SBAS813 June 2018 ADS8688AT
PRODUCTION DATA.
The device includes a single-ended auxiliary input channel (AUX_IN and AUX_GND). The AUX channel provides direct interface to an internal, high-precision, 16-bit ADC through the multiplexer because this channel does not include the front-end analog signal conditioning that the other analog input channels have. The AUX channel supports a single unipolar input range of 0 V to VREF because there is no front-end PGA. The input signal on the AUX_IN pin can vary from 0 V to VREF, whereas the AUX_GND pin must be tied to AGND.
When a conversion is initiated, the voltage between these pins is sampled directly on an internal sampling capacitor (75 pF, typical). The input current required to charge the sampling capacitor is determined by several factors, including the sampling rate, input frequency, and source impedance. For slow applications that use a low-impedance source, the inputs of the AUX channel can be directly driven. When the throughput, input frequency, or the source impedance increases, a driving amplifier must be used at the input to achieve good ac performance from the AUX channel. Some key requirements of the driving amplifier are discussed in the Input Driver for the AUX Channel section.
The AUX channel in the ADS8688AT offers a true 16-bit performance with no missing codes. Figure 79 and Figure 80 show some typical performance characteristics of the AUX channel.
Mean = 32767.15, sigma = 0.83 |
fIN = 1 kHz, SNR = 88.2 dB, SINAD = 88.1 dB, THD = –102 dB, SFDR = 102 dB, number of points = 64k |