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