SLLS288B - FEBRUARY 1998 - REVISED MARCH 1998
The TUSB2040A hub is a 3.3-V CMOS device that provides up to four downstream ports in compliance with the USB specification 1.0 version. Pin 21 (EXTMEM) enables or disables the EEPROM interface. When EXTMEM is low, the TUSB2040A is functionally equivalent to the TUSB2040 hub and the product ID (PID) displayed during enumeration is General Purpose USB Hub. For this configuration, pins 9 and 10 are the BUSPWR\ and GANGED input pins, respectively.
If programmable vendor ID(VID) and product ID(PID) descriptors are desired, pin 21 must be high (EXTMEM = 1) and a SGS Thompson M93C46 or equivalent EEPROM must be connected to pins 9 and 10. For this configuration, the values for BUSPWR\ and GANGED are stored in the EEPROM and pins 9 and 10 become the EEPROM interface.
The TUSB2040A supports bus-power and self-power modes. The power switching to the downstream ports can either be controlled individually or ganged using external devices to switch power and to detect overcurrent conditions. Outputs from the external power devices provide overcurrent inputs to the TUSB2040A OVRCUR\ pins and in the case of an overcurrent condition, the corresponding PWRON\ pins will be disabled by the TUSB2040A. In the GANGED operation, all PWRON\ signals transition simultaneously, and any OVRCUR\ input can be used.
The hub requires a 48-MHz clock signal to sample data from the upstream port and generate a synchronized 12-MHz USB clock signal. The hub supports the flexibility to use any device that generates a 48-MHz clock. Because the majority of oscillators are active devices, the low power suspend mode of the TUSB2040A will not function because there is no way to stop the oscillator from driving the internal clock. An oscillator with a TTL output not exceeding 3.6 V can be used by connecting its output to the XTAL1 terminal and leaving the XTAL2 terminal open. For crystal or resonator implementations, use the XTAL1 terminal as the input and the XTAL2 terminal as the feedback path. Because the crystal is required to resonate at 48 MHz, a tuning circuit as shown in Figure 8 may be required.
The upstream port and all downstream ports are USB-compliant transceivers. Every downstream port supports both full-speed and low-speed connections by automatically setting the slew rate according to the speed of the device attached to the port.
View more information about generic part numbers:TUSB2040A
Go to the Engineering Design Center to locate information on other TI Semiconductor devices.