Datasheet

SN65LVPE504
SLLSE46 –SEPTEMBER 2010 www.ti.com
DEVICE OPERATION
Device PowerOn
Device initiates internal power-on reset after Vcc has stabilized. External reset can also be applied at anytime by
toggling RST pin. External reset is recommended after every device power-up. After 50µs (MAX) from the
application of RST, device samples the state of EN_RXD, if it is set H device will enter Rx.Detect state where
each of the four channels will perform Rx.Detect function (as described in PCIe spec). If EN_RXD is set L,
automatic RX detect function is disabled and all channels are enabled with their termination set to Z
RX_DC
.
Receiver Detection
While EN_RXD pin is H and device is not in reset state (RST is H), LVPE504 performs RX.Detect on all its 4
channels indefinitely until remote termination is detected on at least one channel. When termination is detected
on ≥ 1 CH, RX.Detect cycle is limited to 5 more tries on the other channels. At the end of 5
th
try those channels
which failed to detect remote termination will be turned off to save power and their Rx termination is set to
Z
RX-HIGH
. In the event device detects only three channels, all four channels are enabled.
Automatic Rx detection feature on all four channels can be forced off by driving EN_RXD low. In this state all
four channels input termination are set to Z
RX_DC
.
Standby Mode
This is low power state triggered by RST = L. In standby mode receiver termination resistor for each of the four
channels is switched to Z
RX-HIGH
of >50 kΩ and transmitters are pulled to Hi-Z state. Device power is reduced to
<10mW (TYP). To get device out of standby mode RST is toggled L-H.
Electrical Idle Support
A link is in an electrical idle state when the TX± voltage is held at a steady constant value like the common mode
voltage. LVPE504 detects an electrical idle state when RX± input voltage of the associated channel falls below
V
EID_TH
min and stays in this state for at least 20ns. After detection of an electrical idle state in a given channel
the device asserts electrical idle state in its corresponding TX. When RX± voltage exceeds V
EID_TH
max, normal
operation is restored and output start passing input signal. Electrical idle exit and entry time is specified at < 8 ns
(MAX).
Electrical idle support is independent for each channel, however to lower active power it is possible to slave
electrical idle function from channel 1 to CH2-CH4. This mode is selected by driving PS2 to H.
Power Save Features
Device supports three power save modes as below:
1. Standby Mode
This mode can be enabled from any state (Rx detect or active) by driving RST L. In this state all 4 channels
have their termination set to Z
RX-HIGH
and outputs are at Hi-Z. Device power is 10mW (MAX).
2. Auto Low Power Mode
This mode is enabled when PS1 pin is tied H and device has been in active mode, i.e., past Rx detect state
for >250ms (TYP). In this mode anytime Vin
diff_p-p
falls below selected V
EID_TH
for a given channel and stays
below V
EID_TH
for >1µs, the associated CH enters auto low power (ALP) mode where power/CH is reduced
by >80% of normal operating power/CH. A CH will exit ALP mode whenever Vin
diff_p-p
exceeds max V
EID_TH
for that channel. Exit latency from ALP state is 30ns max. To use this mode link latency will need to account
for the ALP exit time for N_FTS. ALP mode is handled by each channel independently based on its input
differential signal level, unless slave mode is activated (PS2=H) when CH1 controls SQ detect of other
channels based on its signal level.
3. Slave Power Mode
This mode is activated by driving PS2 high. Under normal operation squelch detection is handled by each
channel independently. In slave mode SQ detection for CH2, CH3 and CH4 are turned off and squelch
function is slaved to that of CH1. By turning off squelch detection circuitry for three of the four channels
device saves power. To use this feature user must ensure all channels operate simultaneously
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