MIC5337 Datasheet, PDF (8/11 Pages) Micrel Semiconductor – 1.2mm x 1.6mm 300mA Low IQ LDO Ultra Low Dropout with Auto Discharge

Micrel, Inc.
drop across the part. For example: given that the input
voltage is 3.6V, the output voltage is 2.8V and the output
current is 300mA. The power dissipation of the regulator
circuit can be determined using the equation:
P_D = (V_IN – V_OUT1) 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 = (3.6V – 2.8V) × 300mA
P_D = 0.24W
To determine the maximum ambient operating
temperature 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
⎟⎟⎠⎞
The maximum junction temperature of the die, T_J(max) =
125°C.The package thermal resistance, θ_JA = 173°C/W.
MIC5337
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 maximum power dissipation must not be exceeded
for proper operation.
For example, when operating the MIC5337 at an input
voltage of 3.6V and 300mA load with a minimum
footprint layout, the maximum ambient operating
temperature T_A can be determined as follows:
0.24W = (125°C – T_A)/(173°C/W)
T_A = 83°C
Therefore a 2.8V 300mA application can accept an
ambient operating temperature of 83.0°C in a 1.2mm 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
information can be found on Micrel's website at:
http://www.micrel.com/_PDF/other/LDOBk_ds.pdf
September 2008
8
M9999-090908-A