This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

CC1120: Power down procedure

Part Number: CC1120

What is the proper procedure for putting the CC1120 into low power mode?  My current system runs at about 19mA.  If I issue a XOFF or SPWD strobe when idle, it goes up to 28mA.  So, I’m guessing some registers need adjusting.  But, I don’t see any write up about doing that in the manual.  I would expect my draw to go down substantially after issuing a strobe.  Any ideas?  Thanks.

  • Only a SPWD is required. Note that the chip exists power down if you do something on the SPI interface after this. Please verify by monitoring the SPI interface that this is not the case. 

    Note that you have to issue a SPWD from IDLE, see figure 2 in

  • Still not working.  My system draws 35mA with with the radio chip in IDLE mode (MARCSTATE = 0x41), and 43mA when I issue a SPWD strobe from IDLE.   Goes to IDLE after setting up the chip and sending a packet.  System is working fine, just not powering down as intended.

  • - Would you be able to post a plot showing the SPI interface when you issue a SPWD and that show that nothing else is going on on the SPI but after sending the strobe.

    - The current consumption is very high even for IDLE. Are you measuring on a full board? If that is the case, have you tried to measure current just going to the CC1120? 

    - Does the MCU also go down in power down in this case? If so, have you ensured that SO has a defined state to avoid having a floating input on the MCU?

  • The radio chip is the only chip on the SPI bus.  The current is higher because I have a display on that is showing data, but it's a parallel interface not SPI.  The radio chip shows IDLE state after completing startup and sending a packet.  If I turn off the display and power down the CPU leaving the radio chip in IDLE, it draws about 17mA.  Then issuing a SPWD strobe makes it go up to 25mA.

    I also have a test board without the radio chip installed, and in complete power down mode of the CPU, the draw is 0.3mA.

    I'll see if I can set up a scope and get some pics.

  • Please try to measure the current to CC1120 only. Start with IDLE and see if you manage to get the current stated in the datasheet. I can also take a look at the schematic, you can send me a friend request and send it as a PM if you don't want to share it openly on the forum. 

  • It won't let me attach a PDF for some reason.  Nothing special about the design.  Same as TI recommends.

    It will be difficult to measure current directly to the CC1120 without redoing the circuit board (which we may have to do anyway, if we can't get the current down).   We have the chip attached to a 3.3V power plane that powers other chips.  We are still evaluating, but still can't get the current down yet.

  • Did you use the "insert file" option when you tried to attach the PDF?

  • Yeah.  I get an error message about invalid file.  But, it is a PDF and I can open it with a PDF reader. 

    Can you post a link to the design schematic for 420-470Mhz that you consider the correct one?  I want to make sure the one we tailored our design to is correct.  I did have one wrong inductor value, but that didn't have any effect on current draw.  I didn't think it would.

  • Thanks.  That is the same schematic we are using.  I did find one pin on the chip that was inadvertently tied to 3.3V.  It did reduce the current, so progress.  But, still issuing the SPWD strobe makes the current go up by 7mA.  Attached PDF.160-4019A2.pdf

  • I believe C30 has the wrong value but that should not impact power. 

    Have you tried to fix the 3V on wrong pin on a board that you haven't powered up? If the pin you tied 3 V to is designed for a lower voltage you may have damaged the chip causing high current draw. 

  • We fixed the 3.3V issue, but only on boards previously powered up.  We don't have any other than these prototypes yet.  Will try and get the chip changed out and see if that makes a difference.  Thanks for the C30 value difference.