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FAN2512S27X Datasheet(PDF) 3 Page - Fairchild Semiconductor |
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FAN2512S27X Datasheet(HTML) 3 Page - Fairchild Semiconductor |
3 / 10 page FAN2512/FAN2513 PRODUCT SPECIFICATION REV. 1.1.8 5/25/04 3 An Enable pin, available on all devices, allows the user to shut down the regulator output to conserve power, reducing supply current to less than 1µA. The output can then be re-Enabled within 500µSec, fulfilling the fast power-cycling needs of CDMA applications. Depending on the model selected, other control and status functions are available at pin 4 to enhance the operation of the device. The adjustable- voltage versions utilize pin 4 to connect to an external voltage divider which feeds back to the regulator error amplifier, thereby setting the voltage as desired. Two other functions are available in the fixed-voltage versions: in noise-sensitive applications, an external Bypass capacitor connection is provided that allows the user to achieve opti- mal noise performance at the output, while the Error output functions as a diagnostic flag to indicate that the output voltage has dropped more than 5% below the nominal fixed voltage. Applications Information External Capacitors – Selection The FAN2512/13 allows the user to utilize a wide variety of capacitors compared to other LDO products. An innovative design approach offers significantly reduced sensitivity to ESR (Effective Series Resistance), which degrades regulator loop stability in older designs. While the improvements fea- tured in the FAN2512/13 family greatly simplify the design task, capacitor quality still must be considered if the designer is to achieve optimal circuit performance. In general, ceramic capacitors offer superior ESR performance, at a lower cost and a smaller case size than tantalums. Those with X7R or Y5Vdielectric offer the best temperature coefficient characteristics. The combination of tolerance and variation over temperature in some capacitor types can result in signif- icant variations, resulting in unstable performance over rated conditions. Input Capacitor An input capacitor of 2.2µF (nominal value) or greater, connected between the Input pin and Ground, located in close proximity to the device, will improve transient response and noise rejection. Higher values will offer supe- rior input ripple rejection and transient response. An input capacitor is recommended when the input source, either a battery or a regulated AC voltage, is located far from the device. Any good quality ceramic, tantalum, or metal film capacitor will give acceptable performance, however tanta- lum capacitors with a surge current rating appropriate to the application must be selected to avoid catastrophic failure. Output Capacitor An output capacitor is required to maintain regulator loop stability. Unlike many other LDO regulators, the FAN2512/13 family of products are nearly insensitive to output capacitor ESR. Stable operation will be achieved with a wide variety of capacitors with ESR values ranging from 10m Ω to 10Ω or more. Tantalum or aluminum electrolytic, or multilayer ceramic types can all be used. A nominal value of at least 1µF is recommended. Bypass Capacitor (FAN2512 Only) In the fixed-voltage configuration, connecting a capacitor between the bypass pin and ground can significantly reduce noise on the output. Values ranging from 470pF to 10nF can be used, depending on the sensitivity to output noise in the application. At the high-impedance Bypass pin, care must be taken in the circuit layout to minimize noise pickup, and capacitors must be selected to minimize current loading (leakage). Noise pickup from external sources can be considerable. Leakage currents into the Bypass pin will directly affect regulator accuracy and should be kept as low as possible; thus, high- quality ceramic and film types are recommended for their low leakage characteristics. Cost-sensitive applications not concerned with noise can omit this capacitor. Control Functions Enable Pin Applying a voltage of 0.4V or less at the Enable pin will dis- able the output, reducing the quiescent output current to less than 1µA, while a voltage of 2.0V or greater will enable the device. If this shutdown function is not needed, the pin can simply be connected to the VIN pin. Allowing this pin to float will cause erratic operation. Error Flag (FAN2513 Only) To indicate conditions such as input voltage dropout (low VIN), overheating, or overloading (excessive output current), the ERR pin indicates a fault condition. It is an open-drain output which is HIGH when the voltage at VOUT is greater than 95% of the nominal rated output voltage and LOW when VOUT is less than 95% or the rated output volt- age, as specified in the error trip level characteristics. A logic pullup resistor of 100K Ω is recommended at this output. The pin can be left disconnected if unused. Thermal Protection The FAN2512/13 is designed to supply high peak output currents of up to 1A for brief periods, however this output load will cause the device temperature to increase and exceed maximum ratings due to power dissipation. During output overload conditions, when the die temperature exceeds the shutdown limit temperature of 150°C, onboard thermal protection will disable the output until the tempera- ture drops below this limit, at which point the output is then re-enabled. During a thermal shutdown situation the user may assert the power-down function at the Enable pin, reducing power consumption to the minimum level IGND. |
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