MP9484 startup issue/crash?

DC-DC Power Converters
1

Hi,

I’ve designed a SMPS with the MP9485. Schematic enclosed.

https://drive.google.com/file/d/1WspdJop7Vf5S_KeU_9RFPy0s5hs5Iduk/view?usp=drivesdk

With a lab power supply @ 48V it works fine, but any kind of lipo, with intergrated bms, or jus t flicking a switch to give the IC instantly 48V will keep the regulator in an limbo, giving out maybe 60% of the voltage it’s trying to regulate to.

Regulator: MP9485GN-Z
VINnom: 48V, range: 42-58V
VOUT: 5V

with a 120 ohm input resistor, the IC will start every time and regulate 5V with no problem

Here is the 5V rail when it has failed to start.

scope_23
scope_23800×503 16.9 KB

2

Hello,

Apologies for the delayed response.
To clarify, you put the resistor in series at the input and this problem no longer occurs?
Have you checked the inrush current?

Best Regards,
Yu

3

Correct.
.

I believe that it went into this fault state if there is no ramp up with the input voltage.

4

@MPSNow_Yu I do have exactly the same problem with the MP9486A. I believe during startup it enters SCP mode and does not recover. Is there a solution to this problem?

5

Hello,

Is this also using battery input? Have you tried what Daniel did? I’m thinking it may be inrush current.
Recommend looking at waveforms to confirm.

Best Regards,
Yu