MIC5201

Micrel, Inc.

MIC5201

8

June 2005

Applications Information

Figure 1 shows a basic fixed-voltage application with the

unused enable input connected to V

MIC5201-x.xBM

MIC5201-x.xBS

IN

OUT

GND

1µF

EN

Figure 1. Fixed Application

Adjustable regulators require two resistors to set the output

voltage. See Figure 2.

MIC5201BM

IN

OUT

GND

EN

ADJ

3.3µF

R1

R2

V1.242V 1

R2

R1













Figure 2. Adjustable Application

Resistors values are not critical because ADJ (adjust) has a

high impedance, but for best results use resistors of 470kΩ

or less.

Output Capacitors

A 1µF capacitor is recommended between the MIC5201

output and ground to prevent oscillations due to instability.

Larger values serve to improve the regulator’s transient

response. Most types of tantalum or aluminum electrolytics

will be adequate; film types will work, but are costly and

therefore not recommended. Many aluminum electrolytics

have electrolytes that freeze at about –30°C, so solid tanta-

lums are recommended for operation below –25°C. The

important parameters of the capacitor are an effective series

resistance of about 5Ω or less and a resonant frequency

above 500kHz. The value of this capacitor may be increased

without limit.

At lower values of output current, less output capacitance is

required for output stability. The capacitor can be reduced to

0.47µF for current below 10mA or 0.33µF for currents below

1mA.

Input Capacitors

A 1µF capacitor should be placed from the MIC5201 input to

ground if there is more than 10 inches of wire between the

input and the ac filter capacitor or if a battery is used as the

input.

Noise Reduction Capacitors

On adjustable devices, a capacitor from ADJ to GND will

decrease high-frequency noise on the output. See Figure 3.

MIC5201BM

IN

OUT

GND

EN

ADJ

3.3µF

R1

R2

Figure 3. Decreasing Ouput Noise

Minimum Load

The MIC5201 will remain stable and in regulation with no

load unlike many other voltage regulators. This is

especially important in CMOS RAM keep-alive

applications.

Dual-Supply Systems

When used in dual supply systems where the regulator

load is returned to a negative supply, the output voltage

must be diode clamped to ground.

Thermal Considerations Layout

The MIC5201-x.xBM (8-pin surface mount package) has the

following thermal characteristics when mounted on a single

layer copper-clad printed circuit board.

Multilayer boards having a ground plane, wide traces near the

pads, and large supply bus lines provide better thermal

conductivity.

The “worst case” value of 160°C/W assumes no ground

plane, minimum trace widths, and a FR4 material board.

Nominal Power Dissipation and Die Temperature

The MIC5201-x.xBM at a 25°C ambient temperature will

operate reliably at up to 625mW power dissipation when

mounted in the “worst case” manner described above. At an

ambient temperature of 55°C, the device may safely dissi-

pate 440mW. These power levels are equivalent to a die

temperature of 125°C, the recommended maximum tem-

perature for non-military grade silicon integrated circuits.

For MIC5201-x.xBS (SOT-223 package) heat sink character-

istics, please refer to Micrel Application Hint 17, P.C. Board

Heat Sinking.

245 mil

30 mil

50 mil

50 mil

150 mil

Figure 4. Min. Recommended SO-8 PCB Pads Size

PC Board

Dielectric

FR4

160ºC/W

Ceramic

120ºC/W

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