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OPA170: Design check

Marvn Arcangel
Genius 10415 points
Part Number: OPA170
Other Parts Discussed in Thread: TLC2252

Hi Team,

Can you please help with the inquiry below:

On the E-FUSE-VSET, in the left part, when AN_OUT=12, which theoretical value =2.07. but the actual test only had 1.3V on it. Can you help check what is the cause?

The customer uses 2 pcs opa170 in a 4x10 matrix board.

Thanks in advance.

Regards,

Marvin

  • 0
    TI__Genius 12620 points

    Hi Marvin, 

    Did you measure AN_OUT is 12V and the two resistors are the correct resistance value? Where was the 1.3V measured? 

    Regards,
    Ashley

  • 0 in reply to Ashley Kang
    TI__Genius 10415 points

    Hi Ashley,

    The value of AN_OUT is 11.94V

    For the circuit, the resistor R20 value is changed.

    R20=210 ohm, the E-fuse_VSET (theoretical )=2.08V, but actual value =1.298V
    R20=100 ohm, the E-fuse_VSET (theoretical )=1.09V, but actual value =0.914V
    R20=50 ohm, the E-fuse_VSET (theoretical )=0.571V, but actual value =0.565V

    In the board, they only have one circuit like Fig.1, but have 4x10 Fig2. On it.

    Another important point, they change OPA170 to TLC2252 and the E-FUSE_VSET is ok.

    Regards,

    Marvin

  • 0 in reply to Marvn Arcangel
    TI__Genius 12620 points

    Hi Marvin, 

    Thank you for the additional information. The reason the customer is seeing the voltage drop on the inputs is because the OPA170 has back-to-back input diodes internally, making it not ideal for comparator use case. This is shown in the datasheet on page 18 (see below for snippet). 

    The TLC2252 does not have these diodes which is why the operation works as normal. I recommend switching to the TLV9351 instead to avoid this issue. 

    Please let me know if you have further questions.
    Thank you!

    Best Regards,
    Ashley