SPRUJB6B November 2024 – May 2025 AM2612
There is one internal ADC reference buffer in the device, REFBUF0, to provide a precise reference of 1.8V to the ADCs. REFBUF0 is internally associated with ADC2. ADC0 and ADC1 are not associated with any internal REFBUFs.
The ADC can operate with the internal reference or an external reference. Both internal and external reference are connected to the same package balls. Only one reference can be active at any given time.
ADC Reference connection is shown in Figure 7-126.
The voltage rails ADC_VREF*_G0 connect to ADC0 and ADC1.
The voltage rails ADC_VREF*_G1 connects to ADC2 and REFBUF0.
If the internal reference is used for ADC0 and ADC1, a board connection is required to connect ADC_VREF*_G0 to ADC_VREF*_G1.
The internal reference is based on internally routed circuitry with added signal conditioning to improve the signal quality of the 1.8V rail. Because of this, there is no situation in which using the VDDA18_LDO as a reference is to be considered. When using the internal reference, the VREF pins cannot have an external reference voltage applied to them. When using the external reference, routing VDDA18_LDO as the external reference keeps the signal conditioning circuits from being leveraged and which results in lower signal quality of the 1.8V rail.
Internal references are disabled by default in hardware. If an external reference is not used, the internal reference buffers can be enabled by the application for driving the ADC reference.
The ADC_REFBUF0_CTRL register is used to enable ADC Reference Buffer 0.
The MASK_ANA_ISO register must be set to 0x7 before ADC reference buffers are enabled. This prevents any undesirable behavior where the voltage monitors trigger an SOC reset.
There are voltage monitors on all the reference voltage rails for safe the reliable operation of ADC.
The TOP_CTRL.ADC_REF_COMP_CTRL register is used to enable the reference monitor comparators.
The status of the ADC reference rails is indicated in the ADC_REF_GOOD_STATUS register.