CC115L: Best practices For MISO/SO (GDO1) pin behavior

Austin Guevara

Part Number: CC115L

Tool/software:

Background:
We initialized all GDOx outputs to High impedance (3-state) as specified by the Data sheet and operation is as expected. However, this product is a battery powered device and power consumption is extremely important when we went to produce a sample run an abnormality was noticed.

Issue:
We noticed some current variance between boards and after some hardware debugging came across what appears to be SO/MISO acting as a floating pin when CS is not pulled low. The lab found a board that would draw ~47uA in its idle state but if they shorted GDO1 to ground the current would drop to 0.79uA.

Next Steps:
I haven't seen anywhere in the data sheet that suggests there should be a Pull-Up or Pull-Down on MISO. Is this standard procedure? Are we missing some other configuration step here? In the refrence design I don't see anything mentioned? What could be the cause of this?

5 months ago

0 TheGhostOf 5 months ago

Mastermind 6470 points

Looked in an old post on power consumption: "Note that the SO pin is high Z when not used and if the corresponding input in the MCU is set as input this input will get a not defined level causing higher current consumption."

0 Austin Guevara 5 months ago in reply to TheGhostOf

Prodigy 10 points

TheGhostOf Thank you for your quick response. Can you link the old post you are citing here. That makes sense, but is the conclusion to then toggle the SO pin on the MCU to be an output when CS is high, or should I be using a different default state for GDO1 than high Z?

0 ZC 5 months ago in reply to Austin Guevara

TI__Genius 17955 points

Hi Austin,

TheGhostOf's post is here: https://e2e.ti.com/support/wireless-connectivity/other-wireless-group/other-wireless/f/other-wireless-technologies-forum/264836/cc1101-doesn-t-enter-in-power-down-mode

I am double-check what the recommendation is here and will need to give clarification Monday or Tuesday next week.

Regards,

Zack

0 Austin Guevara 5 months ago in reply to ZC

Prodigy 10 points

I look forward to hearing what you find!

+1 TheGhostOf 5 months ago in reply to Austin Guevara

Mastermind 6470 points

I would set the IOs to something else than high z to avoid this issue. That will save you for an extra external pull-up.

0 Austin Guevara 5 months ago in reply to ZC

Prodigy 10 points

Any updates?

0 ZC 5 months ago in reply to Austin Guevara

TI__Genius 17955 points

Hi,

Please follow TheGhostOf's advice here (and I have marked his reply as the answer).

If you do find time to post your results to this thread, this would help other users with a similar question.

Regards,

Zack

0 Austin Guevara 4 months ago in reply to TheGhostOf

Prodigy 10 points

In our testing this is probably the best solution to the problem. Since our design only has this radio module on our SPI lines the best solution was to set GDO1 to 0x2F which forces it to be either Low (default) or high when CS is high, SPI is inactive. Alternatively, if SPI is shared between multiple devices the best bet would be to put a PULL-UP on the MISO line.

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CC115L: Best practices For MISO/SO (GDO1) pin behavior