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I came across this package

enter image description here

Never saw anything like this before. Does anyone know what it is and how it's supposed to be mounted?

Federico Russo
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2 Answers2

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It's a (granted, fugly) TO-220 derived package used by Allegro for current measuring parts like the ACS756, datasheet. (I don't know if other manufacturers also use this kind of package.) The thick bent connections are for the current to be measured, in the case of the ACS756 up to 50A. This requires careful PCB layout (yes, the heavy pins are soldered in a PCB \$-\$ obviously not suited for paste-in-hole reflow, and hand-soldering will be tough as well :-))

Soldering pattern

Possibly other manufacturers prefer screw connections for low resistance current shunts like these ones from Isabellenhütte:

current-sense resistors

I don't know why Allegro prefers soldering over screw mounting.
I found this application, also based on an Allegro device (ACS715) which uses indeed screw connections.

enter image description here

What I find strange is that they pump 30 A through two ordinary SOIC pins. I would at least have replaced pins 1-2 and 3-4 by two tabs, I think. 15A through an SOIC pin seems like a lot.

stevenvh
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  • +1. Have you used this yourself? For what kind of product? – Federico Russo Jul 31 '11 at 11:38
  • @Federico - I've known it being used for measuring current in high power dimmers (5kW). Not a project I worked on myself. – stevenvh Jul 31 '11 at 11:44
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    Soldering is preferred over screw mounting because it makes assembly easier (cheaper), eliminating a "screw the part down" step, it takes less board real estate, it is more consistent, and it is more reliable. Fun fact: you can over-tighten a screw on a plated-through hole and crush the plating barrel, potentially disconnecting the inner layers. Board shops (the good ones, anyway) recommend against plating through screw holes. If you need to connect a screw to a circuit on the board, leave out the plating on the hole and stop the outer layer pads short of the hole. – Mike DeSimone Jul 31 '11 at 12:14
  • Also, if you don't have parts packed in all around this part, it can be a candidate for paste-in-hole. The technique would be similar to the one used by the Samtec QTH series for its alignment pins. – Mike DeSimone Jul 31 '11 at 12:19
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Very strange. I have never see its like either.

I can think of 2 reasons for this package:

  1. Two separate heat-sinks linked to different parts of the circuitry that shouldn't be connected.

  2. A high voltage or high current portion of the internal circuitry, such as a very high current photo-triac.

Majenko
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  • I've never seen high power photo-triacs. I don't think they exist. Usually they keep separate components for the power on one side, and the isolation on the other side. – Federico Russo Jul 31 '11 at 14:20
  • They're like dragons and fairys. Just because you haven't seen one doesn't mean they don't exist ;) – Majenko Jul 31 '11 at 14:50
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    Sentence one and sentence two are separate sentences. There's no causal connection between them, like "therefore". – Federico Russo Aug 01 '11 at 09:10