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Part Number: OPT8241
Hi,
I am looking for some guidance on designing a LED driver for Time of Flight Illumination. I have tested the OPT8241-CDK-EVM and gone over the SBAA209A document and 3D Time of Flight TI Training Videos. I am using the HexLED design from the evaluation kit as my reference. The requirements for the LED driver are:
I was planning on using shunt switching to drive the LEDs as TI states it is recommended "as it enables higher frequency performance". My questions are:
Side note: I posted a related design question in the LED Driver forum here but was told the LM3409 was most likely not the right part and they have not designed anything like this. I figured I'd post here instead as there seems to be more specific knowledge about LED Drivers for TOF.
Thanks!
Hi Ben,
LM3409 would work well for this application. You cold also consider using TPS92515 as LED current is only 2A to 3A. I read through your post in the other forum and I understand why they don't think it can be done.
LM3409 would not dim at 20MHz in the proposed circuit. As 20MHz is an exceptionally high frequency for any power electronics system, we made a separate app note to ensure customers are able to design these systems successfully. As you can see in the app note, LM3409 would only function as a constant current source which is drawn in this circuit diagram.
LM3409 is the current source and the recommended N MOSFET is CSD16301Q2. You would have to connect ILLUM_N signal from OPT8241 to a buffer and use that buffer to drive the N MOS gate. LM3409 will continue to provide current continuously as the MOSFET switches at 20MHz modulation frequency. You should connect ILLUM_EN output of OPT8241 to the enable input of LM3409 to save power while the LEDs are not illuminating. This turns off the power circuitry when the camera is not under exposure. Same comments apply for TPS92515.
The app note covers how to design the high frequency modulation at such high currents. Along with this post, you should be well covered on how to use DCDC converters to make the illumination driver. Please let me know if this answers your question.
Regards,
Subhash
Thank you for the response. Knowing that the LM3409 and the TPS92515 are good choices for my application is helpful. I am unable to see the diagram in your post (not sure if it didn't link properly, or if the issue is on my end).
I have just a few more questions...
Thanks!