The TPS1H100 current limit is intended to act as a fast, self-resetting fuse - it's not meant to regulate any current, just prevent it from exceeding a threshold.
Yep, I realised this when I read the datasheet a bit more carefully. Still a nice feature.
Just PWM the LEDs, if they're basic 12V resistor-ballasted strips.
I'm not sure what you mean by "resistor-ballasted strips"? The LEDs in question are cheap 12V "under cabinet" modules, which may or may not work ok at higher voltages: I have purchased
three different models for testing, two of which are fine at higher voltages, but
the ones I would prefer to use (due to colour rendering, beam characteristics, and physical size) run very hot at higher voltages. Hence my interest in current limiting; 200mA provides full brightness (~2.5W) while leaving these LEDs nice and cool.
While I can approximate this with a gamma curve, it may be difficult to get all LEDs on a given power supply chain to be equally bright under varying levels of charge (there will be
some voltage drop along the cable length). House bank battery voltage can vary between something like 14.5V and 11.5V, and while some change in brightness is acceptable I need the lights to function throughout this range. PWMing at too high a voltage might also stress the LEDs, even if they're not running hot; each "on" pulse would drive a higher current through the LED than it is designed for. I am not sure how important this is, but it's something I've been thinking about.
If you need a closed-loop solution, sense their current and use that to inform whichever algorithm you use to choose the PWM setpoint. They're LEDs; it's not like you need to do this at a very high rate.
This might be the way forward, but I'm not sure the current sensing ability of the TPS1H100 is precise enough?
If you're using LEDs with integral drivers, you're out of luck on anything above on/off control, unless you really want to roll your own proper LED drivers.
There
are PWM dimmable LEDs with integrated drivers for automotive use; I have also been experimenting with four reading lights using
dimmable G4 LED modules with built in drivers, which behave very well at all voltages and dim very well with PWM. In fact they're quite lovely, very similar to halogens. Maybe I should be looking for something similar for my in-ceiling lights.
Edit: Actually, looking at the datasheet again, the current sense precision is better than ±5% at the currents we're talking about here - that should be plenty good enough. So I'll need to integrate the current measurement with the PWM gamma curve. Should be doable.