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AMS3108 датащи(PDF) 7 Page - Advanced Monolithic Systems Ltd |
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AMS3108 датащи(HTML) 7 Page - Advanced Monolithic Systems Ltd |
7 / 10 page AMS3108 Micropower 700mA Low Noise Fast Transient Response LDO 02/11/2010 www.advanced-monolithic.com Phone (925) 443-0722 7 Fax (925) 443-0723 Device Summary The AMS3108 is a high voltage low drop out linear regulator with a current capability of up to 700mA. The LDO has an input voltage range of 1.5V to 12V with an output voltage as low as 0.6V and is stable with a wide range of ceramic, tantalum, and electrolytic output capacitors. Shutdown/Enable The Enable (on/off) input threshold voltage is 1.1V. When disabled the LDO quiescent current decreases to a typical value of <1µA. Fault Protection Short circuit and over-temperature shutdown disable the converter and LDO in the event of an overload condition. Overtemp shutdown disables the device when the junction temperature exceeds 145 ºC. The output current is internally limited to 800mA. Input Capacitor An input bypass capacitor ranging from 1µF to 10µF is required. The capacitor should be placed as close as possible to the device and not be placed more than 1 inch from the LDO. Output Capacitor The output capacitor requirements range from the minimum value required to guarantee stability to larger values required to meet the extreme transient response requirements. Values range from 10 to 22µF X5R ceramic capacitors. Due to the extreme voltage coefficient of X5R ceramic capacitors, the voltage rating should be at least double the maximum applied voltage. Bypass Capacitor If the ByPass (BYP) is available, connecting a capacitor between the BYP pin and ground can significantly reduce output noise. Values can range from 0pF to 10nF, depending on the sensitivity to output noise in the application. The start-up speed of the AMS3108 is inversely proportional to the size of the bypass capacitor. Applications requiring a slow ramp-up of output voltage should consider larger values of bypass capacitance. Likewise, if rapid turn- on is necessary, consider omitting CBYP. Because the ByPass (BYP) pin is high-impedance, careful considering must be taken in the PCB layout to minimize noise pickup, and capacitors must be selected to minimize current leakage. Current leakage into the BYP pin will directly affect the regulator’s accuracy and should be kept low as possible. Using high quality ceramic and film type’s capacitors are recommended for their low leakage characteristics. Adjustable Version: Feedback Resistor Selection Choosing AMS 3108 with adjustable output voltage option allows the user to select an output voltage by using an external resistor divider. AMS 3108 uses a 0.6V reference voltage at the positive terminal of the error amplifier. To set the output voltage a programming resistor from the adjust pin (ADJ) to ground must be selected (See Pg.1). A 10kΩ resistor is a good selection for a programming resistor R2. A higher value may result in an excessively sensitive feedback node while a lower value will draw more current and degrade the light load efficiency. The equation for selecting the voltage specific resistor is: R 1 = Vout Vref -1 ·R2 = 1.8V 0.6V -1 ·10kΩ = 20kΩ Table 1: Adjustable Feedback Resistor values VOUT (V) R1 (kΩ) (R2=10kΩ) 1.8 20.0 2.5 31.6 3.3 45.3 5.0 73.2 Power Good During operation, fault conditions can occur unexpectedly. Such conditions include input voltage dropout (low VIN), overheating, or overloading (excessive output current). If any of these conditions occurs, the PG pin will set an “error flag”. The PG pin, which is an open-collector output, will go LOW when VOUT is less than 95% or the specified output voltage. When the voltage at VOUT is greater than 95% of the specified output voltage, the PG pin is HIGH. A logic pull-up resistor of 10KΩ is recommended at this output. The pin can be left disconnected if unused. |
Аналогичный номер детали - AMS3108 |
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Аналогичное описание - AMS3108 |
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