feature

Fixed 1.0V, 1.2V, 1.3V, 1.5V, 1.8V, 2.5V, 3.3V, 3.5V, 3.6V, 3.8V Adjustable Output Power Good Indicator with Open Drain Output 180mA Output Current 100µA Ground Current Cbypass fast support for CDMA applications for low noise operation High ripple rejection

application

Processor power-up sequence

PDA, mobile phone

Portable Electronic Devices

PCMCIA Vcc and Vpp regulation/switching

General Instructions

The FAN2558 /9 low voltage CMOS LDO features fixed or adjustable output voltage, 180mA load current, time delay power good output (open drain) and 1% output accuracy with good line and load regulation. External bypass capacitors provide ultra-low noise operation. The FAN2558/9 low voltage LDO contains two thermal shutdown and short circuit protections. The output is stable with 1µF, low ESR capacitor. The FAN2558/9 series are available in 5-lead SOT-23 , 6-lead SOT-23 and 2x2mm MLP-6 packages. FAN2558: fixed output with good output power LDOFAN2558ADJ: adjustable output with good power LDO output 2.5V, 3.3V, 3.5V, 3.6V and 3.8V. Custom output voltage options are also available.

notes:

1. Using Mil Standard 883E, Method 3015.7 (Human Body Model) and EIA/Jesd222C101-A (Charging Device Model)

2. Junction temperature resistance is an important function of PCB material, board thickness, board thickness and number of layers copper plane, number of vias used, diameter of vias used, available copper surface and additional heat sink characteristics

Electrical Characteristics

VIN = VIN Min (Note 5) to 5.5V, VIN = VIN, ILOAD = 100 mA, TEMP = -40°C to +85°C unless otherwise noted. Typical value at 25 degrees Celsius

Note:

3. Parts that guarantee ±1% output voltage accuracy can be provided according to customer requirements.

4. Measured at constant junction temperature using low duty cycle pulse test.

5. Minimum VIN = 2.7V or (VOUT+1V), whichever is greater.

Function description

Using BiCMOS technology, the FAN2525/FAN2559 product family is optimized for use in small battery powered systems. These LDOs offer a unique combination of high ripple rejection, low noise, low power dissipation, high tolerance to a variety of output capacitors, and less than 1 microamp "off" current. In the circuit, a differential current sense amplifier controls series P-channel MOSFETs for high ripple rejection. A separate error amplifier compares the load voltage at the output with an on-board trimmed low-voltage bandgap reference for output regulation. Thermal shutdown and current limit circuits protect the device from extreme conditions. When the device temperature reaches 150°C, the output is disabled. Re-enable when the device cools by 10°C. Users can turn off devices that use the enable control pins at any time. The current limiting circuit is cut off, resulting in a consistent power-on/enable delay and providing safe short-circuit current density even in the narrow traces of the PCB. A carefully optimized control loop accommodates a range of ESR values for the output bypass capacitors, allowing the user to optimize space, cost, and performance requirements. The enable pin turns off the regulator output to conserve power, reducing supply current to less than 1 µA. The fixed voltage fan 2559 has a noise bypass pin. A well-powered diagnostic function can be used to indicate that the output voltage has dropped to within 5% of its nominal value. The six-pin adjustable voltage version utilizes pin 5 to connect to an external voltage divider, which is fed back to the regulator error amplifier to set the output voltage to the desired value.

application information

External Capacitors - Selecting the FAN2558/FAN2559 gives the user the flexibility to use a wide variety of capacitors compared to other LDOs. The innovative design approach greatly reduces sensitivity to ESR and reduces the stability of the regulator loop of older designs. And these improvements are mainly reflected in the FAN2558/FAN2559 series, which greatly simplifies the design task, if the designer wants to achieve the best circuit performance. In general, ceramic capacitors offer superior electroslag remelting performance, as well as a smaller case size than tantalum capacitors.

input capacitor

An input capacitor of 2.2µF (nominal) or larger, connected between the input pin and ground, placed in the closed position close to the device, will improve transient response and ripple rejection. Higher values will further improve ripple rejection and transient response. Input capacitors are recommended when the input source (battery or regulated AC voltage) is far away from the device. What is the benefit of high-quality ceramic, tantalum, or metal film capacitors with acceptable performance; however, in extreme cases, the capacitor may have to consider inrush current ratings. Output Capacitor An output capacitor is required to keep the regulator loop stable. Various capacitors have ESR values from 0Ω to 400 megohms. Multilayer ceramic, tantalum or aluminum electrolytic capacitors can be used. A nominal value of at least 1µF is recommended. Note that the choice of output capacitor affects load transient response, ripple rejection, and has a slight effect on noise performance. An internal resistor of about 100µm is connected. In shutdown mode, the output capacitor is faster between VOUT and GND. Bypass Capacitor (FAN2559 only) In fixed voltage configuration, connecting a capacitor between the bypass pin and ground can significantly reduce output noise. Values from 0pF to 47nF can be used, depending on the sensitivity to output noise in the application. At high impedance bypass pins, careful board 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.

