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DP83TC812S-Q1: LED strap connections

Jonathan Jank
Intellectual 1095 points

Part Number: DP83TC812S-Q1
Other Parts Discussed in Thread: DP83TG720EVM-MC

I’m confused by the LED strap connections on the DP83TC812 device.  The datasheet has two modes for the LED pins.

Figure 7-5 shows the LED strapping, but doesn't identify which Mode is associated with each picture.   And, it uses Rp as an identifier.   

Table 7-5 shows what to use for Rh for Mode 1 or 0, but Rh doesn't appear in Figure 7-5.    This is confusing.

What LED strap connection do you use with mode 1 for the LED pin?

thanks

  • 0
    TI__Mastermind 43325 points

    Hi Jonathan,

    For Rp, use a 2.49kOhm resistor. For mode 1, follow the configuration using VDDIO. Rcl will be a current limiting resistor to protect the LED from excess current when toggled.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Intellectual 1095 points

    Hi Gerome,

    we are still not understanding.   

    In Figure 7-5:  Is Mode 1 the left diagram or the right side diagram?

    If Mode 1 is the left diagram then what value should Rp be in that diagram ? 

    Table 7-5 says that Rh is OPEN for Mode 1.   (we know that internally there is a 9k pulldown on this pin as shown on p13)

    thanks, JJ

  • 0 in reply to Jonathan Jank
    TI__Mastermind 43325 points

    Hi JJ,

    My apologies on the confusion. For mode 1, please follow the left side diagram. Rp will be 2.49 still. What the table says is that by default the pin would strap into mode 1, but you can still attach a pulldown resistor to keep a pin set at mode 1. Especially for the LED pins where an LED would be connected, it is recommended to follow the left side of Example 7-5.

    An example of this circuit in play is the DP83TG720EVM-MC user's guide, section 6.1. There, LED0 is set up for either pull-up or pull-down with both systems in place, with the switch being a jumper configuration. 

    Sincerely,

    Gerome