The TUSB2077A hub is a 3.3-V CMOS device that provides up to seven downstream ports in compliance with the USB 2.0 specification. Because this device is implemented with a digital state machine instead of a microcontroller, no software programming is required. Fully compliant USB transceivers are integrated into the ASIC for all upstream and downstream ports. The downstream ports support full-speed and low-speed devices by automatically setting the slew rate according to the speed of the device attached to the ports. The configuration of the BUSPWR terminal selects either the bus-powered or self-powered mode. The introduction of the DP0 pull-up resistor disable terminal, DP0PUR, makes it much easier to implement an onboard bus/self-power dynamic-switching circuitry. The three-LED indicator control output pins also enable the implementation of visualized status monitoring of the hub and its downstream ports. With these new function pins, the end equipment vendor can considerably reduce the total board cost while adding additional product value.
The EXTMEM pin (pin 47) enables or disables the optional EEPROM interface. When EXTMEM is high, the vendor and product IDs (VID and PID) use defaults, such that the message displayed during enumeration is General Purpose USB Hub.
The TUSB2077A supports bus-powered and self-powered modes. External power-management devices, such as the TPS2044, are required to control the 5-V power source switching (on/off) to the downstream ports and to detect an overcurrent condition from the downstream ports individually or ganged. An individually port power controlled hub switches power on or off to each downstream port as requested by the USB host. Also when an individually port power controlled hub senses an overcurrent event, only power to the affected downstream port will be switched off. A ganged hub switches on power to all its downstream ports when power must be on for any port. The power to the downstream ports is not switched off unless all ports are in a state that allows power to be removed. Also, when a ganged hub senses an overcurrent event, power to all downstream ports will be switched off.