MP8862 3.6V to 5V Possible? Max Current?

Hello all,

I’ve created a buck-boost circuit to serve as a UPS for a 5V single board computer, so that the main 12V power can be removed and the 3.6V Lipo can take over without interruption.

I’m using the MP8862 and the 12V to 5V buck operation works fine. However the boost operation from 3.6 to 5V has been problematic. I had it working real well on a couple of boards but then the function was lost on both of them. Under load, the IC seems to just enter hiccup mode with the accompanying squeal.

The configuration I have is with the 4.7uH 2Amp inductor, and two 22uF capacitors on input and output, and I changed the OC resistor from 21.5K to 47K, which is what made it work when it ran fine. I’m also running the default I2C registers (5V, enabled, etc).

I’ve played with changing the inductor to a different value, adding more caps, both ceramic and electrolytic (which seem to make things worse), as well as the OC resistor back to 21.5K.

I’m just wondering if the 3.6 to 5v operation @ 400mA is possible at all, since it seems a bit border-line according to the datasheet. Could someone confirm either way, just as a sanity check?

Thanks in advance for any information!

The data sheet seems to imply that 5V 2A is possible off a 3.6V input. So are you sure the input is really 3.6 and not drooping? Also this looks like a fancy digital part, are you sure the “worx” bit is set to one?

Thanks jshannon,

The input is fine, I’ve looked at it all with the oscilloscope.

I haven’t used the i2c interface at all but the register defaults seemed to work before, as in Enabled to 5V. If by worx you mean the ‘go’ bit, I think that one is not necessary if you are not changing the default voltage level.

Anyhow I might order the Eval board just to perform a sanity check, but I’m also considering the MT3608 on SEPIC configuration, to save on cost and complexity.