SOIC 8 Pin Orientation
Recently, messing around with the MAX771 Step Up switching controller (see below), and looking to develop around 90V to power some low current retro technology.
Note this circuit shows the MAX 773, in our case we're using the MAX 771
Finding MAX 771 8 pin DIP packages is a bit tricky, and quite expensive, which can be problematic for bread-boarding or prototyping.
Exhibit 2
So far so good ...But when came time to orient the package then came an interesting diversion. Which pin is pin one. As you can see from the image below (Exhibit 3), there is a dot, but it is not exactly aligned, and there is not a notch removed from either end..
Below are some examples of orientation drawings you might expect to find in DIP8 and SOIC extracted from various data sheets
These are all variations on a theme which provides chip orientation. But the SOIC MAX 771 appears different it exhibits NONE of these attributes and it seems a bit of a big call to use the yellow dot, which is not properly aligned between pins. This required more investigation ...
The MAX 771 SOIC chip is small, the black plastic 3.1 x 4.8mm, to get some perspective seem next to the tip of a pencil in Exhibit 8 below
Note this circuit shows the MAX 773, in our case we're using the MAX 771
Exhibit 1
Finding MAX 771 8 pin DIP packages is a bit tricky, and quite expensive, which can be problematic for bread-boarding or prototyping.
So I went with the SOIC package 5 for $15 off EBAY, and also the SOIC8, SOP8 to DIP8 adapter, because this will not be the only time I'm sure when we are trying to prototype SOIC packages. Note the MAX 771 installed in the adapter, pressing down on the top outside of the adapter releases the spring clips which connect the the SOIC package, and it can be easily removed/installed. (click any photo to get a full size view)
Exhibit 2So far so good ...But when came time to orient the package then came an interesting diversion. Which pin is pin one. As you can see from the image below (Exhibit 3), there is a dot, but it is not exactly aligned, and there is not a notch removed from either end..
Exhibit 3
Typical DIP and SOIC8 package markings
Below are some examples of orientation drawings you might expect to find in DIP8 and SOIC extracted from various data sheets
The Partial Notch
The Full Notch
The Dot
The Chamfer
These are all variations on a theme which provides chip orientation. But the SOIC MAX 771 appears different it exhibits NONE of these attributes and it seems a bit of a big call to use the yellow dot, which is not properly aligned between pins. This required more investigation ...
Investigating the MAX 771
The MAX 771 SOIC chip is small, the black plastic 3.1 x 4.8mm, to get some perspective seem next to the tip of a pencil in Exhibit 8 below
Exhibit 8
Closer examination reveals something interesting, which can just be detected in the image on the right (exhibit 8). Changing the light, and zooming the microscope, reveals clearly identified notch right over pin 1 ...Voila !!
So as it happens, using the YELLOW DOT would have been ok on this occasion, and we are none the wiser if the intent is to mark the pin with both the dot and the notch ….
All the best ...Peter
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