• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 561 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLC6C5712-Q1: Require max output current to be less than 10mA

Paul Toms
Prodigy 40 points
Part Number: TLC6C5712-Q1
Other Parts Discussed in Thread: TLC5951

Hi,

Figure 4 in the "TLC6C5712-Q1 Application Reference Guide " shows a minimum "max output current" of 10mA which is set with ref resistor of 61k. I am driving several types of LED some of which require only 2mA to give the required brightness. To achieve the required resolution in dot correction control for these, I really need the max current to be 2mA.

The only way I can see of doing this is to put a shunt resistor in parallel with the LED in order to divert a proportion of the current away from the LED. This works to a degree but I'd like the shunt current to be fixed rather than vary with Voutx. I could I suppose replace the shunt resistor with a discrete current source. Anyway, I'm wondering what thoughts others might have about overcoming this 10mA lower limit.

Thanks,

Paul

  • 0
    TI__Expert 5380 points
    What is the current resolution required for this application? What is the application.

    Generally speaking, there is a 8-bit DAC for each channel, so if setting max 10mA current, we can have 0.04mA/step resolution. You can definitely realize the 2mA output current.
  • 0 in reply to Anda Zhang
    Prodigy 40 points

    I'm looking for a current resolution of 2mA/256 i.e. about 8uA. The application is for illuminating several die on a silicon wafer where each die comprises an array of photodiodes. The illlumination comes from a board housing 30 LEDs and 3x TLC6C5712 devices. We are trying to ensure each die sees exactly the same LED brightness and hence we need very fine control of the LED brightnesses - and some of the LEDs are being driven to only 2mA max. We also use a microcontroller to adjust the brightness according to board temperature in order to counter the brightness drop off as temperature increases.

    I've now done some simulations whereby diodes are placed in parallel with the LEDs and this gives a better result than using a resistor. May be this is the way forward for me.

  • 0 in reply to Paul Toms
    TI__Expert 5380 points

    Hi Paul,

    Is this automotive application? If not, we also have TLC5951 which can support the 2mA max output current with a two range 7-bit DC, as well as 8-bit color group BC, these two features are analog dimming features.At the same time, it is a 24 channel device, which can help to save your device number.

  • 0 in reply to Anda Zhang
    Prodigy 40 points

    Hi Anda,

    The application is not for automotive. It is for production test for illuminating our sensors under controlled lighting conditions and verifying they work OK. 

    I think I looked at the TLC5951 but discounted it because I wanted 8-bit DC and I also needed to be able to switch the LEDs on/off directly with a microcontroller GPIO. The sensors which we test have to be exposed to non-PWM light (analogue dimming) but we nevertheless need to be able to switch them on/off at 1kHz to produce a flicker. We also needed 50mA max current. The TLC6C5712 is ideal for all of this.

    Thanks for your suggestion. I'll certainly have another look at the TLC5951 but in the meantime will close off this issue. Thanks for your help.

    Paul