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TI Introduces Low-Power 24-Bit Data Converter for High-Resolution Measurements in Portable Applications

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Texas Instruments (TI) Incorporated introduced a 24-bit delta-sigma analog-to-digital converter (ADC) from the company's Burr-Brown product line featuring low power consumption (90uA) and miniature size (MSOP-10). This easy-to-use ADC is ideal for high-resolution measurements where performance, space and power consumption are critical, such as handheld instrumentation, portable medical equipment, industrial process control and weigh scales. The ADS1244 consists of a third-order delta-sigma modulator and digital filter. The analog modulator has a +/-5V differential input stage. The digital filter rejects both 50Hz and 60Hz signals, completely settles in one cycle and outputs data at 15 samples per second. "By combining high resolution, low power, simplicity-of-use and small size, the ADS1244 provides an unequaled price/performance value for space-constrained measurement applications," said Jim Todsen, product manager for TI's data acquisition products. The ADS1244 is designed to easily connect to microcontrollers, such as TI's MSP430 family of ultra-low-power microcontrollers, to offer a complete data acquisition solution. Multiple ADS1244s can be connected together to create a synchronously sampling multi-channel measurement system. A simple two-wire serial interface provides all the necessary control. Data retrieval, self-calibration and Sleep Mode are handled with a few simple waveforms. When only single conversions are needed, the Sleep Mode can be used to shut down the ADS1244 when idle between measurements -- dramatically reducing overall power consumption. Power is typically less than 270uW in normal operation and less than 1uW in Sleep Mode. The ADS1244 supports 2.5V to 5.25V analog supplies and 1.8V to 3.6V digital supplies. Texas Instruments Incorporated Semiconductor Group, SC-02295, Literature Response Center, P.O. Box 954, Santa Clara, CA 91380. Tel: 1-800-477-8924, ext. 4500 TI Web Site

TI has offered over-sampling converters for several years. The ADS1244 was introduced for applications that could have used over-sampling but havenıt implemented it due to issues with power, price or size. Previous converters included the ADS1100, a 16-bit converter that is available in the larger SOT package. The ADS1244 is a higher performance part. It is the companyıs first 24-bit converter to offer reduced power and size, while lowering the price. And that makes it attractive for high volume applications. It has a couple features for more industrial-type applications such as the portable units that have a notch at the 50-60 Hz frequency response. It also supports fairly large signal swings of +/- 5 volts, allowing it to be used in a large variety of applications. This converter has a two-pin serial interface which makes it very simple to communicate with. The interface is read-only. One of the pins is a shift-clock, and the other is a doubled-duty output that indicates when dataıs ready by changing the state from high to low. It serves as both an interrupt and a data ready signal as well as a data out signal. The press release indicates that the converter outputs data at 15 samples/second, which for applications like test equipment or medical equipment doesnıt sound very fast. However, for applications like handheld multi-meters the 15 samples/second update rate is all they need. Additionally, home medical instrumentation, used for measuring human body signals, has even lower bandwidth requirements. For example, if youıre measuring body temperature, a typically slow-changing parameter, these data rates are more than sufficient. It is possible to have a much faster data rate with 15 Hz rejection, but the settling time for the digital filter is much longer than the conversion time. If you use a multiplexer, youıre going to have to wait a lot longer than when youıre just measuring one channel. So TI designed this chip to multiplex easily and to settle in a single cycle. The ADS1244 is easy to connect to TI microcontrollers such as the MSP430 but it will also connect to others such as a Hitachi microcontroller. Itıs obviously going to be easier with TIıs MSP430 because it is well suited to provide a clock signal to the ADS1244. Microcontrollers from other companies can do it but will require a little more planning because they may need an external oscillator to generate the clock. Designs usually have a signal and reference channel that need to be synchronized, and having an external clock makes it very easy. The ADS1244 enables you to create a synchronous multi-channel measurement system. TI says you can connect as many as you want since there is no limitation. However, a typical number of channels will be two to four. The specs state the power is typically 270 uW in normal operation. So if you have a 2-channel solution, with two devices, it would be 540 uW. However, that power specification applies to when you are continuously converting. You can go into the sleep mode between every conversion and the power will approach zero, limited of course by the leakage current. It goes into the sleep mode approximately 50 ms after converting data. When the S-clock signal changes to low it begins converting immediately. In cases where you are doing single shot conversions at a much lower frequency than 15 samples/second, you can idle the part and further reduce the power. The ADS1244, with its low power and small size, should catch the eye of hand-held device designers that have only low charge available to them. The ADS1244 comes in an MSOP-10 package, and is available now from TI and its authorized distributors. Suggested resale pricing is $2.95 in 1,000 piece quantities. Product Folder

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