Driven by integrated functionality and shrinking form factors, the demand for portable devices such as the cellular phone, PDA and DVD player has been growing significantly for the last few years. These portable devices require rechargable batteries and peripherals that will need to be replaced during the “life” of the portable device. The need to power portable devices has opened a huge market for counterfeiters to supply cheap replacement batteries and peripherals. Many of these items may not have the safety and protection circuits required by the OEM. Indeed, these counterfeit batteries may violate both mechanical and electrical safety requirements related to short-circuit protection, charge safety and other specifications.
It is usually impossible for consumers to determine the quality of a replacement power device without purchasing it and possibly learning their lesson “the hard way”. In addition, this can lead to a potentially dangerous situation for the end-users. Adding simple and effective portable system authentication technology allows the OEMs to ensure customer satisfaction and protects their business. More importantly, safety is guaranteed throughout the life of the product. This article discusses the simple identification (ID) and the more complicated challenge-and-response CRC and SHA-1/HMAC-based battery authentication schemes – battery authentication architectures that meet today’s counterfeit battery challenges to protect OEM potential business and ensure the end-user safety and satisfication.
Identification based authentication scheme
Several schemes are currently used to identify when a battery pack is intended for portable products. The most common is the form-factor, or physical connection. Every cell phone battery pack on the market has a different form-factor. The battery pack’s physical size is not even consistent in all the phones manufactured by the same company. While the form-factor identification method affords some protection level for the low-volume runners, high-volume batteries are much more likely to be counterfeited. It would be a cost-saving solution to standardize form-factors and not change them. Many OEMs are moving towards this economic model. However, this design provides opportunities for counterfeiters to replicate the battery pack by measuring its physical dimension.
To improve the battery identification, an electrical identification scheme should be used so that a simple physical counterfeit is no longer enough to replicate the battery. Figure 1 shows the ID authentication functional block diagram. The challenger, or host, sends a command to read the data from the device (responder). The data includes product family code, identification number (ID), and cyclic redundancy check (CRC) value. Each device has a unique ID number. The response data is compared with the data in the host. If the information from the device is valid, then the host enables the system’s operation. If not, it may inhibit its operation and provide a system error code and a warning signal to the end-user. The ICs, in this example the bq2022 and bq2023, provide a unique ID for each device. Figure 2 shows the battery pack typical application circuit with the ID chip. The host “communicates” with the chip through a dedicated general purpose I/O to determine if an ID is available and valid. The ID authentication scheme eliminates a significant number of non-OEMs; however, the ID issued by the device is available to anyone with an oscilloscope. It is still possible for the counterfeiters to replicate the ID to the issued command, but it increases the cost to implement a fake ID. Some non-OEMs go after batteries and peripherals for such high-volume products that adding a cheap microcontroller to the system is acceptable. To counter this threat, a more robust authentication scheme must be employed.
Figure 1 - ID Authentication Functional Block Diagram
Figures 2 and 2a. Typical Application Circuit with ID Chip