MPM3683-7 Power On issue

DC-DC Power Converters
1

We have recently had issues with the MPM3683-7 powering down during operation.
This would power up correctly (Vin=3.5V, Vout=1.2V), but after running for few minutes to a few hours it would power off down to zero volts. Vin is still there, but Vout=0. Sometimes I can cycle the power and it would come back, but it would still do the same thing. Other times, it won’t come back.
I have replaced the part and then it seems to work as normal.
Can you check my schematic:

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image1121×419 137 KB

I have a few questions:

  1. should the SW pins be tied together or can they be left unconnected (I followed your layout recomendation of leaving them unconnecte?
  2. Is the external bias connection correct the way I drew it on the schematic?
2

Hi,
For the SW pins, we recommend tying them together. Please refer to EVB schematic below

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.

Is that a 10ohm for R28? We recommend higher resistance to limit the current to the VCC. 100k or higher should be good.

For external biasing, please follow the voltage thresholds listed in datasheet. 1.2V is too low.
Best to supply 3.3V.

Best,
Nouman

3

Hi Nouman,
I see you recommend tying the SW pin together, but what will happen if they are left unconnected?

On the external biasing, we are inputting 3.5V to the VCC through the 10ohm. Is this OK if we change the 10ohm to 100kohm. 1.2V is not used for external biasing. 1.2V is our desired output.

Thanks.