TPS40170: Output Unstable

Dear Team,

I have attached the schematic, please kindly review it.
BR
Kevin

Hi Kevin,

Thank you for sharing the schematic and the waveforms.

How are you measuring the output voltage? Also, what current load is added when inserting the SFP?

Would you be able to take a waveform of the inductor current, SW, and VOUT when the SFP is inserted?

Thanks,
Katelyn

Hi Kevin,

I want to follow up with you on this e2e thread. Could you help clarify a couple questions?


How are you measuring the output voltage? Also, what current load is added when inserting the SFP?

Would you be able to take a waveform of the inductor current, SW, and VOUT when the SFP is inserted?

Thank you,
Katelyn

Dear Katelyn,

Thanks for the support here.
The RD will measure the waveform after the Chinese New Year.
So he will get back to you after 2/11.

BR
Kevin

Hi Katelyn,

Sorry for reply so late.

I measured the output voltage by measuring the  both side of the C30 cap. The input voltage is 48V. We use TPS40170RGYR to convert to 3.3V

PS I also find input voltage 48v always causing reset, and input voltage 12v sometimes causing reset. 

and the SW inductor current and output voltage is as the followeing when I insert SFP to RJ45 module

if you need more information, please let me know 

thanks

Hello,

Thank you for sharing this waveform. Does the output voltage recover after a period of time, or does it shut off until the SFP to RJ45 module is removed?

Thanks,
Katelyn

Hello,

It shut off until I remove the SFP to RJ45 module.

thanks

Hello,

Do you know what the loading current of this module is?

I calculate that current limit will be about 5A.

Can you try doubling the ILIM resistor?

Best Regards,

Katelyn

Hello,

Did you have a chance to try doubling the ILIM resistor?

Thanks,
Katelyn

Yeah! I change from 12k to 30k resistor, but It still shut off. It look like no improvement.

Could you help reviewing the following part. Does it effect the output voltage stable?

thanks

Thanks Katelyn!!


We will follow component choices to improve stable and check the inductor again.

Due to the design bug of the specific fiber to RJ45 module and fiber to RJ45 module is not use in our customer, we decide to close this thread.

Thanks

Best Regards,

Smith