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BQ25895: Bq25895 Overkill for my simple battery charge and DPPM requirement?

kowshik Gudimetla
Prodigy 40 points
Part Number: BQ25895
Other Parts Discussed in Thread: BQ25606

Tool/software:

Hi TI,

I am having below requirements for my portable wifi extender project. 

1. The system is powered by a 3.7V Lipo 1800mAh battery, that should be chargeable using a USB input.

2. The voltage of battery and USB should be cut down to 3.3V and should be given to my system (it doesn't draw more than 700mA)

3.I don't want to use I2C to control the BQ25895. I simply want to configure it to charge my battery by default and seamlessly switch the output from battery to USB using the power path feature. Can the IC be configured to do that without any software configuration I want a plug and play solution?

4. Would you recommend configuring the IC to generate 3.3V when both USB and battery are present to power my entire load? Or should I boost the 3.7V from the battery to 5V and use an external LDO to further reduce this boosted 5V to 3.3V? I want to know if your IC can directly regulate the USB/3.7V battery voltage (even when the battery voltage drops to around 3.4V).

5. I want to know if my load should be connected to the PMID pin? or SYS pin, i believe it's PMID but want to still cross-check

6. If software configuration is mandatory for my IC, then can you recommend me some other part number that is more of a plug and play solution?

  • 0
    TI__Genius 9405 points

    Hello Kowshik,

    Thanks for reaching out.

    For your application, a standalone (resistor-configurable) charger with power path is the simplest solution. The BQ25606 is essentially the standalone version of the BQ25895, so it may be a good fit.

    I'd recommend using an external DC/DC to regulate your downstream components to 3.3V. When an input source is connected, the BQ25895 regulates SYS based on whether VBAT is above or below VSYS(MIN). More details are available in section 8.2.6.1 of the datasheet, and the relevant table from section 7.5 is included below.

    System loads typically connect to SYS, but the BQ25895 can also boost from the battery to PMID, which is often used for charging portable devices.

    Let me know if you have any questions. I'd be happy to help.

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Prodigy 40 points

    Hi Alec,

    Thanks alot for the reply and also suggesting the other part number. So a couple of questions

    1. In BQ25606, should I be connecting my load to SYS pin? If yes, what will the voltage be at SYS pin when USB is not present? is it directly the voltage of BAT?

    2. In BQ25895, how to configure the voltage that we get at PMID pin? What if I want PMID pin to output constant 5V irrespective of the power source? Should it be configured using I2C?

  • 0 in reply to kowshik Gudimetla
    TI__Genius 9405 points

    Hello Kowshik,

    1. Yes, your load should be connected to the SYS pin. When no USB input is present, SYS will be connected to BAT through the BATFET (Q4) with the voltage difference between SYS and BAT being the VDS of the BATFET.

    2. Yes, the PMID voltage in boost mode is configurable via I2C. By default, the OTG_CONFIG bit = 1 (OTG enabled), and the BOOSTV bits are set to 1001 (PMID = 5.126V). Boost mode is enabled if the OTG pin is HIGH, OTG_CONFIG bit = 1, and no input source is detected at VBUS. More details are available in section 8.2.5 of the BQ25895 datasheet. Therefore, it's possible to boost 5V to PMID from the battery without writing to the device registers via I2C.

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Prodigy 40 points

    Thanks alec,

    one last question, do we have boost option in the BQ25606? i believe it isn't there right? Do you have any parts with standalone battery charger with DPPM, boost converter and no need of HOST interface? If there are no options I'll try to go with BQ25895.

    Also, can you point me to some resource where I can learn what's the use of OTG functionality? How is it related to boost converter functionality? isn't OTG simply a way to interface external USB devices? 

    Thanks

  • 0 in reply to kowshik Gudimetla
    TI__Genius 9405 points

    Hello Kowshik,

    The BQ25606 can boost from BAT to VBUS. It has DPM and is standalone, meaning it is not controlled by a host.

