SPRUIM2H May 2020 – October 2023 AM2431 , AM2432 , AM2434 , AM6411 , AM6412 , AM6421 , AM6422 , AM6441 , AM6442
The AFE contains a single 12-bit successive approximation ADC which can be connected to one of eight user selectable analog inputs for each step executed by the FSM sequencer. There is also an option to configure the ADC to operate in differential mode where it samples the differential voltage applied to two of eight user selectable analog inputs.
The ADC sits idle until the FSM sequencer sends a Start of Conversion (SOC) pulse. Once the FSM sequencer sends a SOC pulse to the ADC, it begins sampling the analog input signal on the rising edge of SOC and continues sampling the analog input signal one cycle of SMPL_CLK after the falling edge of SOC. The SOC pulse width will be the value of SAMPLEDELAY plus one SMPL_CLK periods, so the total ADC acquisition time will be the value of SAMPLEDELAY plus two SMPL_CLK periods. The ADC captures the analog input signal at the end of the acquisition period and starts conversion, which requires thirteen SMPL_CLK periods to digitize the sampled input. An EOC signal is returned to the FSM sequencer to indicate the digital data is ready.
The ADC output is positive binary weighted data ranging from 0 to (212 - 1). When configured for single-ended mode, ADC output data values 0 to (212 - 1) represents a corresponding input voltage that ranges from the ADC negative reference (REFN) voltage to the ADC positive reference (REFP) voltage. When configured for differential mode, ADC output data values 0 to ((212/2) - 1) represents a corresponding negative differential input voltage that ranges from the REFP voltage to the REFN voltage and output data values (212/2) to (212 - 1) represents a corresponding positive differential input voltage that ranges from the REFN voltage to the REFP voltage.
Using the minimum values of OPENDELAY and SAMPLEDELAY, the ADC can sample an analog input every 15 SMPL_CLK periods.
Figure 12-5 illustrates the operation of the FSM sequencer and ADC AFE, with indicators showing when the hardware configuration defined by ADC_STEPCONFIG_j and ADC_STEPDELAY_j registers are applied.
Figure 12-5 assumes both steps shown are software enabled with averaging turned off, an OPENDELAY value of 1, and SAMPLEDELAY value of 0. The analog input is sampled for the duration of the SOC pulse plus one cycle of the SMPL_CLK. If the value of OPENDELAY were 0, it would appear as if the time associated with the Open portion of the FSM waveform would be removed from all the waveforms.