MIC37100-1.5BM 查看數據表（PDF） - Micrel

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MIC37100-1.5BM

1A Low-Voltage µCap LDO

Micrel 

Micrel, Inc.

without operating in dropout, NPN-based regulators

require an input voltage of 3.7V at the very least. The

MIC37100 regulator will provide excellent performance

with an input as low as 3.0V or 2.5V respectively. This

gives the PNP based regulators a distinct advantage

over older, NPN based linear regulators.

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

VIN

ENABLE

SHUTDOWN

MIC37102

IN OUT

R1

EN ADJ

GND

R2

VOUT

COUT

VOUT

= 1.240V⎜⎛1 +

⎝

R1 ⎟⎞

R2 ⎠

Figure 2. Adjustable Regulator with Resistors

The MIC37102 allows programming the output voltage

anywhere between 1.24V and the 6V maximum

operating rating of the family. Two resistors are used.

Resistors can be quite large, up to 1MΩ, because of the

very high input impedance and low bias current of the

sense comparator. The resistor values are calculated by:

R1

=

R2⎜⎜⎝⎛

VOUT

1.240

−

1⎟⎟⎠⎞

Where VO is the desired output voltage. Figure 2 shows

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.

MIC37100/37101/37102

Thermal resistance consists of two main elements, θJC

(junction-to-case thermal resistance) and θCA (case-to-

ambient thermal resistance). See Figure 3. θJC is the

resistance from the die to the leads of the package. θCA

is the resistance from the leads to the ambient air and it

includes θCS (case-to-sink thermal resistance) and θSA

(sink-to-ambient thermal resistance).

SOIC-8

JA

JC

CA

ground plane

heat sink area

AMBIENT

printed circuit board

Figure 3. Thermal Resistance

Using the power SOIC-8 reduces the θJC dramatically

and allows the user to reduce θCA. The total thermal

resistance, θJA (junction-to-ambient thermal resistance)

is the limiting factor in calculating the maximum power

dissipation capability of the device. Typically, the power

SOIC-8 has a θJC of 20°C/W, this is significantly lower

than the standard SOIC-8 which is typically 75°C/W. θCA

is reduced because pins 5 through 8 can now be

soldered directly to a ground plane which significantly

reduces the case-to-sink thermal resistance 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

operation of the device. To prevent this maximum

junction temperature from being exceeded, the

appropriate ground plane heat sink must be used.

700 TJA =

600

500

400

300

200

100

0

0 0.25 0.50 0.75 1.00 1.25 1.50

POWER DISSIPATION (W)

Figure 4. Copper Area vs. Power SO-8

Power Dissipation

September 2007

12

M9999-090607

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