QT2022/32 - Data Sheet: DS3051
Figure 20: LED Stretching for Link/activity Combined Mode
Packet
Activity
Event
25/50ms
25/50ms
LED
50/100ms
50/100ms
Note 1) : This assumes the link is up
2) : The direct drive LED output in this diagram is shown as active low
8.7 Analog Control Pins
This section describes the low-speed analog control pins on the product.
8.7.1 Loss of Signal Threshold Adjust Pin (ITH_LOS)
The ITH_LOS pin is used to set the analog loss of signal (LOS) alarm threshold. The LOS alarm includes hystere-
sis. An LOS alarm is declared when the peak-to-peak signal at the fiber receiver drops below the assert threshold
level (signal level ‘A’ in Section 50, “LOSOUTB Hysteresis,” on page 198). The LOS alarm is cleared when the
peak-to-peak signal increases above the deassert threshold level (signal level ‘B’ in Section 50, “LOSOUTB Hys-
teresis,” on page 198).
The analog LOS alarm drives the LOSOUTB signal output to indicate an alarm state. Refer to Section 8.4.2,
“Receive Loss-of-Signal Pin (LOSOUTB),” on page 69 for details. The analog LOS alarm does not perform any
other actions.
The alarm threshold is set by connecting a resistor between the pin and ground. The resistor value determines the
threshold. The hysteresis is fixed for a given alarm threshold.
The analog LOS detector is always enabled. If the pin is left open (no resistor to ground) the LOS detector will
never assert.
Please consult AMCCs’ Application Note “Implementing LOS for the QT2022/QT2032” for more information on
design practices with the LOS feature.
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