PocketBeagle draining the battery when powered off?

[Stuart Longland]

Hi all,

We've got a project built around the PocketBeagle single board computer
which uses a single LiPo 18650 cell as a back-up supply.

The cell is connected to the PocketBeagle along with a 10kOhm
thermister, as per recommendations.

We're find that after running `poweroff` from the shell, and seeing all
LEDs on the PocketBeagle turn off, cells that start with a healthy
voltage of around 4V, are found to have a voltage of just 2.2V when
measured a fortnight later.

The cells we're using are these ones:
https://core-electronics.com.au/polymer-lithium-ion-battery-18650-cell-2600mah-solder-tab.html

…and the circuit is fairly simple (attached). We've seen this on two
revisions of our project. The first revision did not include a RTC, but
in spite of this, still suffers the problem.

Is there a reason why the batteries are getting so heavily drained? Is
there a work-around without having to resort to MOSFET switching of the
battery?

Regards,
--
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...
...it's backed up on a tape somewhere.

[Dan Julio]

Hi Stuart,

I tried to use the PocketBeagle with the battery and also found the extra current draw.  Ultimately I communicated with Octavo and got the following reply.  The OSD3358-SM SiP used on the pocketbeagle internally connects the LDO1 regulator to both the RTC clock input (VDDS_RTC) as well as the VDDS input.  The extra current is taken by the connection to the VDDS power input.  The answer from Octavo is copied below.

https://octavosystems.com/forums/topic/unexpected-current-consumption-with-pmic-sleep-mode-for-battery-charging/#post-6895

"The additional current consumption comes from the fact that the OSD335x and OSD335x-SM use TPS65217C PMIC.  If you look in the application note from TI (http://www.ti.com/lit/ug/slvu551i/slvu551i.pdf), you can see that in the case of the TPS65217C, both VDDS and VDDS_RTC are connected to the LDO1 output of the PMIC.  The additional current consumption that you see is a result of the VDDS power input being connected to the LDO1.

Unfortunately, the connection between VDDS and LDO1 is internal within the SiP and cannot be modified on the OSD335x and OSD335x-SM.  However, we are in the process of characterizing the OSD335x C-SiP to see if it can support the power use case where VDDS is not connected to LDO1.  We should have that characterization finalized in early January.

Additionally, the TL5209 is enabled with an internal pull up within the OSD335x family of devices.  In the OSD335x and OSD335x-SM, this connection cannot be modified.  However, in the OSD335x C-SiP, there is a pin, SYS_VDD1_CTL, that will allow a user to disable the TL5209."

[Stuart Longland]

Hi Dan,

On 23/10/19 1:39 am, Dan Julio wrote:
> I tried to use the PocketBeagle with the battery and also found the
> extra current draw.  Ultimately I communicated with Octavo and got the
> following reply.  The OSD3358-SM SiP used on the pocketbeagle internally
> connects the LDO1 regulator to both the RTC clock input (VDDS_RTC) as
> well as the VDDS input.  The extra current is taken by the connection to
> the VDDS power input.  The answer from Octavo is copied below.
>
> https://octavosystems.com/forums/topic/unexpected-current-consumption-with-pmic-sleep-mode-for-battery-charging/#post-6895
>

>> Unfortunately, the connection between VDDS and LDO1 is internal within
>> the SiP and cannot be modified on the OSD335x and OSD335x-SM. However,
>> we are in the process of characterizing the OSD335x C-SiP to see if it
>> can support the power use case where VDDS is not connected to LDO1. We
>> should have that characterization finalized in early January.

Ahh right, so in other words, this is a quirk of the OSD3358 used in the
PocketBeagle that cannot be changed. I was hoping there was some
register I could kick to fully power off the chip. Ahh well.

Interesting that it powers the on-chip RTC, as this didn't seem to be
working when we connected a battery, hence we made a new revision of the
board with a I²C RTC (MCP7940N).

We'll put our heads together and see if we can come up with a suitable
switching arrangement that allows automatic disconnection of the
PocketBeagle from the battery when powered off without interfering with
the charging capabilities.

Thankfully it's not like the OSD3358 is drawing kilowatts from that
battery, so we have a few options. :-)