• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 18 subscribers
  • Views 168 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

SN74AVC4T774: SN74AVC4T774PW

Avi Rose
Prodigy 30 points
Part Number: SN74AVC4T774
Other Parts Discussed in Thread: SN74AXC4T774

Hi ,

In my design I using SN74AVC4T774 between MCU to SPI peripherals.

In my design the inputs of the SN74AVC4T774 are placed in Hi-Z when my MCU is in reset.

In the data sheet of the SN74AVC4T774 it is written:

"

Since this device has CMOS inputs, it is very important to not allow them to float. If the inputs are not driven to
either a high VCC state, or a low-GND state, an undesirable larger than expected ICC current may result. Since
the input voltage settlement is governed by many factors (for example, capacitance, board-layout, package
inductance, surrounding conditions, and so forth), ensuring that they these inputs are kept out of erroneous
switching states and tying them to either a high or a low level minimizes the leakage-current

"

I like to know if I need external pull-up or pull-down resistors to the SN74AVC4T774 in my design.

Thanks,

Avi.

  • 0
    TI__Genius 16510 points

    Hey Avi, 

    The referenced paragraph refers to the treatment of any unused I/Os on the device. During the time that your MCU is in reset, you can drive /OE high to disable the device, or use weak pulldowns on the unused I/Os so they are forced to a known state. If adding external pulldowns isn't feasible for the system, please also see the AXC4T774 that is a newer gen. of this device (whilst also supporting lower voltage range) and includes dyanmic pulldown resistors to allow for floating inputs.

    Thanks,

    Jack 

  • 0 in reply to Jack Guan
    Prodigy 30 points

    Hi Jack, I looked on the SN74AXC4T774 data sheet. I did not find where it is written it includes dynamic pull down resistors to allow for floating I/O inputs. Thanks, Avi.

  • 0 in reply to Avi Rose
    TI__Genius 16510 points

    Hey Avi,

    Please see this FAQ with explanation of pulldown resistors on AXC4T774. The datasheet is planned for future updates to provide this information as well.

    Thanks,

    Jack 

  • 0 in reply to Jack Guan
    Prodigy 30 points

    Hi Jack,

    1. Thanks a lot for the answer, it looks to me that this information solve the issue.

    2. Our customer do not have PCB space to add external resistors so replace the AVC4T774 with AXC4T774 is excellent solution for our customer.

    3. Just to clarify: is the feature "built in dynamic pull-down" is the same feature as "Integrated pulldown resistors" which I see in TI direction control voltage selection matrix in TI web site ?

    4. I still hesitate since the this feature of  built in dynamic pull-downs at the I/O does not mention in the data sheet and also does not written as a feature in the direction control voltage selection matrix in TI web site. Can I trust and forward the FAQ explanation to our customer ?

    5. Is there any formal document of TI that approve that in AXC family of Voltage Translators have built in dynamic pull-downs at the I/O

    Thanks for the support and understanding,

    Avi.

  • 0 in reply to Avi Rose
    TI__Genius 16510 points

    Hey Avi,

    Avi Rose said:
    3. Just to clarify: is the feature "built in dynamic pull-down" is the same feature as "Integrated pulldown resistors" which I see in TI direction control voltage selection matrix in TI web site ?

    Yes this is correct. This feature allows for the glitch-free power sequencing feature that is discussed further here. Additionally, see this FAQ that can be referenced as well, similar to the customer's application. 

    Avi Rose said:
    4. I still hesitate since the this feature of  built in dynamic pull-downs at the I/O does not mention in the data sheet and also does not written as a feature in the direction control voltage selection matrix in TI web site. Can I trust and forward the FAQ explanation to our customer ?

    Yes the FAQ can be provided to the customer for awareness. 

    Avi Rose said:
    5. Is there any formal document of TI that approve that in AXC family of Voltage Translators have built in dynamic pull-downs at the I/O

    At the moment no, the FAQs are the only references. However, it is part of our future efforts to provide this documentation in the datasheet of the AXC family devices to clear up any doubts. 

    Regards,

    Jack