The oscillator frequency is determined by a resistor and capacitor connected to the RC pin of the TPS40210. The capacitor is charged to a level of approximately VDD/20 by current flowing through the resistor and is then discharged by a transistor internal to the TPS40210. The required resistor for a given oscillator frequency is found from either Figure 1 or Equation 14.
For most applications, a capacitor in the range of 68 pF to 120 pF gives the best results. Resistor values should be limited to between 100 kΩ and 1 MΩ as well. If the resistor value falls below 100 kΩ, decrease the capacitor size and recalculate the resistor value for the desired frequency. As the capacitor size decreases below 47 pF, the accuracy of Equation 14 degrades and empirical means can be needed to fine tune the timing component values to achieve the desired switching frequency.