LMH0024_09 Datasheet, PDF (5/8 Pages) National Semiconductor (TI) – 3.3V SMPTE 259M / 344M Adaptive Cable Equalizer

Block Diagram
Device Operation
BLOCK DESCRIPTION
The Equalizer Filter block is a multi-stage adaptive filter. If
Bypass is high, the equalizer filter is disabled.
The DC Restoration / Level Control block receives the dif-
ferential signals from the equalizer filter block. This block
incorporates a self-biasing DC restoration circuit to fully DC
restore the signals. If Bypass is high, this function is disabled.
The signals before and after the DC Restoration / Level Con-
trol block are used to generate the Automatic Equalization
Control (AEC) signal. This control signal sets the gain and
bandwidth of the equalizer filter. The loop response in the
AEC block is controlled by an external 1µF capacitor placed
across the AEC+ and AEC- pins. Cable Length Indicator
(CLI) is derived from this block.
The Output Driver produces SDO and SDO. SDO and
SDO may be forced to mute by activating MUTE.
CABLE LENGTH INDICATOR (CLI)
The cable length indicator provides a voltage to indicate the
length of cable being equalized. The CLI voltage decreases
as the cable length increases.
MUTE
MUTE can be used to manually mute or enable the LMH0024
outputs. MUTE must be tied to a low-level input or ground for
SDO and SDO to be active. Applying a high input to MUTE
will mute the LMH0024 outputs.
20172502
INPUT INTERFACING
The LMH0024 accepts either differential or single-ended in-
put. The input must be AC coupled. Transformer coupling is
not supported.
The LMH0024 correctly handles equalizer pathological sig-
nals for standard definition serial digital video, as described
in SMPTE RP 178.
OUTPUT INTERFACING
The SDO and SDO outputs are internally loaded with 50Ω.
They produce a 750 mV_P-P differential output, or a
375 mV_P-P single-ended output.
Application Information
PCB LAYOUT RECOMMENDATIONS
Please refer to the following Application Note for the CLC034
on National's website: AN-1372, “LMH0034 PCB Layout
Techniques.” The PCB layout techniques in this application
note apply to the LMH0024 as well.
REPLACING THE GENNUM GS9064
The LMH0024 is footprint compatible with the Gennum
GS9064. Pin 16 (MUTE) of the LMH0024 must be connect to
ground for correct operation.
SUPPLY CURRENT VS. CABLE LENGTH
The supply current (I_CC) depends on the amount of cable be-
ing equalized. The current is highest for short cable and
decreases as the cable length is increased. Figure 1 shows
supply current vs. Belden 1694A cable length for 270 Mbps
data.
5
www.national.com