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TLC5947 SCLK Slew rate limitation.

Go
Genius 4220 points
Other Parts Discussed in Thread: TLC5947

Hi,

I found the specs for the SCLK input Pulse duration, but I couldn't find the specs for SCLK input pulse slew rate.

is there any limitation for that?

Thanks

Go

  • 0
    TI__Intellectual 955 points


     Hello Go,

     TLC5947 recommend condition and switchingcharacteristics are defind with 1~3ns input rising and falling time as Figure7 and 8 as described by Fig. 7 and 8. But function wise, I think it is no problem even if the rising and falling time of input signal is 1us if setup and hold time of SIN,SCLK,XLAT are enough time with one chip operation (stand alone operation. No cascade operation).

     Thank you and best regards,

     K.Nakai

       

  • 0 in reply to Kazuya Nakai
    Genius 4220 points

    Hi, Nakai san

    Thanks for your comment.

    Here are the SCLK&SDA Waveform with different SCLK slewrate.

    My customer had a problem with slower slewrate SCLK operation.(LEDs sometimes flickered)

    Regarding the faster slewrate SCLK, no problem.

    Do you have any idea for the reason of the problem?

    Is there any other point that we need to check?

    Your advice would be much appreciated.

    Regards,

    Go

  • 0 in reply to Go
    TI__Intellectual 955 points

     Hello Go,

     I think the GND line impedance between TLC5947 and controller may be not low. If GND line has some large imperdance, some difference voltage between TLC5947 GND and controller GND is genarated when TLC5947 output turned on and off. Then some wrong data may be written into TLC5947 by SCLK level is recognized as high and low repeatedly around threshold voltage level because of slow rising transient of SCLK. 

     If this is the reason of the problem, probably the problem is not happend when the data is sent into TLC5947 while BLANK signal is 'H' because TLC5947 output is allways during high BLANK level. Can the customer try the test? Also I recommend you to ask the customer to check how much difference voltage between TLC5947 and controller is generated when the flickering is happend. If the difference voltage is more than 200mV, it may be large. If the difference voltage is large, GND imperdance is needed to reduce by thick wire using or thicker GND pattern or wider GND pattern using. 

     Can I ask you some questions?

     1. How many TLC5947 are cascaded in series?

     2. What position IC is the issue IC from controller? Is it the farthest IC from controller? or the nearest IC? 

     3. Are TLC5947s and the controller for TLC5947 mounted onthe same board? Or is each board separated?

     4. What is the SCLK frequency?

     5, What is resistor value of the resistor mounted between TLC5947 IREF pin and GND?

     6. Whatis VCC voltage?

     Thank you and best regards,

     K.Nakai.