THVD1400V: RS-485 IC real-world failure conditions when A/B pins are exposed externally

Mithali M

Part Number: THVD1400V
Other Parts Discussed in Thread: THVD2419, THVD1419, THVD1400, THVD2429

Tool/software:

Hello,

I’m using the THVD1400VDRCR IC in an RS-485 application, where the A and B pins are routed to external terminals for field connections (e.g., to an access controller). The IC is powered with 5 V, and A/B are protected with a bidirectional TVS diode to ground.

I want to better understand the real-world failure conditions for this device.

In one instance during testing, the IC was damaged while the board was powered ON (12V supply).The chip heated up rapidly, and the transceiver became non-functional, with A pin showing a short to GND and system 5V showing a short to ground as well.

So I’m now looking for clarification on:

Under what scenarios can the A/B pins cause permanent damage to the IC?
For example, if someone accidentally connects 12 V DC or shorts A or B to GND, does the internal protection or the TVS handle that safely?
Are there known cases where surge, bus contention, or continuous overvoltage can lead to internal shorts or overheating?

I’m trying to build robust protection into the design and would appreciate guidance on:

Worst-case conditions that can cause the transceiver to fail
Whether series resistors or isolation are recommended
Any application notes or stress test data available for reference

4 months ago

0 Leah Jones 4 months ago

TI__Prodigy 430 points

Hello Mithali,
12V is relatively fine and shouldn't break the device; normal range is -7V-12V. In general, just 12V won't break the device, but if the 12V is causing a lot of current the device could heat up too quickly and cause damage. This protection cannot handle long continuous overvoltage events. This protection is only for voltage spikes.

There are very many of these cases happening, this is quite common, but such cases can be avoided.

Unfortunately, this device is not surge protected, so I would recommend you take a look at the THVD1419 or the THVD2419. If you want to keep this device, I will link an app note that might be helpful. https://www.ti.com/lit/ug/tiduas1b/tiduas1b.pdf?ts=1751310040836

Let me know if you have any other questions.

Sincerely,
Leah

0 Mithali M 4 months ago in reply to Leah Jones

Prodigy 10 points

Thank you for the input. I will let you know if I have any further doubts on the same.

0 Mithali M 4 months ago in reply to Mithali M

Prodigy 10 points

Can THVD2419 be used as a drop-in replacement for THVD1400 in the 10-pin 3×3 mm VSON package? Are they pin-to-pin compatible?

If not, then can you suggest a part that is drop-in and pin-to-pin compatible to THVD1400 in the 10-pin 3×3 mm VSON package?

0 Leah Jones 4 months ago in reply to Mithali M

TI__Prodigy 430 points

I think it would be helpful if I took a look at your schematic, but these questions can help if you're not comfortable sharing it.
What are you connecting slr to? What is the data rate you are aiming for? If you are grounding SLR, then yes this could work as a drop in replacement and I would recommend the THVD2429.

0 Mithali M 4 months ago in reply to Leah Jones

Prodigy 10 points

Any specific reason for recommending THVD2429 ?

0 Leah Jones 4 months ago in reply to Mithali M

TI__Prodigy 430 points

I recommend the 2429 because it has a signaling rate up to 20 Mbps, but if you only need up to 250 kbps then I'd go with the 2419.

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THVD1400V: RS-485 IC real-world failure conditions when A/B pins are exposed externally