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EUP7917-13VIR1 Datasheet(PDF) 9 Page - Eutech Microelectronics Inc |
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EUP7917-13VIR1 Datasheet(HTML) 9 Page - Eutech Microelectronics Inc |
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9 / 12 page  EUP7917 DS7917 Ver1.2 Mar. 2008 9 Application Note External Capacitors Like any low-dropout regulator, the EUP7917 requires external capacitors for regulator stability. The EUP7917 is specifically designed for portable applications requiring minimum board space and smallest components. These capacitors must be correctly selected for good performance. Input Capacitor An input capacitance of 1µF is required between the EUP7917 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. Any good quality ceramic, tantalum, or film capacitor may be used at the input. 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. There are no requirements for the ESR on the input capacitor, but tolerance and temperature coefficient must be considered when selecting the capacitor to ensure the capacitance will be 1µF over the entire operating temperature range. Output Capacitor The EUP7917 is designed specifically to work with very small ceramic output capacitors. A ceramic capacitor (temperature characteristics X7R, X5R, Z5U, or Y5V) in 1 to 22µF range with 5mΩ to 500mΩ ESR range is suitable in the EUP7917 application circuit. The output capacitor must meet the requirement for minimum amount of capacitance and also have an ESR (Equivalent Series Resistance) value which is within a stable range (5mΩ to 500mΩ) No-Load Stability The EUP7917 will remain stable and in regulation with no external load. This is specially important in CMOS RAM keep-alive applications. Capacitor Characteristics The EUP7917 is designed to work with ceramic capacitors on the output to take advantage of the benefits they offer: for capacitance values in the range of 1µF to 4.7µF range, ceramic capacitors are the smallest, least expensive and have the lowest ESR values (which makes them best for eliminating high frequency noise). The ESR of a typical 1µF ceramic capacitor is in the range of 20mΩ to 40mΩ, which easily meets the ESR requirement for stability by the EUP7917. The ceramic capacitor’s capacitance can vary with temperature. The capacitor type X7R, which operates over a temperature range of -55°C to +125°C, will only vary the capacitance to within ±15%. Most large value ceramic capacitors ( ≈2.2µF) are manufactured with Z5U or Y5V temperature characteristics. Their capacitance can drop by more than 50% as the temperature goes from 25°C to 85°C. Therefore, X7R is recommended over Z5U and Y5V in applications where the ambient temperature will change significantly above or below 25°C. Noise Bypass Capacitor Connecting a 0.01µF 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. Adjustable Operation The adjustable version of the EUP7917 has an output voltage range of 1.2V to 4.5V. The output voltage of the EUP7917 adjustable regulator is programmed using an external resistor divider as shown in Figure3. The output voltage is calculated using: Where: Vref= 1.2V typ. (the internal reference voltage) Utilize the following equation for adjusting the output to a particular voltage: Choose R2=50k to optimize accuracy, power supply rejection, noise and power consumption. Figure3. Adjustable Regulator with Resistors ) R R (1 V V 2 1 ref O + × = − = 1 1.2V V R R O 2 1 |
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