I have this ic: https://www.ti.com/product/SN74CBT3251

However, if you look at the actual packaging, there is not a circle, in order to figure out pin 1.

This is a picture of the IC:

enter image description here

Can someone give me a tip, on how to identify which is pin 1?

  • 3
    \$\begingroup\$ Instead of a circle, sometimes you get a vertical bar on the left side. Pin 1 is the lower left pin when the bar is to the left. \$\endgroup\$
    – Hearth
    Jan 6, 2021 at 2:23
  • 1
    \$\begingroup\$ wb5rvz.org/common/locatingPin1 Use number 5 (lettering orientation) last! I once saw a spectacular failure when a junior engineer ignored the other markings and used the lettering. \$\endgroup\$
    – Mattman944
    Jan 6, 2021 at 2:55

2 Answers 2


I am sure the other answers are probably right. But the package has a subtle asymmetry. One side is beveled slightly. That side is the side where pin 1 will be found. See picture (annotated by me, but from datasheet linked in question).

enter image description here

  • 4
    \$\begingroup\$ +1 As always for these questions, refer to the datasheet (or any supplemental packaging datasheets, if it's not in the part datasheet directly). \$\endgroup\$
    – Shamtam
    Jan 6, 2021 at 5:00
  • \$\begingroup\$ @Shamtam OP included a link to the datasheet in the question. OP probably didn't notice this subtle feature as a pin 1 indicator. I know it was a revelation to me when I finally noticed it, years ago. I couldn't believe the datasheet contained no pin 1 information for the SSOP. So I went back again and again until I noticed the little chamfer or bevel on one side. \$\endgroup\$
    – mkeith
    Jan 6, 2021 at 5:47
  • \$\begingroup\$ The datasheet shows a shaded area as "pin 1 ID area" but I'm not seeing any corresponding feature in the photo. Looks like they replaced the shaded area with a (very subtle) crosswise bar somewhere in production. But yes, the chamfer/bevel is consistent. \$\endgroup\$
    – CCTO
    Jan 6, 2021 at 14:43
  • \$\begingroup\$ @CCTO the chamfer inside the red circle makes one side of the IC distinct from the other. That chamfer identifies the side of the IC where pin 1 can be found. When the chamfer side is to the left in the top view, pin 1 is in the upper left hand corner. The shading is not meaningful. The label "1" is meaningful. \$\endgroup\$
    – mkeith
    Jan 6, 2021 at 17:54
  • \$\begingroup\$ I shouldn't say the shading is not meaningful. My take on it is that the shading is intended to indicate the pin 1 quadrant of the IC. But the shading exists in the drawing only. It does not correspond to any physical feature in the IC. \$\endgroup\$
    – mkeith
    Jan 6, 2021 at 20:10

The white stripe on the left is a marker indicating here that pin 1 is on the bottom, left-hand side.

If @CL is not mistaken, the datasheet of this IC is here; you could check there.


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