LMH0384 Datasheet, PDF (11/16 Pages) National Semiconductor (TI) – 3 Gbps HD/SD SDI Extended Reach and Configurable Adaptive Cable Equalizer

Application Information
APPLICATION CIRCUIT (SPI MODE)
Figure 8 shows the application circuit for the LMH0384 in SPI
mode.
FIGURE 8. Application Circuit (SPI Mode)
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REPLACING THE LMH0344
In pin mode, the LMH0384 is a drop-in replacement for the
LMH0344SQ SDI cable equalizer. When replacing an
LMH0344 with an LMH0384, it is important to consider the
following points:
1. The LMH0384 auto sleep function is mapped to pin 12
which is a ground pin on the LMH0344SQ. When this pin
is grounded on the LMH0384, the auto sleep function is
disabled. To enable auto sleep mode on the LMH0384,
pin 12 must be pulled high.
2. Pin 4 and pin 9 on the LMH0344SQ are true ground pins.
For the LMH0384, pin 4 and pin 9 may be driven logic
low in pin mode (they do not require a true ground
connection).
3. The LMH0384 has lower input capacitance than the
LMH0344 which allows for improved input return loss.
The input return loss network may need to be modified.
In most cases, the LMH0384 should provide superior
input return loss.
4. The LMH0384 default output common mode voltage is
different than that of the LMH0344. In most cases, this
should not cause an issue. The LMH0384 and LMH0344
outputs can both be DC coupled to National's SDI
reclockers and cable drivers. In addition, the LMH0384
output can be DC coupled to LVDS and other inputs that
require lower input common mode voltages than the
LMH0344. The LMH0384 output common mode voltage
is adjustable via the SPI.
PCB LAYOUT RECOMMENDATIONS
For information on layout and soldering of the LLP package,
pease refer to the following application note: AN-1187,
“Leadless Leadframe Package (LLP).”
The SMPTE 424M, 292M, and 259M standards have strin-
gent requirements for the input return loss of receivers, which
essentially specify how closely the input must resemble a
75Ω network. Any non-idealities in the network between the
BNC and the equalizer will degrade the input return loss. Care
must be taken to minimize impedance discontinuities be-
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