EL4543 Datasheet, PDF (12/16 Pages) Intersil Corporation – Triple Differential Twisted-Pair Driver with Common-Mode Sync Encoding

EL4543
ended input RGB signals to three fully differential waveforms
with sync encoded on the discrete common modes of each
color channel and then drives the signals through a length of
CAT-5 cable. The signal is received by the EL9110, which
can provide 6-pole equalization for both high and low
frequency signal transmission line losses. Then the EL9110
converts the differential RGB video signals back into single
ended format while extracting the common mode component
for decoding. The single ended RGB signal is taken directly
from the output of the El9110 and is ready for the output
device. The Common Mode Decoder Circuit receives the
common mode signals directly from each of the three
EL9110's common mode output pin, decodes and transmits
H_SYNC and V_SYNC to the output device.
Sync Transmission
The EL4543 encodes H_SYNC and V_SYNC signals onto the
common mode output of the differential video signals; Red,
Green and Blue respectively. Data Sheet Figure 8 clearly
illustrates that the sum of the common mode voltages results
in a fixed DC level with no AC content; thus eliminating EMI
interference.
Output Drive Protection
The EL4543 has internal short circuit protection set typically
at 60mA. if the output is shorted for extended periods of time
the increased power dissipation will eventually destroy the
part. To realize maximum reliability the output current should
never exceed 60mA. The 50Ω series back load matching
resistor provides additional protection.
Supply Voltage
While the EL4543 can be operated on ±5V split rails, single
supply 0V to 5V is the most common usage. It is very
important to note that the input logic thresholds are relative
to the negative supply pin, and therefore single supply,
ground referenced logic will not work when driving the
EL4543 on split rails. The amplifiers have an input common
mode range from 0V to 3.5V with a 0V to 5V supply. The
common mode output DC level range is a linear function of
the power supply, see Data Sheet Figures 15, 16, 17 &18.
The common mode input switching threshold as well as the
Enable/Disable input is a linear function of the supply
voltage, see Data Sheet Figure 1.
Disable and Power Down
The EL4543 provides an enable disable function which
powers down, logic input high, in 900ns and powers up, logic
input low, in 212ns. Disabled the amplifiers supply current is
reduced to 1.8mA (Positive Supply) and 0mA (Negative
Supply). Note that Enable/Disable threshold is a linear
function of the supply voltage levels. The Enable/Disable
threshold voltage level is compatible with standard
TTL/CMOS and referenced to the lowest supply potential.
Proper Layout Technique
A critical concern with any PCB layout is the establishment
of a “healthy” ground plane. It is imperative to provide
ground planes terminated close to inputs to minimize input
capacitance. Additionally, the ground plane can be
selectively removed from inputs to prevent load and supply
currents from flowing near the input nodes.
In general the following guidelines apply to all PCB layout:
• Keep all traces as short as possible.
• Keep power supply bypass components as close to the
chip as possible - extremely close.
• Create a healthy ground with low impedance and
continuous ground pathways available to all grounded
components board-wide.
• In high frequency applications on multi-level boards try to
keep one level of board with continuous ground plane and
minimum via cutouts - providing it is affordable.
• Provide extremely short loops from power pin to ground.
• If it is affordable, a ferrite bead is always of benefit to
isolate device from Power Supply noise and the rest of the
circuit from the noise of the device.
Power Dissipation Calculation
When switching at high speeds, or driving heavy loads, the
EL4543 drive capability is ultimately limited by the rise in die
temperature brought about by internal power dissipation. For
reliable operation die temperature must be kept below T_JMAX
(125°C). It is necessary to calculate the power dissipation for
a given application prior to selecting package type. Power
dissipation may be calculated:
4
PD = (V_S × I_S) × Σ(C_INT × V_S2 × f) + (C_L × V_{O2 UT} × f)
1
where:
• V_S is the total power supply to the EL4543 (from V_S+ to V_S-)
• V_OUT is the swing on the output (V_H - V_L)
• C_L is the load capacitance
• C_INT is the internal load capacitance (80pF max)
• I_S is the quiescent supply current (40mA max)
• f is frequency
Having obtained the application's power dissipation, the
maximum junction temperature can be calculated:
T_JMAX = T_MAX + Θ_JA × PD
12
FN7325.5
October 26, 2005