Overcurrent Fault Issue with STM32G0 + TCPP02-M18 PD Implementation
Our team is using the STM32G0 with the USBPD stack and the TCPP02-M18 as the protection circuit. Please find the attached schematic for reference.
We are configuring the PD contract with a maximum of 15V, 3A. When connecting an HP G11 laptop to the USB-C port, the contract is successfully negotiated, but we observe repeated hard resets. Upon investigation, the resets are linked to the TCPP nFAULT signal going low, indicating an overcurrent fault.
When we short the sense resistor (R10) in the schematic, the fault does not occur. We also tried adding a 0.1 µF capacitor across the sense resistor, but the fault still occurs.
When we limit the PD contract in software to 15V, 2.9A, the faults no longer appear. We are using Nexperia GANB4R8-040CBAZ MOSFETs, which have a drain-to-gate capacitance greater than 20 pF, so an additional capacitor should not be necessary.
We also tried reducing the sense resistor R10 to 7m Ohms, but the same overcurrent fault still occurs. Please see the attached scope captures for reference. The captures show the nFLAG signal (yellow) and IANA voltage (purple). The IANA scaling is 7 mV/A × 39 (gain) = 273 mV/A, meaning each 200 mV grid corresponds to approximately 733 mA.
From the waveforms, the trip current (IANA voltage at the falling edge of nFLAG) varies significantly.
In Scope Capture 1, Vtrip= 0.95V, corresponding to 2.89 A.
In Scope Capture 2, Vtrip = 0.54 V, corresponding to 1.98 A.
According to the datasheet, the internal trip threshold is around 1.7–1.8 V, yet we are observing trips as low as 0.54 V, as evidenced by the scope traces.
Could you please advise what might be causing this variability in the trip point? Any guidance or suggestions on how we can further debug or tune this behavior would be greatly appreciated.
