SPRUJ17H March 2022 – October 2024 AM2631 , AM2631-Q1 , AM2632 , AM2632-Q1 , AM2634 , AM2634-Q1
There are two internal ADC reference buffers in the device, REFBUF0 and REFBUF1, to provide precise reference of 1.8V to ADC. REFBUF0 is associated with ADC0, ADC1, and ADC2. REFBUF1 is associated with ADC3 and ADC4.
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 7-114.
The voltage rails ADC_VREF*_G0 connect to REFBUF0 ,ADC0, and ADC1 and ADC0.
The voltage rails ADC_VREF*_G1 connects to ADC1 and ADC2.
The voltage rails ADC_VREF*_G2 connects to REFBUF1, ADC3, and ADC4.
If the internal reference is used for ADC1 and ADC2, 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.
The internal reference buffers are designed to provide sufficient source current for the maximum operational requirements of each module. Therefore, using a single reference buffer for all ADC modules is not recommended as the buffer is unable to source sufficient current. REFBUF0 is to be used for ADC[0:2] and REFBUF1 is to be used for ADC[3:4].
Internal reference are disabled by default. If external reference is not used, 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. Similarly, the ADC_REFBUF1_CTRL register is used to enable ADC Reference Buffer 1.
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 three 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.