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Method to Extend Shelf Life of Computer Motherboard Battery Using Isolation Circuit Disclosure Number: IPCOM000028739D
Original Publication Date: 2004-May-28
Included in the Prior Art Database: 2004-May-28
Document File: 1 page(s) / 69K

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A simple FET load switch circuit is placed between the system board's coin battery and the battery backed-up loads. The P-Channel FET switch is enabled during system board manufacturing by using the Manufacturing Bypass jumper shown in the figure to test the battery backed-up load circuits. The FET load switch disconnects the battery from the load circuits when it's on the "shelf" prior to chassis installation. When the system board is installed in to a system chassis, the mounting screw then re-connects the battery to the circuit.

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Method to Extend Shelf Life of Computer Motherboard Battery Using Isolation Circuit

Refer to the Figure below for the following description of the battery isolation circuit. The typical battery loads are shown on the right side, and are powered by VBAT_OUT and by +3.3Vaux. During normal system operation the circuits operate from +3.3Vaux, which remains active as long as the system is plugged into an active AC line circuit. When the system is experiencing an AC power loss, or is unplugged for other reasons, the circuits operate from VBAT_OUT. VBAT_OUT is activated whenever the P-Channel FET switch is enabled, via an input signal, -ON/+OFF. The -ON/+OFF signal is minus active or ON, and will be in the minus active state only when a manufacturing bypass enable jumper is positioned between pins 2-3, or when the system board is mounted in to a chassis and a mounting screw is installed such that a connection to the chassis ground is made. The -ON/+OFF signal is inactive high or OFF when the manufacturing bypass enable jumper is positioned in the default disable location, between pins 1-2, and that the system board is on the shelf, or not installed in a chassis.


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