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TLC59711: Cascading 30 units with relatively high Vf LEDs

YaD
Prodigy 60 points
Part Number: TLC59711

Hello All,

A costumer was looking to use 30 TLC59711 units in cascade for an HMI interface.

The original design had VLED=Vcc=Vreg=3.3, after checking the used LED forward drop at 10mA, the supplier estimate the maximum value at 3.5V.

and for that I have changed the Vled tp 5V with 4.9kOhm Ref resistor for approximately 10mA current limit and left the Vcc=Vreg=3.3V to keep the voltage compatibility with the MCU.

My questions are as follow : 

- is there any recommendation for the coupling capacitors ? 

- Should I add some series resistors to the SDI & SCK pins ( 22Ohm)

- as for the last of the cascade, any recommendation in particular for the SDO/SCKO pins ? 

Thank you in advance for the support

  • +1
    TI__Genius 12915 points

    Hi Yad,

    Please see my feedback below as green mark

    - is there any recommendation for the coupling capacitors ? 
    There is no specific recommendation for the capacitors. 10uF parallels with 0.1uF in your schematic is OK.

    - Should I add some series resistors to the SDI & SCK pins ( 22Ohm)
    If the distance between 2 units is short, I do not think it is necessary to add the series resistors.

    - as for the last of the cascade, any recommendation in particular for the SDO/SCKO pins?
    They can be floating or connecting to GND.

  • 0 in reply to Hardy Wu
    Prodigy 60 points

    Thanks Hardy for the feedback.

    Much appreciated