feature

Ultra Low Power 200mA at 200mV Voltage Drop Output Voltage 3.3V 200mA at 75μA Ground Current Enable/Disable Control SOT33-5 Package Thermal Limit 300mA Peak Current

application

Cell Phones and Accessories Camcorders and Video Recorders Laptops, Notebooks and Palmtops

illustrate

The FAN2504 micropower low dropout regulator utilizes CMOS technology in cell phones, notebooks and notebooks and other portable computer equipment. Features include very low power dissipation, low off current, low voltage drop, excellent loop stability, the ability to accommodate a wide variety of external capacitors and a compact SOT2 3-5 surfacemount package. The FAN2504 has a significant improvement over its predecessor. BiCMOS designs are pin compatible with many popular devices. The output is thermally overloaded. A bypass capacitor can be connected to pin 4 for best noise performance.

Absolute Maximum Ratings (1) Stresses in excess of the Absolute Maximum Ratings may damage the device. The unit may not be operational or operable under the recommended operating conditions and it is not recommended to stress parts to these levels. Additionally, prolonged exposure to stresses higher than recommended operating conditions may affect device reliability. These absolute maximum ratings are for stress ratings only.

notes:

1. Functional operation under any of these conditions is not implied. Performance and reliability are only guaranteed if recommended operating conditions are not exceeded.

2. The applied voltage must be limited within the specified range.

3. Based on thermal limit junction temperature:

4. Using Mil Standard 883E, Method 3015.7, Human Body Model 4 kV minimum. Machine model at least 400 VJEDEC Method A115-A.

Recommended Operating Conditions The Recommended Operating Conditions table defines the conditions under which actual equipment operates. Recommended operating conditions are specified to ensure optimum performance to data sheet specifications. Fairchild does not recommend exceeding or designing in the Absolute Maximum Ratings.

Function description

Designed in CMOS process technology, the FAN2504 has been carefully optimized for use in small battery powered devices. It offers a unique combination of low power consumption, extremely low voltage drop, high tolerance to various output capacitors, and the ability to disable outputs less than 1µA in user state control. In the circuit, the differential amplifier controls the current through the series P-channel MOSFET and compares the output to the on-board load voltage with a low-drift bandgap reference. The series resistance through the p-channel MOSFET is about 1Ω, resulting in unusually low load voltages compared to older bipolar transistor designs. There is an overload protection circuit on board. If the device temperature exceeds the specified maximum value, the on-board circuit turns off the output and remains suspended before re-enabling it until it cools down. The user can turn off the device at any time using the enable control pins. Carefully designed output conditioning amplifiers guarantee loop stability over a wide range of ESR values with external output capacitors. A wide range of values and types can be accommodated, allowing the user to select capacitors meeting (if space, cost and performance) requirements for reliable operation over temperature, load and tolerance variations. Depending on the model selected, there are a number of controls and status functions that can be used to enhance the operation of the LDO regulator. The enable pin allows the user to turn off the regulator output to save power, reducing supply current to less than 1µA. The adjustable voltage version of the device uses pin 4 to connect to an external voltage divider that feeds back to the regulator error amplifier, thus setting the voltage as desired. In Fixed Voltage Version: An external bypass capacitor connection is provided in noise-sensitive applications to allow the user to switch on the output, while the error output is used as a diagnostic flag indicating that the output voltage has dropped more than 5% below the rated fixed voltage.

application information

External Capacitors - Choice Compared to other LDO products, the FAN2504 supports a variety of capacitors. Innovative Design This approach significantly reduces sensitivity to ESR (equivalent series resistance), which degrades the stability of the regulator loop in older designs. While these improvements greatly simplify the design task, the quality of the capacitor must still be considered if the designer is to achieve optimal circuit performance. Generally speaking, ceramic capacitors come in lower cost and smaller boxes than tantalum. With X7R or Y5V dielectrics provide the best temperature coefficient characteristics. In some capacitor types, the combination of tolerances and temperature changes can result in significant changes resulting in erratic performance beyond rated conditions. Input Capacitor 2.2µF (nominal) or larger input capacitor, connected between the input pin and ground, located close to the device to improve transient response and noise rejection. Higher values provide better input ripple rejection and transient response. One when the input source, battery or regulated AC voltage is located remotely from the device. Any good quality ceramic, tantalum, or metal film capacitor has acceptable performance; however, tantalum capacitors with inrush current ratings must choose options appropriate to the application to avoid catastrophic failure.

