TPS23753A: 24VAC and 12V DC input into same connector

Hi Parag,

Thanks for reaching out.

The resolution of the picture is not high so I may not see the circuit very clear. It is better to attach a pdf. version schematic if possible.

Please see my preliminary comments.

1.The output should be isolated with the input in most of applications. I could not see what is the circuit on the bottom. Please make sure VCC_12V should refer to PGND and isolated to AGND.

2.I saw APD was used. Make sure APD refers to AGND and AGND is isolated to PGND.

3.The wide input voltage range (12V – 48V/57V) of the flyback needs a careful design to avoid the duty cycle won’t exceed TPS23753A’s 76% max value; at low input voltage and high current condition, TPS23753A's CS pin voltage won't be too high and coupled inductor won't be saturated. 

Best regards,

Diang 

Hi Diang ,

What about 12V DC and 24VAC how can this circuit works ?
Attaching PDFSCH_XNO-8080R_Power_PCB.pdf

Hi Diang,

Have you gone through the Design schematic ?
Does TI have any solution ?

Hi Parag,

Please see my comments on my last post.

You can refer PMP8803 (https://www.ti.com/tool/PMP8803) for the way to use APD pin. It must refer to RTN.

Also, the wide input voltage range (12V – 48V/57V) of the flyback needs a careful design to avoid the duty cycle won’t exceed TPS23753A’s 76% max value; at low input voltage and high current condition, TPS23753A's CS pin voltage won't be too high and coupled inductor won't be saturated.

Best regards,

Diang

Hello Diang,

How i am going to use two voltages one 24VAC and 12DC on a single input connector   . Basically the PD controller will use APD pin for the 24VAC ,but what if 12DC came , in that case it should be bypass the PD controller and APD logic and will provide 12V directly and the output .
Have you gone through the schematic pdf which i attached earlier ?

Please let me know your response on this .Basically this type of circuit are use in the Surveillance camera ,were we can provide 12DC and 24AC to same input connector pin . 
hoping to get input from your soon 

Hi Parag,

Thanks for your reply.

I will get back to you in 2-5 business days. 

Best regards,

Diang

Hi diang
waiting for your response 

Hi Parag,

With the holidays this week, many device experts are currently out of the office. They will look into this and provide you a response when they return. Please expect some delay accordingly.

Thanks,
Field

Hi Field ,

I could really appreciate response here . i am kind on of struck here need you inputs on this queries as soon as possible  

Hi Parag,

Let me reach out to Diang and see what I can find out. Apologies for any delay.

Thanks,
Field

Hi Parag,

Thanks for your patience.

I have went though the schematic. My major concern is there seems has no valid isolation in your current circuit. Please see the nodes in red cycle is from primary side and in green cycle is from secondary side. They could be conductive coupled here. Please let me know if the isolation is needed or not.

Since you have 12-V output, may I know if you can have 24-V AC isolated and have 12-V DC no isolated? If so, you can refer PMP8803 (https://www.ti.com/tool/PMP8803) for the way to use APD pin.

On the Vout side, you can use the 12-V DC oring with the 12-V output:

Best regards,

Diang

Hello diang,

thank you for the explanation,

But one thing is that 24VAC and 12DC are coming from the same input connector . please check input details.. need some logic to bypass the PD controller when 12DC is at the input .in case of the 24VAC only PD controller should come into picture and when 12V DC is applied it should bypass PD controller and should directly be at the output 

Hello Diang,

Have you got chance to look into it ?

Hi Parag,

12-V is a very low input for PoE. I think you may need to consider TPS23756 or TPS2376. TPS23756 is recommended consider it has DC/DC controller and its startup circuit.

You can refer the below reference design: TPS23756EVM (https://www.ti.com/tool/TPS23756EVM)

Best regards,

Diang

Hi Diang,

Please see below attached schematic and provide your feedback on it . 
Supply 24AC and 12 DC will be coming through same pins .POE_Board_SCH_701-1-04025_A1.pdf

Hi Parag,

Thanks for your updated schematic.

We currently have a busy schedule and may reply later for the E2E. Sorry for the inconvenience. 

Best regards,

Diang

You can go though the attached schematic check list first.0045.PoE Schematic Checklist.xlsx

PoE PD Schematic Review Guidelines (https://www.ti.com/lit/an/slvaf59/slvaf59.pdf?ts=1650385648793) will be helpful too.

Best regards,

Diang

Hi Diang,

Thank you for the Document 
24 AC and 12 DC logic is added in the schematic which i shared , hope to get your feedback on that circuit as soon as possible.

Hi Parag,

Thanks for your updates. TI has weekend & holiday from 12/23-26 in US. We will try to rely you by the end of the next week.  

Best regards,

Diang

Hello Diang

Thank you for the review and response 

Hi Parag,

No problem. I will close this thread for now. Please feel free to reach out to us if you have further questions.

We wish you and your team a fantastic end to the year!

Best regards,

Diang