The Voltage Reference (VREF) is a device that produces a fixed (constant) voltage, providing references to the analog comparators and external circuitry. The voltages include /2, /3 and /4 dividers of the VDD power supply as well as external sources. The macrocell also has an option to output reference voltages on PIN __ and __.

Activation

Set a source for ‘Source selector’ and set PIN __ or __ to Analog Input/Output.

VREF0 and TEMP SENSOR share PIN __ output. VREF0 cannot connect to PIN1 if TEMP SENSOR is Enabled in the design.

Parameters

Force bandgap on:

The bandgap must be on for analog components to function correctly. Typically, the bandgap is powered on and off dynamically based on usage in the system to save power. However, the bandgap can be forced on all the time. This improved turn on response time of analog components.

Bandgap output delay time:

There is a selectable delay that is added after the bandgap voltage has become valid. This gives analog blocks time to start up before valid data is acquired.

• Auto-Delay: Default

• 100us

• 550us: select if charge pump is used.

Please see power control settings under ‘Project Settings’ for detailed information on Charge Pumps

Output active buffer:

• Disable: Vref is routed directly through to the output pin

• Enable: Vref is routed through an op-amp output buffer before it reaches the output pin

Chopper clock frequency:

• 2 MHz

• 1 MHz

Opamp offset chopper:

• Enable: Low offset voltage, reduces low frequency noise

• Disable

Source Selector:

• None

• ACMP0 Reference Voltage

• ACMP1 Reference Voltage

• VDD/2

• VDD/3

• VDD/4

The Vref output pin will slave its output from the input to the selected analog block. The output reference can be changed from the sources’ properties window.

Output:

• PIN__: is only for VREF1;

• PIN__: is only for VREF0;

Table 1.

VDD	Practical VREF range	Note
2.0V-5.5V	50mV ~1.2V
1.7V – 2.0V	50mV ~1.1V	Higher than 1.1V negative input, the comparator may show wrong result