MOD (Pin 4/Pin 1): Pulse-Width Modulation Input. The
voltage on the MOD pin controls the output duty cycle. The
linear control range is between 0.1 • VSET and 0.9 • VSET
(approximately 100mV to 900mV). Beyond those limits,
the output will either clamp at 5% or 95%, or stop oscillating
(0% or 100% duty cycle), depending on the version.