MIC49150
Quick Method
Micrel
Enable
The fixed output voltage versions of the MIC49150 feature an
active high enable input (EN) that allows on-off control of the
regulator. Current drain reduces to “zero” when the device is
shutdown, with only microamperes of leakage current. The
EN input has TTL/CMOS compatible thresholds for simple
logic interfacing. EN may be directly tied to V
IN
and pulled up
to the maximum supply voltage
Determine the power dissipation requirements for the design
along with the maximum ambient temperature at which the
device will be operated. Refer to Figure 3, 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 maxi-
mum power dissipation required. If the maximum ambient
temperature is 50°C and the power dissipation is as above,
513mW, the curve in Figure 3 shows that the required area of
copper is less than 100mm
2
.
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.
Adjustable Regulator Design
The MIC49150 adjustable version allows programming the
output voltage anywhere between 0.9Vand 5V. Two resistors
are used. The resistor value between V
OUT
and the adjust pin
should not exceed 10kΩ. Larger values can cause instability.
The resistor values are calculated by:
V
R1
=
R2
×
OUT
–
1
0
.
9
Where V
OUT
is the desired output voltage.
MIC49150
10
January 2002
MICREL [ MICREL SEMICONDUCTOR ]
