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TLC59401/TLC5941 use without GSCLK

Matthieu Narbonne
Prodigy 40 points
Other Parts Discussed in Thread: TLC5947, TLC5941, TLC5940

Hello,

We are worried about using this LED driver.
Can you confirm that the following installation (and use) is possible:

- Vcc: 5V
- Riref: 2kohm for Imax 20mA
- TEST: routed on Vcc
- MODE: routed on Vcc
- GSCLK: routed on GND
- SCLK: pin_cpu
- INS: pin_cpu
- SOUT: pin_cpu
- XLAT: pin_cpu
- BLANK: pin_cpu
- Xerr: Not Used

With this setup, I think I can do this:
- We are in “dot correction” configuration.
- We manage leds  On/Off by DCn modification.
- We can change the Led brightness via DCn register.
- I couldn’t control status because I must drive the MODE input...

 

For simplicity, in our case, we can’t connect GSCLK, so we think we may only use the "dot correction”.

Is-it correct?

Thanks

  • 0
    TI__Guru 61115 points

    Hello Matthieu,

    Sorry, but the GSCLK is absolutely needed for this part. The part just turns on the outputs, if a GSCLK is connected. In addition, there are no default values for the gray scale register, therefore your connection will not work.

    Please have a look at TLC5947 which has 24 channels, but does not need a separate grayscale clock.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 40 points

    Ok thanks I will try.

    Matthieu

  • 0 in reply to Matthieu Narbonne
    Prodigy 120 points

    Dears sir.

    What's happen if generation of GSCLK is stopped?

    Could you confirm that the output will be maintened?

    Thank in advance

    Iko

  • 0 in reply to iko ria
    TI__Guru 61115 points

    Hello Iko,

    What do you mean with "if the generation of GSCLK is stopped"? Do you mean you stop for a while to keep the outputs on for longer than in general? How long is this while? What do you want to achieve with stopping the GSCLK? Why not just making the GSCLK slower?

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 120 points

    Hi.

    In case of there isn't presence of timer/pwm. We must make GSCLK signal with a I/O port.

    I have see in the datasheet that the GSCLK signal is just used for increment an internal counter. I think i can draw an analogy with timer/pwm module in µC with clear ouput on mach function...

    So , in my mind, if the GSCLK signal is stopped, the internal counter is stopped too...and the output keep the same state...

    (result is: ON LED are FULL TIME ON, to the next blank signal...)

    Could you confirm this way?

    Regards.

    Iko

  • 0 in reply to iko ria
    TI__Mastermind 36110 points

    You are correct that if you stop applying a clock signal to the tLC5941 (TLC5940) GSCLK pin, the internal counter does not count and the outputs remain fixed and do not change.  Note that if you pull BLANK high, the outputs turn off and the internal counter is reset.  You can not turn the outputs on again without a GSCLK signal.

  • 0 in reply to Matthew Day
    Prodigy 120 points

    Hi

    ok thanks.

    I'll put some feedback about my application

    Best regards.

    Iko

  • 0 in reply to iko ria
    Prodigy 120 points

    Hi, i had made some test and i can talk about my solution.

    In my application, i haven't TIMER/PWM to generate clock signal for GSCLK. I can't do clock signal manualy (however at 500 Hz frequency...).

    So i made this:

    1) Initialisation of the device:

      - G.S. witht random value (10 for exemple)

      - Dot with zero value

    2) make some pulse on GSCLK, to activate outputs.

    3) Drive ouputs with the Dot system, via current correction...

    at this time we don't need clock signal...


    I 've just test this durring some days, with good result, but i want to have your feed back.

    Thanks in advance
    Iko

     

     

  • 0 in reply to iko ria
    TI__Guru 61115 points

    Hello Iko,

    1)    Initialisation of the device:
      - G.S. witht random value (10 for exemple)
      - Dot with zero value

      Must input both value(GS/DC) for turned on.and these are selected by MODE pin.

       MODE=H ; DC Data

       MODE=L ; GS  Data

      But customer’s condition is below.

      - MODE: routed on Vcc

      In this case, input DC data only.

     

    3)Drive ouputs with the Dot system, via current correction...

      Need more information

     

     If they can’t assign of  pwm pulse for GSCLK, what about below circuit?

     It just turned on/off.

     1854.NoGScounter.pdf

  • 0 in reply to Brigitte
    Prodigy 120 points

    Hi.

    You're in the right.

    I had take care about your explains for my last message and test. MODE pin isn't route on VCC but drive by mcu. In this case i can initiate GS and DOT values...

     

    Brigitte said:
    If they can’t assign of  pwm pulse for GSCLK, what about below circuit?
     It just turned on/off.

     

    You're RIGHT ^^

    but, we can adjust the brightness with different value of DOT...

     

     

  • 0 in reply to iko ria
    Prodigy 120 points

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    Hi.
    I have some problems with the TCL5941. I work in the automotive field.
    For reasons of hardware and software, I can’t do PWM on GSCLK (just some very low speed transition).
    Also, in terms of GrayScale, I initialize all output ON, and I drive the LEDs ON / OFF via the power generator (Dot Correction).
    So the output can remain active or inactive for a relatively long time (leds are used on Dashboard)...
    My tests confirmed the operation however, for the customer these card fail and the device burn out...
    Can you confirm that this component supports the way I pilot?

     

    Thanks for you're answers...

     

  • 0 in reply to iko ria
    TI__Guru 61115 points

    Hello Iko,

    Do I understand right that you initialize greyscale with all outputs on? How are you doing this? After startup the values in the grayscale register are random and therefore I wonder how you turn on all outputs at the same time.

    If your initialization works fine and you are able to turn on all outputs, then you can work without the GS register and GSCLK. The IC is able to work in this way.

    If you need more support, I need more details on your application. At the moment I am a little confused on your initialization and turning on of the outputs. In addition what exactly means burn out.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 120 points

    Hi Brigitte, scuse me for late answer...

    During my initialisation process, i want to be sure that all output are ON in redars of grayscale control. So i set grayscale value in first step.

    My second step is to set current (dot correction) to zero. In this case, all led are OFF.

    After this init process, i use this device just with dot correction to drive leds ON or OFF.

    The power of led is provide by car battery...So there are lots of spikes in tension and current...

    [Vpwr]----[resistor : 620Ohms]----[led]----[your current generator]

     

    Other question : What's happen if there are reverse current in Vpwr?

     

    Thank in advance for your support ^^

    Regards.

    Iko

  • 0 in reply to iko ria
    TI__Guru 61115 points

    Hello Iko,

    What do you mean with reverse current in Vpwr? Do you mean that Vpwr increases its value because something in the system charges it?

    If this is correct, I do not see an issue as long as the voltage on the specific pin of our IC is above the absolute maximum rating.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 120 points

    hi Brigitte.

    On a car line battery, use of power lights or windscreen wiper cause transient pulses in volt and current.

    I made some measurement, and i saw negative current pulses sometimes... Accordinly, there are negative current pulses on leds power line...

    I haven't see some spec on the datasheet about this...

     

     

  • 0 in reply to iko ria
    TI__Guru 61115 points

    Hello Iko,

    Do you expect negative current going through the LEDs? I think the current will charge the capacitors connected on the LED power line, generating a higher voltage on that line.

    So even if there is negative current on the LED power line, I do not expect that the TLC594xx would observe that current at all.

    TLC504xx is with the LEDs just a load on a power supply. I think you should check if the power supply generating the LED voltage should be checked, if it can work with negative current.

    Best regards,
    Brigitte