DP83826I: Circuit diagram when strapping LED pins

Atsushi Takahashi

Part Number: DP83826I

Tool/software:

Hi Team,

The customer will be using it in Basic mode.
Could you provide a circuit diagram for strapping the LED pins?
I would like to know both for strapping to low and to high.

I have read the following text in the datasheet, but I would like more specific information.
"In BASIC mode, the LED polarity will always be active low. In the case that the LED pin must be strapped low, a 1 kΩ pull-up resistor in series with the LED should be used and a 5 kΩ pull-down resistor. This will result in the strap selecting 0. Please note that using higher resistance may decrease the brightness of the LED."

Best Regard,

2 months ago

+1 Alvaro (Al-vuh-roe) Reyes 2 months ago

TI__Genius 16726 points

Hi Atsushi,

I see how this is confusing, in Basic mode LED0 will always behave as active low. The default state of LED0 is '1' which is Auto-negotiation enabled. If this is desired, then there is no need for an additional bootstrap. To set LED0 to '0', auto-negotiation disabled (not recommended) refer to the drawing below. Note that I used a 1.5kΩ PD instead of the data sheet recommended 5kΩ.

Regards,

Alvaro

0 Atsushi Takahashi 2 months ago in reply to Alvaro (Al-vuh-roe) Reyes

Intellectual 845 points

Hi Alvaro-san,

Thank you for your answer.

The 1kΩ series resistor value may affect the driving of the LED.

Could you tell me the best way to improve this?

For example,
- Reduce the series resistor value. How small can it be?
- Use a FET
- Other

0 Alvaro (Al-vuh-roe) Reyes 2 months ago in reply to Atsushi Takahashi

TI__Genius 16726 points

Hi Atsushi,

May I ask why the customer wants to disable auto-negotiation in the first place?

As long as the voltage on the pin is below 0.6V, it'll go into Mode 0.

Figure 1 - Bootstrap DC Characteristics from Electrical Characteristics section in data sheet

Regards,

Alvaro

0 Atsushi Takahashi 2 months ago in reply to Alvaro (Al-vuh-roe) Reyes

Intellectual 845 points

Hi Alvaro-san,

I know that Auto-negotiation is very flexible, but I don't think it only has advantages.
Are there any disadvantages that users should be aware of?
Please let me know if there are any situations in which Auto-negotiation should be disabled.

0 Alvaro (Al-vuh-roe) Reyes 2 months ago in reply to Atsushi Takahashi

TI__Genius 16726 points

Hi Atsushi,

You're correct, everything has advantages and disadvantages. With auto-negotiation is enabled it will take slightly longer to link up (in the millisecond range), but it will ensure a more stable link. The use case for Forced Speed (auto-negotiation disabled) is niche, as both ends of the link will need to the forced at the same speed.

Please see this FAQ for more information

Regards,

Alvaro

0 Atsushi Takahashi 2 months ago in reply to Alvaro (Al-vuh-roe) Reyes

Intellectual 845 points

Hi Alvaro-san,

Thank you for your answer.

I was able to understand that it is general to enable auto-negotiation.

I'll close this case.

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DP83826I: Circuit diagram when strapping LED pins