Power Stage Selection Considerations For High-Current Voltage Regulators

Determining the power loss for sustained output current and whether a cooling solution is needed.

There are several key things to consider when selecting a power stage for high-current voltage regulators:

1. What area does the power stage need to fit in?
2. What is the continuous output current?
3. What is the maximum peak current?
1. This should not exceed the peak current rating of the power stage.
4. What is the power loss for sustained output current?
1. This can be calculated using Infineon’s power loss calculator or use the datasheet power loss estimate as shown below.

Fig. 1: Power loss vs. current curve.

1. Does it need a cooling solution?
1. Consult with a thermal expert for the system under design.
2. A good estimate of the temperature of the power stage can be made by using the thermal characteristics of the power stage. For example, the table below in figure 2, which was taken from one of our datasheets, shows the thermal impedance of a power stage. The thermal resistance from junction to top of package is 16.7 K/W. To calculate the temperature of the junction, use the formula: 16.7 * (Power Loss) + temperature of heatsink.

Fig. 2: Power stage thermal impedance table.

1. With the thermal information, estimate how much current the power stage can sustain by referencing the thermal derating curve like the one below in figure 3. This graph condition is with no heatsink and no airflow, so use the thermal resistance to ambient in this condition.

Fig. 3: Power stage thermal derating curve.

An example design:

• Area: will fit 2 x 5x6mm power stages
• DC current = 60A
• 30A per phase
• Peak current = 90A
• 45A peak per phase
• Ploss at sustained Iout = 2.5W
• Junction temperature = 2.5*16.7=41.75 Degree delta from junction to top of power stage
• Add heat sink temperate as well