MIC49150

Micrel

MIC49150

10

January 2002

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 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

The

θ

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

should not exceed 10k

Ω. Larger values can cause instability.

The resistor values are calculated by:

R1 R2

V

OUT

=× 







09

1

.

–

Where V

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

to the maximum supply voltage