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CC2541 DC Current Consumption (Layout Issue?)

Philipp Klein
Prodigy 90 points
Other Parts Discussed in Thread: CC2541

Hi everyone,

I've got an issue with the power consumption of the CC2541. The situation is as follows: I've got a custom PCB which is derived from a perfectly working board (with only slight differences of the schematics). On the new board, the CC draws about 500µA current, even in sleep mode. If I put exactly this CC onto the old board, this current offset is gone. If I solder it back onto the new board the offset is measurable again. I verified this with at least 3 CC chips. The new board without the CC shows no current draw so it has no built-in short circuits.

Except for this current offset the new board is performing very well with good RF performance. So I guess this is not a problem.

Unused peripherals (I²C, ADC input) are not connected and not in use. The problem occurs with the original TI stack (1.2.1) and with my custom firmware.

Any ideas what might cause the CC to draw that much current in sleep mode? Your help is much appreciated.

Best Regards,

Philipp

  • 0
    Guru 31280 points

    Hi,

    Several things to check:

    1. You said there are only "slight differences", what are those differences?
      Pull up or pull down resistors?
    2. I2C not connected, is this part of a chip completely grounded on both versions
      of the PCB?

     
    You should also mention, in detail, any other info you might consider important for solving

    this issue.

  • 0 in reply to Igor Sherer
    Prodigy 90 points

    Hi Igor,

    thank you for your reply.

    1. There are differences regarding the outer shape and the layer sequence and widths of the PCB. Also, LEDs and buttons are missing on the new board which were placed on the old board. Pull up/down resistors are not different from the old board.
    2. I²C is not grounded on both versions.

    One thing that might be interesting: I see a measurable resistance (between 10 and 50 kOhm) between the battery terminals of the new board (measured with a standard digital multimeter). On the old board the resistance goes up to the upper end of the measurable range (> 10 MOhm) after charging the capacitors to the voltage the DMM is supplying (which is not enough to power up the device).

    BR, Philipp

  • 0 in reply to Philipp Klein
    Guru 31280 points

    Hi,

    This measurable resistance present when the CC2541 chip is assembled or not?

  • 0 in reply to Philipp Klein
    TI__Genius 10955 points

    When the LEDs are missing, it is still important that you set P1.0 and P1.1 as outputs (unless they are pulled high or low externally). These two pins do not have internal pull-up, and if left floating, they will cause excessive power consumption. You should also make sure that the other unconnected I/O pins are left in their reset state.

  • 0 in reply to hec
    Prodigy 90 points

    The resistance was measured with the CC being soldered onto the board.

    All unconnected GPIO pins are set to output and low.

  • 0 in reply to Philipp Klein
    Prodigy 90 points

    The problem is solved: It was a layout mistake on our side. Do not connect DCOUPL to Vcc...

    Thank you for all your answers anyway.