MIC5219 Datasheet, PDF (11/12 Pages) Micrel Semiconductor – 500mA-Peak Output LDO Regulator

MIC5219
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 figures.
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 there-
fore 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 Micrel
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
V_IN
IN
OUT
V_OUT
EN BYP
GND
1µF
Figure 5. Low-Noise Fixed Voltage Regulator
Figure 5 shows a basic MIC5219-x.xBMX fixed-voltage regu-
lator circuit. A 1µF minimum output capacitor is required for
basic fixed-voltage applications.
MIC5219-x.x
V_IN
IN
OUT
V_OUT
EN BYP
GND
2.2µF
470pF
Micrel
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
V_IN
IN
OUT
V_OUT
EN ADJ R1
GND
1µF
R2
Figure 7. Low-Noise Adjustable Voltage Regulator
Figure 7 shows the basic circuit for the MIC5219 adjustable
regulator. The output voltage is configured 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 perfor-
mance, R2 should not exceed 470kΩ.
MIC5219
V_IN
IN
OUT
EN ADJ
GND
V_OUT
R1
2.2µF
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.
July 2000
11
MIC5219