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Nexperia F/F problem

I have a test circuit for some single flip flops, I'm testing a TinyLogic NC7SZ74:

And Nexperia 74LVC2G74:

It's just a divide-by-2 circuit, not-Q to D, preset and clear pulled high.

With some difficulty I got the TinyLogic US8 parts soldered to adapters and into the circuit. Work great.

I then mounted the easier SOT Nexperia flops. As far as I can tell they have the same pin-out. Supply voltage is 3 volts, 1 MHz input. Put in same circuit they immediately start pulling ~30mA! The output at the data outputs is noise and spiky garbage.

Tried another part from the reel. Same result. Put the TinyLogic part back in. works fine.

There isn't any dot indicator on these parts that I can see but the datasheet says there should be. Just a black bar along the bottom(?) I assumed that the 1 pin is at the bottom left when the lettering is upright read left to right as usual.

Wondering user error and if so what I might have done wrong, or if possibly defective parts?

Reply to
bitrex
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The obvious question is did you try reversing one of the parts? I've never known lettering to be rigorous for chip orientation. How about photos of the top and bottom of the part?

--

  Rick C. 

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Reply to
Rick C

Flipping it would put GND where VCC is and vice versa, dead short thru the protection diodes. current limit on my supply was set at 50mA it didn't engage.

Well I can try it but I didn't order too many of these for testing. I should probably always get batches of 10 or 20 I guess.

Reply to
bitrex

I'm having trouble getting a good pic of the lettering even under high magnification, there's something there though other than the darker "bar."

Reply to
bitrex

Top row looks like "O85" maybe? D85?

Bottom row is definitely "94Z"

Black bar to the left running the width of the chip, about 1/5th its total area

Bottom of chip is featureless

Reply to
bitrex

Try ohming the Vcc/Gnd pins. Does that tell you anything?

--

  Rick C. 

  + Get 1,000 miles of free Supercharging 
  + Tesla referral code - https://ts.la/richard11209
Reply to
Rick C

They don't have reference drawings on the datasheet?

Reply to
krw

Floating-inputs can make currents that high. Whether an open input will create such a current is a function of what voltage it floats too, and is not predictable. When struggling with soldering, an apparently-soldered connection may in fact be open underneath. A floating input causing internal rail-rail current can certainly cause logic malfunction.

--
 Thanks, 
    - Win
Reply to
Winfield Hill

Yeah, it's weird, the US8 parts were the pisser to get mounted, but once I inspected carefully that everything was making contact, no bridges, and continuity-ed all the pins to check out OK they work fine.

The SOP parts seemed superficially a lot easier to hand-mount to the surfboards and seemed to check out as well but something's going wrong.

I'll consider it user error for now and try mounting some more and see what happens. It's curious/irritating the parts have no "dot" indicator as the datasheet says they should, though.

Reply to
bitrex

I've had luck wetting a cotton swab with a small amount of alcohol and swipe across the top. Helps make the pin 1 dot easier to see.

--
Chisolm 
Texas-American
Reply to
Joe Chisolm

Go to the website and get document SOT505-1_518, which shows component orientation in the tape. For tssop8 it says, with the sprocket holes up, pin 1 is on the upper left top corner. That's always the best way to determine orientation.

--
 Thanks, 
    - Win
Reply to
Winfield Hill

So did you ever resolve your problem?

--

  Rick C. 

  -- Get 1,000 miles of free Supercharging 
  -- Tesla referral code - https://ts.la/richard11209
Reply to
Rick C

Away from home for the weekend, got another pack of parts and "surfboards" from another mfgr coming in, standby :)

Reply to
bitrex

Might the flops be counterfeits? Did they come from an authorized distributor?

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics
Reply to
jlarkin

Seems the least likely possibility as they came from Mouser, but possible.

Datasheet says the package is supposed to have a dot indicator but there isn't which is at the very least, annoying.

Reply to
bitrex

I'm trying a different set of "surfboards" from Adafruit, too, as there's a chance the no-name Amazon boards are bad:

Reply to
bitrex

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