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Low PC Battery Disables Targus DOCK190 Legacy Power

June 28, 18 - Posted in: Tech Talk by Kevin Quinn, Thee DocKtor
Low PC Battery Disables Targus DOCK190 Legacy Power

Some PCs appear to disable legacy power from the DOCK190 when its needed most, that is, to power and charge the PC battery! We noticed the issue on a few HP models, but the issue may exist on other PC makes and models. The issue occurs if the battery state is below the HP BIOS setting for the USB charging port when connecting the DOCK190 through the ACC1104 to the associated HP Type-A charging port.

To prevent the phenomenon from occurring connect the ACC1104 to a non-charging port on the PC.

If a non-Charging port is not available on the model (i.e. HP Elitebook 1040 G3), the issue can be overcome by setting the USB Charging Port percentage below the current battery charge state percentage. The HP BIOS default is 10%, which is the lowest available setting. Alternatively, un-check the "USB Charging Port" setting in the HP BIOS.

DocKtor's Note: For those of you interested, what we believe is happening is the PD Contract negotiation fails; the DOCK190 appears to be stuck in a loop between establishing legacy power and Type-C power. The DOCK190 cannot provide Type-C power and legacy power at the same time.The BIOS settings of the HP enable the PC to stop providing charging power on the associated USB port(s) at the BIOS setting battery percentage. This is done on most PCs to preserve PC battery charge for its own use and not for providing charge to downstream devices (i.e. smartphones). The PC toggles the CC lines on the charging port(s) to establish this lower power level for the associated Type-A port(s). When this happens the DOCK190 abandons the legacy power to negotiate a Type-C contract. When a Type-C PD contract is not established with the PC (on the Type-A port through the ACC1104) the legacy power is restored. When the legacy power is restored, the PC responds by toggling the CC lines on the charging port to supply the higher charging port power again - since it now has legacy power enough to supply charging levels to the port(s), but toggling the CC lines again tells the DOCK190 to negotiate a Type-C PD contract - as such the DOCK190 abandons providing legacy power and the whole loops starts again.

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