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Interfacing a CC1101 and TPS62730 to a 3.6V MCU

MoJo JoJo
Prodigy 170 points

Other Parts Discussed in Thread: CC1101, TPS62730

Hi. I'm looking to reduce the current consumption of CC1101 radio that needs to periodically transmit data. The idea is to wake up say once every 10 seconds and send a short transmission of about 100ms.

Texas recommends the TPS62730 to reduce the supply current to 2.1V, but then you need level conversion to talk to the microcontroller. The TPS62730's quiescent current is quite high (our entire system idles at 3uA) so if we wanted to run the MCU from it we would have to switch between 2.1V and our battery voltage of 3.6V constantly, which doesn't sound like a good idea.

For the wake-on-radio polling mode it seems like we would have to dedicate a GPIO pin to switching the regulator out of bypass mode, but we may have to do that if we need a PA at some point anyway. What setting for the GPIO should be used to make sure it switches at the right time?

What options are there for level switching? Pull-up resistors seem like a possibility with the MCU only pulling the lines low. Is there any kind of sample implementation available?

Thanks.

  • 0
    TI__Guru**** 317180 points

    Note that the maximum voltage on a CC1101 pin is VDD+0.3V. This means that either the MCU and CC1101 has to run on the same supply or a level shifter has to be used.

    To control the Bypass pin on the TPS the XOSC_STABLE signal can be used (table 41 i the UserGuide)

  • 0 in reply to TER
    Prodigy 170 points

    Thanks. Maybe a resistor/zenner combo could limit the voltage to an acceptable level. Generally speaking when people implement this design do they run the micro off the same regulator, switching voltage often? I'm concerned that a device designed to run for years without crashing probably shouldn't switch supply voltage by 1.5V every few seconds.

  • 0 in reply to MoJo JoJo
    Prodigy 170 points

    Care to comment on this? Do people generally switch their micros constantly along with the radio IC? Looking at the issues with Texas micros and flash memory corruption as voltage falls that doesn't seem like a good idea.

  • 0 in reply to MoJo JoJo
    TI__Guru**** 317180 points

    I would suggest you post a question about this in the forum for the MCU you are using.

    I believe some of the problems seen with flash memory is related to a POR/BOD reset and a program counter that end up at the wrong address. As long as the ramp times 3.6V->2.1V->3.6V is within the specifications for the MCU used the voltage changes should not be an issue.

  • 0 in reply to TER
    Prodigy 75 points

    Can we configure the CC1101 to automatically enable/disable the TPS62730 regulator by connecting GDO2 to ON/BYP, and if so, what setting do we use for iocfg for this PGIO pin?

  • 0 in reply to Benjamin Lonske
    TI__Guru**** 317180 points

    It depends. It will be more natural to control this pin from the MCU since the MCU knows when you may use bypass or not.