www.fairchildsemi.com
FAN2502, FAN2503
150 mA CMOS LDO Regulators
Features
•
•
•
•
•
•
•
wide variety of external capacitors, and the compact SOT23-5
surface-mount package. The FAN2502/03 family of products
offer significant improvements over older BiCMOS designs
and are pin-compatible with many popular devices. The
output is thermally protected against overload.
Ultra Low Power Consumption
150 mV dropout voltage at 150 mA
25 µA ground current at 150 mA
Enable/Shutdown Control
SOT23-5 package
Thermal limiting
300 mA peak current
The FAN2502 and FAN2503 devices are distinguished by
the assignment of pin 4:
FAN2502: pin 4 – ADJ, allowing the user to adjust the
output voltage over a wide range using an external voltage
divider.
Applications
•
•
•
•
Cellular Phones and accessories
PDAs
Portable cameras and video recorders
Laptop, notebook and palmtop computers
FAN2502-XX: pin 4 – BYP, to which a bypass capacitor
may be connected for optimal noise performance. Output
voltage is fixed, indicated by the suffix XX.
Description
The FAN2502/03 family of micropower low-dropout voltage
regulators utilize CMOS technology to offer a new level of
cost-effective performance in GSM and TDMA cellular
handsets, Laptop and Notebook portable computers, and
other portable devices. Features include extremely low
power consumption and low shutdown current, low dropout
voltage, exceptional loop stability able to accommodate a
FAN2503-XX: pin 4 – ERR, a flag which indicates that the
output voltage has dropped below the specified minimum
due to a fault condition.
The standard fixed output voltages available are 2.5V, 2.6V,
2.7V, 2.8V, 2.85V, 3.0V, and 3.3V. Custom output voltage are
also available: please contact your local Fairchild Sales
Office for information.
Block Diagrams
EN
EN
VIN
VIN
Bandgap
Error
Amplifier
BYP
Bandgap
p
VOUT
Error
Amplifier
p
VOUT
ADJ
Thermal
Sense
Thermal
Sense
GND
FAN2502
GND
FAN2502-XX
EN
VIN
ERR
Bandgap
Error
Amplifier
p
VOUT
Thermal
Sense
GND
FAN2503-XX
REV. 1.1.7 2/14/03
FAN2502/FAN2503
Depending on the model selected, a number of control and
status functions are available to enhance the operation of the
LDO regulator. 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
adjustable-voltage versions of the device 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 at pin 4 in the
fixed-voltage versions: in noise-sensitive applications, an
external Bypass capacitor connection is provided that allows
the user to achieve optimal 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.
PRODUCT SPECIFICATION
Bypass Capacitor (FAN2502 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, highquality ceramic and film types are recommended for their
low leakage characteristics. Cost-sensitive applications not
concerned with noise can omit this capacitor.
Applications Information
Control Functions
External Capacitors – Selection
The FAN2502/03 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 featured in the FAN2502/03 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 significant 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 superior 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 tantalum 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 FAN2502/
03 family of products are nearly insensitve to output capacitor ESR. Stable operation will be achieved with a wide
variety of capacitors with ESR values ranging from 10mΩ 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.
REV. 1.1.7 2/14/03
Enable Pin
Applying a voltage of 0.4V or less at the Enable pin will
disable 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 (FAN2503 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 opendrain 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 voltage, as specified in the error trip level characteristics.
A logic pullup resistor of 100KΩ is recommended at this
output. The pin can be left disconnected if unused.
Thermal Protection
The FAN2502/03 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 temperature 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 x VIN.
3
