RT/CT is the oscillator timing pin. For fixed frequency operation, set the timing capacitor charging current by connecting a resistor from VREF to RT/CT. Set the frequency by connecting timing capacitor from RT/CT to GND. For the best performance, keep the timing capacitor lead to GND as short and direct as possible. If possible, use separate ground traces for the timing capacitor and all other functions.

The UCC28C4x-Q1’s oscillator allows for operation to 1 MHz. The device uses an external resistor to set the charging current for the external capacitor, which determines the oscillator frequency. TI recommends timing resistor values from 1 kΩ to 100 kΩ and timing capacitor values from 220 pF to 4.7 nF. The UCC28C4x-Q1 oscillator is true to the curves of the original bipolar devices at lower frequencies, yet extends the frequency programmability range to at least 1 MHz. This allows the device to offer pin-to-pin capability where required, yet capable of extending the operational range to the higher frequencies. See Figure 7-1 for component values for setting the oscillator frequency.