SC563 Datasheet, PDF (14/16 Pages) Semtech Corporation – Dual Output 300mA LDO Linear Regulator

SC563
Applications Information (continued)
Example
A SC563LH is used to provide outputs of 3.3V, 150mA
from LDO1 and 1.8V, 250mA from LDO2. The input
voltage is 4.2V for LDO1 and 2.5V for LDO2, and the
ambient temperature of the system is 60°C.
P_D= 0.15X(4.2 – 3.3) + 0.25X(2.5 – 1.8)
= 0.31W
and
T_J = 60 + (0.31 x 90) = 87.9°C
This calculation shows the junction temperature is 87.9°C
and it is below the maximum junction temperature of
125°C for this power dissipation. This example also dem-
onstrates that with separate input voltages for LDO1 and
LDO2, the total power dissipation can be reduced with
the lower LDO output voltage fed by a lower input
voltage.
Layout Considerations
The diagram in Figure 3 below illustrates proper layout of
a circuit. The layout considerations are listed below:
• Attach the thermal pad of the device to a copper
pad with vias connected to the GND plane. This
enables better heat transfer from the device to
the PCB.
• Place the input and output capacitors close to
the device for optimal transient response and
device behavior. Extra copper trace length
between the device input and output to the
capacitor soldering pad introduces parasitic
inductance.
• Connect all ground connections of the input
and output capacitor directly to the ground
plane whenever possible to minimize ground
potential differences on the PCB. Shown in the
evaluation board layout below, the SC563
thermal pad, ground pins, and the input and
output capacitors are all connected to the
ground plane through vias .
Figure 3 — SC563 Layout Example
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