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SN74AVC4T245Q1 leakage with VCCA switched off!

Carsten Thiele
Expert 7335 points
Other Parts Discussed in Thread: SN74AVCH4T245

Hi Team,
could you please help with the leakage current issue with SN74AVC4T245Q1.
In sleep mode VCCA (UG1V8) is switched off. Pin10,11,12,13 is n.c.
Pin 4,5,6,7 are inputs controlled by the Telematic modul which is switchted off in sleep mode.
They measured at VCCB about 2.4mA in sleep mode! Which is not acceptable.

I have seen in another forum thread that it is not recommended to switch off VCCA because of leakage.
I want to double check if the following reconfiguration VCCA = 3.3V, VCCB = 1.8V and change direction with DIR = GND will solve the problem.
Appreciate your feedback.
Many thanks in advance.
Best regards,
Carsten

  • 0
    TI__Guru 62240 points
    Hi Carsten ,

    I will move this into the translation forum for support .
  • 0
    TI__Expert 6335 points
    Carsten,

    I will need to confirm with my co-workers. I just started supporting these level translators. Sorry for this delay.

    Can you clarify "In sleep mode VCCA (UG1V8) is switched off"? Does this mean that the VCCA pin was left floating? Or was it shorted to GND? I'd just like to be specific if you don't mind.

    Also, I want to confirm your proposed changes to the schematic that you posted:

    1. VCCA is tied to 3.30V instead of 1.80V
    2. VCCB is tied to 1.80V instead of 3.30V
    3. Both DIR pins are tied to GND instead of VCCA, in order to switch the data transmisson path (B-to-A instead of A-to-B)

    Regards,
    Nirav
  • 0
    TI__Intellectual 2530 points

    Hi

    -This part has Vcc isolation feature, which should prevent the leakage current. Pulling Vcc to 0V, puts the outputs in High-Z state.

    -Are any of your inputs floating? Unused I/O need to be at a defined state (Gnd or Vcc)

    -Is Q1 part mandatory? SN74AVCH4T245 (non q1) is an option, since it has bus hold circuitry that might help.

    - VCCA = 3.3V, VCCB = 1.8V and change direction with DIR = GND can be a valid option, as the part will work in this configuration. During power up can Vcca power up first? That would solidify the workaround.

    Thanks