AM26LV32E-EP: Spice model and transients information

Hi Carlo,

Unfortunately, it doesn't look like we have a SPICE model for this or other similar differential line receiver devices. TI and other semiconductor companies typically provide IBIS models for this type of device to model the electrical characteristics. These models describe I-V and V-T characteristics for a device to perform signal analysis and simulations without disclosing internal characteristics. An IBIS model for this device is available on the store page:
https://www.ti.com/product/AM26LV32E-EP/toolssoftware

AM26LV32E-EP is rated for IEC61000-4-2 standard protection up to the specified values in the datasheet. We do not have data on other transient immunity tests for this particular device. For extended protected, we recommend the use of an external TVS diode on the bus lines close to the connections to the board. Let me know if you'd like more information on these devices and how they can be implemented in your system.

I don't think we have information on this or similar devices in regards to lightning immunity. Are you interested in a particular protected standard such as section DO-160 section on induced lightning transients?

Regards,
Eric

Hi Eric,

Thank you for looking into this.

Do we also have an IBIS model for AM26LV31E-EP?

Regards,
Carlo

Hi Carlo,

The model for the non-EP version of AM26LV31E should model this device well when the simulation temperatures do not stretch into the high-rel range. If this is necessary for the simulation, let me know and I'll look for another similar device model. 

Regards,
Eric

Good morning,

Thanks you for the reply.

We were considering using TVS to protect the interface, but due to cable shielding I am not sure any would be needed.

We have imposed cable injection lightning requirements of MIL-STD-461G CS117

Multiple Stroke, Waveform 5B, First Stroke at  125V/400A, Second stroke at 25V/80A

Multiple Stroke, Waveform 3 (1 & 10 MHz),  First Stroke at  250V/50A, Second stroke at 125V/25A

Multiple Burst, Waveform 6, 400V/20A.

These are applied to a bundle with shielded twisted pairs and shielded twisted triples.  A total of 21 shields.  I estimate internal peak voltages on the lines as follows:

Waveform 5A, +/-9.6 V

Waveform 3 (1 MHz), +/-2.4 V

Waveform 3 (10 MHz), +/-24 V

Waveform 6, +/-480 mV

If they do require protection from these transients, I am not sure I could choose a TVS that would allow operation of the interface.  I just want some way to tell if these levels will allow continued operation of the RS422 Bus.

Thanks,

Jacob Maloney

Hi Jacob,

The absolute Maximum input voltage range for the bus pins on AM27LV32E-EP specify the device will withstand voltages of +-14v on the pins. This seems like it would be sufficient for some but not all of the waveforms you've done calculations for. To increase the system's resilience, you may include a TVS which can clamp these waveforms below the device's Maximum input ratings. Alternatively, you may select another transceiver such as AM26LS32A which have integrated fault protection. 

As far as functional interrupt is concerned, as long as the waveform is coupled equally on both bus lines, the receiver will not see a change in input differential. Exceeding the recommended input voltage of the device may cause undesired behavior. As long as the absolute maximum specifications are not exceed, the device will return to normal operation once the transient has passed. 

Here is an application report that describes some TVS implementations for protection specifically for IEC standard protection, but you may find that the concepts apply to your estimates as well.
Protecting RS-485 Interfaces Against Lethal Electrical Transients

Let me know if you have questions about this article or would like more recommendations for fault protected RS-485/RS-422 transceivers.

Regards,
Eric