ISL15100 Datasheet, PDF (6/9 Pages) Intersil Corporation – Single differential driver

ISL15100
Applications Information
Product Description
The ISL15100 is a differential operational amplifier designed for
line driving in power line communications (PLC). It is a low
distortion, current mode feedback amplifier that draws
moderately low supply current. Due to the current feedback
architecture, the ISL15100 closed-loop -3dB bandwidth is
dependent on the value of the feedback resistor. The desired
bandwidth is selected by choosing the feedback resistor, R_F, and
then the gain is set by picking the gain resistor, R_G.
Feedback Resistor Values
The ISL15100 has been designed and specified with R_F = 1kΩ
for A_V = +16. As is the case with all current feedback amplifiers,
wider bandwidth at the expense of slight peaking, can be
obtained by reducing the value of the feedback resistor.
Inversely, larger values of the feedback resistor will cause rolloff
to occur at a lower frequency.
Quiescent Current vs Temperature
The ISL15100 was designed to have the quiescent current
increase with temperature, which maintains good distortion
performance at high temperatures.
Supply Voltage Range
The ISL15100 operates with bipolar supply voltages from ±4.0V
to ±6.6V (±6.65V maximum). Optimum bandwidth, slew rate,
and video characteristics are obtained at higher supply voltages.
Single Supply Operation
If a single supply is desired, values from +8.0V to +13.2V (+13.3V
maximum) can be used as long as the input common mode
range is not exceeded. When using a single supply, be sure to
either:
1. DC bias the inputs at an appropriate common mode voltage
and AC-couple the signal.
2. Ensure the driving signal is within the common mode range of
the ISL15100.
Multi-Tone Power Ratio (MTPR)
G.hn PLC uses OFDM modulation to digitally encode data for
communication. A carrier spacing of 24.41kHz is used in power
lines, and 48.82kHz is used in phone lines.
In multi-tone signaling, linearity is shown in the MTPR
measurement. MTPR measures the difference in power of a
carrier tone vs. a missing tone.
-30
-40
-50
-60
MTPR
-70
-80
-90
-100
1.50
1.52
1.54
1.56
1.58
1.60
FREQUENCY (MHz)
FIGURE 4. PLC SIGNAL TONES WITH 25kHz SPACING
Figure 4 shows ISL15100's MTPR performance for a narrow
frequency span.
Disable Linearity
Unlike DSL, communication in PLC systems is half duplex
meaning only one device can transmit at a time. When the line
driver is not transmitting, it is disabled and the receiver is
enabled. Figure 5 shows the shared transmit and receive signal
path of two ends. When Txa is transmitting, optimal MTPR is
achieved if Txb is removed. Since Txb cannot be removed, the
best MTPR occurs if the line driver is a very high impedance
when disabled.
R_BM are resistors to limit fault currents, and to provide a driving
impedance to the transformer, thus setting its frequency span.
R_BM is typically low in value (<10Ω).
FIGURE 5. Tx AND Rx SIGNAL PATH. CASE1:[Txa: ON, Rxa: OFF, Txb: OFF, Rxb: ON]. CASE2:[Txa: OFF, Rxa: ON, Txb: ON, Rxb: OFF]
6
FN8577.0
September 19, 2013