Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Does SN65HVD1786D needs TVS diodes?

Status
Not open for further replies.
B

BenzT

Junior Member level 3
Joined
Mar 24, 2017
Messages
27
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
224
Hi,

I am planning to use SN65HVD1786D for RS485 communication. Normally we use TVS diodes at the pair of cables to avoid transient surges.

Since SN65HVD1786D has inbuilt fails safe modules for power short, Is it mandatory to have any TVS diodes like SMAJ12CA at the A and B lines?
 
Last edited:

Hi,

reading the datasheet helps.

The first lines of the datsasheet in section "1 Features" show:
* Bus-Pin Fault voltage limits and
* ESD voltage limits.

--> if your input signal is beyond these limits, then you need additional protection.

Klaus
 

It has been given as +/- 16KV.

I generally uses SMAJ12CA. I think, no need to put this SMAJ12CA. Am i correct?
 

SMAJ12CA can handle much more energy than the internal protection in SN65HVD1786D.
ESD/transients/glitches in the real world is not as predictable as "16 kV discharge from a human body model".
I would use the TVS diodes.
 
  • Like
Reactions: BenzT

    B

    BenzT

    Points: 2
    Helpful Answer Positive Rating
SN65HVD1786D is meant for protection of power supply short with the RS485 lines.


If i use SMAJ12CA at the lines like this ( RS485 A --> SMAJ12CA --> GND ) and Say if 24V is shorted with RS485 A line; will this permanent short destroy the SMAJ12CA?
 

BenzT said:
SN65HVD1786D is meant for protection of power supply short with the RS485 lines.


If i use SMAJ12CA at the lines like this ( RS485 A --> SMAJ12CA --> GND ) and Say if 24V is shorted with RS485 A line; will this permanent short destroy the SMAJ12CA?
Click to expand...

Yes, to handle shorts to the power supply without failure, the voltage of the TVS diodes must be selected so they don't conduct at the supply voltage.
Otherwise they will overheat and fail to a short unless the power supply is very weak (low current limit).

SMAJ12CA is not the right TVS diode to handle shorts to the 24V supply.

You can find good information here:
https://www.intersil.com/content/da...ce/overvoltage-protection-rs485-bus-nodes.pdf
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top