SPRS950F December 2015 – May 2019 DRA744 , DRA745 , DRA746 , DRA750 , DRA756
Refer to the PDF data sheet for device specific package drawings
To address the system clock emissions between devices, place a ~10 to 130 Ω resistor in series with the clock signal. Use a trial and error method of looking at the shape of the clock waveform on a high-speed oscilloscope and of tuning the value of the resistance to minimize waveform distortion. The value on this resistor should be as small as possible to get the desired effect. Place the resistor close to the device generating the clock signal. If an external crystal is used, follow the guidelines detailed in the Selection and Specification of Crystals for Texas Instruments USB 2.0 Devices (SLLA122).
When routing the clock traces from one device to another, try to use the 3W spacing rule. The distance from the center of the clock trace to the center of any adjacent signal trace should be at least three times the width of the clock trace. Many clocks, including slow frequency clocks, can have fast rise and fall times. Using the 3W rule cuts down on crosstalk between traces. In general, leave space between each of the traces running parallel between the devices. Avoid using right angles when routing traces to minimize the routing distance and impedance discontinuities. For further protection from crosstalk, run guard traces beside the clock signals (GND pin to GND pin), if possible. This lessens clock signal coupling, as shown in Figure 8-33.