CAT6242 Datasheet, PDF (10/14 Pages) ON Semiconductor – 1.3 Amp CMOS LDO Voltage Regulator

CAT6242
APPLICATIONS INFORMATION
Input Decoupling (C_IN)
A ceramic or tantalum 1 mF capacitor is recommended and
should be connected close to the CAT6242’s package.
Higher capacitance and lower ESR will improve the overall
line and load transient response.
Output Decoupling (C_OUT)
The minimum output decoupling value is 2.2 mF and can
be augmented to fulfill stringent load transient
requirements. The regulator works with ceramic chip
capacitors as well as low−ESR tantalum devices. Larger
values improve noise rejection and load regulation transient
response. The CAT6242 is a highly stable regulator and
performs well over a wide range capacitor Equivalent Series
Resistances (ESR).
Thermal Considerations
As power in the CAT6242 increases, it may become
necessary to provide thermal relief. The maximum power
dissipation supported by this device is dependent upon
board design and layout. Mounting pad configuration on the
PCB, the board material, and the ambient temperature affect
the rate of junction temperature rise for the part. When the
CAT6242 has good thermal conductivity through the PCB,
the junction temperature will be relatively low even with
high power applications. The maximum dissipation the
CAT6242 can handle is given by:
ƪ ƫ _{PD(MAX) +}
T_J(MAX) * T_A
R_qJA
(eq. 1)
Since T_J is not recommended to exceed 125°C, then with
CAT6242 soldered to 645 mm² (1 sq inch), 1 oz copper area,
FR4 PCB material can dissipate in excess of 1 W when the
ambient temperature (T_A) is 25°C. Note that this assumes the
pad in the center of the package is soldered to the dissipating
copper foil. See Figure below for R_qJA versus PCB area for
heat dissipating areas smaller than 645 mm². Power
dissipation can be calculated from the following equations:
P_D [ V_IN(I_GND ) I_OUT) ) I_OUT(V_IN * V_OUT) (eq. 2)
or
V_IN(MAX)
[
P_D(MAX) ) (V_OUT
I_OUT ) I_GND
I_OUT)
(eq. 3)
300
250
1 oz C.F
2 oz C.F
200
1 oz Sim
2 oz Sim
150
100
50
0
0 25 50 75 100 125 150 175 200 225 250 275 300
650
Copper heat spreading area (mm²)
Figure 22. Thermal Resistance vs. PCB Copper Area
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