[TPS65920] Backup mode current consumption @ BKBAT

Hi Antony,

Although it doesn't help much I can confirm to have seen similar results while doing a 99% similar test. One idea which might bring down the power consumption (which I unfortunately first realized later than at the time of doing my test) is to set the CK32K_LOWPWR_EN-bit in TPS65950 in order to let the 32kHz clock run in low power mode when VBAT is low.

I however haven't tested the effect of this yet. In case you do this, could you please update this thread to let me know if this is the magic trick of bringing down the BKBAT draw from the measured 7.56uA to the specified 2.25uA?

Best regards and thanks
  Søren

Hi Søren,

It drops 1.7xuA with  CK32K_LOWPWR_EN=1.  Do you think there's any side effect with this setting?

Antony

Thanks Soren.

Antony,

In backup there is no need for excess consumption. So, this setting is ok.

Regards,

Gandhar.

Hi Gandhar,

You are welcome, but apparently setting this bit doesn't solve the whole topic? As I understand the reply it saves ~1.7uA out of ~7.5uA, which still leaves the total consumption at ~5.8uA, which is around 2.5 times what to expect from the datasheet (2.25uA)? Any ideas about how to get the last step down to 2.25uA?

Best regards and Thanks
  Søren

Hi Søren,

I'm sorry that I made some misunderstanding. 

After applying the setting, the backup mode current is around 1.7uA now. 

Antony

Hi Antony,

No worries. I'm just glad that this did the magic trick :-) And that it did it that much that I believed that you "x" meant times and not just a "random" number following the 7 :-) Actually what you now measure it 0.5uA (~20%) less that typical consumption according according to datasheet, which was so great that I couldn't believe it :-)

Thanks for updating me on this - Enjoy your weekend
  Søren

Hi Gandhar,

After enable the CK32K_LOWPWR_EN bit to '1', they found the RTC drift increase from 1sec/Day to 4~5sec/Day.  (VBAT is not avaiable)

- Do you think this is reasonable?

- The above drift is measured with compensation enabled, do you think compensation is nnot working when CK32K_LOWPWR_EN=1?

- Is it normal there's no clock from CLK32kout when CK32K_LOWPWR_EN=1?

- Regarding the backup mdoe current specified in DM (2.25uA), is it done with CK32K_LOWPWR_EN=1 or 0?

Thanks,

Antony

Hi Antony,

Setting 32K to low power is correct and needed for the correct estimation of consumption, data sheet has this setting. Clock will be active in this setting.

I dont have data for drift, I will find out and let you know.

Regards,

Gandhar.

Hi Gandhar,

Are you sure CLK32kout is expected to be on when CK32K_LOWPWR_EN=1?

AFAIR it's expected to be switched off (as found by the questioner) in order to save power, but I might remember wrong?

Thanks for clarifying and double checking
  Søren

Hi Antony,

Your reading are all correct.

In low power mode the clock drift is normal. The 32K clk is active in this mode. When the setting is in normal mode then you will see an approximate increase of 4uA. This is what you are seeing.

Unfortunately your customer will have to pick one of two options - power vs. accuracy..

Regards,

Gandhar.

Hi Gandhar,

Sorry for being a bit slow on this tonight (EU time), but just to be 100% sure. Are you saying, that the CLK32kout-pin is expected to be on/driven even when CK32K_LOWPWR_EN=1? In this case there might be something "wrong" with Antony Lins setup since he is reporting that it's off (please see his last post on this thread) when setting the bit.

Best regards and thanks for the continued support
  Søren

Hi Gandhar,

When you said "Unfortunately your customer will have to pick one of two options - power vs. accuracy", do you mean the higher RTC drift is expected?

Antony

Hi Antony,

Yes, you are correct.

Regards,

Gandhar.