MIC2845A Datasheet, PDF (15/18 Pages) Micrel Semiconductor – High Efficiency 6 Channel Linear WLED Driver with DAM™, Ultra Fast PWM™ Control and Dual Low IQ LDOs

Micrel Inc.
T_J(max) = 125°C, is the maximum junction temperature of
the die and θ_JA, is the thermal resistance = 60°C/W.
Substituting P_TOTAL for P_TOTAL(max) and solving for the
ambient operating temperature will give the maximum
operating conditions for the regulator circuit.
For example, when operating the MIC2845A LDOs
(LDO1 = 2.8V and LDO2 = 1.5V) at an input voltage of
3.6V with 150mA load on each, the maximum ambient
operating temperature T_A can be determined as follows:
P_LDO1 = (3.6V – 2.8V) x 150mA = 0.120W
MIC2845A
P_LDO2 = (3.6V – 1.5V) x 150mA = 0.315W
P_TOTAL=0.120W+ 0.315W = 0.435W
= (125°C – T_A)/(60°C/W)
T_A = 125°C – 0.435W x 60°C/W
T_A = 98.9°C
Therefore, under the above conditions, the maximum
ambient operating temperature of 98.9°C is allowed.
April 2010
15
M9999-041210-C