SN65HVD30: Signal attenuation issue after the transformer

Tess Chen

Intellectual 2675 points

Part Number: SN65HVD30

Hi,

Please find the master and slave schematic based on SN65HVD30 in the below.

Master:

Slave:

Issue:

Comparing to design without transformer, the signal output at T4 from master attenuate obviously with no load.

Output signal tested with transformer:

Question:

1.Any suggestion to improve for the schematic?

2.Transformer is desinged for isolation and the output should be +/-1.5V AC. The signal tested directly at Z/Y pin is correct. What should be taked into consideration for adding an transformer here?

Best Regards,

Tess Chen

over 5 years ago

0 Hao L over 5 years ago

TI__Mastermind 25705 points

Tess,

I have rarely seen people put transformer on the bus. If you want isolation, you may want to consider isolated RS-485 transceivers.

www.ti.com/.../products.html

Or you could apply discrete components at the digital pins, like mentioned in this blog.

e2e.ti.com/.../the-hidden-cost-of-your-optocoupler-for-isolated-rs-485-designs

If you have to use transformers, I don't see any issues about the schematic. However I didn't find the datasheet of the transformer. I assume SN65HVD30 runs at 10MHz. If so, what's the insertion loss of the transformer at this frequency? Another option is trying putting the load step by step. For example check the waveform with only one transformer to see if it makes sense.

Regards,

Hao

0 Tess Chen over 5 years ago in reply to Hao L

TI__Intellectual 2675 points

Hi Hao,

Thanks for your suggestion. Issue is fixed by open wire between transformer's PIN2 and GND.

0 Hao L over 5 years ago in reply to Tess Chen

TI__Mastermind 25705 points

Tess,

Thanks for your update. It makes sense.

Hao

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SN65HVD30: Signal attenuation issue after the transformer