BQ32000: how to understand "OF"?

Hi Lane,

Thank you so much for your reply. And I still have a few doubts.

1. According to the DATASHEET and your reply, The statement that "originally the OF flag bit was 1, but when switching from VCC to backup power supply, the OF will reset to 1" is confirmed. However, in our test, we manually sets OF to 1, and after the following 2 ways that lead to backup switchover, OF could not reset from 1 to 0:

A. Disconnect the VCC directly, so that the IC will be forced to switch to the backup power supply (we uses 3V battery as the backup power supply);

B. Manually reduce VCC from 3.3V to 2.3V gradually(2.3V is lower than backup power VBACK 3V and internal reference voltage VREF 2.8V);

Therefore, we wanna know further whether the backup switchover mentioned in DATASHEET includes the above two scenarios. If so, why the result differs from the DATASHEET, if not, what is the meaning of the backup switchover actually;

2. "the crystal oscillator did not produce at least four consecutive periods of the 32KHz clock"  What is the criteria to regard one pulse as a qualified pulse, when the pulse width is larger than a certain value, or judged by the rising/falling time or some other indicator;

3.DATASHEET only mentions the action of OF when the main power supply switches to the backup power supply. What happens if the backup power supply switches to the main power supply.

4. Except for the backup switchover and the detection of four consecutive dropped pulses, are there any other scenario that may leads to change of OF? If there is, what scenario and how OF changes?

Best regards,

Jerry

Hi Jerry,

A1. Yes, the datasheet statement on supply switchover would include these two scenarios. Based on the wording in the datasheet, I would expect that OF = 0 after the supply switchover.

Occasionally there is inaccurate data in the datasheet that must be updated. We would need more information for confirmation: 

• Is the XTAL meeting datasheet requirements?:

Does the oscillator drop any pulses when switching from VCC -> Vback -> VCC? If no>

• when OF = 1 before VCC -> Vback -> VCC, what is OF after switchover?
• when OF = 0 before VCC -> Vback -> VCC, what is OF after switchover?

A2. For a typical XO, the XO output is sinusoidal. For a typical RTC, there is an internal counter to count each oscillator period. The qualifying criteria would be related to the amplitude of the pulse and correct oscillation frequency.

A3. I assumed that the datasheet only specified for switchover from VCC to Vback because the registers cannot be accessed by I2C when the device is powered from the backup supply.

A4. These would be the only scenarios resulting in OF bit change

Kind regards,
Lane

Hi Lane

Thanks for your reply, following is our information for your questions, and the bottom is my confusion.

A1.The XTAL we used is 9H03200031 from TXC Corporation. The nominal frequency of this XTAL is 32.768kHz, the load capacitance is 12.5pF, and ESR is 70KΩ at maximum, which all meet the requirement of BQ32000 datasheet. 

A2.The oscillator does not drop any pulses when switching from VCC -> Vback -> VCC. 

No matter OF = 1 or 0 before VCC -> Vback -> VCC, OF keeps the original value after switchover.

Q.Based on your reply, the qualifying criteria relates to the amplitude of the pulse, what is the exact upper and lower threshold which is regarded as a failure.

We found that the pulse of the XTAL output is a sinusoidal (same as the input) combined with a tiny swinging bias at approximately 10mV.

Kind Regards,

Jerry

Hi Jerry,

Thanks for the information. Based on your findings, it seems the datasheet has a typo and OF is unchanged on supply switchover.

I will submit the request to confirm this behavior and update the datasheet.

I do not have the answer to your question. Due to the age of this device, design support is limited.

Kind regards,
Lane

Hi Lane,

What is the conclusion after confirming about the behavior of OF. If that was turn out to be a typo and needs to update the datasheet, when shall we get the latest datasheet.

Kind regards,

Jerry

Hi Jerry,

bq32000 doesn't have an EVM, and we don't have any designs with bq32000 readily available. Additionally, the California COVID lockdowns and the holidays have impacted our available resources. I don't think we will be able to provide an answer until January. We'll provide a status on the datasheet update if we determine it is necessary.

Regards,