[EE] RS485 ESD protection

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[EE] RS485 ESD protection

Neil
Anyone have a favourite part or circuit-section for very good RS485
ESD/voltage-spike protection?

I'm re-designing a lighting control board for someone and they've fried
a handful of RS485 interfaces in the past.  Those chips had 7kV of
protection.
We have no practical way to measure the ESD, but I want to make this a
protected as possible... only a handful of boards will be built, so
let's assume cost no issue for now.

Any thoughts on this (LTC2862)?...
https://www.analog.com/media/en/technical-documentation/data-sheets/2862af.pdf
And with these, does it help to add TVS'es as well?  What about a
digital isolator between the RS85 interface chip and the microcontroller?

Thanks.



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Re: [EE] RS485 ESD protection

John Lawton
The LTC2862A has headline '7kV protection' but in fact only +/-60V for
'line faults'.

Also, in the case of the lighting control board was there a common
connection?
If not then a large potential difference between the common lines could
also cause failure.

Some additional TVS diodes could be used to help protect against the above.

John


On 26/01/2021 21:25, Neil wrote:

> Anyone have a favourite part or circuit-section for very good RS485
> ESD/voltage-spike protection?
>
> I'm re-designing a lighting control board for someone and they've fried
> a handful of RS485 interfaces in the past.  Those chips had 7kV of
> protection.
> We have no practical way to measure the ESD, but I want to make this a
> protected as possible... only a handful of boards will be built, so
> let's assume cost no issue for now.
>
> Any thoughts on this (LTC2862)?...
> https://www.analog.com/media/en/technical-documentation/data-sheets/2862af.pdf
> And with these, does it help to add TVS'es as well?  What about a
> digital isolator between the RS85 interface chip and the microcontroller?
>
> Thanks.
>
>
>

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Re: [EE] RS485 ESD protection

Harold Hallikainen-3
In reply to this post by Neil
I used some devices from Littlefuse for both 485 and USB transient
protection. I don't have access to the part number right now...

Harold



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Re: [EE] RS485 ESD protection

Alan Pearce
In reply to this post by John Lawton
Well, the 7kV protection is HBM (Human Body Model) ESD, whereas the 60V
is ground differential, rather different things.

i would agree that some form of TVS unit is likely to be useful,
although I doubt it would be full protection against ground bounce
problems - that would only get cured by isolation.

As to what TVS devices to use, Bourns seem to be a major player in this
area, with devices for protecting USB ports and the like which would be
the sort of devices I would use.


On Tue, 26 Jan 2021 22:07:20 +0000
John Lawton <[hidden email]> wrote:

> The LTC2862A has headline '7kV protection' but in fact only +/-60V
> for 'line faults'.
>
> Also, in the case of the lighting control board was there a common
> connection?
> If not then a large potential difference between the common lines
> could also cause failure.
>
> Some additional TVS diodes could be used to help protect against the
> above.
>
> John
>
>
> On 26/01/2021 21:25, Neil wrote:
> > Anyone have a favourite part or circuit-section for very good RS485
> > ESD/voltage-spike protection?
> >
> > I'm re-designing a lighting control board for someone and they've
> > fried a handful of RS485 interfaces in the past.  Those chips had
> > 7kV of protection.
> > We have no practical way to measure the ESD, but I want to make
> > this a protected as possible... only a handful of boards will be
> > built, so let's assume cost no issue for now.
> >
> > Any thoughts on this (LTC2862)?...
> > https://www.analog.com/media/en/technical-documentation/data-sheets/2862af.pdf
> > And with these, does it help to add TVS'es as well?  What about a
> > digital isolator between the RS85 interface chip and the
> > microcontroller?
> >
> > Thanks.
> >
> >
> >  
>

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Re: [EE] RS485 ESD protection

David Duffy (AVD)
In reply to this post by Neil
I've used the SM712-TP with a pair of 100mA polyswitches in the data
lines before.

https://www.digikey.com.au/products/en?keywords=SM712-TPMSCT-ND
David...

On 27/01/2021 7:25 am, Neil wrote:

> Anyone have a favourite part or circuit-section for very good RS485
> ESD/voltage-spike protection?
>
> I'm re-designing a lighting control board for someone and they've fried
> a handful of RS485 interfaces in the past.  Those chips had 7kV of
> protection.
> We have no practical way to measure the ESD, but I want to make this a
> protected as possible... only a handful of boards will be built, so
> let's assume cost no issue for now.
>
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