TPS23758: ESD Issue

Hi Diang,

Customer feedbacked that the ESD performance wouldn't better after they added the schottky and 3.3uF capacitor you mentioned. Do you have other suggestions?

Besides, customer also feedbacked the +4kV performance is OK, but the TPS23758 is very easy to trigger self-protection in -4kV (shut down output). The mainly problem is the Self-protection of TPS23758 and customer want to know how to reset TPS23758 after it is powered off by ESD or how to avoid power-off. Thanks.

Best Regards,

Ryker

Hi Ryker,

Thanks for your feedback.

For TPS23758, the specific comments are the Schottky (place near RTN and VSS in layout), and the VC cap increase based on our experience. There are other general comments via https://www.ti.com/lit/an/slva233a/slva233a.pdf for components and layout aspects. 

Besides, could you let me know if the ESD failure is mainly at 12V AUX or 37-57V PoE? If 12V AUX, TPS23758 cannot fully operating at 12V VDD. It needs VDD-VSS > 13 V at least, so AUX needs to be > 13V + hotswap 0.7V body diode drop + other drops.

Best regards,

Diang

Hi Diang,

1、R&D has tried lots of ways (Including Schottky and increase VCC cap) to improve ESD performance but they don't work.

2、The ESD failure is mainly at 37-57 PoE. They also have tried to use 24V AUX but it doesn't work.

3、How to reset the TPS23758 when ESD failure (The TPS23758 can't be reset by MCU, because MCU is powered by TPS23758 and MCU would power off when TPS23758 occurs ESD failure)? Could we use below circuit to reset IC (should we pull down DEN and then pull up DEN), or do you have some simple solutions? Thanks.

Best Regards,

Ryker

Hi Ryker,

Thanks for your additional information.

1. For TPS23758, one additional possible cause is the sync FET on 2nd side may be influenced. Can customer try with a diode on 2nd side and disconnect the CP pin with a 100V diode replace for PSR? 

2. Also for boards with 4 layers or more, normally you can have a sufficient area to pull the GND polygon, does customer accept redo the layout?

3. Pulling DEN to VSS will make the PD's internal hotswap between RTN-VSS turning off. It is not an official reset. But it is good to try. 

May I know what is the behavior when TPS23758 fails? I assume you do not have Vout, but will the TPS23758's VCC-RTN drop and will the TPS23758's FB-RTN or COMP-RTN drop?

Best regards,

Diang

Hi Diang,

Thanks for your suggestions.

1. I have told customer the suggestion and let them try the suggestion.

2. Customer is using 10 layers board now, you can refer below PCB file from customer.

PCB-UTi586A_MAIN_V1_2.brd

3. Customer only uses 12V adapter for power supply and don't connect PoE, so they can't reset the device by pulling DEN to VSS. Do you have other reset solution?

4. The behaviors after TPS23758 fails: VB=0V, VCC=4.27V, FB=0V, COMP=0V. 

Best Regards,

Ryker

Hi Ryker,

Thanks for your information.

Ryker She said:

3. Customer only uses 12V adapter for power supply and don't connect PoE, so they can't reset the device by pulling DEN to VSS. Do you have other reset solution?

If turn off the 12V and turn on again, will be able to reset? Besides, if using 12V AUX, TPS23758 cannot fully operating at 12V VDD. It needs VDD-VSS > 13 V at least, so AUX needs to be > 13V + hotswap 0.7V body diode drop + other drops.

Ryker She said:

4. The behaviors after TPS23758 fails: VB=0V, VCC=4.27V, FB=0V, COMP=0V. 

VCC = 4.27V below UVLO and the PWM CTL is not working. 

Best regards,

Diang

Hi Diang,

• What's the risk if they use 12V AUX and how to understand TPS23758 cannot fully operating at 12V VDD? They have produced about 500pcs systems and all use 12V AUX, but they don't meet some issue with 12V AUX. Thanks.
• It can be reset by turning off the 12V and turning on again. But it needs add an external circuit. Is it only way to reset TPS23758?

Best Regards,

Ryker

Hi Ryker:

- TPS23755 has PD CTL and PWM CTL. At 12V the PD CTL part is not fully working. The PWM CTL part could work.

- For me it is the most straight forward way to reset. Other ways like DEN pull down may not work and harder to be implemented 

Best regards,

Diang

Hi Diang,

Does the PD controller belong to PoE detection part? Thanks.

Best Regards,

Ryker

Hi Ryker,

Yes, roughly PD CTL is related to all VSS based pins including DEN, sourced by VDD-VSS. Roughly PWM CTL is related to all RTN based pins, internally sourced by VDD-RTN and VC-RTN.  

Best regards,

Diang