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LTC2864 and ESD

Category: Hardware
Product Number: LTC2864

We are using the LTC2864-2 in an existing design and it's behaving as expected.

We have a new design of the system, which opens the Interface I/O side of the design to ESD problems. We're trying to meet IEC61000-4-2 Level 4 of +/-15kV.

We've added a number of TVS diodes around the system, trying to harden it. We have a number of LDO regulators and a Microcontroller. After performing 1-2 x 15kV ESD strikes, we notice that the LTC2864-2 we're using is the damaged part. The strange part is that we're seeing a short to ground through one of the RS485 exposed pins (pin 6 and pin 7 of the LTC2864-2), which is the Z and Y Driver Output pins on the device. 

I would have expected these to be protected up to +/15kV ESD as per the datasheet. However, I suspect the issue may be the Driver Enable pin that is actually get hit, which in turn is damaging the internal circuits and shorting the Driver Output pins to ground.

I hope you can help me on this.

Thanks in advance,

Best regards,

Mike O'Keeffe

  • Hi Mike,

    The +/-15kV ESD spec on the LTC2864 datasheet is for Human Body Model (HBM), not for IEC 61000-4-2. They are two different test models, and the IEC 61000-4-2 strike current is higher. Please see below datasheet spec example. 



  • Hi Jane,

    Thanks for your reply. I can't find this table in the LTC2864 datasheet. I have revision C 03/14 directly from your website. 

    This still doesn't solve my problem. I need to harden our device to meet +/-15kV and possibly even further. As I mentioned I'm striking on the side of RO,RE,DE and DI trying to see what are the weak points. During my testing I found that the Z,Y Outputs are the ones that are getting damaged, which I'm surprised by, as I'm not striking on that side of the device. I was expecting RO,RE,DE and DI to get damaged. 

    Can you suggest a method to protect the device from both sides or should I just add TVS diodes, current limiting resistors to every pin?



  • Hi Mike

    The above table is from a different datasheet. I just want to show you if a part guarantees any IEC 61000 specs, the datasheet should show with details. Please see below figures regarding the HBM and IEC61000-4-2:

    Please be sure you can strike on the correct pin. You can damage the part or even other parts on your board or system. You can add a short wire on top of a pin that you need to strike on for Air Discharge test.

    The LTC2864 doesn’t guarantee any IEC 61000 spec. To achieve the IEC 61000-4-2 level 4 (+/15kV Air Discharge and +/-8kV Contact Discharge) with LTC2864, external protections are needed. TVS diodes on the bus lines will help to achieve level 4. Current resistors will help on the RE, DE, RO, and DI pins. It is challenged to find TVS clamps at low voltage, like 6V. We have boards with SMCJ33CA on bus lines achieved level 4.  You should always test and verify TVS diodes in your application since it could impact data rate, and it is also layout and system dependent.