MIC5202

Micrel

MIC5202

6

March 2006

Thermal Considerations

Applications Information

External Capacitors

A1µF capacitor is recommended between the MIC5202 output

and ground to prevent oscillations due to instability. Larger val-

ues 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 recom-

mended. Many aluminum electrolytics have electrolytes that

freeze at about –30°C, so solid tantalums 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

1 mA. A 1µF capacitor should be placed from the MIC5202

input to ground if there is more than 10 inches of wire be-

tween the input and the AC filter capacitor or if a battery is

used as the supply.

ENABLE Input

The MIC5202 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

of the MIC5202 may be enabled separately.

General Notes

The MIC5202 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. Thermal shutdown is

independant on both halfs of the dual MIC5202, however an

over-temperature condition on one half might affect the other

because of proximity. 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.

Both MIC5202 GROUND pins must be tied to the same ground

potential. Isolation between the two halfs allows connecting

the two 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 Tempera-

ture

The MIC5202-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.

Part I. Layout

The MIC5202-xxBM (8-pin surface mount package) has the

following thermal characteristics when mounted on a single

layer copper-clad printed circuit board.

245 mil

30 mil

50 mil

50 mil

150 mil

Minimum recommended board pad size, SO-8.