A display driver IC which adjusts an oscillator frequency is provided. The display driver IC includes: a register map which stores a trim code, a window size, compensation information, and a compensation option; an oscillator which generates an oscillator clock based on the trim code; a timing controller which generates an internal synchronization signal based on the oscillator clock; a DSI block which outputs a first data valid signal which is activated based on a data clock and image data packet update; and a frequency compensating block which compares a periodic value of the oscillator clock calculated based on the data clock and the internal synchronization signal with a target periodic value and generates a compensation trim code obtained by compensating the trim code based on the compensation option, in accordance with the first data valid signal.