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CC2540 low VCC power on problem

Vincent Lau
Prodigy 180 points
Other Parts Discussed in Thread: CC2540, CC2541

Hi, all

As I am using a 2.4V Ni-MH Battery to driver CC2540 directly, the battery voltage may be lower than 2V which is the minimum limit of CC2540, when the battery is over- discharge. I have done an interesting "VCC down and up" experiment on keyfob dev-kit and my own cc2540 board. I am using a DC power to drive CC2540's VCC. Firstly, power down VCC from 2V to 1.75V. Of course, CC2540 should not work as the minimum limit 2V here. But there is a larger current loss(Up to 200mA) on VCC when it is on 1.75V ! Then I continue downing the VCC lower than 1.75V, the current loss disappear(Lower than 2mA). Secondly, power up VCC from 1.5V to 1.78V. The larger current loss (Up to 200mA)is back again on VCC when it is 1.78V ! In contrast with power-down, the current loss will grow when I continue to power up VCC from 1.78V to 3V slowly. The CC2540 will not go to work even the VCC is higher than 2V.
What is the problem? Thanks a lot!

  • 0
    Guru 22270 points

    Hello Vincent,

    The CC2540/CC2541 have both Power On Reset (POR) and Brown Out Detection (BOD) circuitry.  Your slow decrease in voltage would trigger the BOD when it drops below the 1.80V.  On reset, the port pins are forced to inputs with pull-ups enabled.  Below that, you will get static power drain from the port pins especially if something connected to them (LEDs) since the device is no longer in reset

    As for the powering up, the BOD and POR should hold the device in reset until the voltage rises above both levels.  If you are not seeing this, then it may be due to the fact that this slow increase is causing problems with the clocks or other LDO you may be using.

    Also, if you have TPS voltage regulator, it may have its own low voltage drop out reset conditions.

    Information on BOD and POR can be found in the CC254x User's Guide swru191 section 5.  http://www.ti.com/lit/swru191 The electrical characteristics can be found on the Datasheet for the CC2540.

    A suggested solution would be to have an external power monitor or a comparator circuit to ensure the device switches on and off at 1.80 and 2.0 V respectively, or an LDO that matches or is configurable to those set points.

    Thanks,