-
2022-09-23 11:26:54
Fan 2514, Fan 2515, 200mA CMOS LDO regulator to enable fast startup
Features: Ultra Low Power Support Optimized for CDMA Time Periods 200mA at 200mV Voltage Drop at 200mA 75μA Ground Current Enable/Disable Control SOT33-5 Package Thermal Limit 300mA Peak Current
Applications: Cell Phones and Accessories PDA Camcorders and Video Recorders Notebooks, Notebooks and Palmtops
Description: The fan2514/15 micropower low dropout regulators utilize CMOS technology to deliver a new level of cost-effective performance in GSM, TDMA and CDMA mobile phones, notebooks and notebook laptops, and other portable device features including extremely low power consumption and Low shutdown current, low voltage loss, excellent loop stability, the ability to accommodate a wide variety of external capacitors and compact SOT2 3-5 surface mount components. In addition, the FAN2514 /15 series provides the fast power cycle time applications required by CDMA handsets. These products have significant improvements over older BiCMOS designs, and are pin-compatible with many popular devices. The output is thermally protected against overload. The difference between the FAN2514 and FAN2515 devices is the assignment of pin 4: FAN2514: Pin 4 – ADJ, allowing the user to adjust a wide range of output voltage separators using an external voltage. FAN2514-XX: Pin 4 – BYP, bypass capacitor can be connected for best noise performance The output voltage is fixed and denoted by the suffix xx. FAN2515-XX: Pin 4 – err, indicates that the output voltage has dropped below the specified minimum value due to a fault condition. Standard fixed output voltages are 2.5V, 2.6V, 2.7V, 2.8V, 2.85V, 3.0V and 3.3V.
Functional Description Designed in CMOS process technology, the FAN2514/15 series are carefully optimized for use in small battery powered devices, offering unique low power consumption, extremely low dropout voltage, high tolerance to various output capacitors, and the ability to Disable the output to less than 1 µA under user control In the circuit, the differential amplifier controls the current through the series P-channel MOSFET, connecting the load voltage at the output to the on-board low-drift bandgap reference series resistor The path of the P-channel MOSFET is about 1 µm , resulting in an unusually low voltage drop under load compared to older bipolar transistor designs. There is an overload protection circuit on board. When the device reaches a temperature above the specified maximum, the on-board circuitry shuts down and reduces the output until the output cools down before re-enabling. Users are also free to turn off devices that use the enable control pins at any time. The output conditioning amplifier ensures the stability of the external output capacitor over a wide range of ESR values by careful design of the loop.
A range of values and types are available to allow the user to select capacitors meeting his space, cost and performance requirements, as well as reliable over temperature, overload and out of tolerance operating variations. Depending on the model selected, there are a number of controls and status functions available to enhance the LDO regulator. There is an enable pin on all devices that allows the user to turn off the regulator output to conserve power, reducing supply current to less than 1 microamp. The adjustable voltage version of the device utilizes pin 4 to connect to an external voltage divider, which is fed back to the regulator error amplifier to set the voltage as desired. In Fixed Voltage Version: Provides an external bypass capacitor connection in noise sensitive applications, allowing the user to obtain the best noise performance at the output, when a false output is used to indicate that the output voltage has dropped more than 5% below the rated fixed voltage.
Application Information External Capacitors - Selecting the FAN2514/15 allows users to use a variety of capacitors Innovative design approach significantly reduces ESR (effective series resistance) compared to other LDO products, reducing regulator performance Loop stability in older designs . The improvements to the Fan2514/15 series greatly simplify the design task, and capacitor quality must still be considered if the designer is to achieve optimum circuit performance. In general, ceramic capacitors offer superior ESR performance at a lower cost and smaller case than tantalum alloys. Those with X7R or Y5V dielectrics offer the best temperature coefficient characteristics. Combination of Tolerance and Variation Excessive temperature of certain capacitor types can cause significant variation, resulting in unstable performance beyond rated conditions. Input Capacitor 2.2µf (nominal) or larger, connected between the input pin and ground, located close to the device, will improve transient response and noise rejection. Higher values will provide better input ripple rejection and transient response. Put in when the input source battery or regulated AC voltage is located away from the device. Any high-quality ceramic, tantalum, or metal film capacitor will provide acceptable performance, but tantalum capacitors have inrush current ratings suitable for the application that must be selected to avoid catastrophic failure. Output Capacitor An output capacitor is required to maintain regulator loop stability. Unlike many other LDC regulators, the FAN2514/15 family of products has an output capacitor ESR. Stable operation Various capacitors have esr values from 10MΩ to 10Ω or more. Tantalum or aluminum electrolytic, or multilayer ceramic types can be used.
