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P4080
In addition, it is recommended that there be several bulk storage capacitors distributed around the PCB,
feeding the VDD, BVDD, OVDD, CVDD, GVDD, and LVDD planes, to enable quick recharging of the smaller
chip capacitors. These bulk capacitors should have a low ESR (equivalent series resistance) rating to
ensure the quick response time necessary. They should also be connected to the power and ground
planes through two vias to minimize inductance. Suggested bulk capacitors 100-330 µF (AVX TPS
tantalum or Sanyo OSCON).
3.5 SerDes Block Power Supply Decoupling Recommendations
The SerDes block requires a clean, tightly regulated source of power (SVDD and XVDD) 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 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 ESR SMT
tantalum chip capacitor and a 100 µF, low ESR SMT tantalum chip capacitor. This should be done for
all SerDes supplies.
3.6 Connection Recommendations
To ensure reliable operation, it is highly recommended to connect unused inputs to an appropriate signal
level. All unused active low inputs should be tied to VDD, BVDD, CVDD, OVDD, GVDD, and LVDD as
required. All unused active high inputs should be connected to GND. All NC (no-connect) signals must
remain unconnected. Power and ground connections must be made to all external VDD, BVDD, CVDD,
OVDD, GVDD, LVDD, and GND pins of the device.
The Ethernet controllers 1 and/or 2 input pins may be disabled by setting their respective RCW
Configuration field EC1 (bits 360-361) to 0b11, and EC2 (bits 363–365) to 0b111 = No parallel mode
Ethernet, no USB. When disabled, these inputs do not need to be externally pulled to an appropriate
signal level.
EC_GTX_CLK125 is a 125-MHz input clock shared among all dTSEC ports. If the dTSEC ports are not
used for RGMII, the EC_GTX_CLK125 input can be tied off to GND.
If RCW field DMA1 = 0b1 (RCW bit 384), the DMA1 external interface is not enabled and the
DMA1_DDONE0 pin should be left as a no connect.
If RCW field I2C3 = 0b11 (RCW bits 369–370) is selected, the SDHC_WP and SDHC_CD input signals
are enabled for external use. If SDHC_WP and SDHC_CD are selected an not used, they must be
externally pulled low such that SDHC_WP = 0 = write enabled and SDHC_CD = 0 = card detected. If
RCW field I2C3 != 0b11, thereby selecting either I2C3 or GPIO functionality, SDHC_WP and SDHC_CD
are internally driven such that SDHC_WP = write enabled and SDHC_CD = card detected and the
selected I2C3 or GPIO external pin functionality maybe used.