DS125BR820 Datasheet, PDF (40/62 Pages) Texas Instruments – Low-Power 12.5 Gbps 8-Channel Linear Repeater

DS125BR820
SNLS491B – JULY 2014 – REVISED FEBRUARY 2015
8 Applications and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.1.1 Signal Integrity in 40G-CR4/KR4/SAS/SATA/PCIe Applications
In 40G-CR4/KR4/SAS/SATA/PCIe applications, specifications require Rx-Tx link training to establish and
optimize signal conditioning settings for data rates up to 12.5 Gbps. In link training, the Rx partner requests a
series of FIR coefficients from the Tx partner at speed. This polling sequence is designed to pre-condition the
signal path with an optimized link between the endpoints. Link training occurs at the following data-rates:
PROTOCOL ⁽¹⁾
40G-CR4
40G-KR4
SAS-3
PCIe Gen-3
Table 10. Link Training Data-Rates
OPERATING DATA RATE (Gbps)
10.3125
10.3125
12.0
8.0
(1) There is no link training with Tx FIR coefficients for the respective lower generation data rates.
The DS125BR820 works to extend the reach possible by using active linear equalization to the channel, boosting
attenuated signals so that they can be more easily recovered at the Rx. The repeater outputs are specially
designed to be transparent to Tx FIR signaling in order to pass information critical for optimal link training to the
Rx. Suggested settings for the A-channels and B-channels are given in Table 11 and Table 12. Further
adjustments to EQx and VODx settings may optimize signal margin on the link for different system applications:
Table 11. Suggested Device Settings in Pin Mode
CHANNEL SETTINGS
EQx
VODx[1:0]
PIN MODE
Level 1
Level 6 (1, 0)
Table 12. Suggested Device Settings in SMBus Modes
CHANNEL SETTINGS
EQx
VODx
VOD_DB
SMBus MODES
0x00
110'b
000'b
The SMBus Slave Mode code example in Table 13 may be used to program the DS125BR820 with the
recommended device settings.
REGISTER
0x06
0x0F
0x10
0x11
0x16
0x17
WRITE VALUE
0x18
0x00
0xAE
0x00
0x00
0xAE
Table 13. SMBus Example Sequence
COMMENTS
Set SMBus Slave Mode Register Enable.
Set CHB_0 EQ to 0x00.
Set CHB_0 VOD to 110'b.
Set CHB_0 VOD_DB to 000'b.
Set CHB_1 EQ to 0x00.
Set CHB_1 VOD to 110'b.
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