TPS23756: Auxiliary power supply

dave lan

Part Number: TPS23756

hi sir/madam,

Now the customer USES our POE PD scheme TPS23756, but it is the auxiliary power supply, the circuit is as the attachment. Now if the customer connects the earth to the earth-POE, what's wrong with it?tidr391-TPS23756.pdf

over 7 years ago

0 Thomas Amlee over 7 years ago

TI__Genius 9230 points

Hi Dave,

By earth-POE, are you referring to CHGND in the schematic or PWRGND on the primary side? Could you clarify?

Thanks,
Tom

0 dave lan over 7 years ago in reply to Thomas Amlee

Intellectual 520 points

Hi Thomas,

0 dave lan over 7 years ago in reply to dave lan

Intellectual 520 points

Hi Thomas，
Now the customer wants to use the auxiliary power supply, so as to make the plate convenient, the TPS23756 RTN is connected with VSS, and then the C17 are replaced by the resistance of 0ohm。so is there a problem?

0 Thomas Amlee over 7 years ago in reply to dave lan

TI__Genius 9230 points

Hi Dave,

Sorry for the delay. I thought I had answered, but it must have been a dream.

Firstly, shorting RTN to VSS completely negates the safety features allowed by the internal pass FET (thermal shutdown, operational current limit, and inrush current limit). For the sake of currrent protection, I cannot recommend this.

Secondly, by shorting PWRGND to PGND, you are breaking isolation & will have problems with conducted emissions from the noisy switched DC/DC converter. The point of isolating the ground planes is to prevent the switching noise from interfering with the data also being carried by the Ethernet port. For more information on EMI, I would read this: www.ti.com/.../slua469.pdf

Thanks,
Tom

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TPS23756: Auxiliary power supply