ZHCS527G January 2007 – April 2025 LM5574
PRODUCTION DATA
The junction-to-ambient thermal resistance of the LM5574 varies with the application. The most significant variables are the area of copper in the PCB and the amount of forced air cooling provided. The junction-to-ambient thermal resistance of the LM5574 mounted in the evaluation board varies from 90°C/W with no airflow to 60°C/W with 900 LFM (Linear Feet per Minute). With a 25°C ambient temperature and no airflow, the predicted junction temperature for the LM5574 is 25 + ((90 × 0.6) = 79°C. If the evaluation board is operated at 0.5A output current, 70V input voltage and high ambient temperature for a prolonged period of time the thermal shutdown protection within the IC can activate. The IC turns off to allow the junction to cool, followed by restart with the soft-start capacitor reset to zero.