• State Resolved
  • Locked Locked
  • Replies 13 replies
  • Answers 7 answers
  • Subscribers 20 subscribers
  • Views 537 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.

SN74AVC4T245: ICCB becomes about 2.5mA when VCCA power is not supplied.

Kazuya Nakai59
Guru 20120 points
Part Number: SN74AVC4T245
Other Parts Discussed in Thread: SN74AXC4T245

 Hello guys,

 One of my customer is about to release their new mobile product to the market.

 SN74AVC4T245 is used for voltage translation of control signal between 3.3V and 1.8V in the product.

 They have the following problem at this moment.

 [Problem]

  ICCB becomes about 2.5mA when VCCA power is not supplied.

 Their condition are the followings

  VCCA = 1.8V

  1DIR = VCCA  (through 100 kohm, 1A -> 1B direction )

  2DIR = GND  (through 100 kohm, 2B -> 2A direction)

 1A1 = 1A2 = GND (direct to GND)

 2A1 = 2A2 = open

 VCCB = 3.3V

 1OE = 2OE = GND (through 100 kohm)

 1B1 = 1B2 = open

 2B1 = 2B2 = GND (direct to GND)  

  They found that ICCB (VCCB consumption current) was increased to about 2.5mA when VCCA (1.8V) was powered down (open state) for sleep mode of A side.

  The device datasheet says on page 6 that ICCB = 8uA (Max) with VCCA = 0V and VCCB = 0V~3.6V conditions.

  The customer question is the follow.

  Q. Why our ICCB is much larger (2.5mA) than datasheet spec (8uA)?

      Could you please tell me how to reduce ICCB?

 Your reply would be much appreciated. (Sorry. Their schematic can not be attached because they don't want to disclose their schematic) 

 Best regards,

 Kazuya.

 

  • 0
    Guru 243790 points

    "Open" is not necessarily the same as "0 V".

    But this problem is probably caused by a floating voltage at any I/O pin. (See [FAQ] How does a slow or floating input affect a CMOS device?)

    Add pull-up or -down resistors too all I/Os that might float, or simply use the SN74AXC4T245.

  • 0 in reply to Clemens Ladisch
    Guru 20120 points

     Hello Clemens

     Thank you for your reply. The customer belives all input pins are fixed high or low level as the attached.

     Hello TI guys,

     The customer allowed me to disclosed their schematic for  SN74AVC4T245 ICC measument on E2E.

     I atttached their measument schematice.

     Please take a look and could you please tell me how to reduce ICCA?

     Also they have the following question. Colud you please give me your reply?

     Q. If SN74AVC4T245RSV is replaced with SN74AXC4T245, can the ICC problem be solved?

     Your reply would be much appreciated.

     Best regards,

     Kazuya.

    /cfs-file/__key/communityserver-discussions-components-files/151/SN74AVC4T245RSV_5F00_ICC_5F00_121720a.pdf

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 42640 points

    Hey Kazuya,

    When one of the supplies is at 0 V the outputs are disabled. Since the outputs are also inputs, its likely that the floating node at the output is causing the increased Icc. If this is the case then the SN74AXC4T245 can likely fix this issue or you can just add pull-downs.

  • 0 in reply to Dylan Hubbard
    Guru 20120 points

     Hello Dylan,

     Thank you very much for your reply. As you said, ICCA became 0uA when "2A1" and "2A2" pins were pulled down to GND

    with 10k ohm.

     Could I ask you a few questions for the customer as the follows?

     Q1. What is the different point between AVC and AXC?

            In case of AXC,  is any internal pulldown circuit is connected to each I/O pin when one of the supplies (VCCA or VCCB)

            is at 0 V?

     Q2. The followings are electronic characteristics about ICCA and ICCB in AVC datasheet.

      As you see, "Io=0" is described as a test condition.

     Could you please tell me what "Io=0" meaning is? The customer wants to know this meaning.

     Does this meas output terminals are open?

     Your reply would be appreciated.

     Thank you again and best regards.

     Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 42640 points

    Hey Kazuya,

    AXC has a wider operation range as well as a more robust power up. This FAQ should help answer the second part of the question.

    Io refers to no output current. This an important condition for ICC since the current being driven at a High output comes from the supply. Eliminating that, you only see the current consumed by the device.

  • 0 in reply to Dylan Hubbard
    Guru 20120 points

     Hello Dylan,

     Thank you very much for your reply.

     Could I ask you one additional question as the following customer question?

     Q. I can understand that Io=0 is important to measure ICCA/B parameters when VCCA/B, both are powered on.

         But when either VCCA or VCCB is powered off, all output buffers are disabled as you said. In the case, the device has no output pin.

         So I think "Io=0" condition is not applied for the cases of "VCCA=1.2V to 3.6V and VCCB=0V" and "VCCA=0V and VCCB=1.2V to 3.6V" conditions.

         Is my understanding correct?

     Thank you again and best regards,

     Kazuya.

  • 0 in reply to Kazuya Nakai59
    Guru 243790 points

    The test conditions are shared for all three cases. When the outputs are disabled, the Io condition indeed is meaningless.

  • 0 in reply to Clemens Ladisch
    Guru 20120 points

     Hello Clemens,

     Thank you very much for your reply. I could understand well because of your reply.

     Hello Dylan,

     The customer is dissatisfied with the contents of SN74AVC4T245 datasheet (document No.SCES576G).

     Because the following points are not discribed in the datasheet.

     1. When either VCCA or VCCB is powered off, output buffer is disabled.

     2. When either VCCA or VCCB is powered off, the other side consumption current is increased

         unless the pin set for output is pulled down or pulled up.

     3. The customer could not realized that the pin which set for output is disabled in the power down situation

         because it seems that "Io=0" condition of ICCA, ICCB are applied for all power situation in section 6.5, Electrical Characteristics.

     So the customer wants TI to consider the  current datasheet modification to avoid misunderstanding.

     Could you please consider the datasheet modification?

     Thank you and best regards,

     Kazuya. 

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 42640 points

    Hey Kazuya,

    Customer feedback is very important to us, I'll log this for future data sheet updates.

  • 0 in reply to Dylan Hubbard
    Guru 20120 points

     Hello Dylan,

     Thank you very much for your positive reply.

     The customer is eagerly expecting TI to modify the datasheet.

     Also they are looking foward to seeing modified SN74AVC4T245 datasheet.

     Thank you again and best regards,

     Kazuya. 

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 24485 points

    Hello Kazuya-san,

    We have many datasheets that require modification, and therefore we have to prioritize those which have a critical error or ones that have many errors.

    We strive to provide clarity through all of our documentation and we will mark this for a future update, but may not be able to get to this in a short time as we continue to work on many datasheet improvements.

    Best,
    Michael

  • 0 in reply to Michael J Schultis
    Guru 20120 points

     Hello Michael, Dylan,

     Thank you very much for your strong supports.

     Michael,

     I understood well what you said.

    We just want and expect TI to consider the modification at the next datasheet update timing.

    Thank you again and best regards,

     Kazuya.  

  • 0 in reply to Kazuya Nakai59
    Guru 20120 points

     Hello Dylan,

     I sent you a friend request because I'd like to talk you with offline.

     If you don't mind it, could you please give me your reply?

     Thank you and best regards,

     Kazuya.