MIC5236 Micrel Semiconductor, MIC5236 Datasheet - Page 10

• Manufacturer Part Number: MIC5236
• Description: Low Quiescent Current Cap LDO Regulator Preliminary Information
• Manufacturer: Micrel Semiconductor

MIC5236
Thermal Characteristics
The MIC5236 is a high input voltage device, intended to
provide 150mA of continuous output current in two very small
profile packages. The power SOP-8 and power MSOP-8
allow the device to dissipate about 50% more power than
their standard equivalents.
Power SOP-8 Thermal Characteristics
One of the secrets of the MIC5236’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,
(junction-to-case thermal resistance) and
ent thermal resistance). See Figure 5.
from the die to the leads of the package.
from the leads to the ambient air and it includes
sink thermal resistance) and
resistance).
Using the power SOP-8 reduces the
allows the user to reduce
factor in calculating the maximum power dissipation capabil-
ity of the device. Typically, the power SOP-8 has a
20 C/W, this is significantly lower than the standard SOP-8
which is typically 75 C/W.
MIC5236
JA
(junction-to-ambient thermal resistance) is the limiting
Figure 4. Remote Enable with Short-Circuit
SHUTDOWN
ENABLE
V
5V
Figure 5. Thermal Resistance
IN
200k
printed circuit board
SOP-8
Current Foldback
JC
4.7 F
CA
JA
CA
IN
EN
. The total thermal resistance,
CA
MIC5236
1N4148
SA
is reduced because pins 5
GND
200k
(sink-to-ambient thermal
OUT
ERR
AMBIENT
JC
JC
CA
heat sink area
ground plane
CA
dramatically and
is the resistance
is the resistance
(case-to-ambi-
C
CS
OUT
V
V
ERR
OUT
(case-to-
JC
JC
of
10
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.
Figure 6 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 maxi-
mum allowable temperature rise must be calculated to deter-
mine operation along which curve.
For example, the maximum ambient temperature is 50 C, the
Using Figure 6, the minimum amount of required copper can
be determined based on the required power dissipation.
Power dissipation in a linear regulator is calculated as fol-
lows:
If we use a 3V output device and a 28V input at moderate
output current of 25mA, then our power dissipation is as
follows:
From Figure 6, the minimum amount of copper required to
operate this application at a T of 75 C is 25mm
Quick Method
Determine the power dissipation requirements for the design
along with the maximum ambient temperature at which the
device will be operated. Refer to Figure 7, which shows safe
operating curves for three different ambient temperatures:
25 C, 50 C and 85 C. From these curves, the minimum
T is determined as follows:
T
T
P
P
P
P
T = T
J(max)
A(max)
T = 125 C – 50 C
T = 75 C
D
D
D
D
Figure 6. Copper Area vs. Power-SOP
= (V
= (28V – 3V)
= 625mW + 7mW
= 632mW
J(max)
= 125 C
IN
= maximum ambient operating temperature
– V
Power Dissipation
900
800
700
600
500
400
300
200
100
– T
0
OUT
0
A(max)
0.25 0.50 0.75 1.00 1.25 1.50
POWER DISSIPATION (W)
) I
25mA + 28V
OUT
+ V
IN
· I
GND
T
250 A
JA
)
November 2000
2
.
Micrel