TUSB2046B,pdf(4 Port Hub for t

DESCRIPTION/ORDERING INFORMATION
The TUSB2046B is a 3.3-V CMOS hub device that provides one upstream port and four downstream ports in
compliance with the Universal Serial Bus (USB) specification as a full-speed hub. Because this device is
implemented with a digital state machine instead of a microcontroller, no firmware programming is required.
Fully-compliant USB transceivers are integrated into the ASIC for all upstream and downstream ports. The
downstream ports support both 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 the self-powered mode.
Configuring the GANGED input determines the power switching and overcurrent detection modes for the
downstream ports. External power-management devices, such as the TPS2044, are required to control the 5-V
source to the downstream ports according to the corresponding values of the PWRON terminal. Upon detecting
any overcurrent conditions, the power-management device sets the corresponding OVRCUR terminal of the
TUSB2046B to a logic low. If GANGED is high, all PWRON outputs switch together and if any OVRCUR is
activated, all ports transition to the power-off state. If GANGED is low, the PWRON outputs and OVRCUR inputs
operate on a per-port basis.
The TUSB2046B provides the flexibility of using a 6-MHz or a 48-MHz clock. The logic level of the TSTMODE
terminal controls the selection of the clock source. When TSTMODE is low, the output of the internal APLL
circuitry is selected to drive the internal core of the device. When TSTMODE is high, the TSTPLL/48MCLK input
is selected as the input clock source and the APLL circuitry is powered down and bypassed. The internal
oscillator cell is also powered down while TSTMODE is high.
Low EMI emission is achieved because the TUSB2046B is able to utilize a 6-MHz crystal input. Connect the
crystal as shown in Figure 6. An internal PLL then generates the 48-MHz clock used to sample data from the
upstream port and to synchronize the 12 MHz used for the USB clock. If low-power suspend and resume are
desired, a passive crystal or resonator must be used. However, a 6-MHz oscillator may be used by connecting
the output to the XTAL1 terminal and leaving the XTAL2 terminal open. The oscillator TTL output must not
exceed 3.6 V.
For 48-MHz operation, the clock cannot be generated with a crystal using the XTAL2 output because the internal
oscillator cell supports only the fundamental frequency.
See Figure 7 and Figure 8 in the input clock configuration section for more detailed information regarding the
input clock configuration.