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SN74AVC4T774: Current Consumption Too High

michael bowes
Prodigy 20 points
Part Number: SN74AVC4T774
Other Parts Discussed in Thread: CC2564MODA, BOOST-CC2564MODA

I'm using the CC2564MODA DUAL Mode Bluetooth Module in a new design and am finding that the power consumption when the bluetooth module is in Shutdown mode is higher than excpected, about 3mA all together. I believe that the source of the higher current consumption is the level shifters I'm using, the SN74AVC4T774RSVR. I know that the Bluetooth is in shutdown mode because the Shutdown enable line is driven to ground. I have been comparing the module I'm developing with and without the Bluetooth hardware and the module without Bluetooth hardware installed doesn't draw this extra current. When I tried disabling the outputs on the level shifters using their output enable pins the current draw only increases. I have also been comparing my modules current consumption to that of a development board I purchased from TI, the BOOST-CC2564MODA, I removed the level shifters from that dev. board for comparison and didn't see a difference in the current draw, so perhaps the Bluetooth module is drawing the extra current after all. Is there a schematic available for this dev. board? I haven't been able to find one as yet. Below if have attached the Bluetooth Portion from the schematic for my design. I also used documentation from the TI wiki site as a reference regarding the Bluetooth modules integration with these level shifters.

  • 0
    TI__Guru 62170 points
    Hi Michael,

    Welcome to e2e!
    Thanks for the detailed explanation and schematic provided.
    I see that the DIR1 is tied to Vcca such that signal flow is A to B. When the level shifter is disabled, the input circuitry is still active and hence I will suggest having the B port tied to ground as well.
    It is true for all the other IO ports as well. When Hi-Z, the IO ports will have its input circuitry active. you can try having the IO ports with weak pull-down resistors to see if the Icc current goes down.
  • 0 in reply to ShreyasRao
    Prodigy 20 points
    Given this new information and per my schematic. For the signal channels that have DIRn pulled to GND such that the signal flow is Bn->An I should connect a weak pull down resistor(~100kΩ) between Bn and Ground to force the Input circuitry into a low power state. If this seems right to you I will try it out on the bench an report back with my findings. The CC2564MODA Bluetooth module enables it's own pull-ups on the UART and Debug pins when in shutdown, assuming 1MΩ for those pull-ups I believe 100kΩ pull-downs should be sufficiently weak while holding the input signals within the level shifters' VIL threshold.