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Original question:

DP83826E: LEDS in basicmode (contimued)

DP83826E: DP83826E LEDs documentation mistake (revisit 2023)

Matt Ooi
Prodigy 130 points
Part Number: DP83826E

Hi there, I am referencing article https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1171778/dp83826e-leds-in-basicmode-contimued?tisearch=e2e-sitesearch&keymatch=DP83826E#

As there seems to be a conflict between the "Accepted Answer" noted there, the datasheet, and the EVM module schematics. 

The "Accepted Answer" noted in the thread above does not in fact agree with the datasheet or EVM module schematics as shown in the screenshot below. 

In the EVM module, it appears that, in fact, the LEDs do not require VCC pullup in order to function and that the LEDs are driven directly via GPIO of the DP83826E. 

I think this really should be made more clear in the documentation and anyone who comes across the other thread. I was unable to find any info of sourcing current in the documentation either. It seems like an oversight in the datasheet to clearly spec if this GPIO (for LEDs) is sink/source open drain and/or sourcing/sinking electrical characteristics. Only info provided is recommendation to bootstrap which remains unclear.

I'd like some design support on this to clarify the correct implementation to avoid overdriving the LED pins. 

TI EVM module screenshot source: www.ti.com/.../snlu262.pdf

  • 0
    TI__Mastermind 25955 points

    Hi Matt,

    I am not sure if I understand your question completely. Are you struggling on the implementation of the LED for DP83826EVM? If so here is the explanation is the following:

    • Since all the strap we have for LEDs in DP83826EVM are pull down. Therefore, the LED is acting as active high. If the LED is acting as active high, so we connect the LED directly to ground to make sure the LED to turn on when the Pin goes high. That is why we connect all the LED to ground instead of VCC.

    --

    Regards,

    Hillman Lin

  • 0
    Prodigy 130 points

    Hi Hillman, thanks for the response. I am struggling with the LED power requirements for the GPIO pins:

    Based on your response, we are to believe the diode receives power through the DP83826, correct? Thus, active high, the LED is illuminated. During inactive/low, we pulldown to 0V to ensure shutoff. 

    My qualm is that the datasheet seems to omit details regarding the GPIO LED pins--mainly, how much current can be sourced? And are we to assume the GPIO active high voltage = VCC? The datasheet does not specify. 

    I am asking specifically because I want to know if I can drive bulkhead (panel mount) LEDs directly off this pin, or if I need to use a switched power source. They are slightly higher power than a 0603 LED. 

  • 0 in reply to Matt Ooi
    TI__Mastermind 25955 points

    Hi Matt,

    Active High of GPIO pin equals to VDDIO voltage.

    --

    Regards,

    Hillman Lin