Huawei U8185 Maintenance Manual page 31

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U8185

Maintenance Manual

The PM8029 checks the pin voltage of VCHG. If the voltage meets the requirements listed in

the following table, the PM8029 notifies the MSM by generating the ITCHGVAL interrupt.

When VCHG–VDD is lower than 100 mV , the PM8029 shuts off its internal transistor, deems

the power supply as disconnected, and generates an interrupt.

The PM8029 detects the charger to select power input mode and switch between charger and

battery modes. If V (VCHG) > V (B+), the charger voltage is higher than the battery voltage

and the pass transistor is enabled. The phone is then powered by the charger. If V (VCHG)

V (B+), the battery voltage is higher than the charger voltage and the pass transistor is

disabled. The phone is then powered by the battery. To disable the phone to automatically

switch to use the charger power, you can configure the phone software. VCHG is grounded by

connecting in parallel with a 47 k resistor and a 4.7 uf capacitor. If no charger is connected to

the phone, the resistor can pull VCHG to 0 V to make sure that the charger is detected as not

connected. The parallel connected capacitor protects the EMC, provides linear filter, and

ensures circuit stability.

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Issue 1.0 (2012-03-23)

Trickle charging

Huawei Proprietary and Confidential

9 Principles and Failure Analysis

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