In an example, a system includes an oscillator circuit on a chip. The oscillator circuit includes a charging current generator including a current mirror and an amplifier, where the amplifier is coupled to a pin of the chip. The oscillator circuit also includes a first switch coupled to the pin, a second switch coupled to the pin and to a charging resistor, and a third switch coupled to the amplifier and an internal resistor, where the internal resistor is internal to the chip. The oscillator circuit includes a bias current source coupled to the current mirror. The system includes an external resistor coupled to the pin, where the external resistor is external to the chip. The system also includes an external capacitor coupled to the pin and coupled in parallel to the external resistor, where the external capacitor is external to the chip.