LM5175: LM5175PWP VOUT low

user6541087

Part Number: LM5175

Hi Team,

I would like to get your input below regarding our customer inquiry with LM5175.

Design input 12V - 28V, output 14.6v 10A

The actual input voltage is 12V; the output voltage is 4.0V. Pin23 VCC has 6.8v, and VCC has 150Hz low pulse signal. Is the chip starting protection? What is the reason that the output voltage can not reach the design value?

lm5175_2.pdf

BEST REGARDS

Let me know if you have any questions with the customer.

over 4 years ago

0 EM over 4 years ago

TI__Genius 11215 points

Hello Hu,

Thanks for your question.

The problem might be that maybe the device is entering hiccup mode. Are you starting the converter without any load connected to it? Is the Vout increasing if you let the converter run for a while?

Could you please provide in addition the scope picture of the voltage on the SS pin?

Other than this, I would like to point out that the sense resistance Rs is only 1m Ohm in the schematic, which means that this resistor is also very sensitive to noise and the peak inductor current is very high. I would suggest to read this article to make sure that this resistor is properly chosen:

https://e2e.ti.com/blogs_/b/powerhouse/archive/2017/03/01/four-switch-buck-boost-layout-tip-no-3-separating-differential-sense-lines-from-power-planes?tisearch=e2e-sitesearch&keymatch=lm5175

Kind regards,

Elisabetta

0 EM over 4 years ago

TI__Genius 11215 points

Hello,

I haven’t heard back from you, so I’m assuming you were able to resolve your issue. If not, just post a reply below (or create a new thread if this one has been locked due to time-out).

Thanks,

Elisabetta

Power management

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LM5175: LM5175PWP VOUT low