Figure 9-7 shows the use of a TLVx365 op amp as a SAR ADC input and reference pin driver. Sensors, which are used for interfacing with the physical environment, exhibit high output impedance and cannot drive SAR ADC inputs directly. The TLVx365 devices exhibit a very low-input bias current of 20 pA (maximum), and therefore do not load these high-output impedance sensors. A wide-GBW amplifier connected to the output of these sensors is needed to charge the switching capacitors at the SAR ADC input and to settle fast, to the required accuracy, within the given acquisition time.

The ADC core draws transient current from the reference input during the conversion (digitization) phase, which must be driven with a wide-GBW amplifier to offer fast settling and maintain a stable reference voltage for excellent digitization performance. The TLVx365 reference buffer is used in a composite loop with the OPA378 precision amplifier because of limitations in precision performance of wide-GBW amplifiers. The precision amplifier maintains low-offset output, whereas the TLVx365 provide the output drive and fast-settling performance.

Figure 9-7 TLVx365 as a SAR ADC Driver