April 2003

7

MIC5212

MIC5212

Micrel

Applications Information

Input Capacitor

A 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. 1.0

µF minimum is recommended. Larger

values improve the regulator’s transient response. The out-

put capacitor value may be increased without limit.

The output capacitor should have an ESR (Effective Series

Resistance) of about 5

Ω or less and a resonant frequency

above 1MHz. Ultra-low-ESR capacitors may cause a low-

amplitude oscillation and/or underdamped transient response.

Most tantalum or aluminum electrolytic capacitors are ad-

equate; film types will work, but are more expensive. Since

many aluminum electrolytic capacitors have electrolytes that

freeze at about –30

°C, solid tantalum capacitors 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

0.47

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

1mA.

No-Load Stability

The MIC5212 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.

Dual-Supply Operation

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.

Power SO-8 Thermal Characteristics

One of the secrets of the MIC5212’s performance is its power

SO-8 package featuring half the thermal resistance of a

standard SO-8 package. Lower thermal resistance means

more output current or higher input voltage for a given

package size.

Lower thermal resistance is achieved by joining the four

ground leads with the die attach paddle to create a single-

piece electrical and thermal conductor. This concept has

been used by MOSFET manufacturers for years, proving

very reliable and cost effective for the user.

Thermal resistance consists of two main elements,

θ

JC

(junction-to-case thermal resistance) and

θ

ent thermal resistance). See Figure 1.

θ

from the die to the leads of the package.

θ

from the leads to the ambient air and it includes

θ

sink thermal resistance) and

θ

resistance).

θ

JA

θ

JC

θ

CA

printed circuit board

ground plane

heat sink area

SO-8

AMBIENT

Figure 1. Thermal Resistance

Using the power SO-8 reduces the

θ

allows the user to reduce

θ

θ

factor in calculating the maximum power dissipation capabil-

ity of the device. Typically, the power SO-8 has a

θ

20

°C/W, this is significantly lower than the standard SO-8

which is typically 75

°C/W. θ

through 8 can now be soldered directly to a ground plane

which significantly reduces the case-to-sink thermal resis-

tance and sink to ambient thermal resistance.