FC1286 Datasheet, PDF (4/4 Pages) First Components International – 1.5A Ultra Low Dropout Positive Adjustable Regulator

FC1286-XX 1.5A Ultra Low Dropout Positive Adjustable Regulator
Stability
The FC1286-XX requires the use of an output capacitor as part of the frequency compensation in order to make the
regulator stable. Typical designs for the microprocessor application use standard electrolytic with typical ESR in the range
of 50 to 100m and an output capacitance of 100uF to 1000uF. Fortunately as the capacitance increases, the ESR
decreases resulting in a fixed RC time constant. The FC1286-XX takes advantage of the phenomena in making the
overall regulator loop stable. For most applications a minimum of 100uF aluminum electrolytic capacitor insures both
stability and good transient response.
Thermal Design
The FC1286-XX incorporates an internal thermal shutdown that protects the device when the junction temperature
exceeds the maximum allowable junction temperatures. Although this device can operate with junction temperatures in the
range of 150к, it is recommended that the selected heat sink be chosen such that during maximum continuous load
operation, the junction temperature is kept below this number. The example below shows the steps in selecting the proper
surface mount package.
Assuming, the following conditions: Vout =2.5V, Vin =3.3V, Vctrl =5V, Iout =2A DC Avg.
Calculate the maximum power dissipation using the following equation: Pd =Iout*(Vin-Vout) + (Iout/60)*(Vctrl-Vout)
Pd =2*(3.3-2.5) + (2/60)*(5-2.5) =1.68W
Using table below select the proper package and the amount of copper board needed.
Package
Copper Area
JA (к/W)
Max Pd (Ta=25к)
TO-263-5L
Pad Size 1.4” * 1.4”
25 ~ 45
2.4W ~ 4.4W
Max Pd (Ta=45к)
2.0W ~ 3.6W
Note: Above table is based on the maximum junction temperature of 135к.