DS34LV86T: Back Biasing on DS34LV86T when not powered

Russell Wetherley1

Part Number: DS34LV86T
Other Parts Discussed in Thread: DS34LV87T

Hello E2E,

We are using the DS34LV86 to interface with another terminal outside of our unit. If this device is not powered, we are experiencing back-biasing if the outside terminal has power to the interfacing signals. I suspect that this is back-biasing is going through the DS34LV86 ESD diodes.

Would I be correct in this assesment?

Are there any drop-in alternative parts that would not be back-biasing voltages if power is not applied to the device.

Are there any RS-485 devices that would not back bias when power is not applied to VCC (i.e. equivalent to 5V-tolerant ICs)?

Thank you for the help!

Regards,

Russell

over 7 years ago

0 Hao L over 7 years ago

TI__Mastermind 25705 points

Russell,

Sorry to hear your problem. I want to make sure I understand the situation. When the device is not powered, which pin does it back-bias through input pin? Please note there is a resistor divider at the input stage that is connected to Vcc and Gnd.

Regards,

Hao

0 Russell Wetherley1 over 7 years ago in reply to Hao L

TI__Expert 4255 points

Hello Hao,
From the customer:

What we have is the driver (DS34LV87T) on a host platform that is powered. The receiver is on my board and is not powered. We are seeing a voltage the rail of my DS34LV86T (even though there is no power applied on my board). Since this is the only interface connected, I'm assuming that it is the DS34LV86T differential input pins that this current is going through (ESD diodes?) I'll try and get some scope plots tomorrow.

Regards,

Russell

0 Hao L over 7 years ago in reply to Russell Wetherley1

TI__Mastermind 25705 points

Russell,

What is the voltage level you saw on DS34LV86T rail? Can you try to add some loading (some resistors) to see if the rail would be dragged down? Please let me know your results and what concerns you have. Maybe we can find a way to work around.

Regards,

Hao

0 Miguel Robertson over 7 years ago in reply to Hao L

TI__Guru 62920 points

Hi Russell,

Do you have any updates from the customer regarding this?

Thanks,
Max

0 Russell Wetherley1 over 7 years ago in reply to Miguel Robertson

TI__Expert 4255 points

Hi Max,

Our customer was out all last week. I will ping him to see where he is at with capturing the scope shots.

Russell

0 Miguel Robertson over 7 years ago in reply to Russell Wetherley1

TI__Guru 62920 points

Hi Russell,

Just checking in on this. Did you end up hearing anything back from the customer?

Thanks,
Max

0 Russell Wetherley1 over 7 years ago in reply to Miguel Robertson

TI__Expert 4255 points

Hi Max, yes it is closed. There was another component on the board that was the source of the issue.

Thank you for the support. Sorry for the goose chase.

Russell

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DS34LV86T: Back Biasing on DS34LV86T when not powered