DS80PCI402_15 Datasheet, PDF (14/54 Pages) Texas Instruments – 2.5-Gbps / 5.0-Gbps / 8.0-Gbps 4-Lane PCI-Express Repeater With Equalization and De-Emphasis

DS80PCI402
SNLS324E – APRIL 2011 – REVISED JANUARY 2015
www.ti.com
8.3 Feature Description
8.3.1 4-Level Input Configuration Guidelines
The 4-level input pins use a resistor divider to help set the four valid levels. There is an internal 30-kΩ pullup and
a 60-kΩ pulldown connected to the package pin. These resistors, together with the external resistor connection
combine to achieve the desired voltage level. Using the 1-kΩ pullup, 1-kΩ pulldown, no connect, or 20-kΩ
pulldown provide the optimal voltage levels for each of the four input states.
LEVEL
0
R
F
1
SETTING
1 kΩ to GND
20 kΩ to GND
FLOAT
1 kΩ to V_DD/V_IN
Table 1. 4-Level Input Voltage
3.3-V MODE
0.1 V
0.33 × V_IN
0.67 × V_IN
V_IN – 0.05 V
2.5-V MODE
0.08 V
0.33 × V_DD
0.67 × V_DD
V_DD – 0.04 V
Typical 4-level input thresholds:
• Level 1 to 2 = 0.2 V_IN or V_DD
• Level 2 to 3 = 0.5 V_IN or V_DD
• Level 3 to 4 = 0.8 V_IN or V_DD
To minimize the start-up current associated with the integrated 2.5-V regulator, the 1-kΩ pullup and pulldown
resistors are recommended. If several 4-level inputs require the same setting, it is possible to combine two or
more 1-kΩ resistors into a single lower value resistor. As an example; combining two inputs with a single 500-Ω
resistor is a good way to save board space. For the 20 kΩ to GND, this should also scale to 10 kΩ.
Table 2. Equalizer Settings⁽¹⁾
LEVEL
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
EQA1
EQB1
0
0
0
0
R
R
R
R
Float
Float
Float
Float
1
1
1
1
EQA0
EQB0
0
R
Float
1
0
R
Float
1
0
R
Float
1
0
R
Float
1
EQUALIZATION BOOST RELATIVE TO DC
EQ – 8 BITS [7:0]
dB at
dB at
1.25 GHz 2.5 GHz
dB at
4 GHz
0000 0000 = 0x00
2.1
3.7
4.9
0000 0001 = 0x01
3.4
5.8
7.9
0000 0010 = 0x02
4.8
7.7
9.9
0000 0011 = 0x03
5.9
8.9
11.0
0000 0111 = 0x07
7.2
11.2
14.3
0001 0101 = 0x15
6.1
11.4
14.6
0000 1011 = 0x0B
8.8
13.5
17.0
0000 1111 = 0x0F
10.2
15.0
18.5
0101 0101 = 0x55
7.5
12.8
18.0
0001 1111 = 0x1F
11.4
17.4
22.0
0010 1111 = 0x2F
13.0
19.7
24.4
0011 1111 = 0x3F
14.2
21.1
25.8
1010 1010 = 0xAA
13.8
21.7
27.4
0111 1111 = 0x7F
15.6
23.5
29.0
1011 1111 = 0xBF
17.2
25.8
31.4
1111 1111 = 0xFF
18.4
27.3
32.7
SUGGESTED USE
FR4 < 5 inch trace
FR4 5 inch 5–mil trace
FR4 5 inch 4–mil trace
FR4 10 inch 5–mil trace
FR4 10 inch 4–mil trace
FR4 15 inch 4–mil trace
FR4 20 inch 4–mil trace
FR4 25 to 30 inch 4–mil trace
FR4 30 inch 4–mil trace
FR4 35 inch 4–mil trace
10 m, 30-awg cable
10 m – 12m cable
(1) The suggested equalizer CTLE settings are based on 0 dB of TX preshoot/de-emphasis. In PCIe Gen 3 applications which use TX
preshoot/de-emphasis, the CTLE should be set to a lower boost setting to optimize the RX eye opening.
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