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Original question:

TUSB8041: Startup and Programming Mode/Endpoint

TUSB8041: SMBus on the TUSB8041

chris s
Prodigy 25 points

Part Number: TUSB8041

I have a TUSB 8041 in a design. I flipped several of the USB 2. 0 pairs, so I need to configure the USB 2.0 polarity register/OTP. I'm trying to do this over SMBus

According to the datasheet, I need to pull  SMBUSz/SS_SUSPEND down, then I need to keep the SMBUS data lines pulled up while the hub IC boots. The hub IC will wait indefinitely until the SMBus host clrs the CFG_ACTIVE bit.

On my board, I have SMBUSz/SS_SUSPEND pulled down. The configuration of the address bits doesn't matter, because I'm not even getting that far. I have both CLK and DAT pulled up to 3V3 through 4.7K resistors. On startup, the hub immediately connects to the upstream port, which means it is not entering SMBus mode.

I do notice that the voltage level on the lines is not 3v3, but is more around 1.2V. This would indicate that the lines are sinking current. Why? The SMBus host is not the issue, with the TUSB disconnected, the lines come up to 3V3.

Thanks,