SNAS811 July 2020 – May CDCE6214
A typical application using the I2C interface and a 25-MHz crystal input is shown in Figure 35. The two ends of 25-MHz XTAL are connected to pin 1 and 2. The REFSEL pin is pulled down to select a secondary input. The HW_SW_CTRL can be pulled either low or high if EEPROM is used, or kept floating if EEPROM is unused. 1.8 V, 2.5 V, or 3.3 V can be supplied to the VDD_REF and VDD_VCO pins, as well as VDDO_12 and VDDO_34 pins with filtering. Data and clock lines of I2C must be pulled to VDD_REF using pullup resistors. The PDN can be connected to the MCU if a hardware reset is required, otherwise it can be left floating. The GPIO1 and 4 pins can be connected to the MCU if needed, otherwise they can be left floating. Unused outputs can be left floating.