1997

3-173

MIC5208

Micrel

3

No-Load Stability

The MIC5208 will remain stable and in regulation with no load

(other than the internal voltage divider) unlike many other

voltage regulators. This is especially important in CMOS RAM

keep-alive applications.

Thermal Shutdown

Thermal shutdown is independent on both halves of the dual

MIC5208, however, an overtemperature condition in one half

may affect the other half because of proximity.

Thermal Considerations

Multilayer boards having a ground plane, wide traces near the

pads, and large supply bus lines provide better thermal

conductivity.

The MIC5208-xxBMM (8-lead MSOP) has a thermal resis-

tance of 200

°C/W when mounted on a FR4 board with

minimum trace widths and no ground plane.

PC Board

θ

JA

Dielectric

FR4

200

°C

MSOP Thermal Characteristics

For additional heat sink characteristics, please refer to Micrel

Application Hint 17, “Calculating P.C. Board Heat Sink Area

For Surface Mount Packages”.

Applications Information

Supply/Ground

Both MIC5208 GND pins must be connected to the same

ground potential. INA and INB can each be connected to a

different supply.

Enable/Shutdown

ENA (enable/shutdown) and ENB may be enabled sepa-

rately. Forcing ENA/B high (> 2V) enables the associated

regulator. ENA/B requires a small amount of current, typically

15

µA. While the logic threshold is TTL/CMOS compatible,

ENA/B may be forced as high as 20V, independent of V

Input Capacitor

A 0.1

µF capacitor should be placed from IN to GND 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.

Output Capacitor

An output capacitor is required between OUT and GND to

prevent oscillation. Larger values improve the regulator’s

transient response. The output capacitor value may be in-

creased without limit.

The output capacitor should have an ESR (effective series

resistance) of about 5

Ω or less and a resonant frequency

above 500kHz. Most tantalum or aluminum electrolytic ca-

pacitors are adequate; film types will work, but are more

expensive. Since many aluminum electrolytics have electro-

lytes that freeze at about –30

°C, solid tantalums are recom-

mended for operation below –25

°C.

At lower values of output current, less output capacitance is

required for output stability. The capacitor can be reduced to

0.22

µF for current below 10mA or 0.1µF for currents below

1mA.