Other Parts Discussed in Thread: TPS61165, LM5157
Hello,
We're looking to drive a string of high current LEDs from a battery source (12V) that have a Vf in the range of 5 to 9v in either a 2s or 3s configuration and ideally up to 4p although if necessary we can replicate the design several times for the parallel strings. The application requires these specific LEDs and for this application, a boost topology is required along with the ability to provide dimming via PWM. We are looking for a compact, low cost design.
The LED manufacturer uses a TPS61165 in their demo board in a 3S1P configuration, but their design is limited in the peak supply current. The LEDs are designed for a If of 500mA with an If_max of 700mA. Unfortunately this puts it outside of conventional LED boost drivers.
Found the LM5157x-Q1 chip with the following reference design, but without any design information associated with this:
According to the Web bench designer, it provided the following design for a 30V boost with 700mA output, but is not setup as a constant current drive for LEDs.
1) Is it possible to utilize the LM5157x-Q1 as a constant current LED driver as indicated in the datasheet? How would you handle the PWM input?
2) How is the FB network in this application calculated?
3) How would you handle the compensation network in the case of varying / dimming the LED?
4) Is there a better method?
