MIC5219

Micrel

MIC5219

12

April 2001

P

P

The power dissipation at 500mA must also be calculated.

P

P

This number must be multiplied by the duty cycle at which it

would be operating, 12.5%.

P

P

The total power dissipation of the device under these condi-

tions is the sum of the two power dissipation figures.

P

P

P

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

IN

OUT

GND

1µF

EN

BYP

Figure 5. Low-Noise Fixed Voltage Regulator

Figure 5 shows a basic MIC5219-x.xBMX fixed-voltage regu-

lator circuit. A 1

µF minimum output capacitor is required for

basic fixed-voltage applications.

MIC5219-x.x

IN

OUT

GND

470pF

EN

BYP

2.2µF

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

capacitor is used.

Adjustable Regulator Circuits

MIC5219

IN

OUT

GND

EN

ADJ

1µF

R1

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

1.242V

R2

R1

1









Although ADJ is a high-impedance input, for best perfor-

mance, R2 should not exceed 470k

Ω.

MIC5219

IN

OUT

GND

EN

ADJ

2.2µF

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.