Some RS485 questions (shielding, filtering etc)

[cupoftea]

Hi,
Do you know of any common mode chokes for RS485 lines?
I cant find any, but assume a USB2.0 common mode choke would do?
Also, are RS485 cables always shielded?

As per bottom of page 10 of the following, why do RS485 shields (in cables) need to be directly connected to ground at one end, but connected to ground via an RC network at the other end?.....this sort of connection isnt recomended for any other signals/voltage rails in cables?

https://www.ti.com/lit/an/snla049b/snla049b.pdf?ts=1626807085082

 

[KlausST]

Hi,

As per bottom of page 10 of the following, why do RS485 shields (in cables) need to be directly connected to ground at one end, but connected to ground via an RC network at the other end?.....this sort of connection isnt recomended for any other signals/voltage rails in cables?

all the explanation is given in the according section.

I don´t want to copy and paste it here.

(added) But this is not only true for RS-485. It´s true generally for differential signalling without dedicated DC-blocking and biasing of the receiver side.

Klaus

added:
We use WÜRTH (Wurth / Wuerth) common mode chokes: 744 231 371 for RS-485 interfaces.

 

[cupoftea]

Thanks, thats a nice small common mode choke, though i wonder if the interwinding capacitance may thus be too great or something?...(though admittedly probably not as USB2.0 CM chokes are even smaller)

When i went to Wurth...

RS485 / RS422 | Application Guide | Würth Elektronik

Find all required electronic components at a glance, helpful EMC and layout tips directly in the circuit diagram as well as important background info

www.we-online.com

..the smallest RS485 CM choke i could find was 6 by 3mm....this one..

WE-SLM SMT Common Mode Line Filter | Passive Components | Würth Elektronik Product Catalog

L 11 to 470 µH | IR 300 to 400 mA | RDC max. 0.18 to 0.58 Ω | Order Samples Free of Charge & Request Quotes Online | High Quality | Fast Delivery

www.we-online.com

 

[KlausST]

Hi,

common mode signal line chokes down to 0603 size (1.6mm x 0.85mm)

WE-CNSW SMT Common Mode Line Filter | Passive Components | Würth Elektronik Product Catalog

IR 90 to 2000 mA | RDC max. 0.05 to 5.5 Ω | Order Samples Free of Charge & Request Quotes Online | High Quality | Fast Delivery

www.we-online.com

Klaus

 

[cupoftea]

Thanks, i like that but its v small....

Do you think this one (2 lines) will be ok for USB 2.0 and RS485?...

https://product.tdk.com/en/system/files?file=dam/doc/product/emc/emc/cmf_cmc/catalog/cmf_commercial_signal_acm2520_en.pdf

Also, is this one OK for USB2.0 and RS485?......

https://www.we-online.com/catalog/datasheet/744232090.pdf