fs1117 Fortune Semiconductor Corporation, fs1117 Datasheet - Page 8

• Manufacturer Part Number: fs1117
• Description: 1.0a Adjustable & Fixed Voltage Ldo Linear Regulator
• Manufacturer: Fortune Semiconductor Corporation

FS1117
14. Application Description
The FS1117 keeps a constant 1.25V between the
output pin and the adjust pin. By placing a resister
R1 across these two pins a constant current flows
through R1,assign to the ladj current and into the R2
resister
producing
a
voltage
equal
to
the
(1.25/R1)*R2+ladj*R2 which will be added to the
1.25V to set the output voltage. This is summarized
in the above equation. Since the minimum load
current requirement of be FS1117 is 10mA, R1 is
typically selected to be 121Ω resistor so that it
automatically
satisfies
the
minimum
current
requirement . Notice that since ladj is typically in the
range and should only be considered when a very
precise output voltage setting is required. For
example, in a typical 3.3V application where
R1=121Ω and R220Ω the error due to ladj is only
0.3% of the nominal set point.
14.1 Stability
The FS1117 requires the use of an output
capacitor as part of the frequency compensation
in order to make the regulator stable. For most
applications a minimum of 10μF aluminum
electrolytic capacitor insures both stability and
good transient response.
14.2 Thermal Design
The FS1117 incorporates an internal thermal
shutdown that protects the device when the junction
temperature
exceeds
the
maximum
allowable
junction temperature. Although this device can
operate with junction temperatures in the range of
150℃, it is recommended that the selected heat sink
be chosen such that during maximum continuous
load operation the junction temperature is kept
below the temperature.
Pd=VOUT × IOUT
T
=TA+Pd × θ J
< 150℃
J
A
14.3 Layout Consideration
The output capacitors must be located as close to
the VOUT terminal of the device as possible. It is
recommended to use a section of a layer of the PC
board as a plane to connect the VOUT pin to the
output capacitors that may result due to excessive
trace inductance.
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