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DS160PR810: SMBus/I2C Pull-Up Resistance Values When Not in Use

ttd
Mastermind 9355 points

Part Number: DS160PR810
Other Parts Discussed in Thread: DS160PT801

SMBus/I2C Pull-Up Resistance Values When Not in Use

I have a question regarding the SMBus/I2C pull-up resistance values for the products listed below.

Part Number         Pin              Required Pull-Up Resistance
DS160PR810   GAIN0 / SDA       1 kohm to 5 kohm
              RX_DET / SCL      1 kohm to 5 kohm

DS160PT801   SMBCLK            2 kohm to 5 kohm
              SMBDAT            2 kohm to 5 kohm
              EE_CLK            2 kohm to 5 kohm
              EE_DAT            2 kohm to 5 kohm

The datasheet specifies that pull-up resistors should be connected as shown above.

Q1
Do these resistance values indicate that the total pull-up resistance during SMBus/I2C communication
just needs to fall within the specified range?

Q2
Do these pins have built-in pull-up resistors?
I would like to confirm whether a pull-up resistor of several tens of kohm should be added to the circuit when SMBus/I2C communication is not in use.

Note:
We are currently considering manually switching between SMBus and I2C communication using a jumper switch.

 

  • 0
    TI__Expert 7803 points

    1. SMBus/I2C interface standard defines the range of pullup to be 1kohm to 5kohm. As long as PU is in this range, there is no issue. 

    2. No. There are no built-in resistor for SCL/SDA. Confirmed: If SMBus/I2C communication is not used, a large pull-up resistor to VCC should be used. 

  • 0 in reply to Charles
    Mastermind 9355 points
    Charles said:
    No. There are no built-in resistor for SCL/SDA. Confirmed: If SMBus/I2C communication is not used, a large pull-up resistor to VCC should be used. 

    About DS160PT801, should I set the resistance value to the maximum value for RPULL_UP, which is 5 kΩ? Or do I need a higher resistance value (tens of kΩ)?

    Since actual system operation will likely require checking the STATUS, rewriting the DIAG or EEPROM, and making fine adjustments,
    considering the possibility of using SMBUS in the future, would it be safer to set it to 5 kΩ?

  • 0 in reply to ttd
    TI__Expert 7803 points

    pull-up resistance depends on bus capacitance. Please see this app note for selecting pull-up resistor: https://www.ti.com/lit/an/slva689/slva689.pdf