Another overlooked design consideration is communicating with a battery that is used in a series application such as shown in Figure
1. This is an issue because data and clock for SMBus are relative to the ground point of the circuit, and batteries utilized in series
applications shift the ground of the higher-voltage section. That is, the actual ground point is equal to the voltage of the lower-battery
section (10-16.8V DC on a UBBL10/13) and continually shifts throughout the battery discharge. This requires the use of an isolated
input for proper communication or a shorting path will exist to system ground.
Figure 1: Batteries Shown in Series Configuration
Several companies make optical and inductive isolators for I2C and SMBus, including NXP Semiconductors and Analog Devices, Inc.
It is good practice to add some ESD protection and filtering to the battery communication interface.
Larson Electronics, LLC
Phone: (800) 369-6671
Fax: (903) 498-3364
www.larsonelectronics.com
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