Features: Ultra Low Power 150mA 150mV Voltage Drop 150mA 25µA Ground Current Enable/Disable Control SOT33-5 Package Thermal Limit 300mA Peak Current

Applications: Cell Phones and Accessories Camcorders and Video Recorders Notebooks, Notebooks and Palmtops

Description: The fan2502/03 series of micro-power low-dropout voltage regulators using CMOS technology provide a new level of cost-effectiveness for cell phones, notebook and notebook portable computers, and other portable devices. Features include extremely low power dissipation, low shutdown current, low voltage drop, excellent loop stability, accommodating a variety of external capacitors and compact SOT2 3-5 surface mount components. The Fan2502/03 series offer significant improvements over the older bicmos design and are pin compatible with many popular devices. This output is thermally protected against overload. The difference between the FAN2502 and FAN2503 devices is the pin 4 assignment: FAN2502-XX: Pin 4 – BYP, bypass capacitors can be connected for best noise performance. The output voltage is fixed and denoted by the suffix xx. FAN2503-XX: Pin 4 – err, indicates that the output voltage has dropped below the specified minimum value due to a fault condition. The standard fixed output voltage available is 2.5V3.3V.

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 is 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.

Functional Description: The FAN2502/03 family of products designed in CMOS process technology are carefully optimized for use in small battery powered devices. They offer a unique combination of low power dissipation, extremely low dropout voltage, high tolerance to a wide variety of output capacitors, and the ability to disable the output to less than 1µA under user control. In the circuit, A differential amplifier compares the low-drift bandgap output voltage on the load board by connecting a p-channel mosfet in series. The series resistance of the p-channel MOSFET is about 1Ω, causing the anomaly. The voltage under load is reduced compared to the older bipolar transistor design. Protection circuits are provided on board for overload conditions. If the device reaches a temperature above the specified maximum, the onboard circuitry shuts down the output, where it remains suspended until it cools down before restarting. The user can use the enable control pins at any time. 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 accommodated types allows users to select capacitors that meet space, cost, performance requirements, and operate reliably at over-temperature. Loads and tolerances vary. 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.

An enable pin, available on all devices, allows the user to turn off the regulator output to save power, reducing supply current to less than 1µA. An adjustable voltage version of the device utilizes pin 4 to connect to an external voltage divider for feedback to the regulator error amplifier, thereby setting the voltage as desired. There are two other functions on pin 4 of the fixed-voltage version: In noise-sensitive applications, an external bypass capacitor connection is provided, allowing the user to obtain the best noise performance at the output. The error output is used as a diagnostic flag to indicate that the output voltage is more than 5% lower than the rated value by a fixed voltage. Application Information External Capacitors - Select FAN2502/03 supports a variety of capacitors compared to other LDO products. 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, ceramic capacitors come in lower cost and smaller boxes than tantalum. With X7R or Y5V dielectric provides the best temperature coefficient characteristics. Combination of Tolerance and Variation Excessive temperature of some capacitor types can cause significant variation, resulting in unstable 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 FAN2502/03 family of products has an ESR for output capacitors. Stable operation is achieved with various capacitors with a wide range of esr values from 10 MΩ to 10Ω or more. Tantalum or aluminum electrolytic, or multilayer ceramic types can be used. A recommended nominal value is at least 1µf. Bypass Capacitor (FAN2502 only) In fixed voltage configuration, connect a capacitor between the bypass pin and ground to reduce output noise. A value range of 470 pF can use 10 nF, depending on the output noise in the application. At high impedance bypass pins, care must be taken in circuit layout to minimize noise pickup and capacitor selection to minimize current loading (leakage). Noise pickup from external sources can be considerable. Leakage current into the bypass pin directly affects regulator accuracy and should be kept as low as possible; high quality ceramic and thin film types are recommended for low leakage characteristics. This capacitor is omitted for cost-sensitive applications that are not related to noise. CONTROL FUNCTION ENABLE PIN Applying 0.4V or lower to the ENABLE pin will disable the output, reducing quiescent output current to less than 1µA; a voltage of 2.0V or higher enables 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 error flag (FAN2503 only) indicates input voltage drop (low VIN, overheating, or overload (excessive output current); the error pin indicates a fault condition. It is an open-drain output at Vout High greater than 95% of rated output voltage Low when VOUT is less than 95% or rated output voltage, as specified by the false trip level characteristic. A 100 kΩ logic pull-up resistor is recommended here for the output. If not used, it can be left on pin open. The thermally protected fan 2502/03 can provide high peak output current however, this output load up to 1A for short periods of time makes the device temperature rise and exceed the maximum power rating due to power dissipation. During output when the die temperature exceeds the shutdown limit temperature is 150°C, the onboard thermal protection disables the output until the temperature reaches below this limit; at this point, the output will be re-enabled. In a thermal shutdown condition, the user may assert a power-down feature at the enable pin, reducing power consumption to Lowest level. Thermal Characteristics Fan 2502/03 can provide 150mA output voltage at specified time with operating die (junction) temperature up to 125°C. Once power dissipation and thermal resistance are known, the maximum junction temperature can be calculated. While the power loss is based on known electrical parameters, the thermal resistance is determined by the thermal characteristics of the compact SOT2 3-5 SurfaceMount package and the surrounding PC board mounted on it. The power dissipation is equal to the input-output voltage difference and output current plus ground current Multiply 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 the sot23 is specified at 130°C/W, the θja of the smallest PCB package is at least 235°C/W. This can be improved PCB grounding by providing heat sinks around copper. Depending on the copper size area, the resulting Th JA can range from approximately 180°C/W (1 square inch) to nearly 130°C/W (4 square inches) square inch. The addition of vias, stiffeners, and other reinforcements to the backside copper can reduce this value at the same time. 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 To achieve the full performance of the device, careful circuit layout and grounding techniques are required. 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. The optimal noise compensation amplifier for onboard errors, especially under high load conditions. Large local ground copper areas provide heat dissipation when the high power dissipation significantly increases the device temperature, discussed above. Component side copper wire provides better thermal performance of this surface mount device.