MIC3975-3.3YMM TR Micrel Inc, MIC3975-3.3YMM TR Datasheet - Page 10

• Manufacturer Part Number: MIC3975-3.3YMM TR
• Description: IC REG LDO 750MA 3.3V 8-MSOP
• Manufacturer: Micrel Inc

Specifications of MIC3975-3.3YMM TR

• Regulator Topology: Positive Fixed
• Voltage - Output: 3.3V
• Voltage - Input: Up to 16V
• Voltage - Dropout (typical): 0.3V @ 750mA
• Number Of Regulators: 1
• Current - Output: 750mA (Min)
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Limit (min): -
• Other names: MIC3975-3.3YMMTR; MIC3975-3.3YMMTR

MIC3975
Adjustable Regulator Design
The MIC3975 allows programming the output voltage any-
where between 1.24V and the 16V 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:
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 MSOP-8 Thermal Characteristics
One of the secrets of the MIC3975’s performance is its power
MSO-8 package featuring half the thermal resistance of a
standard MSO-8 package. Lower thermal resistance means
more output current or higher input voltage for a given pack-
age 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
tion-to-case thermal resistance) and θ
thermal resistance). See Figure 3. θ
the die to the leads of the package. θ
from the leads to the ambient air and it includes θ
to-sink thermal resistance) and θ
resistance).
MIC3975
Figure 2. Adjustable Regulator with Resistors
R1 R2
Figure 4. Copper Area vs. Power-MSOP
O

SHUTDOWN
is the desired output voltage. Figure 2 shows
ENABLE



Power Dissipation (∆T
1.240
V
OUT
V
IN
V
OUT

1
IN
EN




MIC3975
1.240V 1
GND
OUT
ADJ
SA




(sink-to-ambient thermal
R2
R1
JC



R1
R2
is the resistance from
CA
CA
JA
(case-to-ambient
is the resistance
)
C
OUT
V
OUT
CS
JC
(case-
(junc-
10
Using the power MSOP-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 MSOP-8 has a θ
80°C/W, this is significantly lower than the standard MSOP-8
which is typically 160°C/W. θ
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.
Figure 4 shows copper area versus power dissipation with
each trace corresponding to a different temperature rise
above ambient.
From these curves, the minimum area of copper necessary for
the part to operate safely can be determined. The maximum
allowable temperature rise must be calculated to determine
operation along which curve.
JA
(junction-to-ambient thermal resistance) is the limiting
ΔT = T
T
J(max)
Figure 5. Copper Area vs. Power-MSOP
J(max)
= 125°C
Figure 3. Thermal Resistance
Power Dissipation (T
printed circuit board
MSOP-8
– T
A(max)

JC

CA
JA
CA
. The total thermal resistance,

CA
is reduced because pins 5
AMBIENT
A
JC
heat sink area
)
ground plane
dramatically and
February 2005
Micrel
JA
of