Power Up; Power Off; Clock Distribution - Nokia RH-128 Service Manual

RH-128
Baseband Description and Troubleshooting

Power Up

The mobile terminal uses the power key and a charger to power up.
Power Key
When the power key is pressed, the PMU enters the power-up sequence. Pressing the power key
causes the POWER_ON pin to VBAT. The POWER_ON signal is not part of the keypad matrix. The
power key is connected to the PM. This means that when the power key is pressed, an interrupt will be
generated to the CBP in order to power on the CBP. The CBP reads the PMU IC's interrupt register and
notifies that it is a KPADPWR_N interrupt. The CBP reads the status of the POWER_ON signal using
the PMU's (I2C) control bus. If the POWER_ON signal stays High for a certain time, the CBP accepts
this as a valid power-on state and continues with the software baseband initialization. If the power key
does not indicate a valid power-on situation, the CBP powers off the baseband.
Charger
Charging is controlled by start-up charging circuitry in order to detect and start charging in case the
main battery is not full and the PMU has no supply.

Power Off

While the PS_HOLD signal from the CBP is high, and the PMU IC is in power-on status. The PMU
continually monitors three events that could trigger a power-off sequence:
The CBP drives the PS_HOLD signal low responding to the pressing of the keypad power button.
Battery voltage drops below power off threshold (Battery Voltage < 3.2 V).
The PMU IC die temperature exceeds its "severe" over-temperature threshold.

Clock Distribution

The CBP derives its internal clock from two clock inputs, VC-TCXO and SLEEP_CLK.
The main clock signal for the baseband is generated from TCXO.
(Temperature-compensated crystal oscillator) The CBP's TCXO clock input supports the frequency 19.2
Issue 1
COMPANY CONFIDENTIAL
Copyright © 2009 Nokia. All rights reserved.
Page 5-9