8.3.3.1 Modulator Overrange

The ADS1287 modulator is inherently stable, and therefore, has predictable input overdrive recovery. If the input is overdriven to cause the modulator to produce a 1 density output in the range of 90% to 100% (10% and 0% for negative overdrive), the output codes may or may not clip resulting from the effect of the digital filter integration. Clipping depends on the duration of the input overdrive. When the input returns to the normal range from a long-duration overdrive (worst case), the modulator returns immediately to the normal 1 density range, but the action of the digital filter delays the return to the normal reading range because of the filter group delay.

In the extreme case of input overdrive (where the overdriven input exceeds the analog supply voltage + V_ESD diode drop), the internal ESD diodes begin to conduct, thus clipping the input signal. When the input overdrive is removed, the diodes recover quickly. Be sure to limit the input current to 10 mA (transient or continuous duty) if an overvoltage condition is possible.