We would like to use MP8860 with a maximum current that is less than the values mentioned on the datasheet, and to also have fine-grained current setting resolution in I2C register IOUT_LIM. We also need to use the I2C to modify the voltage and current setpoint values.
My initial calculation resulted in around 100k resistor for the R_OC (R1 on “typical application” in the datasheet). Is this value still inside stable region for the control loop inside the IC?
Likewise, should we also adjust the (22nF on the datasheet) capacitor that is also connected to the OC pin?
Hi @mps.h78821,
Thank you for posting to the MPS Forums! What level of current are you wanting to set the limit to? The external R_OC resistor is typically used to set the constant current limit between 1-3A.
That 1-3A range is mentioned on the datasheet, but we wanted to have a lower maximum current and also to have better resolution for setting the current limit.
That 100k R_OC resistor value on the 1st post was calculated with around 400mA default maximum (and then rounded by using an easily obtainable preferred-value resistor value).
This design is also based on the assumption that the IOUT_LIM register default value (default 40) can be modified at runtime also when using that 100kΩ R_OC value although the datasheet says that “The OC pin-to-ground resistor should be 21.5kΩ when using the above IOUT_LIM register”.
Since the datasheet specifies the CC limit range between 1-3A, I am not sure it will work for lower current limits. I will check with our team to see if this is the case.
Thanks, please do so.
The upper limit (3A) likely comes from internal FETs, but the lower limit may be due to numerous reasons - depending on what’s inside the IC.
I apologize for the delay. I have confirmed with our team that the external resistor can only be used to set current limits down to 1A. If you do use the IOUT_LIM register to change the limit, I would recommend using the 21.5kohm resistor and 22nF capacitor values mentioned in that section of the datasheet.
Ok, thanks for the guidance. That likely saved us from a PCB revision round.
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