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BQ32000: BQ32000 Trickle charge issue

William Wu
Prodigy 70 points
Part Number: BQ32000

Tool/software:

Hi

Our product uses this RTC IC, and it has already been implemented in a large volume of mass-produced products.

Currently, we are encountering an issue with a new model, but the RTC circuitry, layout routing, test flow, and firmware have not been changed.

However, during testing, it seems that the charging behavior does not achieve the trickle charge function. we would like to know,

1. Is the default setting of this IC configured to follow the path mentioned below when it leaves the factory?

 2. When we read the registers through I2C, the values are as follows:

0x08 value: 0x20

0x09 value: 0x05

These values appear to be the default values set in our firmware, but they don't seem to be functioning as expected.

it seems that we need to reset them in order to enable the trickle charge, 

3. When we write the actual time, what voltage is required to retain this time after a system reset?

currently, we are encountering a situation where the time is lost after a reset when the voltage is above 1.4V.

It seems that a voltage of around 1.6V or higher is needed to retain the actual time.

but the SPEC mentioned the Vback operating range is between 1.4V to 2.0V, is it reasonable?

as the above questions, we would like to know is there any possible to caused this phenomenon even we didn't modify any part, 

  • 0
    TI__Guru* 89200 points

    Hi William,

    Status of charger settings:

    Switching over from backup to Vcc operation will reset these values back to their initial values. 

    At initial state, TCH2=0, so there is no charging.

    The min. Vback supply voltage is 1.4V. When the device is operated using the Vback supply, there is limitation to I2C access.

    The device uses 2.8V as the internal reference voltage (Vref).

    If Vback is less than Vref, the switchover will happen when Vcc is below or above Vback.

    For example, if Vback = 1.4V and Vcc < 1.4V, the device will operate using Vback supply. I2C access is limited.

    When Vcc is > 1.4V, switchover happen, the device will now use Vcc as the power supply. There is no restriction to I2C access.

  • 0 in reply to Noel Fung
    Prodigy 70 points

    Hi Noel,

    Thank you for your prompt reply.

    Is it possible that when the system is reset just as the supercap is charged to 1.4V, the voltage drops below 1.4V after the reset, causing the time data to revert to the default value?

  • 0 in reply to William Wu
    TI__Guru* 89200 points

    Hi William,

    To debug, I suggest monitor the signal at Vcc and Vback pin when the issue happen, this should give us some cue what may be the reason of failure.

  • 0 in reply to Noel Fung
    Prodigy 70 points

    Hi Noel,

    Just a brief description of the operating status of the BQ32000 on our product as shown in the table below.

    You can see that in our revised model, we've added an SPDT switch to the 3V_AUX line to prevent leakage (3V_AUX_RTC). In the original model, 3V_AUX was directly supplied as VCC, 

    We would like to confirm that during the power interruption period, 3V_AUX was pulled low several times. However, the original model did not seem to be affected by this pull low, and the date did not revert to the default value. In contrast, the revised model did revert to the default date. Is this behavior expected?

    Original Version (After the whole test flow, the date can be set correctly)

    Modified Version (After the whole test flow, the date will go back to default)

  • 0 in reply to William Wu
    TI__Guru* 89200 points

    Hi William,

    Do you have the schematic? Who is controlling the SPDT switch?

  • 0 in reply to Noel Fung
    Prodigy 70 points

    Hi Noel, 

    Below is the SPDT circuit, it is controlled by the SoC and uC (and gate),

    for the previous version, we don't have these two parts, the vin just supplied by 3V_AUX

  • 0 in reply to William Wu
    Prodigy 70 points

    one more addition,

    when the supercap voltage is above 0.3V, we'll pass all the processes, 

    this is exactly what I am currently trying to verify—what factors are causing the RTC time to revert to its default state after being written