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TPS2544: Current Limit in CDP Mode

R D1
Prodigy 50 points
Part Number: TPS2544

Hi,

Will TPS2544 work in CDP mode if ILIM_HI is configured for less than 1.5A (say 900mA)? The datasheet mentions a fault condition for overcurrent conditions (the case of a device trying to draw more than the current limit), but then also mentions a deglitch circuit. 

Thank you.

  • 0
    TI__Genius 9630 points

    Hello,

    If a device is connected and understands that the TPS2544 is in CDP, the device may request up to 1.5 A. If your current limit is set at 900 mA, anything above the tolerance of 900 mA will enable the FAULT pin, as an over current condition has occurred. The deglitch circuitry is for accidental FAULT conditions only and does not apply to this case. 

    If you do not plan to use more than 900 mA, consider using SDP mode. SDP is USB 3.0 compliant and outputs a maximum of 900 mA. 

    Thanks,

    Emma

  • 0 in reply to Emma Hoying
    Prodigy 50 points

    Hi,

    So, if I set the CTL1/2/3 pins to 1/1/0 (SDP1), with the proper ILIM_SEL, then a USB 3.0 device will be able to draw up to 900mA? I believe, unlike in CDP mode, a proper enumeration has to succeed before this can happen. My host controller is USB 2.0. In the case of CDP, I observed that the portable device can draw >1A irrespective of enumeration.

    I am more than inclined to supply up to 1.5A to the portable device, but I am unable to find a type A male connector with support for 2A+ (the extra Amps are for the remaining board circuitry) current to power my board.

    Thank you.

  • 0 in reply to R D1
    TI__Genius 9630 points

    Hello,

    Because you have a USB 2.0 host controller, the maximum current draw will be 500 mA, as seen in Table 1 in the TPS2544 datasheet. If you had a USB 3.0 host controller, you would be able to draw up to 900mA with the proper ILIM_SEL and with CTL1/2/3 pin settings to 1/1/0. 

    Also, enumeration occurs for every mode, not just SDP. Primary enumeration is used to determine if the mode is SDP, and secondary enumeration is used to differentiate between CDP and DCP. 

    Thanks,

    Emma

  • 0 in reply to Emma Hoying
    Prodigy 50 points

    Thanks Emma. By "enumeration" I meant device enumeration. The 900mA limit has to be negotiated between the USB 3.0 device and host as part of the device enumeration and configuration process. If a USB 3.0 device does not offer an endpoint with a 900mA max power limit, then even under SDP, the device should not draw 900mA current. I understand the primary and secondary charger detection modes you are referring to.