The nominal value is recommended to be at least 1µF. Bypass Capacitor (FAN2514 only) In fixed voltage configuration, connecting a capacitor between the bypass pin and ground can significantly reduce noise on the output. Values from 470pF to 10nF can be applied depending on the sensitivity to output noise. At high impedance bypass pins, careful circuit layout must be taken to minimize noise pickup, and capacitors must be selected to minimize current loading (leakage). The information that noise can gain from the outside can be considerable. The current leaking into the bypass pin will directly affect the regulator accuracy and should be as low as possible; therefore, it is recommended to use high quality ceramic and thin film types with low leakage characteristics. Cost sensitive applications can ignore this capacitor due to noise concerns. The control function enable pin applies a voltage of 0.8V or less to the enable pin to disable the output, reducing the quiescent output current to less than 1µA, while a voltage of 1.5V or higher will enable the device. If the shutdown function is not required, simply connecting to the VIN pin allows this pin to float which will result in unstable operation. Error flag (FAN2515 only) indicates conditions such as input voltage drop (low VIN), overheating or overload (excessive output current), error pin indicates fault condition It is an open drain output, when voltage is at VOUT High is greater than 95% of rated output voltage and is the voltage specified in the Low False Trip Level Characteristics when VOUT is less than 95% or rated output.
A logic pull-up resistor of 100kΩ is recommended here. If not used, the pins can be left open. The thermally protected FAN2514/15 is designed to deliver up to 1A of peak output current for short periods of time, but this output load will cause the device to heat up and exceed the maximum power rating due to power dissipation. During output when the mold temperature exceeds the shutdown limit temperature of 150°C, the onboard thermal protection will disable the output until the temperature drops below this limit, the output will re-enable. In thermal shutdown conditions, the user can assert the enable pin power down function, reducing power consumption to a minimum.
Thermal Characteristics The FAN2514/15 is designed for a specified output voltage with operating mode (junction) temperature up to 125°C. Once the power dissipation and thermal resistance are known, the maximum junction can calculate the temperature of the device. While the power loss is calculated from known electrical parameters, the thermal resistance is the copper around the compact SOT2 3-5 surface mount package and the PC board it is mounted on. Power dissipation is equal to the input to output voltage drop and output current plus ground current multiplied by the input voltage, or:
The ground pin current signal can be found in the diagram provided in the Electrical Characteristics section. The relational wrapper describing thermal behavior is:
where TJ(max) is the maximum allowable junction temperature of the die at 125°C and TA is the ambient operating temperature. θJA depends on the surrounding PC board layout and can be obtained empirically while θjc
The total value of the resistor chain should not exceed a total of 250kΩ to keep the error amplifier in no-load condition. Programming the output voltage very close to the VIN requires consideration of voltage drop VDO overload, power supply and temperature variations. Note that the low leakage fetCMOS error amplifier does not contribute to the calculation. General PWB Layout Considerations In order to achieve the full performance of the device, be careful that the circuit must adhere to layout and grounding techniques. Establish a small local ground, ground pins, and outputs are recommended to connect bypass capacitors. Input capacitors should be grounded to the main ground plane. The quiet local ground is then routed back to the main duct's ground plane using the feedthrough. In general, high frequency compensation components (input, bypass, and output capacitors) should be as close as possible to the device, especially the output capacitors. It is important to raise the temperature of the device significantly from the onboard error amplifier, especially under high load conditions where a large copper area will provide the heat dissipation issues discussed above when the high power dissipation occurs. Component-side copper traces provide better thermal performance. In contrast, the performance of such surface mount devices is only obtained when copper planes are used on the bottom.