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TCA9617A: Can TCA9617 B side work with TCA9511? And Vol of TCA9617 B side

wang fupeng
Prodigy 120 points
Part Number: TCA9617A
Other Parts Discussed in Thread: TCA9511A, TCA9617B, TCA9509, TCA9548A

Tool/software:

Hi, 

    two questions about TCA9617. 

1. Can TCA9617 B side work with TCA9511 A side? Consider of Vol voltage. 

2. I see Vol of TCA9617 B side is 0.58v max when IoL=30mA. that means the B side driver has a 20ohm resistance, and the actual Vol will be divided with the external pull up resistor. Or the B side has a fixed Vol= 0.53?

  • 0
    TI__Mastermind 48248 points

    Hi wang,

    wang fupeng said:
    1. Can TCA9617 B side work with TCA9511 A side? Consider of Vol voltage. 

    I don't recommend using TCA9617B with TCA9511A (either IN or OUT side). 

    TCA9617B can hit max VOLB of 0.58V on B-side. The internal rise-time accelerators of the TCA9511A trigger around 0.6V. While there might be ~70 mV of margin from the typical spec, I would not recommend pairing the two buffers because the 9617B could be attempting to drive LOW while the RTA from the TCA9511A triggers HIGH. This could lead to oscillations on the I2C bus or false clock edges. 

    wang fupeng said:
    2. I see Vol of TCA9617 B side is 0.58v max when IoL=30mA. that means the B side driver has a 20ohm resistance, and the actual Vol will be divided with the external pull up resistor. Or the B side has a fixed Vol= 0.53?

    B-side has a fixed static voltage offset of VOLB(typ) = 0.53V. When IOLB = 100 uA or 30 mA, the voltage is constant (static) across the open-drain driver. 

    The external PU resistor determines the sinking current IOLB, but the sinking current does not affect the VOLB output voltage. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 120 points

    Tyler

        thanks for your reply. usually for I2C or other open drain application,  we caculate Vol of output using the internal resistance and the external pull up resistance. can you tell me which kind of i2c chip has a fixed Vol and which one use divided voltage? like level shift 9617?9509?, buffer 9511, mux 9548? Many thanks. 

  • +1 in reply to wang fupeng
    TI__Mastermind 48248 points

    Hi Wang,

    9617B, 9509, are both I2C buffers. The open-drain with pull-up resistance calculation matters on the side of the device where the static voltage offset does not exist. SVO is present on B-side of the TCA9617B, and A-side of the TCA9509. Otherwise, the pull-up resistance calculation that you are talking about applies. 

    TCA9511A is a dynamic offset buffer. It has a specified VOL and IOL that can be used to determine PU resistor strength. One thing to note is that VOL will be different on the "IN" vs. "OUT" side of this buffer. The VOL of this buffer will be a VIL+VOS voltage. If your input to the buffer is 100 mV, your output VOL could be as much as 200 mV since VOL + VOS(max) = 100mV + 100 mV according to the datasheet. 

    TCA9548A is a pass-through I2C controlled switch. This device is not a buffer. When determining the PU resistor calculation for this device, you must consider the PU strength on the main I2C channel and the enabled downstream channels. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 120 points

    Got it, Tyler, thanks. 

  • 0 in reply to wang fupeng
    TI__Mastermind 48248 points

    Hi Wang,

    If no further questions, I will close the thread. 

    Regards

    Tyler