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Hi -
I have a design that uses the TPS40305 configured in a feedback regulated constant current configuration to deliver 26A to an LED. This design has been adapted in a similar manner to supply 2A to a smaller LED but now I'm wondering if the TPS40303 be a better choice for more accurate current regulation as it has a lower switching frequency?
Hi
Definitely a controller for a 2A application would be an overkill. The current regulation accuracy would not be a function of the switching frequency but rather on the overall accuracy of the controller. What is the Vin of the application and the number of series/parallel LEDs with their Vf?
Regards,
Gerold
Hi Timothy,
Is accuracy the most important consideration in your design? As Gerold mentioned, a controller seems like overkill for a 2A, single 3.6V diode. If solution size is important, you could probably use a TPS62130 or TPS82130 (integrated module) for this application as described in this application note.
Regards,
Kris
I have to squeeze the performance out of the TPS40305, 04 or 03. I was asking if the 03 was a better choice based on equations 4 and 5 of the Texas Instruments application note by John Tucker "Understanding output voltage limitations of DC/DC buck converters" slyt293.pdf
I looked at equation 4 and thought that since the minimum output voltage is dependent on frequency then the TPS40303 is a better choice than the TPS40305. Ton min is also the same for all three chips. And the upper limit on voltage is not dependent on frequency. Dmax is 5% higher on the 03 vs 05 but I'm more worried about the low end. I haven't figured out the ramifications with the 03 vs 05 since I am doing constant current vs constant voltage but maybe somebody on the forum could help out with that question.
Hi Timothy,
I may not understand the basis of your concerns. With 12V input, and output > ~3.6V across the diode, you will be pretty far from the 70ns minimum controllable on time even with the 1.2MHz switching frequency of the TPS40305. Put another way, assuming +20% tolerance on the 12V supply or a max of 14.4V, you would still be able to have a minimum output voltage of 1.39V (=70ns * 12V * 1.2 * 1.38MHz, where 1.38MHz is the max tolerance on the TPS40305 1.2MHz frequency). This is well below the expected typical 3.6V forward voltage of your LED.
Please let me know if I have misunderstood your concern.
Regards,
Kris
Hi Timothy
Can you please let us know if you still have further questions on this topic?
Regards,
Gerold