Nokia 7280 Service Manual

 RM-14

Nokia Customer Care

7 - System Module

14

COMPANY CONFIDENTIAL

ISSUE 1 11/04

Copyright © 2004 Nokia. All Rights Reserved.

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Since the RM-14 project is equipped with a “fixed battery”, a need of a specific HW reset solu-
tion is required, since this is no longer possible by removing the battery. This request is meet 
by the implementation of a power cut-off switch that disconnects the battery power from the rest 
of the phone. This switch is implemented by 2 P-Channel MOSFET’s inserted in the battery 
power line. 

RTC backup:

A minimum of 10 minutes power supplied to the RTC circuit is required.

Dead battery charge:

A battery safety circuit is protected by battery cell, which must be re-enabled.

Description:

The circuit depicted in  HW Reset circuit-figure is connected to battery at “VBAT” and to the 
phone at VBAT_OUT. The switch referred to as “SW” illustrates the switch, which enables pow-
er, supplied to the phone. This is implemented as a normally open switch in the SIM can. Its 
function is to open when SIM-card is inserted and close whenever it’s extracted. 

Beside of the PA-Module implementation, the rest of the phone will be powered from the 
VBAT_OUT.  

This mode implies a battery that has its cell disconnected from battery terminals by the batter-
ies own protection circuit . 

When the protection circuit is disabled, the battery cell voltage is visible at the battery terminals. 
This means that the voltage of VBAT_OUT equals the battery cells whereas this must be higher 
than the Gate-Source threshold voltage of Q1-2.