sorry for the delay in my reply.
The problem I have with the HV9910 is the step-down configuration requires Vin => 2Vout (according to their datasheet).
That won't work for automotive applications, unless I want to build a largely parallel string of leds.
I have tried their flyback buck-boost configuration, but I'm not able to get it working properly. I setup a breadboard, following the formulas in Supertex App Note AN-H49 "Buck-Boost-based LED Drivers using the HV9910"
The calculations indicate I need a 6uH inductor with a peak current rating of 8 amps (?!)... well, smallest I have is a 10uH inductor rated at 20a
So I plug the inductor in there, and fire up my circuit, dumping the output into a bank of power resistors, measuring the voltage drop, I'm only seeing approximately 600mA into the resistors, less than half the output I configured Rsense to deliver (0.16 ohms)
I'm using a 7 amp hour 12 volt "gel cel" as my power source, voltage at the battery is about 13.2
The other problem I have with the hv9910 ... in the main datasheet, the formula for buck-boost mode are different than the formula in the app-note ... and they yield grossly different inductor sizes. Any idea why this is, and which one is possibly correct?