We are looking to develop a circuit that will reduce 12 V to 5 V @ 5 A using a low drop out (LDO) linear regulator.
The best device that I found is the MIC29751-5.0WWT.
The heat parameters for this device are good, but the total power dissipated is about 36 W.
We don't know which parameter we need to use when calculating the accumulated heat:
- θJC = 1.5 °C/W (θ junction-to-case)
- θJA = 56 °C/W (θ junction-to-air)
From our calculations: TJ = 2050°C when using θJA or TJ = 128°C when using θJC.
The LDO will be mounted to a metal box directly (without a thermal pad) and the box has a large mass with air blades for transferring heat to the air.
From the literature there is an option to place a high-power resistor in series between input power (12 V) and the input pin of the LDO.
The resistor lowers the voltage at the LDO input at maximum current and still have V-drop-out so the LDO will activate properly.
From my calculations the resistor needs to be 1.2 Ω, 30 W.
Our questions are:
- Is there any other device / circuit / module that can convert the power?
- What parameter do we need to use for the heat calculations?