SN65HVD3083E and SN65LBC180 - the difference of behavior

Dice-K

Other Parts Discussed in Thread: SN65LBC180, SN65HVD3083E

Hello,
I have a question about SN65HVD3083E and SN65LBC180.

I attach a file.

Figure-1 uses SN65HVD3083E, and figure-2 uses SN65LBC180.
A master is one, and slaves are 50.
The master is the transmission.
The slaves are differential signals of the receiving .

When a master does not transmit, a noise (on the negative side a wave pattern of △ of approximately 1V) appears on the line.
(The state of DE is prohibition). SN65HVD3083E

Why the difference of behavior does happen between SN65HVD3083E and SN65LBC180?

The SIGNALING RATE of our product is 9600bps.

Regards,
Dice-K

over 8 years ago

0 Max Robertson over 8 years ago

TI__Guru 62910 points

Hi Dice-K,

Thanks for providing a clear summary of your observations. Just looking at the waveforms I'm not sure why the HVD3083E would be producing these glitches. Is the noise that you are measuring occurring completely randomly, or is it correlated to any other signals in your system (like the enable controls, etc.)? Does similar noise show up on the device power supply as well?

Regards,
Max

0 Dice-K over 8 years ago in reply to Max Robertson

Mastermind 6330 points

Hello Max,
Thank you for your reply.

The noise occur randomly.
The intervals of noise are several msec or dozens of msec.
When number to be connected decreases, it becomes once from several minutes to dozens of minutes.
I attach an example when an interval is short.

I think that the noise is not correlated to the enable control.
I added a postscript in the last document.
I do not control the enable at the Figure-1 timing.
I think that the output is High when I admit it momentarily.
Figure-2 is the timing of the enable control.
Then the noise does not occur.

I did not take the wave pattern about the power supply by the field work.
The situation of the noise is follows.
① There is a noise in market setting product (SN65HVD3083E).
② There is a noise in exchange 1(SN65HVD3083E) in the market.
③ There is no noise in exchange 2(SN65LBC180) in the market
When there is a noise to the power supply, does a difference appear with two kinds of ICs?

Best regards,
Dice-K

0 Max Robertson over 8 years ago in reply to Dice-K

TI__Guru 62910 points

Dice-K,

Yes, it is possible for different ICs to respond differently to noise in the power supply. They could differ in how they filter out power supply noise internally, or they could differ in how under-voltage detection/power-on-reset circuits are implemented. I think it is at least worth probing the VCC rail in order to check if this could be a root cause.

If the noise always occurs when the master device is disabled, then another reason for this difference in behavior could be the amount of leakage current each chip has on its Y/Z outputs. The LBC180 device has output leakage (IOZ) of up to 100 uA, while for the HVD3083E it is at most 1 uA. If this noise is being coupled onto the bus by some external source, having larger leakage current would help to counteract the noise coupling and keep the bus voltage more stable. (If the glitches do not correlate directly to any inputs or output of the transceiver IC, too, then it is most likely that they are being coupled from an external noise source.)

Best regards,
Max

0 Dice-K over 7 years ago in reply to Max Robertson

Mastermind 6330 points

Hello Max,
Thank you for your reply.

I have questions about SN65HVD3083E.
For noise countermeasure, I want to always use it in transmission permission (DE=High). (regardless of the data transmission.)

Is there always a possibility that it becomes easy to destroy an IC by the foreign noises such as surges in comparison with prohibition state (DE=Low) by making permission (DE=High) (it becomes very likely to be the destruction)?
When an IC is more likely to destroy it, please teach me the reason.
In addition, please give me it if there is test data.

Best regards,
Dice-K

0 Dice-K over 7 years ago in reply to Dice-K

Mastermind 6330 points

Hello Max.

Please teach me whether it becomes easy to destroy a SN65HVD3083E when I use it in DE=High fixation.

Best regards,
Dice-K

0 Michael Peffers over 7 years ago in reply to Dice-K

TI__Mastermind 20820 points

Hi Dice-k,

Max is currently traveling through Japan so I am going to jump in here and help out. The SN65HVD3083 and every RS-485 device have a maximum tolerable voltage that is allowed at each pin. The bus pins are typically more robust then the other device pins since the bus pins handle the interaction with the outside world and are therefore more susceptible to electrical over stresses (EOS).

So, with that said, it does not matter whether DE is high or low during an EOS event as the ESD or protection cell on the device will trigger to protect the device against EOS events or burn out if the stress is to much for the IC to handle. The maximum voltage rating on the bus pins of the SN65HVD3083 is -9V and 14V. The protection circuitry will trigger just above these voltages and clamp any EOS to ground protecting the device. The device is rated for stresses up to +/-16kV HBM, stresses outside of this range can permanently damage the transceiver regardless of the state of DE.

Please let me know if this answers your question or not and I will be glad to continue to help!

0 Dice-K over 7 years ago in reply to Michael Peffers

Mastermind 6330 points

Hello Michael,
Thank you for your reply.

I tell my customer as follows.

It is no problem to make transmission permission (DE=High) always.
Regardless of a state of the DE, use it in "Recommended Operating Conditions".

If my customer give me questions again, please help me again.

Best regards,
Dice-K

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SN65HVD3083E and SN65LBC180 - the difference of behavior