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.
Just PWM the LEDs, if they're basic 12V resistor-ballasted strips.
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.
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 is an alternative. other than replacing the resistor ballasted LEDs. You could add a switching regulator (buck converter) in the feed to all the ceiling LEDs in one cabin to maintain a stable 12.0V supply to them as long as the battery voltage is above that level. To minimise the standing current drain, either you'd have to use one with a very low quiescent power consumption, or one with a shutdown pin, with another BAE0910 controlling it, acting as a master switch for the lighting zone.
Another matter: Have you considered what happens to a BAE0910 and the 1Wire bus if its local 5V supply is missing? I suspect bad things happen, and tgat it will drag the bus down, with the possibility of latchup if power is reapplied to it while its connected to a powered 1Wire bus. The cure would be a MOSFET switch between it and the bus that will isolate it if its not powered. A 2N7002 should do the job, Source to DQ, Drain to the bus and gate pulled up to +12V via a fairly large resistor, so it can swing with the bus due to the gate to channel capacitance rather than adding extra capacitive loading. When the +12V is present, there will be at least 7V of positive gate bias and the 2N7002 will be hard on. When the +12V supply is absent, other loads will drag it down to 0V, and there will be 0V of gate bias, so the 2N7002 will be offr.
I had not. Thanks for pointing it out - I have added such a switch to the schematic. You reckon it should sit before or after the ferrite bead on the data input?
Still working on the updated schematic using the TPS1H100; since it wants 3-5V on the IN pin (7V max) I can't drive it with an opto @ 12V - should I drop the idea of a separate floating data GND? Kinda liked the concept, like a pseudo differential signalling scheme, but have no idea how much it would help improve 1-Wire noise rejection. Perhaps not worth the effort?
Yes, it will fluctuate. You'd need an OPAMP based differential amplifier to reference it to U1 Gnd, (see http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/opampvar6.html) and you are increasing the coupling between the 5V/1Wire bus and the power sides of the circuit to the point where the optocoupler may no longer be worth using.
8.3.1 Accurate Current Sense
For version B, the high-accuracy current sense function is internally implemented, which allows a better realtime monitoring effect and more accurate diagnostics without further calibration. A current mirror is used to source 1/K of the load current, flowing out to the external resistor between the CS pin and GND, and reflected as voltage on CS pin.
K is the ratio of the output current and the sense current. It is a constant value across the temperature and supply voltage. Each device was internally calibrated while in production, so post-calibration by users is not required in most cases.
Because its fed by a current mirror, if you simply return all components connected to the CS pin to data ground rather than power ground, the voltage across the CS resistor will be relative to data ground!
However this does have some restrictions. The abs.max ratings say the CS pin cant be taken more negative than 2.7V and the fault condition VCS,H (4.75V) on that pin will be referenced to power ground.
In the vein of "oh god this is such a pile of hacks": How about using a simple 555 circuit on the power side to digitize the CS voltage, pass it thru an opto, then filter it?
Alternatively, any way to get the BAEwhatever to do serial comms of any kind? I'd personally be tempted to drop a $0.50 MCU on the power side, then do isolated comms to that. And yes, I'd be happy to supply those if you want; I've got a tube of PIC12F1501s that I don't particularly like, that can be pre-programmed with the incredibly simple program needed.
There has to be some limit to this madness, and I think we're dangerously close to the point where paying someone to write a Modbus driver for Domoticz is more sensible. Maybe it has already been passed.
There has to be some limit to this madness, and I think we're dangerously close to the point where paying someone to write a Modbus driver for Domoticz is more sensible. Maybe it has already been passed.
Nooooo. That can't possibly be.
We are over-thinking this
Didn't miss it, just didn't have anything to add.
However as you have guarantee that constraint is met without clamping you haven't shown - no comment.
I'd still prefer something with an OPAMP differential amplifier entirely powered by the 5V side, designed to allow an operating common mode range of several volts without affecting the desired 0V-5V signal, and with its inputs protected against damage due to ground offsets up to double the maximum possible battery voltage to allow for transients due to wiring inductance and possible loose connections of the power wiring.
You are going to a lot of work to add current sensing you didn't originally have. Beware of feeping creaturism.
However as you have guarantee that constraint is met without clamping you haven't shown - no comment.I'm sorry, but I'm struggling to decipher this - are you saying I could/should clamp the GNDD offset with a diode somehow?