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[TPS65982] Current limit for multi ports

Ichiro Fukui
Intellectual 1310 points
Other Parts Discussed in Thread: TPS65982, TPS65982-EVM

Hi,

Our customer is willing to use two USB Type-C PD ports, with two TSP65982 devices. On their system, the maximum supply is 5V/4A for two USB ports. 

Customer would like to understand if the current limmit value can be adjusted automaticaly.

For example,

 - Type-C port 1 : 5V/3A, Type-C port1 : 5V/1A

 - Type-C port 1 : 5V/2A, Type-C port 2 : 5V/2A

From datasheet, I undersand that we can choose 1.5[A] or 3.0[A] for Type-C current limit.

regards,

 Fukui

  • 0
    TI__Mastermind 30310 points

    Fukui-san,

    The current limit of the 2 ports is not adjusted automatically, but there are some simple way to manage the current capability of 2 ports using a micro-controller as an I2C master.

    There are 2 ways that current is advertised at 5V: 1st with Type-C Analog detection, 2nd with PD digital negotiation.

    1. Type C -  Advertisement can only be done at 3 levels: Default (500-900mA), 1.5A, or 3 Amps. Since your power supply cannot provide 5V,6 Amps, it would be wise to set both Type-C ports to advertise 5V, 1.5A by default
    2. USB PD - Negotiations can be made with more granularity, down to 10mA steps between 0 & 3 Amps. Since your power supply can provide up to 5V, 4 Amps, the safe option would be to advertise a maximum current of 2 Amps on each port for Source PDO Object 1.

    If 3 Amps is required by one of the ports, you can reduce the current on the other port (Type-C = Default, PD = 1A) and then offer 3 Amps to the port that needs it.

    If this sounds like a reasonable solution in your system, I can provide more details on how to Configure the FW of the ports and how to write I2C commands to the TPS65982 from a micro-controller.

    Do you have a TPS65982-EVM to test with?

  • 0 in reply to Brian Berner
    TI__Intellectual 1310 points

    Brian-san,

    Thanks for reply. I have two questions.

    1. Can EC understand current consumption for each ports?

    2. Regarding USB Type-C PD proposal, if connected device is not supporting PD, does this method still functional?

    Regards,

    Fukui

  • 0 in reply to Ichiro Fukui
    TI__Mastermind 30310 points

    Fukui-san,

    1. The EC can be programmed to know the Type-C value offered by the TPS65982 at Boot and then it will control the TPS65982 after boot and will know the Type-C power offered because it is setting the value. For PD Power, the EC will set the Max current value in each PDO. The Sink can accept a lower Current value than what is offered, and the EC will need to read "Active RDO Contract", Reg. 0x35, Bits 10-19 to see what Current value the Sink is going to use.
    2. Yes, this method is still functional as long as the EC keeps track of the Type-C current advertised. If 3 Amps is advertised and one port, it must be supported. So using the example of 4 Amps at 5V total, the 2nd port will only have 1 Amp left and will need to offer Default (900mA max for USB3 compatibility). The USB Type-C spec allows the Type-C current that is advertised to adjust dynamically, and the EC can change this by modifying "System Configurations", Reg. 0x28, Bits 6-7.

  • 0 in reply to Brian Berner
    TI__Intellectual 1310 points
    Brian-san,
    Thank you. I got it.
    regards,
    Fukui