MIC37100 Datasheet, PDF (12/15 Pages) Micrel Semiconductor – 1A LOW VOLTAGE U CAP LDO REGULATOR

MIC37100/37101/37102
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
V_IN
ENABLE
SHUTDOWN
MIC37102
IN OUT
R1
EN ADJ
GND
R2
V_OUT
C_OUT
Micrel
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_CA (case-to-ambi-
ent thermal resistance). See Figure 3. θ_JC is the resistance
from the die to the leads of the package. θ_CA is the resistance
from the leads to the ambient air and it includes θ_CS (case-to-
sink thermal resistance) and θ_SA (sink-to-ambient thermal
resistance).
V_OUT = 1.240V ^{}1+ _RR21^{}
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 1MΩ, because of the very high input impedance
and low bias current of the sense comparator: The resistor
values are calculated by:
R1 =
R2


V_OUT
1.240
−
1^{}
Where V_O 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
SOIC-8
θ_JA
θ_JC
θ_CA
ground plane
heat sink area
AMBIENT
printed circuit board
Figure 3. Thermal Resistance
Using the power SOIC-8 reduces the θ_JC dramatically and
allows the user to reduce θ_CA. The total thermal resistance,
θ_JA (junction-to-ambient thermal resistance) is the limiting
factor in calculating the maximum power dissipation capabil-
ity of the device. Typically, the power SOIC-8 has a θ_JC of
20°C/W, this is significantly lower than the standard SOIC-8
which is typically 75°C/W. θ_CA is reduced because pins 5
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.
M9999-091604
12
September 2004