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參數(shù)資料
| 型號(hào)： | FAN2535S285X |
| 廠商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | 150 mA CMOS LDO Regulator with Fast Start, Enable |
| 中文描述： | 2.85 V FIXED POSITIVE LDO REGULATOR, 0.22 V DROPOUT, PDSO5 |
| 封裝： | SOT-23, 5 PIN |
| 文件頁數(shù)： | 5/11頁 |
| 文件大小： | 492K |
| 代理商： | FAN2535S285X |
REV. 1.0.2 8/26/03
5
PRODUCT SPECIFICATION
FAN2534/FAN2535
Functional Description
Utilizing CMOS technology, the FAN2534/FAN2535
product family is optimized for use in compact battery
powered systems, offering a unique combination of high
ripple rejection, low noise, low power consumption,
extremely low dropout voltages, high tolerance for a variety
of output capacitors, and less than 1μA "OFF" current.
In the circuit, a differential amplifier controls a series-pass
P-Channel MOSFET, and a separate error amplifier com-
pares the load voltage at the output with an onboard trimmed
low voltage bandgap reference. The series resistance of the
pass P-Channel MOSFET is approximately 1 Ohm, yielding
an unusually low dropout voltage even under high load
conditions.
Thermal shutdown and current limit circuits protect the
device under extreme conditions. When the device tempera-
ture reaches 155°C, the output is disabled, until the device
cooles down by 15°C, then re-enabled. The user can to shut
down the device using the Enable control pin at any time.
The current limit circuit is trimmed, which leads to consis-
tent power on /enable delays, and provides safe short circuit
current densities even in narrow traces of the PCB.
A carefully optimized control loop accommodates a wide
range of ESR values in the output bypass capacitor, allowing
the user to optimize space, cost, and performance require-
ments.
An Enable pin shuts down the regulator output to conserve
power, reducing supply current to less than 1μA. The output
can then be re-Enabled within 150μSec, fulfilling the fast
power-cycling needs of CDMA applications.
Depending on the device type selected, other control and
status functions are available at pin 4. The fixed-voltage
versions are available with either a noise-bypass pin or an
Error flag pin option. The error flag can be used as a diagnos-
tic function to indicate that the output voltage has dropped
more than 5% below the nominal value.
The adjustable-voltage versions utilize pin 4 to connect to an
external voltage divider which feeds back to the regulator
error amplifier, thus setting the output voltage to the desired
value.
Applications Information
External Capacitors – Selection
The FAN2534/FAN2535 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 (Equivalent Series Resistance), which
degrades regulator loop stability in older designs. While the
improvements featured in the FAN2534/FAN2535 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, and a smaller case size than tantalums.
Input Capacitor
An input capacitor of 2.2μF (nominal value) or greater,
connected between the Input pin and Ground, placed in close
proximity to the device, will improve transient response and
ripple rejection. Higher values will further improve 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 in extreme cases
capacitor surge current ratings may have to be considered.
Output Capacitor
An output capacitor is required to maintain regulator loop
stability.
Stable operation will be achieved with a wide
variety of capacitors with ESR values ranging from 0m
up to 400m
. Multilayer ceramic, tantalum or aluminum
electrolytic capacitors may be used. A nominal value of at
least 1μF is recommended. Note that the choice of output
capacitor effects load transient response, ripple rejection,
and it has a slight effect on noise performance as well.
Bypass Capacitor (FAN2534-XX Only)
In the fixed-voltage configuration, connecting a capacitor
between the bypass pin and ground can significantly reduce
output noise. Values ranging from 0pF to 47nF 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
PCB 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, high-
quality ceramic and film types are recommended for their
low leakage characteristics. Cost-sensitive applications not
concerned with noise can omit this capacitor.
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