LMH0384 Datasheet, PDF (11/29 Pages) National Semiconductor (TI) – 3 Gbps HD/SD SDI Extended Reach and Configurable Adaptive Cable Equalizer

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LMH0384
SNLS308G – APRIL 2009 – REVISED JUNE 2015
Feature Description (continued)
The SPI Control block uses the MOSI, MISO, SCK, and SS signals in SPI mode to control the SPI registers.
SPI_EN selects between SPI mode and pin mode. In pin mode, SPI_EN is driven logic low.
The Output Driver produces SDO and SDO.
7.3.2 Mute Reference (MUTE_REF)
The mute reference sets the threshold for CD and (with CD tied to MUTE) determines the amount of cable to
equalize before automatically muting the outputs. This is set by applying a voltage inversely proportional to the
length of cable to equalize. The applied voltage must be greater than the MUTE_REF floating voltage (typically 1.3
V) in order to change the CD threshold. As the applied MUTE_REF voltage is increased, the amount of cable that
can be equalized before carrier detect is deasserted and the outputs are muted is decreased. MUTE_REF may be
left unconnected or connected to ground for normal CD operation.
7.3.3 Carrier Detect (CD) and Mute
Carrier detect CD indicates if a valid signal is present at the LMH0384 input. If MUTE_REF is used, the carrier
detect threshold will be altered accordingly. CD provides a high voltage when no signal is present at the
LMH0384 input. CD is low when a valid input signal is detected.
MUTE can be used to manually mute or enable SDO and SDO. Applying a high input to MUTE will mute the
LMH0384 outputs by forcing the output to a logic zero. Applying a low input will force the outputs to be active.
CD and MUTE may be tied together to automatically mute the output when no input signal is present.
7.3.4 Auto Sleep
The auto sleep mode allows the LMH0384 to power down when no input signal is detected. If the AUTO SLEEP
pin is set high, the LMH0384 goes into a deep power save mode when no signal is detected. The device powers
on again once an input signal is detected. 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 (within 1 μs). The overall system will be limited only by the settling time constant of
the equalizer adaptation loop.
7.3.5 Input Interfacing
The LMH0384 accepts either differential or single-ended input. The input must be AC-coupled. Functional Block
Diagram shows the typical configuration for a single-ended input. The unused input must be properly terminated
as shown.
The LMH0384 can be optimized for different launch amplitudes through the SPI (see Launch Amplitude
Optimization in Programming).
The LMH0384 correctly handles equalizer pathological signals for standard definition and high definition serial
digital video, as described in SMPTE RP 178 and RP 198, respectively.
7.3.6 Output Interfacing
SDO and SDO together are internally terminated 100-Ω LVDS outputs. These outputs can be DC coupled to
most common differential receivers.
The default output common-mode voltage (V_OS) is 1.25 V. The output common-mode voltage may be adjusted
through the SPI in 200-mV increments, from 1.05 V to 1.85 V (see Output Driver Adjustments in Programming).
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 through
the SPI in 100 mV increments from 400 mV_P-P to 800 mV_P-P (see Output Driver Adjustments in Programming).
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