Circuit Protection of Battery Pack
Design Notes:
Protection Application:
The power bus of the battery pack should be protected against an overcurrent runaway condition of the Li-ion cell, as well as from ESD. The control line (e.g. SMBus, I2C, etc.) may also need to be protected against ESD. These are all low voltage (<6VDC) circuits.
Solution Description:
As shown at the left (top), discrete multilayer varistors can be used for layout flexibility with respect to ESD protection. An alternative (left, bottom) is to use a single Diode array to save part count. In both cases, the overcurrent solution can be a strap (or SMD) resettable PTC, or an SMD chip fuse.
Companion Solutions:
Does not apply.
Regulatory Issues:
With respect to safety of the battery pack, the following standards supply test methods: UL 1642 UL 2054 IEC 61960 IEC 62133 With respect to ESD, the IEC 61000-4-2 supplies a test method for verifying that the end product is not susceptible to ESD events.
Unique Features:
Does not apply.
Application Warnings:
Care should be taken during the PTC and fuse selection process to ensure the proper performance of the overcurrent device. The key consideration is the expected temperature of the battery pack as this will affect the trip point and trip time of the overcurrent protector.

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