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TCA9511A: Hot Swappable and Incremental offset function consultar

Andy Liu3
Intellectual 2500 points
Part Number: TCA9511A
Other Parts Discussed in Thread: TCA4311A, TCA9617A

Hi team,

My customer evaluation TCA9511A and TCA4311A, and have some questions, please help me.

1、9511 and 4311 are hot-swappable chips. What is the main difference between them?

2、Sepc mentioned that 9511 and 4311 should have incremental offsets. Can they be directly interconnected? What impact will the direct interconnection have?

3、Can 9511 and 4311 be used as bus drive sources, similar to the function of TCA9617A. When evaluating the I2C bus load, only the bus load after 9617 needs to be calculated, instead of the wiring length before 9617? If so, what are their driving capabilities; if not, how do you understand the bus buffer mentioned in the spec?

There are many problems and the project is urgent. Please help answer as soon as possible. If you have any questions, please feel free to contact us. Thank you very much.

Best  regards,

Andy Liu

  • 0
    TI__Guru 53575 points

    Hi Andy,

    See my answers to your questions below. Is there a particular issue the customer is encountering with one of these devices? Or are they trying to distinguish differences to make a decision on which device to use?

    1. The hot swappable feature of the TCA4311A and TCA9511A keep the devices from impacting an active I2C bus when the device is plugged in and while it powers up. They are able to detect and wait for an idle bus state before connecting the local card to the backplane. They also precharge the SDA and SCL lines in order to reduce the transient on the bus when a connection is made. Once the device is fully active (some time after Vcc > UVLO), the device indicates via the READY pin that it is able to interface with the bus. Non-hot swappable devices such as TCA9617A  lack these features and may inadvertently impact the signals on an active bus during power-up. Such a device should be powered-on with the rest of the system or while the system is idle. 

    There are little functional differences between these devices as TCA9511A was designed to be a pin-to-pin replacement for TCA4311A. However, the newer TCA9511A provides higher Tj ranges, wider VCC ranges, improved rise time accelerator triggering algorithms, and a lower dynamic offset voltage than TCA4311A, so between the two we would recommend the newer device.

    2. The offsets of these two devices are dynamic voltage offsets which work differently than static voltage offsets in devices like TCA9617A. Devices with dynamic voltage offsets will drive an output voltage slightly higher than the input low on the opposite side. When such devices are placed in series, these offsets are additive meaning that final low-level output will be greater than the original voltage by two times the offset value. For example, with an original low-level signal of 0.2V that passes through two TCA4311A's in series with a offset of 60mV, the voltage seen by the final IC would be 0.32V. With only two devices in series, this is not an issue, but more than two series devices should be avoided to ensure the output-low level remains beneath the I2C threshold value. 

    3. Yes, both of these devices are true buffers meaning they redrive the I2C signal and allow for local load-capacitance considerations. In this way, they are similar to TCA9617A. They are capable of driving the maximum capacitive load for each I2C bus and can support weak pull-up resistors (10k specified) with the use of rise-time accelerators. 

    Let me know if there's anything that is unclear and if you have any more questions.

    Regards,
    Eric Schott