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Trouble deciphering schematic abbreviations

Discussion in 'Circuit Simulation & PCB Design' started by hfosteriii, Oct 4, 2017.

  1. hfosteriii

    hfosteriii New Member

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    I'm designing a dimmable led string drive circuit. Reading the datasheet for the ic (OB3372KP), under reference circuit/ application, I run into abbreviations for caps and resistors listed that don't have a value but an "nc" written below. I know this generally means "no connection", but I'm looking for clarification as to why its listed with certain caps or resistors. Is their value not necessary and that specific component only needed if left without a connection/ floating? Do you eliminate the component if there isn't a connection made/ signal input there. Or vice versa. Please advise. I'm including a pic for reference. IC Data.png Thank you in advance for your help.
     
  2. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Welcome to ETO, hfosteriii.

    I'm not familiar with that "nc" usage in this context.

    But, from page nine of this datasheet:
    "After LED short flag is generated, the capacitor at
    pin HCP is charged by a current of about 4uA and
    thus the IC enters Hiccup mode. Once the voltage
    at pin HCP exceeds a threshold of approximately
    2V, the LED short state will be reset and the CMP
    pin are released and GATE and LSD pins are
    allowed to turn on. Then, OB3372 will go into a
    soft-start mode ensuring a smooth recovery for the
    LED current. The value of the capacitor required
    for a given hiccup time is given by:
    upload_2017-10-5_8-24-13.png
    (The underlining is mine).


    This doesn't address the specific components you noted, but given their location(s), I wonder if they are related. That is to say, perhaps they need to be determined once the entire circuit is completed (including output LED load(s).
     
  3. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  4. dave

    Dave New Member

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  5. tomizett

    tomizett Active Member

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    I would agree with KISS, they look like optional components, although that would be a bit unusual for a reference design.

    You also frequently see "NP" for "Not Populated" in the same context.
     
  6. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Perhaps (just a guess) "Not Critical" ?
     
  7. atferrari

    atferrari Well-Known Member

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    After RTFDS that you graciously provided, I dare to say it is related to whether the driver is master or slave.

    Figure 4 and related text seem to have all the necessary references.
     
  8. hfosteriii

    hfosteriii New Member

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    Thank you for the quick replies. As I was thinking about the answers in reference to the reference circuit (ha), I started wondering if it was possible that it might mean "not critical" because , if I'm not mistaken, every one of those pathways would be a low voltage, low current path and doesn't depend on a specific pulse/frequency? Even the pwm dimming input could be any frequency because the pwm that powers the led's is set on the led power side? Am I wrong in any of those assumptions?

    But that still begs the question why a reference circuit would not have the value that they used. That is a circuit already put into practice, no? I could see it in the typical circuit, but they group many of those in/outs so those components are unnecessary anyhow.
     

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