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PCA9306: Please review the schematic, and have a question.

Chase Jeong
Mastermind 7965 points
Part Number: PCA9306
Other Parts Discussed in Thread: LSF0002

Tool/software:

Dear TI experts,

My customer tests PCA9306 in their own PCB. Could you review the schematic first?

(1V8_DOVDD is from LDO.)

They found that if they set R7 to 200Kohm, 3.8V is detected on VREF1.

And if they set R7 to NC, 1.8V is detected on VREF1.

Could you find the reason for this symptom?

Best regards,

Chase

  • 0
    Guru 318700 points

    A small current (limited by R7) flows into VREF2 and out of VREF1. The 1.8 V supply must be able to sink that current, which typical LDOs cannot do. Try adding a resistor of 100 kΩ or less between VREF1 and GND.

    The LSF0002 would be easier to use.

  • 0
    TI__Guru 52698 points

    Hi Chase,

    The phenomenon that Clemens is describing and what seems to be your issue is found in section 8.1.7 "LDO and PCA9306 Concerns" in the PCA9306 datasheet on page 14 of 38. 

    LSF0002 is also a possibility. 

    Regards,

    Tyler