mic37100 Micrel Semiconductor, mic37100 Datasheet - Page 13

• Manufacturer Part Number: mic37100
• Description: Mic37100, Mic37101, And Mic37102 1a Low-voltage ?cap Ldo Regulator
• Manufacturer: Micrel Semiconductor

Figure 4 shows copper area versus power dissipation
with each trace corresponding to a different temperature
rise above ambient.
From these curves, the minimum area of copper
necessary for the part to operate safely can be
determined. The maximum allowable temperature rise
must be calculated to determine operation along which
curve.
For example, the maximum ambient temperature is
50°C, the ∆T is determined as follows:
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:
If we use a 2.5V output device and a 3.3V input at an
output current of 1A, then our power dissipation is as
follows:
From Figure 4, the minimum amount of copper required
to operate this application at a ∆T of 75°C is 160mm
Micrel, Inc.
September 2007
∆T = T
T
T
erature.
∆T = 125°C – 50°C
∆T = 75°C
P
P
P
P
J(max)
A(max)
D
D
D
D
= (V
= (3.3V – 2.5V) × 1A + 3.3V × 11mA
= 800mW + 36mW
= 836mW
= 125°C
J(max)
IN
= maximum ambient operating temp-
– V
– T
OUT
A(max)
) I
OUT
+ V
IN
× I
GND
2
.
13
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, 836mW, the
curve in Figure 5 shows that the required area of copper
is 160mm
The θ
depending upon the availability of copper ground plane
to which it is attached.
JA
of this package is ideally 63°C/W, but it will vary
Figure 5. Copper Area vs. Power-SOIC
2
.
900
800
700
600
500
400
300
200
100
0
0
Power Dissipation
T
POWER DISSIPATION (W)
0.25 0.50 0.75 1.00 1.25 1.50
J
T
= 125°C
A
= 85°C
MIC37100/37101/37102
50°C 25°C
M9999-090607