VSC8641XKO Vitesse Semiconductor Corp, VSC8641XKO Datasheet - Page 122

• Manufacturer Part Number: VSC8641XKO
• Description: IC PHY 10/100/1000 100-LQFP
• Manufacturer: Vitesse Semiconductor Corp
• Type: PHY Transceiverr

Specifications of VSC8641XKO

• Number Of Drivers/receivers: 1/1
• Protocol: Gigabit Ethernet
• Voltage - Supply: 2.5V, 3.3V
• Mounting Type: Surface Mount
• Package / Case: 100-LQFP
• Case: TQFP
• Dc: 07+
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 907-1031

8.7
8.8
8.9
Revision 4.3
August 2009
10BASE-T Harmonics at 30 MHz and 50 MHz
Marginally Violate Specification
Issue: The IEEE 802.3 specification states that in 10BASE-T mode, when the DO circuit
is driven by an all-ones, Manchester-encoded signal, any harmonic measured on the TD
circuit must be at least 27 dB below the fundamental. In VSC8641, this specification is
marginally violated at 30 MHz and 50 MHz when this measurement is made under
corner conditions. Under nominal conditions, this measurement meets the IEEE
specification limits.
Implications: This violation has no practical implication on the performance of the
device. 10BASE-T mode has been validated to work without any issues with cables far
exceeding the IEEE-specified, worst-case limits.
Workaround: None required.
Voltage Overshoot When Using On-Chip Switching
Regulator
Issue: The device’s on-chip switching regulator generates notable voltage overshoot.
Implications: The voltage overshoot from the on-chip switching regulator may lead to
device performance issues such as CRC errors, jitter, or both.
Workaround: When using the on-chip regulator, dampen the overshoot by adding a
snubber circuit on the output of the regulator pins (REG_OUT). This circuit consists of a
15 Ω resistor and 0.001 µF capacitor connected in series to the REG_OUT pins and
ground. For more information about the regulator circuitry connection, see VSC8641
Design and Layout Guide, which is available on the Vitesse Web site at
www.vitesse.com.
Long Link-Up Times Caused by Noise on the
Twisted Pair Interface
Issue: The VSC8641 may experience longer link-up times during the link-up
auto-negotiation process when there is signal noise coming from the link partner on the
other side of a cable.
Implications: Normally, the VSC8641 device successfully links during auto-negotiation
when there is signal noise coming from the link partner. However, on rare occasions
when the VSC8641 device uses the same cable as the link partner, the link-up time can
be significantly increased for successful auto-negotiation.
Workaround: During device initialization, it is strongly recommended that the following
software script is implemented. For more information, see PHY API Software and
Programmers Guide, which is available on the Vitesse Web site at www.vitesse.com.
PhyWrite (PortNo, reg_num(dec), 16_bit_unsigned_data(hex))
PhyRead (PortNo, reg_num(dec))
~ -- Logical NOT
& -- Logical AND
Design Considerations
VSC8641 Datasheet
Page 122