User Guide

RM-11

Troubleshooting - Baseband CC Technical Documentation

Figure 3: Power up

Power Up - Power Key

When the Power key is pressed, the UEM enters the power up sequence. Pressing the

Power key causes the PWRONX pin on the UEM to be grounded. The UEM PWRONX

signal is not part of the keypad matrix. The Power key is only connected to the UEM. This

means that when pressing the power key, an interrupt is generated to the UPP that starts

the MCU. The MCU then reads the UEM interrupt register and notices that it is a

PWRONX interrupt. Then the MCU reads the status of the PWRONX signal using the UEM

control bus (CBUS). If the PWRONX signal stays low for a specific duration, the MCU

accepts this as a valid power on state and continues with the SW initialization of the

baseband. If the power on key does not indicate a valid power on situation, the MCU

powers off the baseband.

Power Up - Charger

In order to be able to detect and start charging in the case where the main battery is

fully discharged (empty) and hence the UEM has no supply (NO_SUPPLY or BACKUP

mode of UEM), charging is controlled by START-UP CHARGING circuitry.

Whenever a VBAT level is detected to be below the master reset threshold (VMSTR-),

charging starts and is controlled by START_UP charge circuitry. Connecting a charger

forces the VCHAR input to rise above the charger detection threshold (VCHDET+) and by

detection charging is started. The UEM generates 100 mA constant output current from

the connected charger's output voltage. The battery’s voltage rises as it charges, and

when the VBAT voltage level is detected to be higher than the master reset threshold

limit (VMSTR+), the START_UP charge is terminated.