Figure 8L.8 LTAoE. Freq = 1 / (0.7 x C x [Ra + 2 x Rb] ). Where Ra is upper resistor and Rb lower resistor, and C is capacitor in Pin #2. True 50% cycle: Diode in parallel to Rb.
Changing the duty cycle: t_{high} ~ 0.693 x Ra x C. t_{low} ~ 0.693 x Rb x C.
