MIC3775_06 Datasheet, PDF (12/13 Pages) Micrel Semiconductor – 750mA μCap Low-Voltage Low-Dropout Regulator

Micrel, Inc.
Figure 5. Copper Area vs. Power-MSOP
Power Dissipation (T_A)
∆T = T_J(max) – T_A(max)
T_J(max) = 125°C
T_A(max) = maximum ambient operating
temperature
For example, the maximum ambient temperature is
50°C, the ∆T is determined as follows:
∆T = 125°C – 50°C
∆T = 75°C
Using Figure 4, the minimum amount of required copper
can be determined based on the required power
dissipation. Power dissipation in a linear regulator is
calculated as follows:
MIC3775
P_D = (V_IN – V_OUT) I_OUT + V_IN×I_GND
If we use a 2.5V output device and a 3.3V input at an
output current of 750mA, then our power dissipation is
as follows:
P_D = (3.3V – 2.5V) × 750mA + 3.3V × 7.5mA
P_D = 600mW + 25mW
P_D = 625mW
From Figure 4, the minimum amount of copper required
to operate this application at a ∆T of 75°C is 160mm².
Quick Method
Determine the power dissipation requirements for the
design along with the maximum ambient temperature at
which the device will be operated. Refer to Figure 5,
which shows safe operating curves for three different
ambient temperatures: 25°C, 50°C and 85°C. From
these curves, the minimum amount of copper can be
determined by knowing the maximum power dissipation
required. If the maximum ambient temperature is 50°C
and the power dissipation is as above, 625mW, the
curve in Figure 5 shows that the required area of copper
is 160mm².The θ_JA of this package is ideally 80°C/W, but
it will vary depending upon the availability of copper
ground plane to which it is attached.
December 2006
12
M9999-121906