U8950 Maintenance Guide V1.0
10 Principles and Failure Analysis
2012-10-22
Huawei Proprietary and Confidential
57
In actual circuits, the hardware raises the OTG to approximately 1.4 V and limits the
maximum current in the beginning of charging to 500 mA. After the charging process is
detected, this limitation is removed using software. FAN5402UCX is capable of detecting its
own temperature. When TJ reaches the temperature threshold TCF, the current is reduced to
end the charging. When TJ is lower than the temperature threshold TCF by 10 degrees, the
charging starts again. When the charging voltage VBUS is lower than the sleep charging
voltage (Vslp), FAN5402UCX enters sleep mode to save the power.
FAN5402UCX is also capable of continuously detecting the charging voltage VBUS. When
VBUS is lower than the threshold VIN (min), the charging stops and waits for a TINT to
re-consider charging.
FAN5402UCX has the following features:
Charging over-voltage protection
Battery over-voltage protection
Battery presence detection
Start-up without battery
Troubleshooting Process
There are two types of common charging failures:
The phone has no response after a charger is connected to it.
The phone displays an animated icon indicating that it is charging, but actually, the
battery is not charged.
For a mobile phone that fails to be charged, check that the I/O connector is not damaged.
The charging indicator is not displayed when the phone is connected to the charger.
A charging indicator is displayed after the charger is connected to the phone but the phone
cannot be charged.
