Hello support team
I have a question / correction (?) regarding the soft start behavior of the MP5048.
I’m quoting the datasheet here:
If the load capacitance is extremely large, the current required to maintain the preset SS time exceeds the start-up current limit. In this case, the rise time is controlled by the load capacitor and the start-up current limit.
My observation from testing and simulation is different. When the start-up current limit is exceeded, the current is not limited, slowing down the slew rate, but an overcurrent fault occurs.
Simulation: When the current during the SS process required to reach the SS time for a large load capacitance exceeds the limit determined on the CLREF pin, the current is not actively limited, but the fault timer starts. This eventually results in shutting down the MP5048.
Configuration:
- VIN = 48 V
- COUT = 1000 uF
- RCLREF = 53.6 kOhm
- RCS = 16.9 kOhm
- CSS = 220 nF
- CTIMER = 10 nF
This should give a nominal soft start current of ~ 965 mA at a SS time of ~ 53 ms. Within tolerances, this is very close to the CLREF SS limit. In case of this simulation, the limit is hit (compare the CS and CLREF pin voltages) and the fault timer starts.
Measurement:
Reference COUT ) 1000 uF: Everything works as expected. The SS current here is lower (component tolerances).
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Now with an excessive COUT = 3000 uF. The fault timer behavior can be observed when the CS pin voltage exceeds the CLREF SS limit.
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I guess the behavior is not correctly documented in the datasheet?
Is this intended behavior?
Best
Daniel
