THVD1429: Question about D port

NOBUO FUJIHARA

Expert 8255 points

Part Number: THVD1429

Hi team,

My customer monitors 4V level in D input port with below condition.

- VCC = 5V

- A port and B port are connected with 120 ohm termination, but no input

- DE = GND

- RE = 5V pull-up

- D input is disconnected (open)

Question) Could you explain the reason why D input port has 4V level with this configuration?

Best regards,

over 4 years ago

0 Max Robertson over 4 years ago

TI__Guru 62910 points

Hello Fujihara-san,

This voltage should not be strongly driven by the device, it is likely just a weak bias resistance that is observed due to leakage currents within the IC and PCB. You can confirm this by adding a weak pull-down or pull-up resistance to the pin to verify that it properly sets the voltage away from this 4 V value.

Regards,
Max

0 NOBUO FUJIHARA over 4 years ago in reply to Max Robertson

TI__Expert 8255 points

Hi Max-san,

May I ask additional question?

In Table1, when D is OPEN, it defines function as "Actively drive bus high by default".

D port is intentionally pulled-up?

Best regards,

0 Max Robertson over 4 years ago in reply to NOBUO FUJIHARA

TI__Guru 62910 points

Fujihara-san,

I believe that is the case, but I am awaiting confirmation from our design team. I will update you once I am certain.

Regards,
Max

0 Max Robertson over 4 years ago in reply to Max Robertson

TI__Guru 62910 points

Fujihara-san,

I can now confirm there is a 2-MOhm internal pull-up from D to VCC.

Regards,
Max

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THVD1429: Question about D port