control function

Enable Pin Connecting 2V or higher to the Enable pin will enable the output, while 0.4V or lower will disable it while reducing quiescent current consumption by less than 1µA. If this shutdown feature is not required, the pin can be permanently connected to the VIN pin. Allowing this pin to float can result in unstable operation. Error flags (power good) fault conditions such as input voltage drop (low VIN), overheating or overload (excessive output current) will set the error flag. The PG pin is an open-drain output when VOUT is less than 95% or the specified output voltage. When the output voltage is greater than 95% of the specified output voltage, the PG pin is high. A 47KΩ logic pull-up resistor is recommended for this output. You can leave the pins disconnected if not in use. Thermal Protection The FAN2558/FAN2559 are designed to provide high peak output current for short periods of time, but sustained excessive output loads at high input to output voltage differences will increase the temperature of the device and exceed maximum ratings due to power dissipation. In an output overload condition, when the die temperature exceeds the shutdown limit of 150°C, the onboard thermal protection will disable the output until the temperature drops approximately 10°C below the limit, at which point the output is re-enabled. During thermal shutdown, the user can assert the power-down function on the enable pin to minimize power consumption. Thermal Characteristics The FAN2558/FAN2559 are designed for a specified output voltage with operating die (junction) temperature up to 125°C. Once the power dissipation and thermal resistance are known, the maximum junction temperature of the device can be calculated. The actual thermal resistance when calculating power dissipation from known electrical parameters depends on the thermal characteristics of the SOT2 3-5 surface mount package and the surrounding PC board copper to which it is mounted. Power dissipation equals input to output dropout and output current plus ground current times input voltage

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 layout of the surrounding PC board and can be obtained empirically. While the θJCSOT2 3-5 package (junction box) is specified at 130°C/W, the θJA for the minimum PWB footprint is 235°C/W minimum. This can be done by heating the surrounding copper ground slot on the PWB. Depending on the size of the copper area, the resulting θJA can range from about 180°C/W for 1 in2 to nearly 4 in2 for 130°C/W. The addition of copper with vias, stiffeners, and other reinforcements on the backside also helps reduce thermal resistance. Heat dissipation from other nearby equipment must be included in design considerations. Once the parameters limiting these two relationships have been determined, the design can be modified to ensure that the device remains unchanged under specified operating conditions. If overload conditions are not considered, the device has the potential to enter a thermal loop, where the circuit goes into off-state regulation, cools, re-enables, then overheats again and shuts down repeatedly due to an unmanaged fault condition. The adjustable version, the FAN2558ADJ, includes an input pin, ADJ, which allows the user to select an output voltage ranging from 1V to near VIN, using an external resistor divider. The voltage VADJ supplied to the ADJ pin is fed to the onboard error amplifier which regulates the output voltage until VADJ equals the onboard bandgap reference voltage of 1.00V (typ). The formula is as follows:

Since the bandgap reference voltage is truncated, an accuracy of 1% of the initial value can be achieved. The total value chain of resistors should not exceed 250KOhm to keep the error amplifier biased under no-load conditions. The programming output voltage is very close to the VIN and needs to take into account the magnitude and variation of the voltage, VDO overload, power supply and temperature variation. Note that the low leakage input to the FET of the CMOS error amplifier does not produce current errors in the bias calculation.

General PCB Layout Considerations

For optimum device performance, careful circuit layout and grounding techniques must be used. Establish a small local ground, ground pin, output and connection bypass capacitors are recommended. The input capacitor should be grounded to the main ground plane. This quiet local ground is then sent back to the main ground using the through-hole plane. In general, high-frequency compensation components (input, bypass, and output capacitors) should be placed as close to the device as possible. Proximity to the output capacitor is especially important for optimum performance, especially during high levels. load conditions. The large local copper area used as a heat sink (as described above) at high power dissipation can significantly increase the device temperature. Component side copper provides significantly better thermal performance. The thermal resistance is further reduced by adding a feed ground plane connecting the device side to the back plane.

Note:

6. Fixed output voltage version. Bypass pin is only available for FAN2559.