JAJSP40A March 2022 – October 2022 ADS117L11
PRODUCTION DATA
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The ADC has two programmable input ranges: 1x and 2x, where the 1x range is defined by VIN = ±VREF and the 2x range is defined by VIN = ±2 · VREF. The 2x input range doubles the available range when using a reference voltage = 2.5 V or less. The 2x input range requires driving the inputs to the 5-V supply rails to exercise the full range when using a 2.5-V reference voltage. When using a 4.096-V or 5-V reference voltage be sure to program the ADC to the high-reference range mode. The 2x range operation is internally forced to the 1x range mode when the high-reference range is selected. See the CONFIG1 register to program the input range. Table 8-2 summarizes the ADC input range options.
INP_RNG BIT(1) | INPUT RANGE (V) |
---|---|
0 | ±VREF |
1 | ±2·VREF |
In some cases, the full available input range is limited by the power supply voltage. For example, the input range exceeds the power supply voltage when using a 3-V power supply with a 2.5-V reference voltage in the 2x range mode.
The ADC provides the option of bipolar or unipolar input signal operation. In bipolar mode, the ADC accepts positive and negative signals (–VREF to VREF) with 15-bit output data resolution for positive signals and 15-bit output data resolution for negative signals. In unipolar mode, the ADC accepts positive signals only (0 V to VREF), providing 16-bit output data resolution. The mode is programmed by the BIP_UNI bit of the CONFIG4 register.
The ADC also provides the option of extended input range operation beyond the standard full-scale range. In this mode, the input range is extended by 25% to provide signal headroom before clipping of the signal occurs. Output data are scaled such that the positive and negative full-scale output codes (7FFFh and 8000h) in bipolar input mode are at ±1.25 · k · VREF, where k is the 1x or 2x input range option.
SNR performance degrades when the signal exceeds 110% standard full-scale range because of modulator saturation. The modulator MOD_FLAG bit of the STATUS register indicates when modulator saturation occurs. Figure 8-4 shows SNR performance when operating in the extended range. See the CONFIG2 register to program the extended range mode.