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EUP7982-30MIR1 Datasheet(PDF) 8 Page - Eutech Microelectronics Inc |
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EUP7982-30MIR1 Datasheet(HTML) 8 Page - Eutech Microelectronics Inc |
8 / 10 page EUP7982 DS7982 Ver 1.4 May.2005 8 Application Information External Capacitors Like any low-dropout regulator, the EUP7982 requires external capacitors for regulator stability. The EUP7982 is specifically designed for portable applications requiring minimum board space and smallest components. These capacitors must be correctly selected for good performance. Input Capacitor A minimum input capacitance of 1µF is required between the EUP7982 input pin and ground (the amount of the capacitance may be increased without limit).This capacitor must be located a distance of not more than 1cm from the input pin and returned to a clean analog ground. 1µF ceramic capacitor are fine for most end use applications. If a tantalum capacitor is used at the input, it must be guaranteed by the manufacturer to have asurge current rating sufficient for the application. No-Load Stability The EUP7982 will remain stable and in regulation with no external load. This is specially important in CMOS RAM keep-alive applications. Output Capacitance The EUP7982 is specifically designed to employ ceramic output capacitors as low as 2.2µF. Ceramic capacitors below 10µF offer significant cost and space savings, along with high frequency noise filtering. Higher values and other types and of capacitor may be used, but their equivalent series resistance (ESR) should be maintained below 0.5Ω. Ceramic capacitor of the value required by the EUP7982 are available in the following dielectric types: Z5U, Y5V, X5R, and X7R. The Z5U and Y5V types exhibit a 50% or more drop in capacitance value as their temperature increase from 25°C, an important consideration. The X5R generally maintain their capacitance value within ± 20%. The X7R type are desirable for their tighter tolerance of 10% over temperature. Noise Bypass Capacitor Connecting a 33nF capacitor between the CBYPASS pin and ground significantly reduces noise on the regulator output. This cap is connected directly to a high impedance node in the bandgap reference circuit. Any significant loading on this node will cause a change on the regulated output voltage. For this reason, DC leakage current through this pin must be kept as low as possible for best output voltage accuracy. The types of capacitors best suited for the noise bypass capacitor are ceramic and film. Unlike many other LDO’s , addition of a noise reduction capacitor does not effect the load transient response of the device. However, it does affect start-up time. The smaller the capacitance value, the quicker the start-up time. Power Dissipation and Junction Temperature Specified regulator operation is assured to a junction temperature of 125°C; the maximum junction temperature should be restricted to 125°C under normal operating conditions. This restriction limits the power dissipation the regulator can handle in any given application. To ensure the junction temperature is within acceptable limits, calculate the maximum allowable dissipation, PD(max), and the actual dissipation, PD, which must be less than or equal to PD(max) The maximum-power-dissipation limit is determined using the following equation: Where: TJmax is the maximum allowable junction temperature. RθJA is the thermal resistance junction-to-ambient for the package TA is the ambient temperature. The regulator dissipation is calculated using: PD=(VI-VO) × IO Power dissipation resulting from quiescent current is negligible. Excessive power dissipation triggers the thermal protection circuit. θJA A J D(max) R T max T P − = |
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