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DS90UB934-Q1: Suggested strap resistors

Kento Adachi
Expert 4465 points
Part Number: DS90UB934-Q1

Tool/software:

Hello experts,

Datasheet specifies recommended suggested strap resistor values as shown below. As customer concerns resistor value variation due to condensation, they would like to use smaller resistor value.

1. Can they use Pullup/Pulldown：1.5kΩ/1.2kΩ (1％) instead of 71.5kohm/56.2kohm to achieve 0.443*VDD18?

2. Can they use PullUp/Pulldown：Open/4.7kΩ instead of Open:10.0kohm?

Thanks,

Kento

  • 0
    TI__Mastermind 28050 points

    Hi Kento,

    We typically recommend using the suggested strap resistor values. With 71.5kohm/56.2kohm, the voltage level would need to decrease by ~6.5% or increase by ~8% for the device to strap to the incorrect IDX setting. With Open/10kohm, any resistor variation shouldn't significantly change the voltage level on the pin. Therefore I don't believe resistor value variation due to condensation would result in incorrect strapping.

    Best,

    Lucas

  • 0 in reply to Lucas Wolter
    TI__Expert 4465 points

    Hello Lucas,

    Based on my customer's know-how, the condensation resistance is ~47kohm. Thus, when condensation occurs, 71.5kohm and 56.2kohm is significantly affected. This is why they want to use 1.5kohm/1.2kohm resistors. Is there any risk to use the 1.5kohm/1.2kohm resistors?

    Also, as for Open/10kohm resistors, the resistor value actually does not affect so much, is it correct? I believe 10kohm or 4.7kohm do not matter beause Rhigh is open.

    Thanks,

    Kento

  • 0 in reply to Kento Adachi
    TI__Mastermind 28050 points

    Hi Kento,

    Our general recommendation is to use the larger resistor values provided in the datasheet to lower the risk of excessive leakage current on the IDX pin. However, the voltage level on the IDX pin is the most important factor which straps the I2C address of the device. If the customer can guarantee that the voltage level remains in the specified range, they can use smaller resistor values.

    Note that it is required to use resistors with 1% tolerance.

    Best,

    Lucas