Integrated circuit with determinate power source control

A determinate power source control for an integrated circuit (10) includes a variable voltage regulator (16), which is operable to receive a supply voltage on the input thereof and output a regulated voltage for input to the integrated circuit (10). A voltage adjustment circuit (22) is operable to generate a voltage adjustment value VADJ for input to the voltage regulator (16) to determine the voltage output thereby. In a determinate operating mode, the voltage adjustment circuit (22) varies the VADJ value to cause the regulator (16) to vary the regulated output voltage to the integrated circuit (10). For each value, the operating speed of the integrated circuit (10) is determined and this information stored in a table (24). Thereafter, the voltage adjustment circuit (22) is placed in an operating mode wherein the voltage adjustment value associated with the optimum operating speeds of the integrated circuit (10) is selected and input to the voltage regulator (16). The voltage adjustment circuit (22) utilizes an on-chip ring oscillator (38) to generate a series of pulses which are input to a counter (48). The counter (48) and ring oscillator (38) are operated for a predetermined amount of time with reference to crystal oscillator (30), and then this value latched into latch (52).