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EL5485 Datasheet(PDF) 9 Page - Intersil Corporation |
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EL5485 Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 9 page 9 All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see www.intersil.com R3 adds a portion of the output to the positive input. Note that the current through R3 should be much greater than the input bias current in order to minimize errors. The calculation of the resistor values as follows: Pick the value of R1. R1 should be small (less than 1kΩ) in order to minimize the propagation delay time. Choose the hysteresis VH and calculate R3: Check the current through R3 and make sure that it is much greater than the input bias current as follows: The above two methods will generate hysteresis of up to a few hundred millivolts. Beyond that, the impedance of R3 is low enough to affect the bias string and adjustment of R1 may be required. Power Dissipation When switching at high speeds, the comparator's drive capability is limited by the rise in junction temperature caused by the internal power dissipation. For reliable operation, the junction temperature must be kept below TJMAX (125°C). An approximate equation for the device power dissipation is as follows. Assume the power dissipation in the load is very small: where: VS is the analog supply voltage from VS+ to VS- IS is the analog quiescent supply current per comparator VSD is the digital supply voltage from VSD to ground ISD is the digital supply current per comparator N is the number of comparators in the package ISD strongly depends on the input switching frequency. Please refer to the performance curve to choose the input driving frequency. Having obtained the power dissipation, the maximum junction temperature can be determined as follows: where: TMAX is the maximum ambient temperature θJA is the thermal resistance of the package Threshold Detector The inverting input is connected to a reference voltage and the non-inverting input is connected to the input. As the input passes the VREF threshold, the comparator's output changes state. The non-inverting and inverting inputs may be reversed. Crystal Oscillator A simple crystal oscillator using one comparator of an EL5485 and EL5486 is shown below. The resistors R1 and R2 set the bias point at the comparator's non-inverting input. Resistors R3, R4, and C1 set the inverting input node at an appropriate DC average voltage based on the output. The crystal's path provides resonant positive feedback and stable oscillation occurs. Although the EL5485 and EL5486 will give the correct logic output when an input is outside the common mode range, additional delays may occur when it is so operated. Therefore, the DC bias voltages at the inputs are set about 500mV below the center of the common mode range and the 200 Ω resistor attenuates the feedback to the non-inverting input. The circuit will operate with most AT-cut crystal from 1MHz to 8MHz over a 2V to 7V supply range. The output duty cycle for this circuit is roughly 50% at 5V VCC, but it is affected by the tolerances of the resistors. The duty cycle can be adjusted by changing VCC value. R 3 V ( SD 0.8 ) R 1 V H -------- × – = I 0.5V SD V REF – R 3 ------------------------------------------ = P DISS V S I S V SD I SD ) × + × N × ( = T JMAX T MAX Θ JA P DISS × + = + - VIN VREF VOUT + - 200 Ω VOUT R4 R3 5V 1MHz to 8MHz 2k Ω C1 0.01µF 5k Ω 1.5k Ω 2k Ω R1 R2 EL5485, EL5486 |
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Similar Description - EL5485 |
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