Murray over 1 year ago in reply to KB Shah

TI__Mastermind 22301 points

KB,

Hi KB, are you referring to the datasheet image?

The LM5148 is the same DC/DC controller as LM5149, where LM5149 uses Active EMI filtering in place of the NC pins.

However without active emi filter the devices are the same.

That datasheet references LM25149-Q1EVM-2100 EVM layout.

https://www.ti.com/tool/LM25149-Q1EVM-2100

Yes it should be OK to tie to negative VOUT.

Hope this helps,

-Orlando

0 KB Shah over 1 year ago

Prodigy 30 points

Thanks for clarification. This resolves my question.

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LM5148: NC pin connectivity