News and New Products

Chip offers authentication, protection to single-cell battery packs

By Margery Conner, Technical Editor -- EDN, 6/30/2006

Cell-phone battery gauges are neither accurate nor consistent: The battery-charge symbol seems to relate only coincidentally to battery charge, causing users to charge their phones when they don’t need to, consequently reducing battery life. However, as the newest generation of cell phones moves into a more intensive data-usage model, service providers are demanding that battery packs have more intelligence because of the fear that counterfeit battery packs will explode in phones carrying the providers’ brand names and making them liable to expensive lawsuits. Meanwhile, some users suggest that vendors are requiring battery authentication to protect themselves from after-market battery-pack sales (see the online Feedback Loop for “Friend or foe: Battery-authentication ICs separate the good guys from the bad,” EDN, Feb 2, 2006, pg 59, www.edn.com/article/CA6301616).

However, Brian Rush, business manager for Maxim’s fuel-gauge line, disagrees with these users’ viewpoint. Service vendors, such as Verizon, are liable in a battery-related accident, he says, so they are pressuring equipment vendors to provide battery authentication. In addition, both equipment and service vendors want to preserve their brand integrity. So, Maxim and other vendors are setting the stage for a new generation of fuel gauges targeting one-cell battery packs in cell phones. Maxim claims that its new DS2790 fuel gauge is the first single-chip approach offering accurate battery-fuel-gauge and protection circuitry for single-cell packs.

The circuitry precisely measures current, accumulated current, voltage, and temperature, and it runs your cell-phone manufacturers’ proprietary fuel-gauge algorithms on its internal 16-bit MAXQ microcontroller. The DS2790 contains 16 kbytes of program memory, which includes 8 kbytes of password-protected EEPROM and 8 kbytes of ROM; 128 bytes of data EEPROM for storing data such as charge parameters, cell characteristics, and manufacturing data; and 512 bytes of data RAM. The ROM contains routines that allow reprogramming over the I2C interface, SHA (Secure Hash Algorithm)-1 authentication, and support for in-circuit debugging. Rush claims that hackers can too easily break simpler authentication codes, so equipment vendors need the complexity of SHA-1. The product is available in 28-pin TSSOP and TDFN packages with prices starting at $2.50 (1000).