A BLANK pulse is required to reset the counters used for the grayscale setting. The grayscale clock increments a counter which shuts off the port once the value set by the serial in data is reached. The blank line pulse is needed to reset the counter to begin the next PWM cycle. Unfortunately, when I want to reset the counters, the LED blink. Is there a different method to reset the counters? The software engineer made a modification to the pin configuration of the their micro that is driving the LED driver by changing the output slope from the original default 2MHz “output speed up” setting to a 10MHz option and the problem was solved, but is there a better way in hardware?
Thanks in advance,
Scott
Hello Scott-san,
To reset GS counter, it must input blank pulse and it's no way to reset it.
Output is forced off at 4096 gsclks until GS counter is reset.
I'd like to know your data timing condition in more detail.
Could you tell me what timing do you input XLAT pulse?
If it's in caseA( input XLAT during GSCLK running), in this case, output data is changed by input data.
If GS counter is over than input data, output is turned on until 4095 gsclk even if input data is less than FFF.
Please use case B.
Thank you and best regards
K.Narisawa
Hello Narisawa,
I work with Scott. Thank you for your reply Narisawa. Found spurious XLAT pulses in the waveforms. Attached are the details you have asked for.
3782.Timing Waveforms.docx
Trying to figure out why there are spurious XLAT pulses.
Thanks,
Madhu
Hello Madhu-san,
Thank you for your pictures.
If Sperious XLAT pulse is for Dot correction data, that data is genaraleted at this latch timming correctly, but if it is for gray scale data, output data is not generated
correctly. TLC5941 verify GScounter and GS input data. If GS counter pass for input GSdata at latch timing, output is turned on to 4095gsclks even if
data is small.
Best Regards
Tried to remove spurious XLAT pulse but the blinking still exists.
I do have a question about the spec. As shown in the attached figure, it indicates that an extra SCLK pulse after the XLAT pulse is required for grayscale data after a dot correction pulse. What happens if this extra SCLK pulse after the XLAT pulse is not provided.
Regaring your question,
In case of no additional SCLK pulse of #193, when input dot correction data after this, MSB of DC data goes to low.
#193SCLK is used for changing switch between GS and DC.
If it's possible ,could you show me output current which you'd like to use?
If it's less than 40mA, I'd like to recommend TLC59461. TLC59461 doesn't need additional SCLK pulse of #193.
Program and pin assign of TLC59461 without #193 SCLK is compatible with TLC5941.
Thank you for the reply. Maximum current in our case is 30mA. We can test it using TLC59461 as you suggested but we don't see any auto-qualified version of it. Please advise.
Do you use TLC5941-Q1 or TLC5941?
If TLC5941-Q1 is, Yes, it's for auto-motive specification. And we don't have TLC59461 like auto motive specificaton.
If device is swapped TLC59461 and TLC5941,and issue will be resolved,it root casse is by #193sclk.
Could you please check this?
We are using automotive version of TLC5941.
I have a question regarding your previous answer below.
“In case of no additional SCLK pulse of #193, when input dot correction data after this, MSB of DC data goes to low.”
If multiple, repetitive grayscale data is sent after dot correction data is sent without pulse #193 of the SCLK, is the MSB of the DC data still affected?
In the timing diagram, it shows a second series of GS data being sent without pulse #193. I am trying to understand if this is a problem with the MSB of the DC data even after many consecutive grayscale data messages. For example, after DC data is sent, there are 20 messages sent for grayscale data before the next DC data is sent. How would this affect the MSB of DC data in this case?
Madhu-san,
I'm sorry that my late response.
Fig18 on datasheet missed no #193SCLK after second grayscale data. we will fix this.
And regarding your question, 20messages grayscale data are not affect . In your case, is it affect for 20 messages of GSData too?
Sorry for the delay. Blinking issue is finally solved. Thanks for you help.
New question.
Radiated noise coming from an external noise source (ex. motor) can affect a PWM signal toggling a transistor driving an LED resulting in LED flicker.
What does the TLC594-1 do internally to reject the same external radiate noise from affecting the PWM output?
TLC5941 has no internally circuit to reject for radiation noise.
TLC5941 has been used for LED panel. But I have never heard noise issue by the PWM output yet.