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LED strobe back light design using TLC5927

Darshan Patel
Prodigy 90 points
Other Parts Discussed in Thread: TLC5927

we are designing LED strobe light panel which has around 900 leds .

features : we wanted to drive it using strobe pulse , so we want constant current operation . we wanted to overdrive leds as they will be operated in strobe mode .

We have chosen TLC5927 , 6 of them will be used in each board. each channel will be connected to 8 leds . let us know weather this product is good for the said application.  All 6 TLC5927 will be controller using single micro.

  • 0
    TI__Genius 14890 points

    There are several things to consider for this application.  

    What is the LED Voltage?  The TLC5927 have an Absolute MAX rating of 20V on the OUT pins.  The recommended operating maximum is 17V.

    What current are you using for the overdrive?  The maximum current per channel is 120mA.

    What is the strobe pulse you are planning?  There are two ways to get a pulse.  You can use the OE pin to turn all outputs Off or On.  You can also write to specific outputs  (at a serial rate of 30MHz) to turn the outputs Off or On.  The output turn on time is very similar from OE or from the CLK/LE input.

    If these questions all fit into the application, then the TLC5927 would be a good fit.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 90 points

    Yes Current and voltage will be fine we will be using 8 leds for single channel . and OE at 4 us pulse as strobe .

    About 8 of TLC5927 will be there on PCB driving 900 leds .

    now we have three such separate led back lights board each having 8 TLC 5927  . now what we can use to connect theses individual boards to single micro controller.

    all three boards are placed nearby . can we use SPI communication with around 12" wire to connect all three boards with the main micro controller board.

  • 0 in reply to Darshan Patel
    TI__Genius 14890 points

    The communication between devices is dependent on the signal integrity.  Depending on your communication speed, you will not have issues.  There are a few things you may try in your evaluation that will help as you build your production systems.  Try running at 20% (or more) higher than your anticipated communication speed.  If you plan on running at 1MHz, try it at 1.2MHz.  You can continue to increase until you find out where you break.  At that point, back off until you have good manufacturing margin.  Additionally, check the wire diameter.  You may run a similar experiment there.

    There aren't any good general rules because each implementation is unique.  There are too many variables than we can evaluate.  Connectors versus solder points, wire diameter, communication speed, general system noise, ambient temperature, wire length / trace length. 

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 90 points

    ok i will do that .

    what will be input current requirement for each TLC5927it is not clearly mentioned in Datasheet . could you please point me out for the same.

  • 0 in reply to Darshan Patel
    TI__Genius 14890 points

    I am sure sure which input current you are asking about.  So I will answer both.  

    The IDD (operating current into the VDD pin) has two components: IC operation and REXT current.  Setting IOUT is based on REXT.  The higher the IOUT, the lower the REXT and the higher the I(REXT).  The table on page 8 of the datasheet covers that.  For REXT = 180 Ohms (IOUT = 104mA), the IDD maximum would be 20mA for VDD = 3V.

    The SDI pin is driven by the controller or the previous SDO.  The SDI pin is a high impedance input so the current is minimal (less than 1uA).  The SDO is capable of 1mA.

    Regards,

    Dick