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BeagleBone® Enhanced Developer Tutorial
How to implement a rechargeable battery system for the BeagleBone® Enhanced (BBE).
It’s simple, safe and very low cost
The power circuitry on the BBE
The BBE has a built-in power management IC (PMIC) based on the TI TPS65217C device. This device contains multiple switch-mode regulators and LDO regulators to provide all voltage levels needed for the entire board.
The PMIC handles power down and wake-up using the POWER button fitted on the BBE next to the RJ45 connector.
Automatic power-down via the button requires some software to be implemented (to do the equivalent of ‘shutdown now’ from the command line). When the button is pressed, an interrupt is generated and the microprocessor is supposed to query the PMIC (via I2C) to learn that the button was pressed, and kick off the shutdown sequence. In the event of a failure here, the power can be switched off by holding the button down for 8 seconds.
The PMIC also contains built-in battery charging capability, which is what is utilised here to charge a battery.
What type of battery can be used?
Any small Lithium Ion (Li-Ion) or Lithium Polymer (Li-Po) single cell can be used, it is advisable to use one with a built-in protection circuit. If it doesn’t have an in-built circuit, it is highly advisable that one with a built-in thermistor is used.
A cell in the range 700mAH to around 2AH is a good choice. An example cell is one from Olimex part code BATTERY-LIPO1400mAh. It should last around 2 hours on a full charge and should fully charge in around 2 hours.
The Olimex battery is just the right size to fit in between the two rows of headers and is flush so that a cape can still be plugged on top.
The BBE has five test pads on the bottom of the board that are suitable for connecting up the battery.
VBAT SENSE +5V TS GND
The Olimex Li-Po has a built-in protection circuit, so you can solder a 10k resistor to TS and GND to simulate the thermistor. (You may or may not wish to do this, please study Li-Po and use your own judgement)
It is desirable to use a connector for the Li-Po and this can be secured to the bottom of the board with some hot-melt glue or positioned somewhere convenient for your assembly.
The LiPo connector needs to be soldered to pins VBAT and GND via wire, and then a zero-ohm link between VBAT and SENSE on the underside.
How to add the battery in two steps
How to implement a rechargeable battery system for the BeagleBone® Enhanced (BBE).
- Solder the 10k resistor and a zero-ohm link as shown here in the yellow boxes.
These are simple 0603 resistors; use a 1% tolerance resistor or 5% should be fine.
Once the resistors and battery cables have been added and tested to be working it can be protected with hot melt glue or epoxy.
- Attach and mount
Attach and mount the connector in a place of your choice using either epoxy or appropriate strong glue.
The connectors are available in straight and right-angle connection:
JST connector
JST right angle connector
How to control the PMIC
The TPS65217C PMIC is very programmable; it has dozens of configuration settings specifically for charging and it has safety timer capability. The PMIC is configured upon startup via I2C.
The PMIC is on i2c channel 1 at an address of 24.
tps@24 {
reg = <0x24>;
compatible = "ti,tps65217";
ti,pmic-shutdown-controller;
interrupt-parent = <0x1>;
interrupts = <0x7>;
linux,phandle = <0x95>;
phandle = <0x95>;
};
};
To control the charger there are system nodes available
debian@beaglebone:/sys/bus/i2c/devices/0-0024$ ls -l total 0 lrwxrwxrwx 1 root root 0 May 25 13:17 driver -> ../../../../../../bus/i2c/drivers/tps65217 drwxr-xr-x 3 root root 0 Jan 1 2000 input -r--r--r-- 1 root root 4096 May 25 20:01 modalias -r--r--r-- 1 root root 4096 May 25 13:17 name lrwxrwxrwx 1 root root 0 May 25 20:01 of_node -> ../../../../../../firmware/devicetree/base/ocp/i2c@44e0b000/tps@24 drwxr-xr-x 2 root root 0 May 25 13:24 power drwxr-xr-x 9 root root 0 Jan 1 2000 regulator lrwxrwxrwx 1 root root 0 Jan 1 2000 subsystem -> ../../../../../../bus/i2c drwxr-xr-x 3 root root 0 Jan 1 2000 tps65217-bl drwxr-xr-x 3 root root 0 Jan 1 2000 tps65217-charger drwxr-xr-x 3 root root 0 Jan 1 2000 tps65217-pmic -rw-r--r-- 1 root root 4096 Jan 1 2000 uevent debian@beaglebone:/sys/bus/i2c/devices/0-0024$ cd tps65217-charger/ debian@beaglebone:/sys/bus/i2c/devices/0-0024/tps65217-charger$ ls -l total 0 -rw-r--r-- 1 root root 4096 May 25 20:01 driver_override -r--r--r-- 1 root root 4096 May 25 20:01 modalias drwxr-xr-x 2 root root 0 May 25 13:24 power lrwxrwxrwx 1 root root 0 Jan 1 2000 subsystem -> ../../../../../../../bus/platform -rw-r--r-- 1 root root 4096 Jan 1 2000 uevent debian@beaglebone:/sys/bus/i2c/devices/0-0024/tps65217-charger$ cd power/ debian@beaglebone:/sys/bus/i2c/devices/0-0024/tps65217-charger/power$ ls -l total 0 -rw-r--r-- 1 root root 4096 May 25 20:02 async -rw-r--r-- 1 root root 4096 May 25 20:02 autosuspend_delay_ms -rw-r--r-- 1 root root 4096 May 25 20:02 control -r--r--r-- 1 root root 4096 May 25 20:02 runtime_active_kids -r--r--r-- 1 root root 4096 May 25 20:02 runtime_active_time -r--r--r-- 1 root root 4096 May 25 20:02 runtime_enabled -r--r--r-- 1 root root 4096 May 25 20:02 runtime_status -r--r--r-- 1 root root 4096 May 25 20:02 runtime_suspended_time -r--r--r-- 1 root root 4096 May 25 20:02 runtime_usage