In the case of using a additional FET+resistor channel the HDR FET can be omitted, so it’s from that.
I don’t really understand how to make a amplifier circuit with just two resistors that will work in this case, but I’m not too knowledgeable about BJTs.
No idea, I know that Mike C used it in his firmware.
I’m not sure what to think of the DAC, it has some advantages but also inconvenients :
- It doesn’t need to pass through a LPF contrary to the PWM signal, so that’s two passives less (one in the linear driver because it can use a combined voltage divider/LPF)
- No problem with the flash since again : no LFP. The transition between the low and high current range can be mostly invisible since there is no need of a delay or blink.
- It uses the internal reference so no need to supply the MCU with a fixed voltage. Although in the case of a dual sense resistor circuit, the HDR FET need to be driven at a fixed voltage to get a (relatively) constant RDSON, or it can be taken out of the equation by using a mux, but in the end might as well use a LDO instead.
- Can lower the sytem clock speed to save power.
Cons
- It’s limited to 8 bits, that makes the smooth ramp more coarse at the bottom of the high current range, as well a decreases the dimming ratio. Although Mike C, before using the dual sense resistor circuit, achieved more than 10bits by switching between the 0.55 Vref and 2.5 Vref (but I think he said that there were some issues with this ). Another solution is to use 3 senses resistors to compensate the lower resolution but I don’t really like this as it takes up more board area and it’s another signal trace to fit in.
- There is only one output pin, even on the xx17s, although that’s okay with multiple sense resistor topology, it becomes a problem if there is multiple power channels like in a tint adjustable light.
I doubt people will buy 70 1616 for 1$ each to build a couple of drivers when they can wait a couple of weeks and buy them from digikey at 80c per quantity of one.
Firmware is Anduril2.