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EL6201CWZ-T7A Datasheet(PDF) 7 Page - Intersil Corporation |
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EL6201CWZ-T7A Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 10 page 7 FN7216.3 August 2, 2007 waveform is a squarewave, and inductive loads can cause as much as 1V of overshoot. This does not mean that the current delivered to the diode has overshoot - just the voltage seen at the EL6201 output. Measurements show that the EL6201 output edge rate is about 300psec - a speed nearly impossible to deliver over practical interconnects to the diode. General Considerations EMI and Grounding From an EMI point of view, the edge rate of the output current is much more important than that of the output voltage. The components are generally small and will be placed over a ground plane, so antenna effects that launch voltage-mode EMI are small. Measurement shows that a practical current edge rate is about 1ns, so interconnect should be over a ground plane and short to minimize inductively launched EMI. Most EMI seems to come from the supply wires connected to the diode/EL6201 board. The internal resistance and inductance of capacitors prevents perfect bypass action, and 150mVP-P noise on the lines is common. There needs to be a lossy series inductance and secondary bypass on the supply side to control signals from propagating down the wires. Alternatively, a series supply resistor can be used, which will also be useful in reducing EL6201 power dissipation. Figure 22 shows the typical connection. The L Series of Figure 22 must be carefully chosen. The goal is to get a series reactance of around 70 Ω at 300MHz, so 40nH would suffice. The inductor should be shielded to reduce EMI and have no saturation effects at the supply currents drawn by the EL6201. Finally, there should be no self-resonance at the operating frequency or its harmonics. Also important is circuit-board layout. At the EL6201’s operating frequencies, even the ground plane is not low- impedance, and ground loops should be avoided. Figure 23 shows the output current loops: For the sourcing current loop, the current flows through the supply bypass capacitor. The ground end of the bypass thus should be connected directly to the EL6201 ground pin (output ground pin of the 8 Ld package). A long ground return path will cause the bypass capacitor currents to generate voltage drops in the ground plane of the circuit board, and other components (such as RAMP and RFREQ) will pick this up as an interfering signal. Similarly, the ground return of the load should be considered as noisy and other grounded components should not connect to this path. Slotting the ground plane around the load’s return will eliminate adjacent grounded components from seeing the noise. RFREQ and RAMP Interfaces RAMP and RFREQ should be connected to the non-load side of the power ground to avoid noise pick-up. Figure 24 shows an equivalent circuit of these pins. VREF is roughly 0.35V for RFREQ and more accurately 1.17V for RAMP. The RAMP and RFREQ resistor should return to the EL6201’s ground very directly lest they pick up high- frequency noise interference. They also should have minimal capacitance to ground. Trimmer resistors can be FIGURE 21. OUTPUT CURRENT WAVEFORM - 1GHz BANDWIDTH +5V VS L Series: 70 Ω reactance at 300MHz (see text) 0.1µF Chip EL6201 GND 0.1µF Chip FIGURE 22. RECOMMENDED SUPPLY BYPASSING SINKING CURRENT LOOP SOURCING CURRENT LOOP SUPPLY BYPASS LOAD RFREQ RAMP GND (8 Ld PACKAGE) FIGURE 23. OUTPUT CURRENT LOOPS EL6201 |
Similar Part No. - EL6201CWZ-T7A |
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Similar Description - EL6201CWZ-T7A |
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