Datasheet
Micrel, Inc. MIC5219
June 2009 12 M0371-061809
P
D
× 50mA = 0.875 × 173mW
P
D
× 50mA = 151mW
The power dissipation at 500mA must also be calculated.
P
D
× 500mA = (5V – 3.3V) 500mA + 5V × 20mA
P
D
× 500mA = 950mW
This number must be multiplied by the duty cycle at which it
would be operating, 12.5%.
P
D
× = 0.125 × 950mW
P
D
× = 119mW
The total power dissipation of the device under these condi-
tions is the sum of the two power dissipation gures.
P
D(total)
= P
D
× 50mA + P
D
× 500mA
P
D(total)
= 151mW + 119mW
P
D(total)
= 270mW
The total power dissipation of the regulator is less than the
maximum power dissipation of the SOT-23-5 package at room
temperature, on a minimum footprint board and therefore
would operate properly.
Multilayer boards with a ground plane, wide traces near the
pads, and large supply-bus lines will have better thermal
conductivity.
For additional heat sink characteristics, please refer to Mi-
crel “Application Hint 17, Designing P.C. Board Heat Sinks”,
included in Micrel’s Databook. For a full discussion of heat
sinking and thermal effects on voltage regulators, refer to
“Regulator Thermals” section of Micrel’s Designing with Low-
Dropout Voltage Regulators handbook.
Fixed Regulator Circuits
MIC5219-x.x
IN OUT
GND
1µF
V
IN
V
OUT
EN BYP
Figure 5. Low-Noise Fixed Voltage Regulator
Figure 5 shows a basic MIC5219-x.xBMX xed-voltage regu-
lator circuit. A 1µF minimum output capacitor is required for
basic xed-voltage applications.
MIC5219-x.x
IN OUT
GND
470pF
V
IN
EN BYP
2.2µF
V
OUT
Figure 6. Ultra-Low-Noise Fixed Voltage Regulator
Figure 6 includes the optional 470pF noise bypass capacitor
between BYP and GND to reduce output noise. Note that the
minimum value of C
OUT
must be increased when the bypass
capacitor is used.
Adjustable Regulator Circuits
MIC5219
IN OUT
GND
V
IN
EN ADJ
1µF
V
OUT
R1
R2
Figure 7. Low-Noise Adjustable Voltage Regulator
Figure 7 shows the basic circuit for the MIC5219 adjustable
regulator. The output voltage is congured by selecting values
for R1 and R2 using the following formula:
V
OUT
=1.242V
R2
R1
+1
Although ADJ is a high-impedance input, for best performance,
R2 should not exceed 470kΩ.
MIC5219
IN OUT
GND
V
IN
EN ADJ
2.2µF
V
OUT
R1
R2
470pF
Figure 8. Ultra-Low-Noise Adjustable Application
Figure 8 includes the optional 470pF bypass capacitor from
ADJ to GND to reduce output noise.