esdintegrated-circuit
I have an ESD protection chip that has been unsoldered from my board, and for which we have lost the orientation. (I.e. we don't know where pin 1 is – the little dot has gone.)
Because of the symmetry of the IC's package, there are two possibilities for the orientation. Is it possible to use a voltmeter or scope to retrieve the orientation of this part?
Ok, here are a few basics on ESD diode parameters:
As for "I just want it to work as designed." What I see is that their original diode provides 8kV ESD protection... and a dynamic resistance that I can't figure out (not published). So take a guess on that parameter "as designed". Besides that, I've already told you in the comments above and I'll repeat here is that its very low capacitance value appears silly for GPIO ports. That board uses much faster diodes on GPIO than on the HDMI port. The "USB-ICTRL/GPIO1" pin does appear shared with USB so perhaps select ESD diodes intended for whatever USB standard that chip supports.
You need an USB application-specific TVS array with sufficiently low capacitance as to not distort the D+ and D- signals. NXP also has a good application note on the subject - the note you cited also mentions it (see page 5).
Essentially, ordinary TVS arrays have sufficient capacitance to distort the edges of the D+ and D- signals, causing issues with the USBIF-mandated eye diagram test. This loss of signal integrity can interfere with communications and is a sure-fire way to fail USB certification.
Many suppliers market USB-specific TVS arrays for ESD protection. They will be rated appropriately - i.e. you don't need to worry about voltage rating etc. - just get one that is intended for USB and you should be OK.
As for the SHIELD connection, you are correct - it is the metal casing of the connector and the braided shield of the USB cable that connects so it, which is likely referenced to protective Earth somewhere on the PC side of things. For EMI reasons it should not be directly tied to the GND signal connection, but should be connected through some impedance. I've seen both parallel resistor / capacitor (as you've shown) and ferrite bead connections between them.
Best Answer
Check the diagram in the datasheet, this chip is 'just' a bunch of 5..7V zener diodes.
If you use a low voltage (<5V) you can test the diodes. If your multimeter uses a low voltage you could even use it to measure the resistance: pins 1-2 should have a low resistance in at least one direction, much lower than 4-5.
But the fact that the dot has disappeared makes me wonder whether the chip should still be trusted. Note that this is a protection chip, so soldering it in and checking that the device works is no guarantee.