THVD1450: ESD TVS selection for THVD1450

Hi Aiden-Kai,

So for TVS selection you need to look at the abs max ratings of the A/B input pins (for this device it is +/-18V). So under a fault condition - the diode must not clamp higher than 18V or lower than -18V ; the clamping voltage will depend on diode and expected worst case fault condition. 

For generalized 1kV surge protection we do have a basic suggestion:

Please note that this is showing an unterminated node - but both end nodes of the bus should have a termination between A and B (120 ohms or greater).

For 1kV surges the components are:

The resistors must be pulse proof. 

This only works up to 1kV - but gives a general idea of what the protection could look like.

For your direct questions:

1. The common mode range is +/-15V - so THVD1450 can operate normally in that input voltage range. In order to not limit the operational range of the THVD1450 a diode with a working voltage of 15V would generally be chosen. However - the main concern here is that there is only 3V between 15V and the max 18V rating - generally speaking the clamping voltage of a 15V diode will be > 18V for many fault conditions. So you may need limit the operational range of the THVD1450 if you need to add an external TVS because you may need to pick a device with a lower working voltage (such as 12V) - so its important to understand how much common mode range you need so you can pick the best diode for application. 

2. Generally speaking lower capacitance is better - but RS-485 devices can drive a lot of capacitance and usually the cabling is worse than TVS. So in general its not that important - but larger values will limit max bus length and/or max datarate. 

Please let me know if you have any other questions and I will see what I can do!

Best,

Parker Dodson

Hi Parker,

    Thanks for your information. The reply is really benefit. I think it is totally resolved my issue.