MIC5323 Datasheet, PDF (10/15 Pages) Micrel Semiconductor – High PSRR Low Noise 300mA μCap Ultra-Low Dropout LDO Regulator

Micrel, Inc.
MIC5323
Thermal Considerations
The MIC5323 is designed to provide 300mA of
continuous current in a very small package. 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:
P_D(max)



T_J(max)
θ_JA
- T_A


Where T_J(max) is the maximum junction temperature,
125°C, and θ_JA represents the junction-to-ambient
thermal resistance, 93°C/W.
Substituting P_D for P_D(max) and solving for the ambient
operating temperature will give the maximum operating
conditions for the regulator circuit consuming P_D watts.
The maximum power dissipation must not be exceeded
for proper operation.
For example, when operating the MIC5323-2.8YMT at
an input voltage of 3.3V and 300mA load with a
minimum footprint layout, the maximum ambient can be
solved for as follows:
0.15W


125C - T_A
93C/W

T_A  111C
Therefore, a 2.8V application at 300mA of output current
can accept an ambient operating temperature of 111°C
in a 6 pin 2mm x 2mm 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 information can be found on Micrel's
website at:
http://www.micrel.com/_PDF/other/LDOBk_ds.pdf
November 2011
10
M9999-110311B