MIC37100/37101/37102

Micrel

M9999-091604

12

September 2004

Minimum Load Current

The MIC37100/01/02 regulator is specified between finite

loads. If the output current is too small, leakage currents

dominate and the output voltage rises. A 10mA minimum load

current is necessary for proper regulation.

Adjustable Regulator Design

IN

R1

R2

EN

OUT

ADJ

GND

MIC37102

ENABLE

SHUTDOWN

V

1.240V 1

R1

R2









Figure 2. Adjustable Regulator with Resistors

The MIC37102 allows programming the output voltage any-

where between 1.24V and the 6V maximum operating rating

of the family. Two resistors are used. Resistors can be quite

large, up to 1M

Ω, because of the very high input impedance

and low bias current of the sense comparator: The resistor

values are calculated by:

R1 R2

V

1.240

1

OUT

=−









Where V

component definition. Applications with widely varying load

currents may scale the resistors to draw the minimum load

current required for proper operation (see above).

Power SOIC-8 Thermal Characteristics

One of the secrets of the MIC37101/02’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 3.

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

SOIC-8

AMBIENT

Figure 3. Thermal Resistance

Using the power SOIC-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 SOIC-8 has a

θ

20

°C/W, this is significantly lower than the standard SOIC-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.

Low-dropout linear regulators from Micrel are rated to a

maximum junction temperature of 125

°C. It is important not

to exceed this maximum junction temperature during opera-

tion of the device. To prevent this maximum junction tempera-

ture from being exceeded, the appropriate ground plane heat

sink must be used.