The ADS58J64 provides a fast overrange indication that can be presented in the digital output data stream via SPI configuration. When the FOVR indication is embedded in the output data stream, this indication replaces the LSB (D0) of the 16 bits going to the 8b, 10b encode, as shown in Figure 7-19.

Figure 7-19 Timing Diagram for FOVR

The fast overrange feature of the ADS58J64 is configured using an upper (FOVRHi) and a lower (FOVRLo) 8-bit threshold that are compared against the partial ADC output of the initial pipeline stages. Figure 7-20 shows the FOVR high and FOVR low thresholds.

The two thresholds are configured via the SPI register where a setting of 136 maps to the maximum ADC code for a high FOVR, and a setting of 8 maps to the minimum ADC code for a low FOVR.

Figure 7-20 FOVR High and FOVR Low Thresholds

The FOVR threshold from a full-scale input based on the ADC code can be calculated by Equation 2:

Equation 2.

Therefore, a threshold of –0.5 dBFS from full-scale can be set with:

• FOVR high = 132 (27h, 84h)
• FOVR low = 12 (28h, 0Ch)