• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 21 subscribers
  • Views 809 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:

SN74LVC1G17: Pulse generator

SN74LVC1G17: What is Vf variation of parasitic diode connected from "GND" pin to "A" input pin?

Kazuya Nakai59
Guru 21595 points
Part Number: SN74LVC1G17

 Hello guys,

 One of my customers has been used SN74LVC1G17 for many their products long time.

 Their input signal voltage connected to the device "A" pin is -0.4V. So they always tested Vf of parasitic diode connected from "GND" pin to "A" input pin of all SN74LVC1G17 they use.

 The Vf average volta was 0.7V~0.6V. But recently they found the Vf voltage was changed to about 0.46V. The Vf voltage went down from 0.6V~0.7 to 0.46V.

 They want TI to answer the following questions. Could you give me your comments for them?

 Q1. They know that Vf is changed by temperature and flowing current value.

       They want to know whether the Vf is changed between factories of front end or not?

 Q2. Also they want to know whether the Vf is changed between wafer material (ingot) lot?

 Q3. What is Vf variation of parasitic diode connected from "GND" pin to "A" input pin roughly?

  Your reply would be much appreciated.

 Best regards,

 Kazuya.

  • 0
    TI__Genius 16735 points

    Hi Kazuya,

    I will get your Vf variation questions to our CQE to see if they know the answer.

    However, I notice the datasheet mentions that the input voltage range is from -.5V to 6.5V. So having -.4V at the input should not be a problem through the datasheet operating temperature range if that is the concern. All parts shipped from TI will follow the datasheet standards.

    I am guessing their concern is that they don't want current to come out of the input of the device when a negative voltage is applied. However, this is operating outside datasheet specs and datasheet doesn't guarantee any specs around Vf for the GND clamp. Our CQE will be able to guarantee any of their answers but I will let you know what they say.

    Thanks!

    -Karan

  • 0 in reply to Karan Kotadia
    Guru 21595 points

     Hi Karan,

     Thank you very much for your reply.

     The customer knows that the Vf is not guaranteed by the device datasheet.

    But they worry about quality of the production lot which 0.46V Vf voltage was observed because the vf of the lot was changed drastically from other lots.  

     Your CQE team comment would be much appreciated.

     Thank you very much again and best regards,

     Kazuya, 

  • 0 in reply to Kazuya Nakai59
    TI__Guru* 97046 points

    Hello Kazuya-san,

    Q1. They know that Vf is changed by temperature and flowing current value.

           They want to know whether the Vf is changed between factories of front end or not?

    Yes - process variations (ie changes in doping level) as well as design changes (ie changes in the semiconductor layout) will change the forward voltage of a diode.

    Here's the equation for diode current:

    Source: http://web.mit.edu/6.012/www/SP07-L15.pdf

    You can see in the first equation that there is a dependence on Na and Nd, which are the carrier concentrations in the P-type and N-type material, respectively. Changes to these values will directly influence the diffusion current (IS) of the diode, and thus the I-V curve as well.

     Q2. Also they want to know whether the Vf is changed between wafer material (ingot) lot?

    Yes - each lot has minor variations. These are accounted for in our datasheet specifcations and test programs. All devices are tested prior to sale as per the datasheet. Vf is not a specification in the datasheet and is not tested.

     Q3. What is Vf variation of parasitic diode connected from "GND" pin to "A" input pin roughly?

    This is not a specification in the datasheet, thus we don't measure it.

    Input clamp diode forward voltage is not a measure of quality or reliability, especially considering that this value is not even listed in the datasheet.  I would recommend that the customer start using a value that is guaranteed by TI to determine quality of devices, such as VOH or VOL.

    We do not characterize or measure the input clamp diode voltage, thus we do not have data to support the customer's request. I can say for certain that the device was tested prior to shipping and it meets the datasheet specifications -- which is a MUCH more stringent set of tests than just a single diode drop check.