DS50PCI402_14 Datasheet, PDF (8/35 Pages) Texas Instruments – 2.5 Gbps / 5.0 Gbps 4 Lane PCI Express Repeater with Equalization and De-Emphasis

DS50PCI402
SNLS320G – APRIL 2010 – REVISED MAY 2011
www.ti.com
Receiver Detection
The Rx detection process is a feature that can set the number of active channels on the DS50PCI402. By
sensing the presence of a valid PCIe load on the output, the channel can be automatically enabled for operation.
This allows the DS50PCI402 to configure inself to the proper lane width, whether it is a 4-lane, 2-lane, or 1-lane
PCIe link.
Automatic Rx Detection is enabled by a combination of PRSNT# and ENRXDET inputs. When these inputs are
set low, Automatic Rx Detection is enabled, cycling of the PRSNT# pin will reset the Rx detection circuitry,
initiating a new receiver detection sequence. Pulling the ENRXDET input to logic 1, allows for manual control of
the input termination.
The table below summarizes control pin and receiver detect operation for the DS50PCI402.
PRSNT#
0
0
0
0
1
Table 7. Receiver Detect Pins for A and B ports (LVCMOS inputs)
ENRXDET RXDETA/B
0
0
Input
Termination
>50KΩ to VDD
50Ω
0
1
>50KΩ to VDD
50Ω
1
0
>50KΩ to VDD
1
1
50Ω
X
X
>50KΩ to VDD
Termination sensed on
Output
Hi - Z
PCIe Input
Hi - Z
PCIe Input
X
X
X
Function
Automatic RXDET: Rx detection state machine
enabled. Outputs will test for the presence of a
receiver input every 12 msec until detection
occurs. Input termination remains >50KΩ to
VDD until receiver is detected. Once receiver is
detected, input impedance to VDD is 50Ω.
Automatic RXDET: Rx detection state machine
enabled. Outputs will test for the presence of a
receiver input every 12 msec for 600 msec and
then stop. Input termination remains >50KΩ to
VDD until receiver is detected. Once receiver is
detected, input impedance to VDD is 50Ω.
Restart detection if RXDETA/B is pulsed low-
high.
Manual RXDET: Rx detection state machine
disabled. Input termination >50KΩ. Associated
output channels in low power idle mode.
Manual RXDET: Rx detection state machine
disabled. Input termination 50Ω. Associated
output channels set to active.
Power down mode: Input termination >50KΩ.
Associated output channels off. Part in power
saving mode. PRSNT# should be held high for
a minimum of 5 us to ensure complete analog
power down. The Automatic RXDET
functionality will be re-initialized on the falling
edge of PRSNT#.
RX Detect: Range of Operation
The Rx detection process used in the DS50PCI402 is designed to be fully compliant with the PCIe 2.0 base
specification. The receiver detection circuitry will accurately detect a receiver when both conditions listed below
are true:
• DS50PCI402 within Recommended Operating Range for Temperature and Supply Voltage
• For receiver Z_RX-DC = 40 (min) to 60 (max) Ohms
Note: To ensure robust system operation, the DS50PCI402 will only signal a valid receiver detection if both
halves of the differential output pair detect a proper 40 - 60 Ohm receiver impedance. If the receiver detection
circuitry senses a load impedance greater than Z_RX-DC on either trace of a differential pair, it will be interpreted as
no termination load present (i.e. the corresponding DS50PCI402 input termination will remain High-Z).
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