• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 20 subscribers
  • Views 1720 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

SN74HC595: Are my chip is defictive?

SN74HC595: All the outputs behave as if they are open-collector/open-drain

David Haworth
Prodigy 20 points
Part Number: SN74HC595

I have some 74HC595 devices (exact marking GM1807FSF E4 SN74HC595N). They were supplied in packs of 10 in what appear to be ESD-safe bags.

All the devices I have tried so far (three from one pack and one from another) behave as if the outputs are open-drain and not the expected push-pull configuration.

I have the OE\ pin connected to ground and the SRCLR\ pin connected to Vcc (nominally 5v). The SER, RCLK and SRCLK pins are driven by an Arduino in slow motion (1s pulses!) so I can easily see what's going on.

The shift register appears to be working correctly - I can see data appearing at the QH' pin.

When the latched Q outputs have no load I see no signal with my multimeter. However, if I add a 10k pull-up to the outputs I see the expected signals.

According to the data sheet, the outputs should be able to source enough current to drive low-current LED devices (70mA max for the package).

Is this a faulty batch? I've also seen that there's a 74LS596 device with open-collector outputs, but there doesn't seem to be a 74HC variant of that device, so it can't simply be a case of incorrect marking. Could there be some interference between the internal latch outputs and the OE connections to the output buffers such that when the latched data is high the output is high-impedance?

[Update] After further research, I've discovered other people with the same problem. It appears that  these devices are counterfeit - possibly remarked 74LS596 devices. Is it possible to confirm that from the batch number (GM1807FSF E4)?

  • 0
    TI__Guru* 97046 points

    Hey David,

    That is possible - can you provide images of the top & bottom of one of the devices?

  • 0
    TI__Prodigy 330 points

    4555.Counterfeit Validation Form_distributed_0001.pdfIn order for TI to begin the verification process all of the following information is required.  Please review the attached customer letter and provide the required information to ti-counterfeit@list.ti.com.

    Required information

    1. Completed Counterfeit Request Form. 

    2. High quality pictures of the bottom & top of the device(s)

    3. High quality pictures of the 2D bar code labels.  

    4. Copies/pictures of shipping documents, i.e. packing slip showing the origin of the devices to TI.  (If this information cannot be provided we are unable to provide verification due to uncertainties regarding chain of custody of the products.)

    5. Provide device application.

      Once the required information is provided and submitted, your request will be reviewed for verification.

    • Important Note: The attachment size limit for the group address (ti-counterfeit@list.ti.com) is 1MB.  Email lisam@ti.com, and j-davenport@ti.com if your attachments are larger than 1MB.

                            

    • TI strongly encourages you to purchase all your TI parts either directly from TI or from authorized TI distributors (http://focus.ti.com/docs/general/distribcountryresults.jhtml) and not from the gray market or brokers.

  • 0 in reply to Emrys Maier
    Prodigy 20 points

    Hi Emrys,

    here's the photo you asked for. Now that I see the logo under high magnification, it doesn't look like a TI logo.

    I bought the chips well over a year ago from a seller on ebay. It's getting increasingly difficult to source DIP devices these days - have to rely on surplus stock sellers and the like. I suspect the seller bought in bulk from a far eastern trader and sold them on in smaller quantities to hobbyists like me.

    The devices behave exactly like 74xy596 devices. Unfortunately I can't tell whether they are LS or HC - the equipment I have available isn't sensitive enough to measure the quiescent current.

  • 0 in reply to David Haworth
    TI__Prodigy 330 points

    David,

    Thank you for the photos of the top and bottom of the devices, however ebay is not a TI authorized distributor. Due to uncertainties in the supply chain regarding chain of custody of the products, TI will only support product verification requests from customers who purchase through authorized distributors.  All other verification requests must be worked through their supply chain.