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BQ25895M: Question about boost output mode

Chase Jeong
Genius 5380 points
Part Number: BQ25895M
Other Parts Discussed in Thread: BQ25629

Tool/software:

Dear TI experts,

My customer considers BQ25895M for their new project.

The application is like external battery pack. They want to make 5V output with Li-ion battery pack.

And here are the questions.

1. I saw about Current Monitoring in Boost Mode. (Section 8.2.14.2), it just described that the device closely monitors LSFET current to ensure safe boost mode operation.

Can I check specific current value through boost mode output via I2C or something else?

My purpose is, if boost output current falls below the threshold I determine, Then I can assert MCU to sleep mode.

2. On the other hand, Can BQ25895M know the status and the specific value of current consumption? for exampe, If the load exceeds the threshold, I can wake up whole device including MCU.

3. What is idle(sleep current) of BQ25895M?

4. Do you have any reference schematic of BQ25895M which is applicable for external battery pack?

Best regards,

Chase

  • 0
    TI__Mastermind 24555 points

    Hi Chase, 

    Please see my comments below. 

    1)The maximum allowable boost mode current is mentioned in section 8.2.5. With default I2C configuration 3.1A is maximum allowable output current at PMID pin. If customer wishes to allow boost mode operation with a lower minimum battery voltage then the maximum allowable output current is 2.4A. 

    Unfortunately, there is not a way to monitor real time boost mode current via I2C or some other method. Additional components would be required. Although, allow me to point out our newer part, the BQ25629, has the ability to report battery discharge current during boost mode via I2C. 

    2)The BQ25895M can output the battery charge current via I2C, but does not have the ability to report the SYS or PMID pin current draw. For the purpose of your question the BQ25895M cannot wake up your whole system based on an increase in load current. 

    3) Quiescent current in different operation modes is listed in the electrical characteristics table on page 7. I do not know exactly what is meant by idle mode in the question. In this state will only battery connected? Is boost converter off? The minimum possible current draw from BQ25895M is typical 12 uA when in ship mode. To be in ship mode Vbus input must be removed and BATFET from battery to SYS and boost output is turned off. 

    4)The BQ25895MEVM User's Guide (linked below) provides the schematic of the EVM board which can be used as reference. Additionally, TI has a power bank (i.e. external battery pack) block diagram on TI.com (also linked below). 

    https://www.ti.com/lit/pdf/sluuba2 

    https://www.ti.com/solution/power-bank 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Genius 5380 points

    Dear Garrett,

    Thank you for your support.

    1. Idle means battery connected and boost converter off.

    You said about ship mode. Can I use ship mode again for minimum current consumption if the battery does not use boost output?

    2. What register address Can I refer for report battery discharge current during boost mode of BQ25629? REG0x28? or REG0x2A?

    3. What is maximum discharging current during boost mode of BQ25629? It seems that 2A is maximum current, regarding page 17.

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Mastermind 24555 points

    Hi Chase, 

    Please see my comments below on your follow-up questions. 

    1)With the device in idle state (i.e. only battery connected and converter off) current draw by BQ25895M is typical 32uA (max 60 uA). If the customer wishes to further reduce current draw they can enter ship mode by setting BATFET_DIS = 1 (REG09 bit 5). Please be aware in ship mode battery power is cutoff from SYS. One of the methods listed in datasheet section 8.2.10.2 must be used to exit ship mode. 

    2)Register address REG0x2A will report battery discharge current during boost mode on the BQ25629. 

    3)The BQ25629 does not have a fixed maximum output current in boost mode because it will vary depending on the boost voltage setting. For 5V boost output the maximum output current is approx. 2.4A. 

    Best Regards,

    Garrett