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Original question:

TLC59401: LED Driver Voltage Drop on each channel

TLC59401: Dot Correction Operation

Peter Overell
Prodigy 70 points
Part Number: TLC59401

Dear Sir / Madam,

We intend to use the TLC59401 in dot correction mode only. Once we set the intensity of each channel via dot correction we want to turn on the LEDs at 100% PWM and turn off the PWM clock. We will then write new Dot Correction values each time we want to change the intensity of the LEDs which will be a maximum frequency of once per minute (but normally twice daily).

Could you confirm we can turn on the LEDs and simply stop the greyscale counter?

Thus we wouldn´t need to use the blank line to reset the greyscale counter (actually we would have to be careful NOT to use it!) and the LEDs will stay on (as set) until we change the dot correction?

This is a follow up to my last question on the voltage drop across the driver on each channel and if we are operating in the linear region of the driver, is the dot correction based on the actual maximum current or the current set resistor current? In my case it is 95mA @ 0.8 V (drop available at driver) and so would I calculate the current from dot correction as a percentage of 95mA or 120mA?

  • 0
    TI__Intellectual 2925 points

    Our experts for this issue are currently celebrating the Chinese national holiday, and they will respond next week.

  • +1
    TI__Genius 12915 points

    Hi Peter,

    To be honest we did not try such usage before. But theoretically it can work without sending GSCLK. Here are somethings I think need to be noticed. There still need one rising edge of GSCLK to trigger the counter and turn on the outputs. And there is no default value in GS register, so you still need to write all GS data to the device when powering up.

    If the voltage on output channel cannot satisfy the knee voltage, the current sinks works at linear state and do not have the full current capability. Taking your case that 95mA @ 0.8V but the resistor setting of IREF is 120mA, the percentage of dot correction need to be calculated from120mA, and clamped below 95mA. if you set the external resistor as 95mA, he percentage of dot correction can be calculated from 95mA

    I am curious why you do not want to use blank line and use dot correction to change the intensity of the LEDs, but not PWM. 

  • 0 in reply to Hardy Wu
    Prodigy 70 points

    Hi Hardy, thank you for your answer.

    To answer your question, we plan to use this device in a steady state configuration where we do not change the intensity of the LEDs very often and so we prefer to eliminate the flicker associated with controlling intensity via PWM or using the blank line of this device.

    Modulating the current to control the intensity of the LED is ideal for our situation and thus are investigating the DC operation without PWM control.

    The other advantage of the DC operation is that we can check the values of the DC register via the serial output to ensure we have set them correctly. This is important for our application where we want to set the LEDs and not change them for long periods, so we need to check they are set correctly.