Dallas Semiconductor Corp. has released its DS2790 for single Li-ion cells, which has fuel-gauging algorithm and customization capabilities traditionally reserved for notebook products with 9-12 cell battery packs.
The DS2790 includes the 16bit MAXQ20 microcontroller with an accumulator-based (MAC) 16bit RISC architecture, program and data memory, and measurement systems for battery current, voltage, and temperature. Its fetch and execution operations are completed in one cycle without pipelining (instruction contains both the operation code and data). The processing core is supported by a 16-level hardware stack, which enables fast subroutine calling and task switching. Data can be quickly and efficiently manipulated with three internal data pointers. Multiple data pointers allow more than one function to access data memory (no need to save and restore data pointers each time).
The DS2790 includes programming memory, data EEPROM, and data RAM. The memory system is arranged in a Harvard architecture, with separate address spaces for program and data memory. The 16Kbyte programming memory consists of 8Kbytes of password-protected EEPROM and 8Kbytes of ROM. With EEPROM, the device can be reprogrammed, thus simplifying and reducing the cost of development and field upgrades. The ROM contains routines that allow reprogramming over an I2C interface, SHA-1 authentication, and support for in-circuit debugging. The chip's 128 bytes of EEPROM is available for storing charge-current parameters, cell characteristics, and manufacturing data. RAM is 512 bytes, and is used for temporary data storage.
The DS2790 also provides precise current, accumulated current, voltage, and temperature measurements. The 12bit-plus-sign current measurements represent an average of 128 individual current samples. The current measurements are internally summed to produce the accumulated current with accuracy within ±2 percent of full-scale measurement. The DS2790 measures voltage as a 10bit-plus-sign value over zero to 4.75V with a resolution of 4.8mV. An on-chip temperature sensor measures the temperature of the battery and reports the results as a 10bit-plus-sign value with a resolution of 0.125°C.
The DS2790's protection circuitry includes an autonomous state machine that checks for over-voltage, under-voltage, and over/underdischarge conditions. The DS2790, in 28-pin TSSOP and TDFN industry-standard UCSP packages, is priced starting at $2.50 each (1,000-up, FOB USA).
