MIC5318_10 Datasheet, PDF (9/11 Pages) Micrel Semiconductor – High Performance 300mA μCap ULDO

Micrel, Inc.
Thermal Considerations
The MIC5318 is designed to provide 300mA of
continuous current. Maximum ambient operating
temperature can be calculated based on the output
current and the voltage drop across the part. Given
that the input voltage is 3.3V, the output voltage is
2.8V and the output current = 300mA.
The actual power dissipation of the regulator circuit
can be determined using the equation:
P_D = (V_IN – V_OUT) I_OUT + V_IN I_GND
Because this device is CMOS and the ground current
is typically <100µA over the load range, the power
dissipation contributed by the ground current is < 1%
and can be ignored for this calculation:
P_D = (3.3V – 2.8V) × 300mA
P_D = 0.15W
To determine the maximum ambient operating
temperature of the package, use the junction-to-
ambient thermal resistance of the device and the
following basic equation:
⎛ ^TJ(MAX) ^{- T}A
⎝ ^{PD(MAX) =}
JA
T_J(max) = 125°C, the maximum junction temperature of
the die θ_JA thermal resistance = 100°C/W.
The table below shows junction-to-ambient thermal
resistance for the MIC5318 in the 6-pin 1.6mm x
1.6mm Thin MLF^® package.
MIC5318
Substituting P_D for P_D(max) and solving for the ambient
operating temperature will give the maximum
operating conditions for the regulator circuit. The
junction-to-ambient thermal resistance for the
minimum footprint is 100°C/W.
The maximum power dissipation must not be
exceeded for proper operation.
For example, when operating the MIC5318-2.8YMT at
an input voltage of 3.3V and 300mA load with a
minimum footprint layout, the maximum ambient
operating temperature T_A can be determined as
follows:
0.15W = (125°C – T_A)/(100°C/W)
T_A = 110°C
Therefore, a 2.8V application with 300mA of output
current can accept an ambient operating temperature
of 110°C in a 1.6mm x 1.6mm Thin MLF^® package.
For a full discussion of heat sinking and thermal
effects on voltage regulators, refer to the “Regulator
Thermals” section of Micrel’s Designing with Low-
Dropout Voltage Regulators handbook. This informa-
tion can be found on Micrel's website at:
http://www.micrel.com/_PDF/other/LDOBk_ds.pdf
Package
6-Pin 1.6x1.6 Thin MLF^®
θ_JA Recommended
Minimum Footprint
100°C/W
Thermal Resistance
September 2010
9
M9999-092810-B