Some problems of USB powered Vbus

Possible sources of Vbus:

A. Supplied by the Pmic, controlled by a gpio for power supply

B. Directly from the charger chip (e.g. bq2419x, OTG mode power can be set)

C. It is also possible to write a register to open Vbus (Does the PHY on the CPU provide 3.3V power?). ）

When the usbcable is connected to the PC, sometimes it can be seen that the power supply is negative because the battery is recharged by Vbus. Power supply is equivalent to

Some powersupply have the ability to prevent power from being plugged in. It will properly increase the voltage

The Vbus and the USB host controller are not too big to be out of the same chip. Vbus can be replaced by an external power supply. There are some times when active hubs can be used. But the active hub does not necessarily work when the vbus is not powered. such as Blekin hub in Vbus no power when the hub does not work properly, and my own hub is able to work properly. So be sure to be careful. Figure out if the Vbus is powered. If v bus does not supply power, use an external power supply to power it. Power from the active hub does not necessarily work.

Vbus General will have the OCP circuit, that is, when inserted when the phenomenon of excessive flow needs to be able to recover normally. When the OCP circuit is bad, or does not work, the vbus will be broken off, causing the USB to not work properly

The Vbus has a working voltage range. Looks like 4.4---around 5.5v (need to be confirmed)

According to the USB specification, from the power side, the USB device is divided into self-powered and bus-powered two device types, the device through the enumeration process of device descriptors to declare their own power requirements. Self-powered equipment does not use hsot/hub power supply, but its own power supply, bus power refers to the device power supply from the Vbus. In the case of a bus-powered device, the USB specification specifies two devices depending on the size of the current being absorbed by the device: low pwer and high power devices, low power devices must not absorb more than 100mA of current under any circumstances, high The power device must not absorb more than 100mA of current prior to proper configuration and, if configured, must not absorb more than 500mA of current in any case. If the device enters the suspend state, the low power device must not absorb more than 500uA of current in any case, high The power device must not absorb more than 2.5mA of current if it is properly configured and the remote Wake function is enabled by the host, otherwise it must not exceed 500uA (2008 usb-if changes the suspend current regulation, the original 500uA current regulation is too strict, So all USB devices suspend current is relaxed to 2.5mA. ）

The Vbus is connected to the PHY, Charger IC, and three parts of the pmic.

A. Connection to PHY is used to detect interrupts such as B session valid,

B. Connect to the Charger IC for charging.

C. Connected to the pmic is for power-on detection, which is actually a boot signal. (This is a required connection)

In Project A's design, Vbus did not receive the Vbus on the PHY. It is only inserted according to the pmic detection Vbus, as well as the wakeup system. This requires additional drivers to detect the insertion of the Vbus, and then notifies the USB OTG driver.

Project X's design Vbus is connected to USB and detects charger insertions directly in the OTG drive.

The implementation of Project Y Vbus connects the pmic and the charger chip, which is then given to the USB PHY by the pmic. Used to prevent the occurrence of OCP or OVP (see Stark Vbus)

Start

There is always a driver that detects the Vbus and ID pins at boot time. Enter host or device according to the pin pin of the Vbus status and ID.

Decide whether to enter the charging state according to Vbus.

ULPI of the PHY need to connect above d+ D - , ID and the VBUS