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ADC0844 Datenblatt(PDF) 9 Page - Texas Instruments |
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ADC0844 Datenblatt(HTML) 9 Page - Texas Instruments |
9 / 24 page ADC0844, ADC0848 www.ti.com SNAS523D – JUNE 1999 – REVISED MARCH 2013 Functional Description The ADC0844 and ADC0848 contain a 4-channel and 8-channel analog input multiplexer (MUX) respectively. Each MUX can be configured into one of three modes of operation differential, pseudo-differential, and single ended. These modes are discussed in Applications Information. The specific mode is selected by loading the MUX address latch with the proper address (see Table 1 and Table 2). Inputs to the MUX address latch (MA0- MA4) are common with data bus lines (DB0-DB4) and are enabled when the RD line is high. A conversion is initiated via the CS and WR lines. If the data from a previous conversion is not read, the INTR line will be low. The falling edge of WR will reset the INTR line high and ready the A/D for a conversion cycle. The rising edge of WR, with RD high, strobes the data on the MA0/DB0-MA4/DB4 inputs into the MUX address latch to select a new input configuration and start a conversion. If the RD line is held low during the entire low period of WR the previous MUX configuration is retained, and the data of the previous conversion is the output on lines DB0-DB7. After the conversion cycle (tC ≤ 40 μs), which is set by the internal clock frequency, the digital data is transferred to the output latch and the INTR is asserted low. Taking CS and RD low resets INTR output high and outputs the conversion result on the data lines (DB0-DB7). APPLICATIONS INFORMATION MULTIPLEXER CONFIGURATION The design of these converters utilizes a sampled-data comparator structure which allows a differential analog input to be converted by a successive approximation routine. The actual voltage converted is always the difference between an assigned “+” input terminal and a “ −” input terminal. The polarity of each input terminal of the pair being converted indicates which line the converter expects to be the most positive. If the assigned “+” input is less than the “ −” input the converter responds with an all zeros output code. A unique input multiplexing scheme has been utilized to provide multiple analog channels. The input channels can be software configured into three modes: differential, single ended, or pseudo-differential. Figure 12 shows the three modes using the 4-channel MUX ADC0844. The eight inputs of the ADC0848 can also be configured in any of the three modes. In the differential mode, the ADC0844 channel inputs are grouped in pairs, CH1 with CH2 and CH3 with CH4. The polarity assignment of each channel in the pair is interchangeable. The single- ended mode has CH1–CH4 assigned as the positive input with the negative input being the analog ground (AGND) of the device. Finally, in the pseudo-differential mode CH1–CH3 are positive inputs referenced to CH4 which is now a pseudo-ground. This pseudo-ground input can be set to any potential within the input common- mode range of the converter. The analog signal conditioning required in transducer-based data acquisition systems is significantly simplified with this type of input flexibility. One converter package can now handle ground referenced inputs and true differential inputs as well as signals with some arbitrary reference voltage. The analog input voltages for each channel can range from 50 mV below ground to 50 mV above VCC (typically 5V) without degrading conversion accuracy. Copyright © 1999–2013, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: ADC0844 ADC0848 |
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