    In OTG mode, the charger boosts the battery voltage to a regulated 5V. This is the voltage typically required to power USB peripherals when the charger side acts as a host.

    TI has several resources on USB OTG. Here are just a few:

    https://www.ti.com/lit/ml/sprp605/sprp605.pdf

    https://www.ti.com/lit/wp/sszy001/sszy001.pdf

    https://www.ti.com/video/6090438391001

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Prodigy 40 points
    Alec Lehman said:
    The BQ25606 can boost from BAT to VBUS. It has DPM and is standalone, meaning it is not controlled by a host.

    I have found the below part in the datasheet it says the output is provided back on the USB port. But that's not my requirement, the output should be provided to load that is connected to SYS pin. Can BQ25606 do that? sorry if I'm understanding it incorrectly.

  • 0 in reply to kowshik Gudimetla
    TI__Genius 9405 points

    Hello Kowshik,

    When an input source is present, the BQ25606 operates in buck mode from VBUS to VSYS. If configured for OTG mode and no input source is present, the converter can boost from BAT to VBUS.

    kowshik Gudimetla said:
    But that's not my requirement, the output should be provided to load that is connected to SYS pin. Can BQ25606 do that?

    It sounds like OTG mode isn't what you need. The BQ25606 cannot boost from BAT to SYS, so I'd recommend using an external boost or buck-boost converter.

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Prodigy 40 points
    Alec Lehman said:
    The BQ25606 cannot boost from BAT to SYS

    Oh that's a news to me, does TI don't have any other product in it's portfolio that can do this boosting of VBAT in the absence of VBUS and give it to load? Basically I want some product that can do this, hope this makes sense.

  • 0 in reply to kowshik Gudimetla
    TI__Genius 9405 points

    Hello Kowshik,

    Unfortunately, we don't have a charger that can boost from BAT to SYS. The closest feature we offer is OTG boost mode on devices like the BQ25606.

    One option is to place your system components on PMID and configure the charger to default to boost mode when no input source is connected. When an input source is connected, PMID will be powered directly by VBUS. However, the tradeoff with this approach is that there is a time delay before the charger enables boost mode when transitioning from input source power to battery power (i.e., unplugging the input source). 

    If this tradeoff is acceptable for your application, then this could be a good solution.

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Prodigy 40 points

    Hi Alex,

    Thanks for the suggestion. Two questions here

    1. When you meant PMID option are you talking about BQ25895?

    2. What is the transition time that you mentioned? 

    3. When you said configure PMID, can it be done through some external resistors or should it be done through a host protocol? If it's a software solution then I'm afraid I can't move ahead with this product.

    Thanks

  • +1 in reply to kowshik Gudimetla
    TI__Genius 9405 points

    Hello Kowshik,

    1. The BQ25895 provides boost output on PMID, whereas the BQ25606 provides boost output on VBUS. However, you can still place your system components on PMID with the BQ25606 because VBUS and PMID share the same node, separated only by the internal input FET. This FET is on during boost operation for the BQ25606, meaning there is no isolation between VBUS and PMID.

    This presents a key tradeoff when using the BQ25606: if an external device or input source is connected to VBUS, there is no separation between your system components on PMID and VBUS. In contrast, the BQ25895 keeps its input FET off, ensuring PMID remains separated from VBUS during boost operation. If you opt for the BQ25606, you may need to add external components to isolate the input source from VBUS while in boost mode.

    2. According to section 9.3.3 of the BQ25606 datasheet, there is a minimum 30ms delay after the adapter is removed.

    3. On the BQ25606, the OTG pin must be pulled high to enable boost mode. On the BQ25895, the OTG pin must also be pulled high, and the OTG_CONFIG bit must be set to 1 (already 1 by default). This configuration does not require a host MCU.

    Each device has tradeoffs: The BQ25606 offers more configurability without a host MCU but leaves PMID exposed to VBUS in boost mode. The BQ25895 ensures PMID is disconnected from VBUS but limits configurability without I2C.

    Best regards,

    Alec