• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 33 subscribers
  • Views 114 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ESD321: TVS protection with series resistor

Billy Parthipan
Prodigy 80 points
Part Number: ESD321

Tool/software:

Hi,

I have been using this part for a while in the configuration shown in Fig. A in almost all my designs. I recently saw this part failed on the programming port at the EMS. I suspect that the programming dongle was plugged in the wrong way around and/or ESD. I am therefore considering an additional protection (current limit the TVS). I prefer configuration I have shown in Fig. B. I however am also thinking if the configuration on Fig. C works better. The value for R1 is 49.9R (and R2 if I use fig. C) and the wattage is 63mW (0402 package).  Can you please tell me if I can get away with Fig.B or if I have to do anything special to implement increased protection. This is for 3V3 logic, programming STM32 MCUs. Ideally I want to protect the MCU and I do not want the TVS fail due to high current. I have limited space, meaning I do not want to increase the TVS wattage (at the moment it is 40W) and/or the resistors. Please note the signals I am dealing with are not very high speed. Reduced component count is good for space and cost saving for this design. Thanks.

  • 0
    TI__Expert 7540 points

    Hi Billy, 

    Figure B will do a better job of initially limiting the current, so I would recommend trying this. If this doesn't provide the protection needed, then I would recommend combining Figure A and B. 

    We don't have any other 3.6V devices in the same package, so if a protection device is needed then it would require a package switch. 

    Best,

    McKenzie

  • +1
    Prodigy 80 points

    Hi McKenzie, Thanks for this reply.

    Combining A&B means R1 to MCU port - TVS to GND - R2 to connector pin? I initially considered this and then discarded because I thought it would slow down the signals more and/or introduce more volts drop, possibly compromising the logic levels. Do you think it is safe for SWD, Fast mode I2C, SPI?

    I can consider other packages if they provide better solution. Please suggest a single device and a 4 in pack devices. Uni directional or bi directional are fine.

    Thanks again for the support.

    Regards

    Billy

  • 0 in reply to Billy Parthipan
    TI__Expert 7540 points

    Hi Billy, 

    Yes, R1 to MCU Port , TVS to GND, R2 to connector pin. So R1 will limit the peak current going into the MCU. I don't think this would compromise the logic levels, but there is a chance the signals will slow down. 

    If you are willing to increase the TVS wattage (40 to 85), then a 4-channel option would be ESDS304. Our next best 1-channel option, besides ESD321, would be ESDS311 (170W). 

    Either way, I think Figure B should help with protection since it is protecting the ESD diode which will help with the performance of the ESD. 

    Best,

    McKenzie

  • 0 in reply to McKenzie Eaker
    Prodigy 80 points

    Hi McKenzie,

    Thanks for these suggestions. I might consider the 85W version ESDS304DBVR for the programming port. I am in the meantime took your suggestion of having a T-Network like below. This is because I also want to protect the MCU port for scenario - The TVS fail short circuit. The circuit now looks like this.

    Thanks for this help. I will click the resolved issue button now. Regards Billy