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TIDA-00349: Supply shutdown problem

Akshay Patel
Prodigy 10 points
Part Number: TIDA-00349
Other Parts Discussed in Thread: TPS60402

We have designed power supply using TIDA-00349 reference design. Schematic of design is attached.

Voltage at different points are V_IN = 24V, N_VCC = 5V, ISO_3.3V = 3.3V. Load current from ISO_3.3V is ~5 mA.

Supply works properly for around 2 - 3 hours, after this output voltage of MCP16311 (N_VCC) drops to 2.0 - 2.5V from 5V and it remains at this voltage until device is restarted. Supply starts working after restarting device by turning off and on V_IN. Same situation occurs when we intentionally short circuit N_VCC and N_GND.  Problem is observed in 7 different hardware.

We removed R11 and connected equivalent load at MCP16311 output, N_VCC remains 5V in this case. Also supply works fine when we bypass isolation section (TPS60402 and transformer).

From current observations, it looks like TPS60402 is forcing MCP16311 in shutdown mode, unable to find reason for such behaviour. Help us with possible reasons and workaround.

/cfs-file/__key/communityserver-discussions-components-files/234/Power_5F00_supply.pdf

  • 0
    TI__Prodigy 655 points

    Hello Akshay,

    sorry for the delay in our response and please allow us until beginning of next week to analyze your issue.

    Thanks and regards

    Alex

  • 0
    TI__Prodigy 725 points

    Hi Akshay,

    for your problem is not so easy to find a starting point to investigate further. You have tested the MCP16311 stand alone and it is working and can only be stopped by shorting it. 

    Also the circuit works when removing the isolation with the TPS60402, right?

    Is something in the complete circuit heating up? How much current is the whole circuit drawing from V_in?

    How does the load at MCP1703, so on the ISO_3.3V rail look like, is this a pure resistive load? Can it happen that this load draws way too much from the rail? What happens if this rails gets shorted? Does a short on this rail also trigger the MCP16311 to stop working?

    In a second step I would recommend to check the current going into the circuit with the TPS60402, maybe remove R11, soldering a short piece of wire and measuring with a current clamp and a scope what is going on there. Do you see a current peak higher then the normal operation current here when the circuit stops working?

    Best regards,

    Steffen