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Programmable fuel gauge suits 1- or 2-cell apps

Posted: 21 Mar 2007 ?? ?Print Version ?Bookmark and Share

Keywords:fuel gauge? MAXQ20? EEPROM? Dallas Semi? xx?

Dallas Semiconductor has launched a programmable fuel gauge for 1- or 2-cell applications. Integrated into the DS2792 are a MAXQ MCU; program and data memory; and a measurement system for battery current, voltage and temperature. These features provide the ability to customize fuel-gauging algorithms in battery-powered products.

At the heart of the DS2792's computing core is the low-power, 16bit MAXQ20 MCU with its accumulator-based, 16bit RISC architecture. Because the DS2792's instructions contain both the operation code and data, its fetch and execution operations are completed in one cycle without pipelining. The processing core is supported by a 16-level hardware stack, which enables subroutine calling and task switching. Data can be quickly manipulated with three internal data pointers. Multiple data pointers allow more than one function to access data memory without having to save and restore data pointers each time.

To allow the user to program proprietary algorithms, the DS2792 contains three types of memory: programming memory, data EEPROM and data RAM. The memory is arranged in Harvard architecture, with separate address spaces for program and data memory. The 8k words of programming memory consists of 4k words of password-protected EEPROM and 4k words of ROM. The inclusion of EEPROM allows the devices to be reprogrammed, which simplifies and reduces the cost of development and field upgrades. The data EEPROM consists of 64 words and is available for storing important data such as charge parameters, cell characteristics and manufacturing data that should remain unaffected by severe battery depletion, accidental shorts or ESD events. The data RAM is 256 words and is used for temporary data storage.

Precise measurements
The DS2792 also provides precise current, accumulated-current, voltage and temperature measurements. Current measurements are internally summed to calculate the accumulated current, which is accurate to within 0.5 percent 4mV over a range of 64mV. Using a 15-milliohm sense resistor, this current accuracy translates to within 0.5 percent 267mA over a 4.2A range. The DS2792 measures voltage as a 10bit value over a 0 to 4.99V range with a resolution of 4.88mV. An on-chip temperature sensor measures the temperature of the battery and reports the results as a 10bit value with a resolution of 0.125C. All measured data and any password-protected reprogramming of the EEPROM memory can be communicated to the host through the DS2792's UART interface.

Typical applications for the DS2792 include digital video cameras, SLR digital still cameras, sub-notebook and ultraportable PCs, industrial PDAs and handheld GPS devices. The DS2792 is available in an 8-by- 4-mm, 28-pin, Pb-free TDFN package. Prices start at $3.28 (1,000-up, FOB USA).

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