We have a difficult application for a buck converter and need some help choosing a controller.
Our wish list is...
- Vin = 19Vdc to 90Vdc (peak), ripple is approx. 5% of peak, with occasional drops to 14V peak.
- Vout = 14.0Vdc, +/-1%, 100mV ripple max.
- Iout = 30A continuous @ 30C ambient.
- 100% duty cycle so output can track input if it occasionally falls below Vdropout.
- Constant current output or current limiting that would allow occasional ultracapacitor and/or battery charging. Circuit would be over-spec'd to allow for continuous operation while limiting, e.g., designed for 20A but current limited to 15A.
- The usual desires for small size and low weight.
We are flexible with the following (but would love to achieve the above specs)...
- Vin-max spec can be as low as 60V.
- Vin-min spec can be as high as 19V and we can use UVLO if output cannot smoothly track input voltages below dropout.
- Vout variance can be as high as +/-2%, either unit-to-unit variance or voltage-under-load changes.
- Output ripple can be as high as 500mV.
- Iout spec can be lowered if we can use dual-phase or multiple load-sharing controllers to achieve 30A.
- Efficiency is secondary to Vin/Vout and Iout specs. We are comfortable with it dropping a lot to achieve the wish-list specs.
Other info...
- Source impedance is 0.2 to 1.5 ohms.
- Vin slew rate is limited, 500V/second or slower.
- Loads will vary considerably; including incandescent lamps, HID lamps, motors, batteries, ultracapacitors.
- Power-up loads could be practically a short-circuit if ultracapacitors and or batteries are discharged.
- Anticipated sales volume is small, 8,000-10,000 pcs./year.
- Cost concerns are tertiary (to a point) as this is a high-end specialized product. Size and weight concerns are secondary. Performance/specs are, by far, the most imporant.
I've been unable to find a controller that meets our wish list needs but the LM5116, LM5117, and LM5119 come close. Each has something we want but none have it all. We're leaning towards the LM5119 as it seems to be the easiest way to get our 30A (using 2x15A, interleaved) but would love to have a 90V input too. But, the LM5117 offers precision current limiting for ultracap/battery charging. Multiple LM5117 would have to be paralleled though. Our other option is to parallel multiple LM5116 (three?, using load share controllers) to reach 30A with 90V input.
The LM5088's Vin-max of 75V and 100% duty capability also looked good but what are its practical Iout limits? How hard would they be to parallel compared to the LM511x controllers?
Any recommendations or possible problems you might see in using any of these controllers at these voltage levels, current levels, or duty cycles?
Thank you!