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EL8401IS-T7 Datasheet(PDF) 11 Page - Intersil Corporation |
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EL8401IS-T7 Datasheet(HTML) 11 Page - Intersil Corporation |
11 / 15 page 11 FN7105.3 March 9, 2006 dissipation could easily increase such that the part will be destroyed. Maximum reliability is maintained if the output current never exceeds ±40mA. This limit is set by the design of the internal metal interconnections. Power Dissipation With the high output drive capability of the EL8200, EL8201 and EL8401, it is possible to exceed the 125 °C absolute maximum junction temperature under certain load current conditions. Therefore, it is important to calculate the maximum junction temperature for the application to determine if the load conditions or package types need to be modified for the amplifier to remain in the safe operating area. The maximum power dissipation allowed in a package is determined according to: Where: TJMAX = Maximum junction temperature TAMAX = Maximum ambient temperature θJA = Thermal resistance of the package The maximum power dissipation actually produced by an IC is the total quiescent supply current times the total power supply voltage, plus the power in the IC due to the load, or: For sourcing: For sinking: Where: VS = Total supply voltage ISMAX = Maximum quiescent supply current VOUTi = Maximum output voltage of the application for each channel RLOADi = Load resistance tied to ground for each channel ILOADi = Load current for each channel By setting the two PDMAX equations equal to each other, we can solve the output current and RLOADi to avoid the device overheat. Power Supply Bypassing and Printed Circuit Board Layout As with any high frequency device, a good printed circuit board layout is necessary for optimum performance. Lead lengths should be as sort as possible. The power supply pin must be well bypassed to reduce the risk of oscillation. For normal single supply operation, where the VS- pin is connected to the ground plane, a single 4.7µF tantalum capacitor in parallel with a 0.1µF ceramic capacitor from VS+ to GND will suffice. This same capacitor combination should be placed at each supply pin to ground if split supplies are to be used. In this case, the VS- pin becomes the negative supply rail. For good AC performance, parasitic capacitance should be kept to a minimum. Use of wire wound resistors should be avoided because of their additional series inductance. Use of sockets should also be avoided if possible. Sockets add parasitic inductance and capacitance that can result in compromised performance. Minimizing parasitic capacitance at the amplifier’s inverting input pin is very important. The feedback resistor should be placed very close to the inverting input pin. Strip line design techniques are recommended for the signal traces. Typical Applications VIDEO SYNC PULSE REMOVER Many CMOS analog to digital converters have a parasitic latch up problem when subjected to negative input voltage levels. Since the sync tip contains no useful video information and it is a negative going pulse, we can chop it off. Figure 29 shows a gain of 2 connections. Figure 30 shows the complete input video signal applied at the input, as well as the output signal with the negative going sync pulse removed. MULTIPLEXER Besides the normal power down usage, the ENABLE pin of the EL8200 can be used for multiplexing applications. Figure 31 shows two channels with the outputs tied together, driving a back terminated 75 Ω video load. A 2VP-P 2MHz sine wave is applied to Amp A and a 1VP-P 2MHz sine wave is applied to Amp B. Figure 32 shows the ENABLE signal and the resulting output waveform at VOUT. Observe the break-before-make operation of the multiplexing. Amp A is on and VIN1 is passed through to the output when the ENABLE signal is low and turns off in about 25ns when the ENABLE signal is high. About 200ns later, Amp B turns on and VIN2 is passed through to the output. The break-before- make operation ensures that more than one amplifier isn’t trying to drive the bus at the same time. PDMAX TJMAX TAMAX – θ JA --------------------------------------------- = PDMAX VS ISMAX Σ VS VOUTi – () VOUTi RLi ----------------- × + × = PDMAX VS ISMAX Σ VOUTi VS- – () I LOADi × + × = FIGURE 29. SYNC PULSE REMOVER 5V 1K VOUT VIN 75 Ω + - 75 Ω 1K 75 Ω VS+ VS- EL8200, EL8201, EL8401 |
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