Micrel, Inc.
MIC5219
P × 50mA = 0.875 × 173mW
MIC5219-x.x
D
VIN
VOUT
P × 50mA = 151mW
IN
OUT
BYP
GND
D
The power dissipation at 500mA must also be calculated.
EN
2.2µF
P × 500mA = (5V – 3.3V) 500mA + 5V × 20mA
D
470pF
P × 500mA = 950mW
D
This number must be multiplied by the duty cycle at which it
would be operating, 12.5%.
Figure 6. Ultra-Low-Noise Fixed Voltage Regulator
P × = 0.125 × 950mW
D
Figure 6 includes the optional 470pF noise bypass capacitor
between BYP and GND to reduce output noise. Note that the
P × = 119mW
D
minimum value of C
capacitor is used.
must be increased when the bypass
The total power dissipation of the device under these condi-
tions is the sum of the two power dissipation figures.
OUT
Adjustable Regulator Circuits
P
P
P
= P × 50mA + P × 500mA
D D
= 151mW + 119mW
= 270mW
D(total)
D(total)
D(total)
MIC5219
VIN
VOUT
1µF
IN
OUT
ADJ
R1
R2
EN
The total power dissipation of the regulator is less than the
maximumpowerdissipationoftheSOT-23-5packageatroom
temperature, on a minimum footprint board and therefore
would operate properly.
GND
Multilayer boards with a ground plane, wide traces near the
pads, and large supply-bus lines will have better thermal
conductivity.
Figure 7. Low-Noise Adjustable Voltage Regulator
Figure 7 shows the basic circuit for the MIC5219 adjustable
regulator.Theoutputvoltageisconfiguredbyselectingvalues
for R1 and R2 using the following formula:
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
“RegulatorThermals” section of Micrel’s Designing with Low-
Dropout Voltage Regulators handbook.
R2
ꢀ
ꢀR1
ꢀ
ꢀ
V
= 1.242V ꢀ + 1ꢀ
OUT
AlthoughADJisahigh-impedanceinput,forbestperformance,
R2 should not exceed 470kΩ.
MIC5219
Fixed Regulator Circuits
MIC5219-x.x
VIN
VOUT
1µF
VIN
VOUT
IN
OUT
BYP
IN
OUT
ADJ
R1
R2
EN
EN
GND
GND
2.2µF
470pF
Figure 5. Low-Noise Fixed Voltage Regulator
Figure 8. Ultra-Low-Noise Adjustable Application
Figure5showsabasicMIC5219-x.xBMXfixed-voltageregu-
lator circuit. A 1µF minimum output capacitor is required for
basic fixed-voltage applications.
Figure 8 includes the optional 470pF bypass capacitor from
ADJ to GND to reduce output noise.
June 2009
12
M0371-061809
MICREL [ MICREL SEMICONDUCTOR ]
