SNVS953G December 2012 – May 2021 LM25018
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 must be larger than the capacitive ripple on COUT.
Using type III ripple circuit equations, the injected ripple at the FB pin is set to a level greater than the capacitive ripple as follows:
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 must be selected to allow for variations in TON, COUT1, and other components. Rr = R4 = 46.4 kΩ is selected for this example application.