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ADS1112IDRCT Datasheet(PDF) 6 Page - Burr-Brown (TI) |
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ADS1112IDRCT Datasheet(HTML) 6 Page - Burr-Brown (TI) |
6 / 18 page ADS1112 SBAS282D − JUNE 2003 − REVISED MARCH 2004 www.ti.com 6 TYPICAL CHARACTERISTICS (continued) At TA = 25°C and VDD = 5V, unless otherwise noted. THEORY OF OPERATION The ADS1112 is a 16-bit, self-calibrating, delta-sigma A/D converter with an input multiplexer. Extremely easy to de- sign with and configure, the ADS1112 allows precise mea- surements to be obtained with a minimum of effort. The ADS1112 consists of a delta-sigma A/D converter core with adjustable gain, a 2.048V reference, a clock os- cillator, and an I2C interface. Each of these blocks are de- scribed in detail in the sections that follow. ANALOG-TO-DIGITAL CONVERTER The ADS1112 A/D converter core consists of a differential switched-capacitor delta-sigma modulator followed by a digital filter. The modulator measures the voltage differ- ence between the positive and negative analog inputs se- lected by the input multiplexer and compares it to a refer- ence voltage, which, in the ADS1112, is 2.048V. The digital filter receives a high-speed bitstream from the modulator and outputs a code, which is a number proportional to the input voltage. MULTIPLEXER The ADS1112 has an input multiplexer that provides for two differential or three single-ended input channels. Two bits in the configuration register control the multiplexer setting. VOLTAGE REFERENCE The ADS1112 contains an onboard 2.048V voltage refer- ence. This reference is always used as the ADC voltage reference; an external reference cannot be connected. The ADS1112 voltage reference is internal only, and can- not be measured directly or used by external circuitry. The onboard reference specifications are part of the over- all gain and drift specifications of the ADS1112. The con- verter drift and gain error specifications reflect the perfor- mance of the onboard reference as well as the performance of the A/D converter core. There are no sepa- rate specifications for the onboard reference itself. OUTPUT CODE CALCULATION The output code is a scaled value that is proportional, ex- cept for clipping, to the voltage difference between the two analog inputs. The output code is confined to a finite range of numbers; this range depends on the number of bits needed to represent the code. The number of bits needed to represent the output code for the ADS1112 depends on the data rate, as shown in Table 1. DATA RATE NUMBER OF BITS MINIMUM CODE MAXIMUM CODE 15SPS 16 −32,768 32,767 30SPS 15 −16,384 16,383 60SPS 14 −8192 8191 240SPS 12 −2048 2047 Table 1. Minimum and Maximum Codes For a minimum output code of Min Code, gain setting of the PGA, and positive and negative input voltages of VIN+ and VIN−, the output code is given by the expression: Output Code + −1 Min Code PGA (V IN )) * (VIN*) 2.048V In the previous expression, it is important to note that the negated minimum output code is used. The ADS1112 outputs codes in binary two’s complement format, so the |
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