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TLC6946: Outputs are turned off during scan line switching?

Art Mecina
Genius 16655 points
Part Number: TLC6946
Other Parts Discussed in Thread: TLC6948, TLC6983

Hello Guys,

Good day.

Our customer wants some clarification on the operation of the TLC694x (TLC6946/TLC6948) matrix LED driver. The inquiry is regarding the multiplexed ES PWM modes.

Do the outputs turn off at the end of each subperiod, during the time that the scan lines are changed (tLSW), regardless of the grayscale data?

Here is the scenario he have specified:

This is best illustrated with the scenario that GS=FFFFh for every single pixel in the frame.

In this scenario, the outputs will be 100% on for the entire sub-period for one scan line, and they will also be 100% on for the entire sub-period for the next scan line.
However, the scan lines need to be switched by the hardware, which is done during the period tLSW, and the LEDs should be off during this switching time.
So does the TLC694x turn off the outputs after a number of GCLKs so that the scan line can be switched before the next subperiod, even when GS=FFFFh, or does the external hardware need to turn off all scan lines itself while switching to the next scan line?
If the TLC694x does turn off its outputs in this scenario, on which count of GCLK does it do so? Is it after 2^n clocks (n=8 or n=7 depending on PWM ES mode) or is it after 2^n + LGSC1 + MGSE2?

Thanks in advance!

Art

  • 0
    TI__Expert 3190 points

    Hi Mecina,

    Yes,  TLC6983 have an internal GCLK counter which is used to decide when turn on the channel and when turn off based on the grayscale data. in line switch time, the GCLK must be stopped, and at that time, the GCLK counter is 2^n + LGSC1 + MGSE2, so the device will turn off the channels until the next GCLK comes. This time slot, we call the line switch time, generally 1~2us is enough.

    Regards,

    Shawn.

  • 0 in reply to Shawn Ding
    TI__Genius 16655 points

    Thanks Shawn!

    To make sure that I am not misunderstanding you, can you please confirm that the following sequence is correct, assuming that all GS data is 0xFFFFh:

    1) TLC6946 receives exactly 2^n GCLKs from controlling device.
    2) During this time, TLC6946 outputs are ON.
    3) TLC6946 receives further LGSC1+MGSE2 GCLKs from controlling device during this time, outputs are still ON.
    4) After last GCLK (total 2^n + LGSC1 + MGSE2) the GCLKs are stopped by controlling device.
    5) All TLC6946 channel outputs are now OFF (even though GS=0xFFFFh).
    6) GCLKs are started again by controlling device.
    7) TLC6946 outputs are now ON.

    I would be grateful if you could confirm that this is precisely correct for the specific situation that all GS data for all pixels is 0xFFFFh.

    Thanks in advance!

    Art

  • 0 in reply to Art Mecina
    TI__Genius 16655 points

    Hello Shawn,

    Any update regarding confirmations above?

    Thanks!

    Art

  • 0 in reply to Art Mecina
    TI__Expert 3190 points

    Hi Art,

    Not exactly. please see my comment below

    1) TLC6946 receives exactly 2^n GCLKs from controlling device.
    2) During this time, TLC6946 outputs are ON.
    3) TLC6946 receives further LGSC1+MGSE2 GCLKs from controlling device during this time, outputs are OFF.
    4) After last GCLK (total 2^n + LGSC1 + MGSE2+1) the GCLKs are stopped by controlling device.
    5) Line switch from the current scan line to the next scan line
    6) GCLKs are started again by controlling device.
    7) TLC6946 outputs are now ON.

    Regards,

    Shawn