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I'm seeing an odd symbol in a schematic provided in a datasheet for the power management chip ADP5091: a ring that goes through a cylinder. The cylinder is connected to the inductor (SW pin) and the ring is connected to the low side transistor of the boost converter. I've tried googling this symbol but unfortunately I can't find anything. Could someone please help me out with this? Thanks in advance!

enter image description here

CreFroD
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    Duplicate [What is that component from the ADP5091 Schematic?](https://electronics.stackexchange.com/questions/454292/what-is-that-component-from-the-adp5091-schematic?atw=1) – StainlessSteelRat Jul 27 '20 at 21:09

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It looks like a current transformer. It would make a lot of sense if there was a current sensor of some type in the circuit. It monitors the current swing in the boost inductor, to switch off the low side FET when the inductor current exceeds some threshhold.

Whether it's a real current transformer (I'm not sure how they could integrate the magnetics in an IC) or an active device that behaves like one is another matter. There's no description of it in the data sheet. Hearth in comments suggests it could be a Hall sensor, which I think is probably more likely than a flux coupled transformer.

Neil_UK
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  • Thanks for your answer, this really makes sense. What confuses me however is that it is drawn as if there was no galvanic connection between the inductor and the low side FET. – CreFroD Jul 27 '20 at 19:03
  • @CreFroD The people who draw the pictures for the datasheets aren't the people who design the parts, they often know little or nothing about electronics. When the picture goes across the engineer's desk for approval for the 19th time (I've been that engineer) he may say it's 'good enough' and let it go, rather than mark up the changes he wants made AGAIN! Looking carefully, a line goes right up to the glyph at the top, and comes out at the bottom, so you can sort of see what's meant to be there, even though it's not drawn in the glyph. Rotating it through 90 degrees would have helped. – Neil_UK Jul 27 '20 at 19:11
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    I'd guess it's probably a Hall effect sensor, which is easy (well, relatively so) to integrate into an IC. Could just be a resistor and an amplifier, but I kind of doubt that for reasons I can't really put my finger on. Maybe I just like Hall effect sensors. – Hearth Jul 27 '20 at 19:12
  • @Hearth A Hall would make more sense as it's sensitive to DC, and you can orient two of them so they're not sensitive to external fields. I come back to the clueless artist and tired engineer conversation - 'it's a current sensor dammit, just find a current sensor symbol, put it in, and go away'. The commonly used symbol for a Hall, a diagonal cross in a box, is not that well known, I had to look it up. – Neil_UK Jul 27 '20 at 19:20
  • A current transformer would probably have 4 terminals – Voltage Spike Jul 27 '20 at 19:36
  • So would a Hall device. I think the arrow going from there to "Boost Controller" denotes a flow of information rather than a literal electrical connection. – Dave Tweed Jul 27 '20 at 21:29