Is it possible for you to use an electronic load to do your test? It looks to me the device is in hiccup mode. This occurs during OCP or SCP. Your load current is too low to be OCP. However, you are using 5ohms to create 1.68A. I wonder if the 5ohms is some how triggering SCP. I don’t know why only at a certain voltage though. The hiccupping theory makes sense to me because when you removed Css the period got shorter. There is a tss between each hiccup.
Can you measure the the voltage at the pins of the device to check if Vin is as said on the on the power supply. Maybe the voltage drop on the cables
Can you measure the fsw of the device under working conditions and the bad condition?
Thanks Vinh, I’ll try to test with an electronic load and report back in the next couple of days.
I agree it appears to be hiccupping. The device “knows” it’s shutting off the output, as the PG line drops low as the output shuts off.
I’ll also try alternative input power sources, although I don’t believe there is an issue there.
I have previously observed the input power… in the oscilloscope image above the Yellow/Ch1 trace is the input (granted, it’s difficult to see in the small image). It’s holding steady at a little over 12V.
This device doesn’t have a pin on which the fsw appears, as far as I’m aware. Is there another way to check this?
Note that I had to run the electronic load in “Constant Resistance” mode for this particular load point, as setting it to constant current @1.6A caused the MPM3650 to switch off its output permanently, and thus I couldn’t capture the behavior in an image easily.
In all other cases, the load was set to constant current mode.
It is very strange to me that it shuts off only at ~1.6-2.0A, but not at the higher currents… I will need to check with the PL. This will take a couple of days.
Thank you Vinh.
I can’t try SW node captures as this device has an integrated inductor, SW node is not available externally.
I’ll aim to try the altered R3 and R4 values in the coming week. Please keep me posted on your progress too.
Thank you Vinh, great to hear you’ve identified the source of the issue.
May I ask when the next MPM3650 revision is planned?
I intend to switch to the MPM3630 in our next PCB revision, as I have the EVM for it, and it appears to be working very well in our application. However, it would be great to know when a revised MPM3650 would be available, as it would allow us to use our current PCB’s. It’s a great device too in terms of high current output in a small package, and ease of use, so it’d be great to have the option to use it with variable loads in the future.
Our next revision for this device will be around 2-3 months. If you would like more business/technical support please reach out to MPS NOW Remote Support.
Hi Vinh,
I was just wondering if you had any updates regarding the next revision of this device?
Will the next revision have a new part number, suffix, or another way to identify newer Vs older revisions?