Output Capacitor An output capacitor is required to keep the regulator loop stable. Unlike many other LDC regulators, the FAN2504 is virtually insensitive to output capacitor ESR. Use a variety of capacitors with ESR values from 10 mΩ to 10Ω for stable operation or more. Tantalum or aluminum electrolytic, or multilayer ceramic types can be used. A nominal value of at least 1 µF is recommended. Bypass Capacitors In fixed voltage configurations, connect a capacitor between the bypass pin and ground to reduce output noise. A value range of 470pF can use 10 nF, depending on the output noise in the application. At high impedance bypass pins, careful circuit layout must be taken to minimize noise pickup. Capacitors must be chosen to minimize current loading (leakage). Noise pickup from external sources can be quite large. The leakage current into the bypass pin directly affects the accuracy of the regulator and should be kept as low as possible; high quality ceramic and thin film types are recommended due to their low leakage characteristics. This capacitor can be ignored for cost-sensitive applications that are not related to noise.

Control Function Enable Pin Applying a voltage of 0.4V or less on the Enable pin will disable the output, thereby reducing the quiescent output current to less than 1µA; voltages greater than or equal to 2.0V; enable the device. This pin can be connected to the VIN pin if the shutdown function is not required. Allowing this pin to float can result in unstable operation. The thermally protected FAN2504 can deliver high peak output currents of 1 A for short periods of time; however, this output loading can cause the device temperature to increase and exceed the maximum ratings due to power dissipation. During output, when the mold temperature exceeds the shutdown limit of 150°C, the on-board thermal protection disables the output until the temperature falls below this limit; at this point, the output is re-enabled. In the event of a thermal shutdown the user can turn on the enable pin to reduce power consumption to a minimum level by igde wen. Thermal Characteristics The Fan 2504 can deliver 150 mA of current at the specified output voltage for operating mode (junction) temperatures up to 125°C. Once power dissipation and thermal resistance are known, the maximum junction temperature can be calculated for the device. Thermal resistance when calculating power dissipation from known electrical parameters is a result of the thermal characteristics of the compact SOT2 3-5 surface mount package and surrounding PC board mounting. 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, IGND, 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, which is 125°C, and TA is the ambient. Operating temperature. θJA depends on the surrounding PC board layout and can be obtained empirically. While the θJC (junction-to-shell)-5 package of SOT23 is specified at 130°C/W, the θJA for the minimum PWB footprint is at least 235°C/W. This can be done by providing a copper ground on the PCB. Depending on the copper area, the resulting Th Ja can be in the range of about 180°C/W from 1 square inch to nearly 130°C/W. Four square inches. The addition of backside copper with vias, stiffeners, and other reinforcements can reduce this value. The heat generated by the heat dissipation of other nearby equipment must be included in the design consideration. Once the limiting parameters in these two relationships have been determined, the design can be modified to ensure that the equipment remains within the specified operating conditions. If overload conditions are not considered, equipment may enter a thermal loop, where the circuit goes off, cools, turns back on, then overheats and shuts down again due to an unmanaged fault condition. General PCB Layout Considerations For optimum device performance, attention must be paid to circuit layout and grounding techniques. Establishing a small local ground connection to the ground pin output and a bypass capacitor is recommended. The input capacitor should be grounded to the main ground plane. The quiet place is to use feed-back vias to the main ground plane. In general, high-frequency compensation components (input, bypass, and output capacitors) should be placed as close to the device as possible. Proximity is especially important for the realization of the output capacitors for the optimal noise compensation amplifier for onboard errors, especially under high load conditions. Large local ground copper areas provide heat dissipation when high power dissipation significantly increases device temperature, discussed above. Component side copper wire provides better thermal performance of this surface mount device, compared to only the underside.