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ISL1550IRZ-T13 Datenblatt(PDF) 11 Page - Intersil Corporation |
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ISL1550IRZ-T13 Datenblatt(HTML) 11 Page - Intersil Corporation |
11 / 13 page ISL1550 11 FN6795.0 March 16, 2012 Applications Information Product Description The ISL1550 is a dual operational amplifier designed for line driving in DMT VDSL2 8MHz, 12MHz, 17MHz and 30MHz bandplans solutions. It is a current mode feedback amplifier with low distortion drawing moderately low supply current. Due to the current feedback architecture, the ISL1550 closed-loop 3dB bandwidth is dependent on the value of the feedback resistor. First, the desired bandwidth is selected by choosing the feedback resistor, RF, and then the gain is set by picking the gain resistor, RG (Figure 3). VDSL CO Applications The ISL1550 is designed as a VDSL line driver for CO. At an output current of ±450mA, the typical supply voltage headroom is 1.5V on each side of the differential output. The average line power requirement for the VDSL CO application is 20dBm (100mW) into a 100 Ω line. The average line voltage is 3.16VRMS. The VDSL DMT peak-to-average ratio (crest factor) of 5.3 implies peak voltage of 16.8VP into the line. Using a differential drive configuration and transformer coupling with standard back termination, a transformer ratio of 1:2.5 is selected. The active termination technique provides better power efficiency by reducing the backmatch resistor by a factor of K = 5. Positive feedback resistors, RP, can be sized to make the effective backmatch impedance larger. The circuit configuration is shown in Figure 35. Power Supply Bypassing and Printed Circuit Board Layout As with any high frequency device, good printed circuit board layout is necessary for optimum performance. Ground plane construction is highly recommended. Lead lengths should be as short as possible (below 0.25”). The power supply pins must be well bypassed to reduce the risk of oscillation. A 4.7µF tantalum capacitor in parallel with a 0.1µF ceramic capacitor is adequate for each supply pin. During power-up, it is necessary to limit the slew rate of the rising power supply to less than 1V/µs. If the power supply rising time is undetermined, a series 10 Ω resistor on the power supply line before the decoupling caps can be used to ensure the proper power supply rise time. For good AC performance, parasitic capacitances should be kept to a minimum, especially at the inverting input. This implies keeping the ground plane away from this pin. Carbon or metal film resistors are acceptable, while use of wire-wound resistors should be avoided because of their parasitic inductance. Similarly, capacitors should be low inductance for best performance. Capacitance at the Inverting Input Due to the topology of the current feedback amplifier, stray capacitance at the inverting input will affect the AC and transient performance of the ISL1550 when operating in the non-inverting configuration. Feedback Resistor Values The ISL1550 has been designed and specified with RF =1.5kΩ for AV = +5 (Figure 3). 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 ISL1550 was designed to slightly increase quiescent current with temperature to maintain good distortion performance at high temperatures. Refer to “Typical Performance Curves” beginning on page 5. Supply Voltage Range The ISL1550 has been designed to operate with supply voltages from ±4.0V to ±6.6V nominal. 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 nominal 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, or 2. Ensure the driving signal is within the common mode range of the ISL1550. - + - + TX1 1:2.5 12.5/k 12.5/k 1.5k Ω AFE 100 FIGURE 35. CIRCUIT CONFIGURATION RP Ω RP 750 Ω 750 Ω RP = RF(K/(K-1)) |
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Ähnliche Beschreibung - ISL1550IRZ-T13 |
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