• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 61 subscribers
  • Views 230 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLC5927 circuit design

Karl Dietmann
Prodigy 10 points
Other Parts Discussed in Thread: TLC5927

Hello,

I have a question regarding the LED driver TLC5927. Currently I am designing a simple circuit using 3 TLC5927 and a PIC microcontroller. I have some questions regarding the connection in cascade an the dimensioning of R-Ext.

1. Are there any problems sharing the 3 CLK on one pin at the microcontroller?

2. Same goes for sharing the LE(ED1) and /OE(ED2)? Are there any additional Pullup/Pulldowns required?

In result I only need 5 Pins for controlling 3 TLC5927 with my microcontroller (common CLK, LE(ED1) and /OE(ED2) plus SDI and SDO)?

3. Calculating the R-Ext: I am trying to controll RGB LEDs (16pcs -> one TLC per color) using Vdd = +5V. The datashee says red max. 2,6V / green max. 3,6V / blue max. 3,6V. The max. current for each color is rated at 10mA. So how do I calculate R-Ext for each TLC (color) in respect to the max. voltage an Vdd. Unfortunately I did not understand the calculation in the datashee concerning this. Say that I want to have the 10mA as max gain.


Thank you for your help in advance


Greetings from Germany

  • 0
    TI__Genius 14890 points

    Karl,

    1.  All 3 drivers can share the same CLK pin.  The only time this might be an issue is if there is a significant distance between the drivers and the CLK signals would be shifted in time.

    2.  There should be no issues with the LE(ED1) and /OE(ED2) signals.  No need for additional pull-up/pull-down resistors.  This depends on the drive of your microcontroller.

    3.  Calculation of REXT is not influenced by the forward voltage of the LEDs.  The TLC5927 is a constant current driver, so the current is not influenced by the loading.  The datasheet shows:

    IOUT,target = (1.25V/Rext) * 15

    To calculate Rext change the formula to:

    Rext = (1.25V/IOUT,target) * 15

    For 10mA, the result is:

    Rext = (1.25V/10mA) * 15 = 1,875 Ohms

    Using the Current Gain as discussed in the "16-Bit Configuration Code and Current Gain" section shows how to adjust the current down from 10mA.  Note that the minimum recommended current is 5mA.  This does include the result of the current gain.  Below 5mA, the device will continue to work, but the output to output skew may increase.

    Regards,

    Dick