MIC5200

Micrel, Inc.

April 2005

8

M9999-040805

Thermal Considerations

Applications Information

External Capacitors

A1µFcapacitorisrecommendedbetweentheMIC5200output

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 ad-

equate; film types will work, but are costly and therefore not

recommended.Manyaluminumelectrolyticshaveelectrolytes

that freeze at about –30°C, so solid tantalum capacitors are

recommended for operation below –25°C. The important pa-

rameters 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

1 mA. A 1µF capacitor should be placed from the MIC5200

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.

The MIC5200 will remain stable and in regulation with no load

in addition to the internal voltage divider, unlike many other

voltage regulators. This is especially important in CMOS RAM

keep-alive applications.

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.

ENABLE Input

The MIC5200 features nearly zero OFF mode current. When

the ENABLE input is held below 0.7V, all internal circuitry is

powered off. Pulling this pin high (over 2.0V) re-enables the

device and allows operation.The ENABLE pin requires a small

amount of current, typically 15µA. While the logic threshold is

TTL/CMOS compatible, ENABLE may be pulled as high as

30V, independent of the voltage on V

PC Board

θ

JA

Dielectric

FR4

160°C/W

Ceramic

120°C/W

Multi-layer 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.

Part II. Nominal Power Dissipation and Die Temperature

The MIC5200-xxBM at a 25°C ambient temperature will oper-

ate 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 dissipate 440mW.

These power levels are equivalent to a die temperature of

125°C, the recommended maximum temperature for non-

military grade silicon integrated circuits.

For MIC5200-xxBS (SOT-223 package) heat sink character-

istics, please refer to Micrel Application Hint 17, “Calculating

P.C. Board Heat Sink Area for Surface Mount Packages”.

Part I. Layout

The MIC5200-xxBM (8-pin surface mount package) has the

following thermal characteristics when mounted on a single

layer copper-clad printed circuit board.

245 mil

150 mil

50 mil

50 mil

30 mil

Minimum recommended board pad size, SO-8.