# MP8862 current drop-out does not meet specification

dear MP

I am struggling with the following problem. I supply MP8862 with 3.3V to obtain 6.5V and I have a resistor load at 10 ohms. The output current would be 0.65 A but actual current is 0.22 A and corresponding Voltage drop at about 2.7 V. Evertything is fine with programming voltage output across all range,. I tried to change the PWM forcing bit to 0 as well to disable overcurrent bit as well. No way, also current limit is set to 60 (3A)
Any idea ?

thanks
Riccardo

Hi Riccardo,

Apologies for the delayed response. Would like to understand in more detail to see what could be happening.
How are you measuring the 0.22A? Is the output dropping to 2.7V when this happens?
As this is boosting, is the input current limit set high enough?

Best Regards,
Yu

Thanks YU

yes indeed. Under the load the voltage drop to 2.7 V and the current flowing on the load is 0.22 A. It should be 6.5 V with a corresponding current of 0.65 A (since the load is a resistor of 10 ohm). thanks a lot for your response. Inductor is 4.7 uH with Irms 5A and Isat=8A. DCR=29.5 mohm. Thanks

Hi Riccardo,

Please provide waveforms probing SW node, output voltage, IL if you can.

Best Regards,
Yu

dear yu i did not have time to provide sw node probing. However I use Vin=3.3 and Vout 6.5 looking at your voltage linear regulation in data sheet of MP8862 page 9 ( the graphs at 1 and 2 A drop down drammatically. are they going to zero or what ? May be that MP8862 is not able to regulate at 6.5V 0.65A with 3.3 V input ? can you provide the linear voltage regulation between 0 and 1 A for 3.3V of input voltage ? thanks

Hi Riccardo,

Please check your input supply current limit to ensure it is set high enough. In boost mode, the input current will be larger than the output current. It is possible it is hitting CC mode which is causing the output voltage to drop.

Hope this helps.

Best Regards,
Yu