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TIDA-00349: Supply shutdown problem

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.