Sony Ericsson W890 Troubleshooting Manual page 82

FUNCTIONAL OVERVIEW Technical Description
SEMC Troubleshooting Manual
W890
Charger Control
Connection Diagram
A programmable charger is used for battery charging.
Limits can be set for the output voltage at CHSENSE- and the output current from DCIO
through the sense resistor to CHSENSE-.
The programmable charger is enabled or disabled by the assertion/negation of the
external signal DCIO. Parts of the programmable charger are activated and deactivated
depending on the level of VBAT. The rest of the programmable charger is activated and
deactivated through I2C.
The programmable charger supports the following functions:
• Constant current charging
• Constant voltage charging
• Trickle charging
• PWM controlled charging
• Over-voltage and over current detection
• Watchdog termination
• DCIO assertion/removal detection
• Voltage and current measure functions
• Low resistive path (reverse mode)
The programmable charger is able to control the voltage and limit the current to a load
seen at CHSENSE-. The programmable charger can also be run in PWM mode to turn
the charging on and off in accordance with the particular period and duty cycle. When the
charging is on, it is set to the current and voltage selected by I2C.
A low resistive path from VBAT to DCIO can be formed when DCIO is not detected. When
this setting is done in the appropriate registers, a lowering of CHREG to 0 V turns on the
external pass device. The pass device is automatically turned off when an external source
is detected on DCIO, or when the watchdog termination block times out. The watchdog
termination block must be active when the external switch is enabled, both in normal
charging mode and in the low resistive path mode. The watchdog is set through the serial
interface, and if it has not been set again before timeout, the watchdog turns off the
external switch. The watchdog is disregarded during trickle charging.
When no battery is present, the system can be booted and supplied from DCIO by
applying the correct voltage on DCIO.
USB Charger
The analog baseband controller contains a standalone USB charger. The USB charger
has a separate input and incorporates full functionality during low VBAT.
The programmable charger supports the following functions:
• Trickle charging
• Constant current charging
• Watchdog termination
• Trickle LED indication
• VBUS assertion/removal detection
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