Datasheet

LMH0395
SNLS323L –AUGUST 2010–REVISED APRIL 2013 www.ti.com
AUTO SLEEP
The auto sleep mode allows the LMH0395 to power down when no input signal is detected. If the AUTO SLEEP
pin is set high, the LMH0395 goes into a deep power save mode when no signal is detected. The device powers
on again once an input signal is detected. If the AUTO SLEEP pin is set low, the LMH0395 will always be on and
will not enter power save mode. The auto sleep functionality can be turned off by setting AUTO SLEEP low or
tying this pin to ground. An additional auto sleep setting available in SPI mode can be used to force the equalizer
to power down regardless of whether there is an input signal or not. Auto sleep has precedence over mute and
bypass modes.
In auto sleep mode, the time to power down the equalizer when the input signal is removed is less than 200 µs
and should not have any impact on the system timing requirements. The device will wake up automatically once
an input signal is detected, and the delay between signal detection and full functionality of the equalizer is
negligible (about 5 ms). The overall system will be limited only by the settling time constant of the equalizer
adaptation loop.
INPUT INTERFACING
The LMH0395 accepts either differential or single-ended input. The input must be AC coupled. The Typical
Application (Pin Mode) diagram shows the typical configuration for a single-ended input. The unused input must
be properly terminated as shown.
The LMH0395 can be optimized for different launch amplitudes via the SPI (see LAUNCH AMPLITUDE
OPTIMIZATION in the SPI Register Access section).
The LMH0395 correctly handles equalizer pathological signals for standard definition and high definition serial
digital video, as described in SMPTE RP 178 and RP 198, respectively.
OUTPUT INTERFACING
The LMH0395 dual output differential pairs, SDO0, SDO0, SDO1, and SDO1 are internally terminated 100Ω
LVDS outputs. These outputs can be DC coupled to most common differential receivers.
The default output common mode voltage (V
OS
) is 1.2V. The output common mode voltage may be adjusted via
the SPI in 200 mV increments, from 0.8V to 1.2V (see OUTPUT DRIVER ADJUSTMENTS AND DE-EMPHASIS
SETTING in the SPI Register Access section). When the output common mode is supply referenced, the
common mode voltage is about 1.35V (for 700 mV
P-P
differential swing). This adjustable output common mode
voltage offers flexibility for interfacing to many types of receivers.
The default differential output swing (V
SSP-P
) is 700 mV
P-P
. The differential output swing may be adjusted via the
SPI. Valid options are 400, 600, 700, or 800 mV
P-P
(see OUTPUT DRIVER ADJUSTMENTS AND DE-
EMPHASIS SETTING in the SPI Register Access section).
The LMH0395 output should be DC coupled to the input of the receiving device where possible. 100Ω differential
transmission lines should be used to connect between the LMH0395 outputs and the input of the receiving
device.
The LMH0395 output should not be DC coupled to CML inputs. If there are strong pullup resistors (i.e. 50Ω) at
the receiving device, AC coupling should be used. The value of these AC-coupling capacitors should be large
enough (typically 4.7 µF) to accommodate for the SD pathological video pattern.
Figure 7 shows an example of a DC-coupled interface between the LMH0395 and LMH0346 SDI reclocker. The
differential transmission line should be terminated with a 100Ω resistor at the receiving device as shown. The
resistor should be placed as close as possible to the LMH0346 input. If desired, this network may be terminated
with two 50Ω resistors and a center-tap capacitor to ground in place of the single 100Ω resistor.
Figure 8 shows an example of a DC-coupled interface between the LMH0395 and LMH0356 SDI reclocker. The
LMH0356 inputs have internal 50Ω terminations (100Ω differential) to terminate the transmission line, so no
additional components are required.
The LMH0395 output drivers are equipped with programmable output de-emphasis to minimize inter-symbol
interference caused by the loss dispersion from driving signals across PCB traces (see OUTPUT DRIVER
ADJUSTMENTS AND DE-EMPHASIS SETTING in the SPI Register Access section). De-emphasis works with
all combinations of output common mode voltage and output voltage swing settings to support DC coupling to the
receiving device.
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