About the detection method of LTC4291-1 & LTC4292


I am considering the LTC4291-1 & LTC4292 chipsets.

PD may be detected correctly in auto mode, and PD may be erroneously detected in semi-automatic mode.

Specifically, it is judged as Class 4 etc. even though Class 8 is connected.

This can be detected correctly or erroneously in semi-automatic mode.

This phenomenon does not occur in auto mode.

So I have a question.

Is there a difference in the detection method between auto mode and semi-auto mode?

Are you detecting it in exactly the same way?

We would appreciate it if you could reply.

Best regards,


  • 0
    •  Analog Employees 
    on Jan 19, 2021 10:15 PM


    What PD are you testing with the LTC4291-1/LTC4292? Is this related to your earlier question here? https://ez.analog.com/power/f/q-a/538676/semi-automatic-mode-operation-of-ltc4291-1-ltc4291

    In Auto mode, the PSE will detect, classify, and power all valid PDs as soon as they are connected. In Semi-Auto mode, the PSE will continuously detect and classify all PDs as soon as they are connected, and report the PD's information to the host controller via I2C. The LTC4291-1/LTC4292 uses three short class events known as a Class Probe to determine the PD's requested class without powering the PD. The host controller must command the PSE to power on the port. After receiving a power on request, the PSE then performs an additional detection and classification before powering the PD.

    It seems like there is either something wrong with your software implementation, or your PD is behaving differently after being classified multiple times.

    Best Regards,