• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 21 subscribers
  • Views 378 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.

SN74LV4T125: what's the input requirement?

Howard Zou
Genius 12365 points
Part Number: SN74LV4T125

Hi,

my customer is using SN74LV4T125 for 1.8V to 3.3V translation. And find that in some board the 1.8V input will degrade to about 1.0V. 

The output is connected to MCU's IO port through a 0ohm resistor. No matter we solder or unsolder the 0ohm resistor, the phenomenon is the same.

It happens about once per 1000 boards.

There is no data about input drive current requirement for this device.

I wonder why the 1.8V would degrade?

  • 0
    Guru 317060 points

    CMOS devices have high-impedance inputs, which should not source or sink any noticeable amount of current.

    I'd guess the device is damaged. (Can you check the input impedance?) The most likely cause of such damage is overvoltage (excessive ringing at signal edges, or ESD).

    What is connected to the SN74LV4T125's inputs?

  • 0 in reply to Clemens Ladisch
    TI__Genius 12365 points

    It's TP(touch panel) signal from screen of an EPOS.

    The TP signal is connected to an analog switch and then connected to input of SN74LV4T125.

    Could you please explain how our device works? Like the input structure, how it translate the voltage level.

  • 0 in reply to Howard Zou
    TI__Genius 16735 points

    Hi,

    This is a diagram of a CMOS input device. Check the input impedance of the damaged devices. If it is not a high impedance to ground, then some ESD event or other usage outside the datasheet spec will have caused the device to get damaged. Current does not flow into the devices. It flows from the Vcc pin into the output, which is how the device level shifts. If the device is not damaged, you need to exchange the part on the board and see if the board has some damage. 

    Thanks!

    -Karan