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BQ25629: About temp range in discharge (battery-only) state

Luke Sakamoto
Intellectual 2125 points
Part Number: BQ25629
Other Parts Discussed in Thread: BQ25628

Tool/software:

Hi team,

Looking at the datasheet, it says the BQ25629's thermister pull-up voltage (REGN) is only held when the VBUS is present. (or below 1 to 4 must be true, to be precise.)

What method do you suggest if they want to read the temp during the discharge?

Initially, they wanted to read from MCU via register, however, the REGN wont be available in dischage it seems.

In other posts there suggestion to enable ADC_EN from 0x26 but i do not believe this will enable the REGN?

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1421361/bq25628-ts-voltage-measurement-signal-is-not-a-dc-signal-it-is-a-pulse-train?tisearch=e2e-sitesearch&keymatch=BQ25628%2520REGN# 

This post suggests to use "8.3.10.5.3 Thermal Protection in Battery-Only Mode" but I believe this is only available in BQ25628.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1381128/bq25628-change-the-charging-and-discharing-temp-range/5330044?tisearch=e2e-sitesearch&keymatch=BQ25628%252520REGN#5330044

Any ideas to read temp in battery-only mode?

Thanks,

Luke

  • 0
    TI__Genius 17725 points

    Hi Luke,

    Enabling ADC and enabling the TS channel will enable the REGN rail for the duration of the ADC read. This should allow you to calculate battery temperature while in battery-only mode. This is a slight impact to quiescent current consumption as required to bias the REGN rail.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    TI__Intellectual 2125 points

    Hi Juan,

    Thanks for the quick reply. This is good news.

    I want to understand a bit more about the internal power path for future reference.

    Does this mean that the ADC power supply comes from REGN?

    Thanks,

    Luke

  • 0 in reply to Luke Sakamoto
    TI__Genius 17725 points

    Hi Luke,

    No the ADCs power supply is internal. REGN is just enabled to power TS. If the TS channel is not enabled but other channels are then the REGN rail wont be enabled.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    TI__Intellectual 2125 points

    Hi Juan,

    Juan Ospina said:
    No the ADCs power supply is internal. REGN is just enabled to power TS.

    Understood.

    Can you review if the below sequence makes sense to you? 

    /////////////////////////////////

    [temp and battery check during battery dischage with intervals]

    1. REGN enable

    2. ADC enable

    3. check temp & battery voltage

    4. ADC disable

    5. REGN disable

    /////////////////////////////////

    Also, it seems like the REGN voltage fluctuate. It looks like the targeted Vout for REGN is 5V, but it will still operate under when the source is 5V with LDO Vdrop.

    When Thermistor is connected as below, shouldn't you also be considering the REGN voltage to accurately monitor the voltage? Is there a relationship beween voltage source (USB VBUS or 1S VBAT) vs REGN?

    The above question is important as the usecase here is targeted under 5V, the USB VBUS is non-PD and the 1S is around 3.3~4.2V.

    Thanks,

    Luke

  • 0 in reply to Luke Sakamoto
    TI__Genius 17725 points

    Hi Luke,

    Luke Sakamoto said:

    Can you review if the below sequence makes sense to you? 

    /////////////////////////////////

    [temp and battery check during battery dischage with intervals]

    1. REGN enable

    2. ADC enable

    3. check temp & battery voltage

    4. ADC disable

    5. REGN disable

    /////////////////////////////////

    To clarify the REGN is automatically enabled and disabled by the device once the ADC is enabled and the TS ADC Channel is enabled. In that situation the sequence would be like so:

    1. ADC Enabled with TS_ADC and TS_BAT enabled.

    2. REGN Enabled by IC

    3. TS Sampled by ADC

    4. REGN Disabled by IC

    5. VBAT Sampled by ADC

    6. ADC Disabled (this depends on if 1-shot mode or continuous, if in continuous it will return to step 2).

    Your firmware will only need to enable the ADC and the ADC Channels and the device automates the rest.

    Luke Sakamoto said:
    When Thermistor is connected as below, shouldn't you also be considering the REGN voltage to accurately monitor the voltage? Is there a relationship beween voltage source (USB VBUS or 1S VBAT) vs REGN?

    To clarify, TS_BIAS has an internal connection to REGN so they will be the same voltage. Since the voltage thresholds are expressed relative to REGN (or TS_BIAS), there should be no impact on behavior due to the voltage source or the voltage on REGN.

    The voltage thresholds are relative to REGN, they are based expected resistance ratios at different temperatures. So even though REGN may be higher when VBUS is present and lower when only a 1S VBAT is present, the device should be able to identify the correct temperature.

    Best Regards,

    Juan Ospina