XTAL1

C1

C2

C

L

XTAL2

TUSB2046B

TUSB2046BI

SLLS413I – FEBRUARY 2000 – REVISED SEPTEMBER 2013

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USB Design Notes

The following sections provide block diagram examples of how to implement the TUSB2046B device. Note, even

though no resistors are shown, pullup, pulldown, and series resistors must be used to properly implement this

device.

Figure 6 is an example of how to generate the 6-MHz clock signal.

are determined using a crystal from Fox Electronics – part number HC49U-6.00MHz 30\50\0-70\20, which means

Figure 6. Crystal Tuning Circuit

Input Clock Configuration

The input clock configuration logic of TUSB2046B is enhanced to accept a 6-MHz crystal or 48-MHz on-the-

board clock source with a simple tie-off change on TSTMODE (terminal 31).

•

A 6-MHz input clock configuration is shown in Figure 7.

In this mode, both TSTMODE and TSTPLL/48MCLK terminals must be tied to ground. The hub is configured

to use the 6-MHz clock on terminals 30 and 29, which are XTAL1 and XTAL2, respectively, on the

TUSB2046B. This is identical to the TUSB2046.

Figure 7. 6-MHz Input Clock Configuration

•

A 48-MHz input clock configuration is shown in Figure 8.

clock input on TSTPLL/48MCLK (terminal 27). XTAL2 must be left floating (open) for this configuration. Only

the oscillator or the onboard clock source is accepted for this mode. A crystal can not be used for this mode,

since the chip’s internal oscillator cell only supports the fundamental frequency.

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