Some parts of the AN170 PDF for the 555/556 timer are poor quality and
barely readable - it just so happens that the automotive regulator app is
very blurred.

Also; I have my doubts about the design shown as it shunts the output (can't
read the resistor value!) and takes its output from a 68 Ohm resistor
feeding the Vcc pin.

Does anyone have any automotive regulator apps for the 555?

The one in AN170 isn't a PWM as such - its just used as a window comparator
with latch, at least its not a self oscillating PWM, it switches on the
field winding when the battery drops to the low threshold and off when it
reaches the high thr.

Thanks.