mt8312 datasheet芯片设计手册资料

MT8312 HSPA+ Application Processor Technical Brief

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2.1 Pin Description 
2.1.1 Ball Map View

                               LPDDR2 ball map view of MT8312

                                LPDDR3 ball map view of MT831

                                 PCDDR3 ball map view of MT8382

2.4 Power-on Sequence 
The power-on/off sequence with XTAL is shown in the following figure:

Note that the above figure shows one power-on/off condition with and without XTAL. The external PMIC MT6323 for application processor MT8312 handles the power ON and OFF of the handset. The following three different methods switch on the handset (when VBAT ≥ 3.2V): 
1. Pulling PWRKEY low (The user presses PWRKEY.) 
2. Pulling BBWAKEUP high 
3. Valid charger plug-in
Pulling PWRKEY low is a normal way to turn on the handset, which turns on regulators as long as the PWRKEY is kept low. MT6323 outputs reset signal RESETB to MT8312 SYSRSTB input. After SYSRSTB is de-asserted, the microprocessor starts and pulls BBWAKEUP high. After that PWRKEY can be released, pulling BBWAKEUP high will also turn on the handset. This is the case when the alarm in the RTC expires. 

Besides, applying a valid external supply on CHRIN will also turn on the handset. However, if the 
battery is in the UV state (VBAT < 3.2V), the handset cannot be turned on in any way. 

The UVLO function in MT6323 prevents system startup when initial voltage of the main battery is below the 3.2V threshold. When the battery voltage is bigger than 3.2V, the UVLO comparator switches and threshold are reduced to 2.75V, which allows the handset to start smoothly unless the battery decays to 2.75V and below. 

Once MT6323 enters the UVLO state, it draws very low quiescent current. The VRTC LDO will still be 
active until the DDLO disables it.

The timing diagram also shows the power-on/off sequence without XTAL. VTCXO is always turned on 
when VBAT is above the DDLO threshold.