DS125BR401SQ Datasheet, PDF (12/52 Pages) Texas Instruments – Low-Power 12.5-Gbps 4-Lane Repeater With Input Equalization and Output De-Emphasis

DS125BR401
SNLS419C – JULY 2012 – REVISED APRIL 2013
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3.3V or 2.5V Supply Mode Operation
The DS125BR401 has an optional internal voltage regulator to provide the 2.5V supply to the device. In 3.3V
mode operation, the VIN pin = 3.3V is used to supply power to the device. The internal regulator will provide the
2.5V to the VDD pins of the device and a 0.1 uF cap is needed at each of the 5 VDD pins for power supply de-
coupling (total capacitance should be ≤0.5 uF), and the VDD pins should be left open. The VDD_SEL pin must
be tied to GND to enable the internal regulator. In 2.5V mode operation, the VIN pin should be left open and 2.5V
supply must be applied to the 5 VDD pins to power the device. The VDD_SEL pin must be left open (no connect)
to disable the internal regulator.
3.3V mode
2.5V mode
Enable
VDD_SEL
Internal
voltage
regulator
2.5V
VIN
VDD
VDD
VDD
3.3V
Capacitors can be
either tantalum or an
ultra-low ESR seramic.
0.1 uF
0.1 uF
0.1 uF
Disable
VDD_SEL
open
Internal
voltage
regulator
VIN
open
VDD
0.1 uF
2.5V
VDD
VDD
0.1 uF
Capacitors can be
either tantalum or an
ultra-low ESR seramic.
0.1 uF
VDD
0.1 uF
VDD
0.1 uF
VDD
0.1 uF
VDD
0.1 uF
Place 0.1 uF close to VDD Pin
Total capacitance should be 7 0.5 uF
Place capcitors close to VDD Pin
Figure 5. 3.3V or 2.5V Supply Connection Diagram
PCIe Signal Integrity
When using the DS125BR401 in PCIe GEN-3 systems, there are specific signal integrity settings to ensure
signal integrity margin. The settings were optimized by extensive testing. Please contact your field representative
for more information regarding the testing completed to achieve these settings.
For tuning the in the downstream direction (from CPU to EP).
• EQ: use the guidelines outlined in Table 2.
• De-Emphasis: use the guidelines outlined in Table 3.
• VOD: use the guidelines outlined in Table 3.
For tuning in the upstream direction (from EP to CPU).
• EQ: use the guidelines outlined in Table 2.
• De-Emphasis:
– For trace lengths < 15in set to -3.5 dB
– For trace lengths > 15in set to -6 dB
• VOD: set to 900 mV
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