So I thought I had fixed my problem of the soft start voltage not being higher than the error amp reference voltage of 1.24V. However, when I switched to new mosftets to handle the increase in vin voltage the soft start voltage has once again dropped to 1.17V. This causes the output voltage and the output current to drop out under load. The original mosfets were FDB8445 the new mosfets are HUF75345S3S. Any ideas? Would it have something to do with the on and off time being different?
Also I tried increasing the SS cap up to 4.7uF with no luck. I believe that the SS current source inside the chip is being effected somehow by the mosfets, but since I don't know how that current source is being generated I'm not sure where to go from here...
Are you using VCCX? This sounds like a MOSFET threshold issue when VCCX is used.
Sorry for the late reply I couldn't access the forum since it was not loading. I am not using VCCX it is connected to GND. It just seems really weird that just switching the mosfets would cause this problem. It seems like it is having trouble switching as fast as the old mosfets.
I'll check into the MOSFETs tomorrow. If the total gate charge is much higher, the switching characteristics will be different.
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