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MIC4420CN Datasheet(PDF) 8 Page - Micrel Semiconductor |
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MIC4420CN Datasheet(HTML) 8 Page - Micrel Semiconductor |
8 / 10 page April 1998 5-39 MIC4420/4429 Micrel 5 Table 1: MIC4429 Maximum Operating Frequency VS Max Frequency 18V 500kHz 15V 700kHz 10V 1.6MHz Conditions: 1. DIP Package ( θJA = 130°C/W) 2. TA = 25°C 3. CL = 2500pF Input Stage The input voltage level of the 4429 changes the quiescent supply current. The N channel MOSFET input stage tran- sistor drives a 450 µA current source load. With a logic “1” input, the maximum quiescent supply current is 450 µA. Logic “0” input level signals reduce quiescent current to 55 µA maximum. The MIC4420/4429 input is designed to provide 300mV of hysteresis. This provides clean transitions, reduces noise sensitivity, and minimizes output stage current spiking when changing states. Input voltage threshold level is approximately 1.5V, making the device TTL compatible over the 4 .5V to 18V operating supply voltage range. Input current is less than 10 µA over this range. The MIC4429 can be directly driven by the TL494, SG1526/ 1527, SG1524, TSC170, MIC38HC42 and similar switch mode power supply integrated circuits. By offloading the power-driving duties to the MIC4420/4429, the power sup- ply controller can operate at lower dissipation. This can improve performance and reliability. The input can be greater than the +VS supply, however, current will flow into the input lead. The propagation delay for TD2 will increase to as much as 400ns at room tempera- ture. The input currents can be as high as 30mA p-p (6.4mARMS) with the input, 6 V greater than the supply voltage. No damage will occur to MIC4420/4429 however, and it will not latch. The input appears as a 7pF capacitance, and does not change even if the input is driven from an AC source. Care should be taken so that the input does not go more than 5 volts below the negative rail. Power Dissipation CMOS circuits usually permit the user to ignore power dissipation. Logic families such as 4000 and 74C have outputs which can only supply a few milliamperes of current, and even shorting outputs to ground will not force enough current to destroy the device. The MIC4420/4429 on the other hand, can source or sink several amperes and drive large capacitive loads at high frequency. The package power dissipation limit can easily be exceeded. Therefore, some attention should be given to power dissipation when driving low impedance loads and/or operating at high fre- quency. The supply current vs frequency and supply current vs capacitive load characteristic curves aid in determining power dissipation calculations. Table 1 lists the maximum safe operating frequency for several power supply voltages when driving a 2500pF load. More accurate power dissipa- tion figures can be obtained by summing the three dissipa- tion sources. Given the power dissipation in the device, and the thermal resistance of the package, junction operating temperature for any ambient is easy to calculate. For example, the thermal resistance of the 8-pin MSOP package, from the data sheet, is 250 °C/W. In a 25°C ambient, then, using a maximum junction temperature of 150 °C, this package will dissipate 500mW. Accurate power dissipation numbers can be obtained by summing the three sources of power dissipation in the device: • Load Power Dissipation (PL) • Quiescent power dissipation (PQ) • Transition power dissipation (PT) Calculation of load power dissipation differs depending on whether the load is capacitive, resistive or inductive. Resistive Load Power Dissipation Dissipation caused by a resistive load can be calculated as: PL = I2 RO D where: I = the current drawn by the load RO = the output resistance of the driver when the output is high, at the power supply voltage used. (See data sheet) D = fraction of time the load is conducting (duty cycle) Figure 3. Switching Time Degradation Due to Negative Feedback MIC4429 1 8 6, 7 5 4 +18 V 0.1µF 0.1µF TEK CURRENT PROBE 6302 10,000 pF POLYCARBONATE 5.0V 0 V 18 V 0 V WIMA MK22 1 µF 2 |
Similar Part No. - MIC4420CN |
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Similar Description - MIC4420CN |
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