SNVS783K January 2012 – August 2021 LM5017
Type III ripple circuit as described in Section 7.3.11 is chosen for this example. For a constant on-time converter to be stable, the injected in-phase ripple should be larger than the capacitive ripple on COUT.
Using the type III ripple circuit equation, the target ripple will be greater than the capacitive ripple generated at the primary-side output if the following condition is satisfied:
Cr = C6 = 3300 pF
Cac = C8 = 100 nF
For TON, refer to Equation 3.
Ripple resistor Rr is calculated to be 57.6 kΩ. This value provides the minimum ripple for stable operation. A smaller resistance should be selected to allow for variations in TON, COUT, and other components. Rr = R4 = 46.4 kΩ is selected for this example application.