MPC8313CVRAFD datasheet(90/100 Pages) FREESCALE

90 / 100 page

MPC8313E PowerQUICC™ II Pro Processor Hardware Specifications, Rev. 2.1

Freescale Semiconductor

System Design Information

22.4

SerDes Block Power Supply Decoupling Recommendations

The SerDes block requires a clean, tightly regulated source of power (XCOREVDD and XPADVDD) to

ensure low jitter on transmit and reliable recovery of data in the receiver. An appropriate decoupling

scheme is outlined below.

Only SMT capacitors should be used to minimize inductance. Connections from all capacitors to power

and ground should be done with multiple vias to further reduce inductance.

•

First, the board should have at least 10

× 10-nF SMT ceramic chip capacitors as close as possible

to the supply balls of the device. Where the board has blind vias, these capacitors should be placed

directly below the chip supply and ground connections. Where the board does not have blind vias,

these capacitors should be placed in a ring around the device as close to the supply and ground

connections as possible.

•

Second, there should be a 1-µF ceramic chip capacitor from each SerDes supply (XCOREVDD and

XPADVDD) to the board ground plane on each side of the device. This should be done for all

SerDes supplies.

•

Third, between the device and any SerDes voltage regulator there should be a 10-µF, low

equivalent series resistance (ESR) SMT tantalum chip capacitor and a 100-µF, low ESR SMT

tantalum chip capacitor. This should be done for all SerDes supplies.

22.5

Connection Recommendations

To ensure reliable operation, it is highly recommended to connect unused inputs to an appropriate signal

level. Unused active low inputs should be tied to NVDD, GVDD, LVDD, LVDDA, or LVDDB as required.

Unused active high inputs should be connected to VSS. All NC (no-connect) signals must remain

unconnected.

Power and ground connections must be made to all external VDD, NVDD, GVDD, LVDD, LVDDA, LVDDB,

and VSS pins of the device.

22.6

Output Buffer DC Impedance

The MPC8313E drivers are characterized over process, voltage, and temperature. For all buses, the driver

is a push-pull single-ended driver type (open drain for I2C).

To measure Z0 for the single-ended drivers, an external resistor is connected from the chip pad to NVDD

or VSS. Then, the value of each resistor is varied until the pad voltage is NVDD/2 (see Figure 60). The

output impedance is the average of two components, the resistances of the pull-up and pull-down devices.

When data is held high, SW1 is closed (SW2 is open), and RP is trimmed until the voltage at the pad equals

NVDD/2. RP then becomes the resistance of the pull-up devices. RP and RN are designed to be close to each

other in value. Then, Z0 = (RP + RN)/2.

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