Other Parts Discussed in Thread: CSD25402Q3A, BQ25895
My circuit is designed to boost from 3.7V to 5V, drawing 3A at the output.I cannot seem to draw more than 2A from the output (approximately 3.3A at input) before the device shows heavy ripple on the output and then goes into some oscillating mode where the output just follows the input.
The WEBench designer spit out this circuit: (My small changes are the values in GREEN)
- I first changed the compensation network to be 15K resistor and 6.8nF cap but then I can draw about 1.6A. When I changed the 15K for 10K I got to 2A current.
- I am using the CSD25402Q3A fet at M3
- I have 20uF at the COUT1 cap
- I made the Rlim lower so I doubt that we are at the limit of the input current
I am testing with a bench supply so the input is stable and can give enough current. I also have a load connected which shows me the exact current drawn.
I am using the same 2.2uH inductor that the Pololu devices that use this chip are using, so I am confident it is fine.
Here is a view of the PCB layout:
Here is a screenshot of the output (when drawing 1.5A, working fine):
Here is a screenshot of the input (when drawing 1.5A, working fine):
Here is a screenshot of the SW pin (when drawing 1.5A, working fine):
Here is a screenshot of the BST pin (when drawing 1.5A, working fine):
Now, when trying to draw more current (more than 2A) then the output first looks like this (there is a sudden change to this level of ripple):
Then (at overload) the SW pin looks like this, so crazy frequencies:
And then the device seems to drop the voltage suddenly to follow the input voltage, here is the output voltage:
Could you please assist me to know what else to change?
