USB-C to HDMI/PD draining Galaxy S8 battery when USB-C HDMI/PD disconnected from power source.

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velvetshelter

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Nov 30, 2022
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Problem: A tablet I am using is having its battery go flat when I connect to a USB-C to HDMI adapter. This problem only occurs when the power supply for the USB-C to HDMI adapter is disconnected. When the USB-C to HDMI adapter is receiving power, everything is fine. When the power supply is disconnected from the wall or switched off, the tablet battery goes flat as it starts to provide power to the USB-C to HDMI/PD. I want to stop the tablet battery from going flat. We need a tablet to run an application that's only available on a tablet. We also need HDMI out from the tablet along with a power supply for the tablet to stop the battery from going flat whilst in use. For this reason with use the powered USB-C to HDMI adapter.

Here are the relevant components and the configuration:

The power supply is from a Satechi 75W Dual type-C PD travel charger (https://satechi.net/products/75w-dual-type-c-pd-travel-charger?variant=19492503781464)
The USB-C to HDMI/PD is a Dell USB-C to HDMI/PD with Power-Pass Through (https://www.dell.com/en-uk/shop/del...ower-pass-through/apd/470-aegy/pc-accessories)
The tablet is a Samsung Galaxy S8 running Android 12 (up-to-date as of 30/11/2022; Kernel: 5.10.43).
The USB-C connector is connected to the 60W power output of the Satechi 75W power adapter at one end and to the power source port of the Dell USB-C to HDMI adapter.

Here is a diagram of the relevant set up:

Problem.png


What I know so far:
Some forums recommend clear the Android System data cache and cleaning the USB connectors. This has been done and has not fixed the issue. This problem also occurs with USB-C to HDMI/PD adapters, Satechi power supplies and USB-C cables fresh out of the box so I think the cause is something else. I've looked at and tested least 20 of each component when they are brand new. This issue occurs every time.

On the tablet there is a switch under USB settings which say 'Charge connected device. Use this tablet to charge the connected device. When turned off, this tablet will be charged instead'. When
the power supply (Satechi) is connected to the mains, this is switch is OFF. When the power supply is disconnected, this switch is ON. I think this is the cause of the USB-C adapter draining the
battery of the tablet. However, this button is available but it is not responsive; I cannot switch it off. If I slide the button to OFF, it snaps back to being on again. This brings me on to question 1:

Is it possible for me to switch this off or is it ultimately determined by the configuration of the hardware?

I've tried going into the Developer Settings and playing around with 'Default USB Configuration' but I don't seem to be able to keep this switch OFF. I have also disabled USB audio routing.
The developer default USB configuration settings don't seem to be saved either. This brings me on to question 2:

Is there anything I can do to have this switch OFF permanently so the USB-C adapter stops draining tablet battery when the power supply for the USB-C adapter isn't connected to the mains?

Any help would be appreciated. Thanks