THVD8000 frequency settings for EN50065-1

Hi Carlos,

I believe only one of our modulation frequencies is completely covered by the standard (F_mod = 125KHz) and also has one in which the tolerance can cause it to graze the top side of the boundary set by EN 50065-1 (F_Mod = 187.5KHz) - so choosing a modulation frequency of 500KHz or greater should push the frequency above the threshold that EN 50065-1 sets. The device does include spread spectrum clocking at 30KHz to help smooth out the spectrum around modulation frequency. I will say we didn't design this device with considerations for EN 50065-1; that doesn't mean this device can't work in these applications but we don't have additional data for this standard. 

At 500KHz modulation you would be able to pass 9600 bps without issue (all modulation frequencies can support 9600bps). That being said you could also run the 57.6kbps at 500KHz modulation - the trade-off is that we don't guarantee that duty cycle distortion caused by IC will be capped to +/-2% - in general you may see around 2.5% to 3% duty cycle distortion (as a general quick appx.  data rate = 1/10th modulation -> +/-2% DCD, 1/5th modulation -> +/-4%, 2/5th modulation -> +/-8%....etc - this isn't a guarantee but generally with every halving of the data-rate/modulation ratio will appx. double the max bounds of DCD - in practice higher modulation frequencies typically have lower DCD rates. 

If you want to avoid that problem than the safest bet is 750KHz which will be able to pass both data-rates. The trade-off with higher modulation frequencies is that you will reduce the maximum effective distance of bus (due to larger AC attenuations + additional jitter added by longer differential bus length) but you will also be able shrink the power coupling inductors with increased modulation frequencies. As an example 750KHz modulation frequency (assuming impedance matched bus) can go about 91m (conservatively), ~213m (with an additional jitter of 5%) and you can push it to ~335m with an addition of 20% jitter. We are currently about to release a note on a THVD8000 repeater if your bus needs to be longer - but that comes at a cost of throughput reductions - please let me know if you have a need for a repeater (there are couple ways to do it either via pure hardware or a software/hardware mix - but both would use 2 THVD8000s to act as the repeater) 

Depending on performance after initial prototype more EMI mitigation techniques may be applied to bus - but generally those are focused on higher frequency signals (most, if not all,  of the methods for mitigating EMI on THVD8000 bus use essentially low pass filtering to remove higher frequency noise generated for the bus). That being said since RS-485 is already pretty EMC friendly due to its differential signaling + the THVD8000 has additional spread spectrum clocking to help reduce concentrations of energy at modulation frequency and spread the energy to help lower magnitude of emissions.  Also things like proper bus setup and impedance matching must be considered as that could cause SI issues which could translate to emissions. 

Please let me know if you have any other questions. 

Best,

Parker Dodson