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Power documentation
This article is separated into sections just like the schematic:
- Charger BQ25792
- 3.3V and 1.8V rails TPS650250
- Battery connector
- Privacy switches
- 5V rail MP3429GL
- 22V LCD rail AP3032KTR
You can view the schematics by downloading the power.kicad_sch file from the repository and opening it in KiCad.
A host controlled charger, that can also operate in default mode without host management. Ensures safe and efficient charging of the battery. See datasheet for all features and full description.
Below are listed all pins that interact with the smartphone's software:
The charger output voltage to the system.
Used for "USB host/charging port detection for VIN1 input. The detection includes data contact detection (DCD), primary and secondary detection in BC1.2, and the adjustable high voltage adapter."
Allow managing the chargers settings through I2C. See register map in datasheet.
Allows the compute module to send enable and disable signals to the charger from a GPIO pin.
Sends an active low, 256μs pulse to the host to report the charger device status and faults.
The TPS650250 device is an integrated power management IC that provides multiple power rails. The TPS650250 provides three highly efficient, step-down converters targeted at providing the core voltage, peripheral, I/O and memory rails in a processor-based system.
The 2 LDOs are not in use, currently we only use 3 DCDCs.
DCDC converter enable pins. A logic high enables the converter, a logic low disables it.
Converter 1 is controlled by the CMs GPIO and can be disabled by the EG25 privacy switch (even if GPIO is high).
Converters 2 and 3 are controlled from the CMs GPIOs.
3.3V A 1600mAh rail is reserved for the power hungry EG25 GSM&GPS IC.
⚠EG25 datasheet specifies max current to 2A.
3.3V B 800mAh rail is reserved for other devices requiring that voltage e.g. camera.
1.8V 800mAh rail is reserved for devices requiring that voltage e.g. screen.
Alerts the host when battery is low. "Active low when PWRFAIL comparator indicates low VBAT condition." The threshold is hardwired (set by the divider connected to PWRFAIL_SNS.)
2 position wire to board terminal block used to connect the battery leads to the system without the need to solder.
Remove power form specific components of the system. Due to different current consumptions of each switched component, each switch operates differently.
E.g. It is not possible to switch the EG25 directly with a small switch because it consumes 2A peak current.
Disables DCDC converter number 1, which is reserved for EG25. In effect EG25 is powered off
Cuts power from microphone.
Cuts power from the camera using a MOSFET.
Boost regulator, it is hardwired to be enabled. No interactions with software.
Boost regulator powering the LCD backlight, supports PWM dimming.
Connected to the CM GPIO, used for switching the regulator using PWM to dim the LCD backlight.
⚠LCD power consumption is unknown due to shit datasheet and no response from the manufacturer. LCD component may change soon.