MIC5239-1.8BM TR Micrel Inc, MIC5239-1.8BM TR Datasheet - Page 10

• Manufacturer Part Number: MIC5239-1.8BM TR
• Description: IC REG LDO 500MA 1.8V 8-SOIC
• Manufacturer: Micrel Inc

Specifications of MIC5239-1.8BM TR

• Regulator Topology: Positive Fixed
• Voltage - Output: 1.8V
• Voltage - Input: 2.3 ~ 30 V
• Voltage - Dropout (typical): 0.35V @ 500mA
• Number Of Regulators: 1
• Current - Output: 500mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Limit (min): -
• Other names: MIC5239-1.8BMTR; MIC5239-1.8BMTR

Current Limit
Figure 4 displays a method for reducing the steady state
short-circuit current. The duration that the supply
delivers current is set by the time required for the error
flag output to discharge the 4.7µF capacitor tied to the
enable pin. The off time is set by the 200kΩ resistor as it
recharges the 4.7µF capacitor, enabling the regulator.
This circuit reduces the short-circuit current from 800mA
to 40mA while allowing for regulator restart once the
short is removed.
Thermal Characteristics
The MIC5239 is a high input voltage device, intended to
provide 500mA of continuous output current in two very
small profile packages. The power MSOP-8 allows the
device to dissipate about 50% more power than their
standard equivalents.
Power MSOP-8 Thermal Characteristics
One of the secrets of the MIC5239’s performance is its
power MSOP-8 package featuring half the thermal
resistance of a standard MSOP-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
(junction-to-case thermal resistance) and θ
ambient thermal resistance). See Figure 5. θ
resistance from the die to the leads of the package. θ
is the resistance from the leads to the ambient air and it
includes θ
(sink-to-ambient thermal resistance).
Micrel
December 2007
SHUTDOWN
ENABLE
Figure 4. Remote Enable with Short-Circuit
V
5V
IN
CS
200k
(case-to-sink thermal resistance) and θ
Current Foldback
4.7µF
IN
EN
MIC5239
1N4148
200k
GND
OUT
FLG
CA
C
OUT
(case-to-
JC
V
V
ERR
OUT
is the
CA
SA
JC
10
Using the power MSOP-8 reduces the θ
and allows the user to reduce θ
resistance, θ
is the limiting factor in calculating the maximum power
dissipation capability of the device. Typically, the power
MSOP-8 has a θ
than the standard MSOP-8 which is typically 200°C/W.
θ
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
appropriate ground plane heatsink 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 maximum allowable temperature rise
must be calculated to determine operation along which
curve.
CA
is reduced because pins 5 through 8 can now be
Figure 6. Copper Area vs. Power-MSOP
temperature
JA
Figure 5. Thermal Resistance
(junction-to-ambient thermal resistance)
Power Dissipation (∆T
JC
of 80°C/W, this is significantly lower
from
being
CA
. The total thermal
JA
)
exceeded,
M9999-121007
JC
dramatically
MIC5239
the