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P82B715: how to use

user6124773
Prodigy 230 points
Part Number: P82B715

Hi:

I want to use TI P82B715. Please help me with the following questions:

1.Can the transmission distance of chip B82B715 I2C reach 1.5m?

2.At a distance of 1.5 meters, I used several of the device drivers?In addition, is the driver side or the load side more appropriate to use?

BR

Rain

  • 0
    TI__Mastermind 31780 points

    Hello Rain,

    1.Can the transmission distance of chip B82B715 I2C reach 1.5m?

    The maximum transmission distance of the P82B715 is limited by the total load capacitance and not the cable length because not all cables have the same amount of capacitance per unit length.  Longer cables will have more capacitance, but other factors may need to be considered as well such as any additional connectors or components in the signal path between the two boards.  I'm not sure what cable you are using, and how much capacitance it has for 1.5m of length, but I would venture that the P82B715 could drive that cable without difficulty.

    2.At a distance of 1.5 meters, I used several of the device drivers?In addition, is the driver side or the load side more appropriate to use?

    I'm not sure I fully understand how you want to configure your system for the I2C distribution tree.  However, you can not connect the Load (Lx/Ly) pins of multiple P82B715 devices to the I2C side (Sx/Sy) pins.  You can only connect the Load pins (Lx/Ly) or I2C Pins (Sx/Sy) to the same type of pin on multiple P82B715 devices.  They use a static voltage offset and the levels are incompatible with each other and therefore can only be connected to the same type of pin. 

    I am assuming that you will be driving a cable with one P82B715 device and have multiple P82B715 devices connected to the far end of the cable and sharing the Load pins (Lx/Ly).  Then each of those devices will be connected to separate I2C devices using the Sx/Sy pins. 

    If I haven't answered your question or my response does not make sense, could you provide a simple diagram of what you would like to do, and I can review it and let you know if I see any problems with the approach.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Prodigy 230 points

    Hi Jonathan:

    My actual operation is as follows, please help support:

  • 0 in reply to user6124773
    TI__Mastermind 31780 points

    Thank you for the extra information.  If I understand this correctly, you have 3 configurations that you would like to implement.  Only Program 3 is correct.  You will always need two P82B715 devices connected together across the long cable in order for the standard I2C devices to function properly. 

    This is a diagram of a standard configuration.  The P82B715 device VCC voltage can be different than the I2C signals.  Your application shows I2C signal levels of 1.8V which is less than the P82B715 VCC minimum voltage.  You would need to set Vcc_S1 and Vcc_S2 to 1.8V, but VCC and VCC_L should be set to a minimum of 3.3V.  However, the Datasheet specifications are only valid for a VCC = 4.5V to 12V.  VCC_L voltage can be less than VCC but it is more common to connect it to VCC as well. 

    This next diagram is a valid configuration if you wanted to connect another P82B715 off the cable as in a Star network.  This would be common if you had multiple slave boards each consisting of 1 P82B715 and an I2C slave device.

    This diagram is a valid configuration for a single slave P82B715 board with multiple I2C Slave Devices (with separate addresses).

    Now, this last diagram I will share with you is an incorrect diagram that should be avoided.  This is similar to what I understand your Program 1 and Program 2 configurations.  You can not connect the Lx/Ly pins of the P82B715 to the standard I2C pins of any I2C device.  This will not function properly and you should implement one of the previous diagrams I have shared with you.

    I hope this helps clarify the proper setup and application of the P82B715 device and answers your questions.

    Regards,
    Jonathan