4. Power Supply and I2C Bus Control
The power supply uses a linear voltage regulator to drop the +5V input supply voltage to one of the supported nominal VDD voltages of
+3.3V, +2.5V, or +1.8 V. A switch is provided on the EVB (SW5) to select the +5V source for the voltage regulator as either the USB
port +5V or an ex5V source. The EVB power supply supports operation in one of 2 general modes that correspond to the two
operational EVB use cases.
• Stand-alone mode: Power can be sourced from either external supply or USB port, but software is not required and no EVB software
tool should be actively connected to Si5XXUC-EVB when being used in Stand-alone mode. In Stand-alone mode the oscillator de-
vice VDD voltage is set via the “VDD_DUT_SEL” switch according to the voltage select table shown below. By default this switch is
set to 1.8V and will need to be changed if evaluating a non-I2C oscillator with 2.5V or 3.3V VDD.
• Software controlled mode: Power can be sourced from either external power supply or USB port, but the Programmable Oscillator
Software tool can be used to set the VDD voltage to the oscillator. In software controlled mode, “VDD_DUT_SEL” switches should
remain set to 1.8V setting regardless of the desired VDD voltage.
The I2C Disable switch is typically set to the “Off” setting (to enable the on-board MCU to drive the I2C bus) unless the user is attempt-
ing to connect an external I2C master to communicate with the oscillator device. The I2C Disable control allows for disabling the on-
board I2C buffer to disconnect the oscillator from the on-board MCU. This disconnection is useful if the user wishes to connect an exter-
nal I2C bus master to communicate with the DUT.
UG298: Si5xxUC-EVB
Power Supply and I2C Bus Control
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