tl497/tl497A pdf datasheet (SW

The TL497A incorporates all the active functions required in the construction of switching voltage regulators. It can also be used as the control element to drive external components for high-power-output applications. The TL497A was designed for ease of use in step-up, step-down, or voltage-inversion applications requiring high efficiency.
The TL497A is a fixed-on-time variable-frequency switching-voltage-regulator control circuit. The switch-on time is programmed by a single external capacitor connected between FREQ CONTROL and GND. This capacitor, CT, is charged by an internal constant-current generator to a predetermined threshold. The charging current and the threshold vary proportionally with VCC. Thus, the switch-on time remains constant over the specified range of input voltage (4.5 V to 12 V). Typical on times for various values of CT are as follows:
TIMING CAPACITOR, CT (pF) 200 250 350 400 500 750 1000 1500 2000