Measuring Battery Voltage - PMIC

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1

Hello,

I have a BB black and was wondering if there is a way to read the voltages for the power supplies, in particular the battery, in order to implement a battery level indicator.

It appears that the PMIC (TPS65217C) provides an easy way to feed the various supply voltages into an ADC pin, even properly scaled to 1.8V, through the MUX_OUT pin. I can read and write the various PMIC statuses through /dev/i2c-0, but unfortunately according to the BB schematic the MUX_OUT pin doesn’t appear to be connected to anything, so it looks like it’s impossible to sample the voltages.

Is there another way to read the battery level that I am missing? If not, it might be a good idea for future revisions to connect the PMIC’s MUX_OUT to one of the AM335x’s ADCs. This shouldn’t create any incompatibilities as the default setting for the MUX is high impedance (see MUXCTRL in the TPS65217 reference manual, http://www.ti.com/lit/ds/symlink/tps65217c.pdf).

2

There is not. LiION batteries typically use fuel gauges as you cannot rely on voltage as an indicator of capacity. I removed this from the design. The BeagleBone has this feature and I am familiar with its function…

I have no plans to add it back in to the BBB.

Gerald

3

Hi Gerald,

Could you explain why you decided to remove this from the BeagleBone Black? I cannot figure out the use of AIN7 in the BeagleBone Black configuration.

I understand its use in the BeagleBone. However in the BeagleBone Black, it seems to me that it should read a fixed value of 1.65V. Am I missing something?

I read in a couple of places that it could still be used to measure the power consumption by adding a shunt resistor. From looking at the schematic of the BeagleBone Black I do not see how this is possible. Do you have any hint on this?

Thanks in advance,
Nicolas

4

It is there to detect if the 3.3V regulator, that is separate from the PMIC, is working. he shunt resistor was removed from the BeagleBone Black design. I felt that detecting the regulator was more important than a feature very few people used.

Gerald

5

It makes sense. Thank you.

Just for the sake of completeness, this detection of the 3.3V regulator would be done by the processor, not directly by the PMIC, correct?

6

Correct. The ADC pins are on the processor, not the PMIC.

Gerald