Texas Instruments Incorporated (TI) announced a high-performance battery monitor IC for Li-Ion- and Li-Polymer-based applications, such as cellular handsets, Internet audio appliances, digital cameras, PDAs, and other portable equipment powered by a single lithium cell. The device measures critical parameters in a battery pack, such as charge, discharge, self-discharge and temperature and employs an auto-calibrating VFC (voltage-to-frequency converter) for continuous charge/discharge integration, allowing unparalleled measurement accuracy over battery operating conditions. With information from the measurement IC, a host system can accurately calculate remaining battery capacity and predict remaining system run or standby times.

TI's bq2023 battery monitor communicates measurement information to the host controller using the SDQ serial interface, a single wire command-based protocol compatible with the Dallas Semiconductor 1-Wire. The part also includes 224 bytes of FLASH memory and a 64-bit ID ROM register. The non-volatile memory integration allows a system designer to add an accurate fuel gauge to a system while replacing serial EEPROMs or ID chips, which are currently used in battery packs to store battery pack characteristics or identification and addressing codes.

For the host to accurately calculate remaining battery capacity and predict run times, battery capacity monitoring must precisely measure the low standby current (<5mA) and pulsed discharge waveforms common in today's ultra-low-power portable devices, such as cellular phones. The bq2023 achieves this with an auto-calibrating, high-resolution VFC, which continuously integrates the potential across a low-value sense resistor in the charge/discharge path of the battery. With a 25mohm sense resistor, the resolution of the converter is better than 0.12mAh. The VFC automatically calibrates measurement offset once per hour to reduce the offset error to 3mV typical (12mV maximum) and ensure accurate battery monitoring over voltage and temperature variations.

The bq2023 monitors the differential voltage drop across a small sense resistor that is connected between the negative terminal of the battery pack and the pack's ground connector. A voltage-to-frequency converter changes this into coulomb counts of charge and discharge with resolutions down to 3.05 uV. An intelligent host controller can interpret these counts into the battery pack's state of charge or discharge. The one-wire communications is compatible with Dallas Semiconductor's 1-wire systems, which is a compliment to that vendor's success with its products. One of the really nice features of the bq2023 is that the part self-calibrates every hour and continuously compensates offset errors in the VFC. The part can also operate off a single lithium cell, down to 2.4 V, and the battery pack characteristics are stored in 224 bytes of flash memory; there are also 8 bytes of secure ID ROM and 32 bytes of RAM. The non-volatile memory stores warranty and identification information as well as other critical battery parameters, even with the cells in deep discharge.

Operating power consumption is 40 uA, with shutdown -- which can be achieved over the one-wire bus -- at a low 1.5 uA. The gain response of the VFC is centered at room temperature with typical numbers of about 94.8 Hz/V with a supply of 2.4 V, down to about 93.6 Hz/V with a 4.2-V supply; the gain falls less than 0.5 Hz/V 20 degrees either side of room temperature.