TPS23753A: Request for SCH and layout review for design based on TPS23753A

Hello,

Can you please send the file in a PDF format? Thank you.

Regards,

Michael Pahl

Dear Sir

please refer to the attachment for PDF format, thanks.

PD.rartwch665PE_v01_20191111_PD.pdf

Dear Sir

please refer to the attachment for PDF format2553.PD.rar, thanks.

Hello,

I reviewed the schematic and here are my comments:

- I do not think you need R4783

- I could not find the FET datasheet, but ensure VDS does not exceed the FET voltage rating

A great resource for designing with the TPS23753A with flybacks is: http://www.ti.com/lit/an/slva305c/slva305c.pdf which will give you many equations for various components in this design.

Additionally, we have a 12Vout reference design with the TPS23753A you can compare your design to: http://www.ti.com/tool/PMP20531

Regards,

Michael Pahl

Hi, Michael 

We met several issues during bring-up for the first samples and which are still bothering us right now. I would like to list the issues and our concerns as below:

1. The first sample can not negotiate with its PSE partner without any modification;

2. The first sample can negotiate with its PSE partner sucessfully after changing  R5004 from 90.9Kohm to 90.9ohm, adding a 100ohm resistor on R4783 and a 1kohm resistor between Pin1 and Pin2 of Q7.

3. Even negotiation is ok, the output is about 6V, and no matter what we tried to change the value of R5016, the output still kept unchanged;

4. But when we increased the value of R5012 from 2kohm to about 4.7kohm, output is about 11.7V. And it seemed that the whole feedback loop was not working, meaning the flyback was functioning under open-loop mode.

5. And for the reference design of SLVA305C, which value of Rcls should we use given that out sample supports 802.af since we was confused by class 0 and class 3?

Looking for your reply soon!  Thanks.

Hello,

1. This makes sense if the class resistor is wrong.

2. The class resistor change is required. The 1K on pins 1 & 2 of Q7 is similar to what the design I sent you has. Again I do not think R4783 is needed unless your system requires a minimum load. Maybe that is where the smaller resistor, translating to a higher load, is affecting the design.

3. This makes sense because the resistor divider is railing. The voltage is 2.47, but the part LMV431A has a ref voltage range of 1.22 and 1.25. 

4. Again this makes sense because this resistor can set the feedback because it current limits the opto, and this is more predominate when the LMV part is railing.
5. Class 0 is a legacy class for legacy parts. If your design is 12W, use Class 3. 

Regards,

Michael Pahl

Hi Sir

1. The exiting first samples following the reference design of PMP8803 can not be modificated much  based on the design you shared before since we have to show them to our customer sooner or later;

2. Unfortunately,the symptoms remain the same even LMV431 was changed to LV431 that output voltage can only be adjusted by changing R5012, changes on other points including divider takes little effect.

3. By the way, it seems there is no output OVP function, need we add a zener between PIN4 and P-GND?

Looking forward your reply soon.

BR

Vincent

sorry, there was a typo:LV431====>TL431.

Hello Vincent,

You said previously you changed the resistor divider, and now you are changing the LMV431 to the TL431. Can you confirm the resistor divider on the board gives the correct reference voltage for the regulator currently on the board?

And can you confirm which part you are asking about for PIN4?

Regards,

Michael Pahl