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TCA9800: Connection with TMP1075

Takashi Yamaguchi
Genius 13300 points
Part Number: TCA9800
Other Parts Discussed in Thread: TMP1075, , TCA9803

Hi team,

My customer is evaluating the TCA9800 with TMP1075 on their board. Please refer to the block diagram from the following link.

/cfs-file/__key/communityserver-discussions-components-files/138/I2C-Temp-Sensor-circuit.pdf

The customer found that there was about 500mV of voltage on the L signal in the signal between the I2C buffer(TCA9800) and the temperature sensor(TMP1075).

The d/s of the I2C buffer states that external pull-up resistor is not required on the B-side, but on the other hand, the d/s of the temp sensor states that external pull-up resistor is required. 

The customer is currently connecting the pull-up resistor as shown in the block diagram, should they remove the pull-up resistor?

Regards,

Yamaguchi

  • 0
    TI__Guru 72751 points

    Hi Takashi-san,

    The TCA980x supplies its own high signal on B side with an internal current source. TMP1075 should be able to 'see' a logic HIGH on the B side without an external pull up resistor. If an external pull up resistor is used on B side, the low level detection algorithm inside the TCA980x may not function properly and may not drive a low from B to A side when the slave drives low in some corner situations. I would recommend removing the external pull ups on B side. If the customer requires faster rise times, they can use the TCA9803 as that device sources 3.3mA of current on B side.

    -Bobby