EL1508CL Intersil, EL1508CL Datasheet - Page 16

• Manufacturer Part Number: EL1508CL
• Description: IC LINE DRIVER ADSL 24-QFN
• Manufacturer: Intersil
• Type: Driverr

Specifications of EL1508CL

• Number Of Drivers/receivers: 1/0
• Voltage - Supply: 5 V ~ 12 V
• Mounting Type: Surface Mount
• Package / Case: 24-VQFN Exposed Pad, 24-HVQFN, 24-SQFN, 24-DHVQFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Protocol: -

current-limit mechanism. This allows safely driving rms
sinusoidal currents of 2 x 100mA, or 200mA. This current is
more than that required to drive line impedances to large
output levels, but output short circuits cannot be tolerated.
The series output resistor will usually limit currents to safe
values in the event of line shorts. Driving lines with no series
resistor is a serious hazard.
The amplifiers are sensitive to capacitive loading. More than
25pF will cause peaking of the frequency response. The
same is true of badly terminated lines connected without a
series matching resistor.
Output AC Coupling
When in power-down mode, several volts of differential
voltage may appear across the line driver outputs. If DC
current path exists between the two outputs, large DC
current can flow from the positive supply rail to the negative
supply rail through the outputs. To avoid DC current flow, the
most effective solution is to place DC blocking capacitors in
series at the outputs, as shown by the 0.22µF capacitors in
Figure 44.
Power Supplies
The power supplies should be well bypassed close to the
EL1508. A 2.2µF tantalum capacitor and a 0.1µF ceramic
capacitor for each supply works well. Since the load currents
are differential, they should not travel through the board
copper and set up ground loops that can return to amplifier
inputs. Due to the class AB output stage design, these
currents have heavy harmonic content. If the ground
terminal of the positive and negative bypass capacitors are
connected to each other directly and then returned to circuit
ground, no such ground loops will occur. This scheme is
employed in the layout of the EL1508 demonstration board,
and documentation can be obtained from the factory.
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16
EL1508
Single Supply Operation
The EL1508 can also be powered from a single supply
voltage. When operating in this mode, the GND pins can still
be connected directly to GND. To calculate power
dissipation, the equations in the previous section should be
used, with V
Feedback Resistor Value
The bandwidth and peaking of the amplifiers varies with
supply voltage somewhat and with gain settings. The
feedback resistor values can be adjusted to produce an
optimal frequency response. Here is a series of resistor
values that produce an optimal driver frequency response
(1dB peaking) for different supply voltages and gains:
TABLE 2. OPTIMUM DRIVER FEEDBACK RESISTOR FOR
VOLTAGE
SUPPLY
±12V
±5V
S
VARIOUS GAINS AND SUPPLY VOLTAGES
equal to half the supply rail.
3.5k
3.5k
2.5
DRIVER VOLTAGE GAIN
3.25k
3.25k
5
March 26, 2007
10
3k
3k
FN7014.5