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BQ25713B: Can I use the BQ25713B with the BQ25970 or do I need to use the BQ2589x?

Ben Rosenberg
Prodigy 40 points
Part Number: BQ25713B
Other Parts Discussed in Thread: BQ25970, , BQ25890, BQ25713

Hello, I am designing a portable 100W USB-C power bank with the BQ25970 switched cap fast charger. I was wondering if the BQ25713B would be suitable as the charge controller for the BQ25970 or if I must use the BQ25890. I plan on using 2 bidirectional buck-boost converters for the 2 usb c ports so that either can charge the battery or discharge up to 100W OTG. This would make the additional buck and boost converters on the BQ25890 unnecessary. The BQ25713B seems to be more useful for my application because of its power path management (PTM), bidirectional buck-boost, and system power monitor so I would prefer to use this IC instead of the BQ25890.

Can you confirm that the BQ25713/B works as the charge controller for the the BQ25970 so that I can buy the evaluation kit and begin development or start looking at other options?

My second question for you is, What would be the best way to implement the bidirectional buck-boost battery charger so that both USB-C ports can charge the battery or discharge to the load? Should I use 2 BQ25713B's (1 for each port)? Or would I be better off with only 1 BQ25713B to act as the system power monitor/battery charger and use a separate buck-boost converter for the load on the other USB-C port? Because there is only 1 battery I only really need 1 bidirectional buck-boost as long as either USB-C port has access to it. 

Best,

Ben

  • 0
    TI__Mastermind 25800 points

    Hey Ben,

    To your first question, the BQ25713 should be able to take the place of the BQ25890. The reason the BQ25890 is because it is an integrated NVDC-type charger. The BQ25713 is a non-integrated NVDC-type charge controller. Because the BQ25970 relies on the input voltage source being managed (in a PPS sense), it cannot regulate a separate system voltage. So the BQ25713 is a good candidate to regulate the system rail while also charging at high currents.

    To your second question, can you draw a block diagram of what you are looking for? You want dual-input, dual buck-boost charging? Is this to double the power/charging current? The main issue with two charging providing charging current is the voltage regulation. It can cause fighting between loops whenever one charger enters the CV loop and the other has not. 

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 40 points

    Hello Joel,

    Attached below is a simplified block diagram of the power bank. I want to use the power bank's two USB-C ports with the PPS spec to control the temperature of two heating elements from both USB-C ports (1 at 100W or both at 70W). I also want to have the capability of charging the battery from either USB-C port and have pass through charging with PTM of the BQ25713B. Only 1 port will Source power from an AC/DC adapter to charge the battery at any time so as long as there is a MUX that selects the channels I think it should be fine. The point of the second buck-boost converter is to have the ability to sink power over both USB-C ports simultaneously. This way I can power two heating elements at 70W each from both ports simultaneously, 2 phones/laptops, or any combination simultaneously. Since both buck-boost converters are managing the two USB-C ports I will likely use an LDO from the MCU or a separate buck-boost to provide system power.

    One thing I did not put in the block diagram was the MCU/AP because I could not overlay the lines with my current software without it looking messy and convoluted. The MCU will communicate with the fuel gauge, buck-boost controllers, and TCPC with I2C, and I believe it will use GPIO to communicate with the mux. In this diagram I included the ACT2861 from Qorvo as a standalone buck-boost converter that complies with USB 3.0 PPS. This way I can use the PPS specification to control the temperature of the heating element(s) with VDM's to limit the current and voltage. If I program the TCPC to give the unidirectional buck-boost priority when a sink is attached to either port then that would always leave the bidirectional buck-boost available for battery charging when a source is attached.

    Another question i have for you is do I need a second charge controller to implement two PPS outputs simultaneously, and would I need to put some sort of load power compensation IC to ensure that either the two ports or the battery are outputting the right power as specified and accounting for derating of the whole system?

    Best,

    Ben

  • 0 in reply to Ben Rosenberg
    TI__Mastermind 25800 points

    Hey Ben,

    I think I'm still a little confused about your block diagram. You are showing a unidirectional buck-boost coming from the battery, but the output shows it bidirectional going into and out of the mux. And are your 70W loads on the Type-C ports or somewhere else in the system not shown?

    I also want to clarify that you cannot charge with PTM mode on the BQ25713. In that scenario, you will need to use the BQ25970 instead. In reality, you would likely have the BQ25713 providing both the system rail regulation and the end of charge control, while the BQ25970 would be largely only operating in the CC region with your PPS Type-C inputs. 

    And if you want to have two PPS outputs, I would suggest 2x BQ25713 that both operate in reverse OTG mode, meaning your battery will supply both PPS rails, but you can rely solely on one charge controller + BQ25970 for charging. 

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 40 points

    Hello Joel,

    Below I attached an updated block diagram. The two USB-C ports will be be bidirectional and have the ability to output 100W on a single port or 70W each on both. One of the BQ25713's will provide system voltage and the BQ25970 will handle the battery charging. I am trying to implement pass through charging with a system that outputs 100W for the load and inputs 45W to the battery. I'm wondering what you think would be the best way to do that.

    I was thinking that either I could either input 45W to the battery with a 45W USB-C charger and boost the power to 100W to the load, or I could use a 100W USB-C charger and buck the power to the battery. I think that using a 100W charger for pass through charging seems more feasible but it is also more costly and requires that only 5A cables be used. I'm not sure how to provide the 100W (20V 5A) to the attached sink when the 45W (3.3-9V 3A) input is only 3A. I believe that the buck-boost controller only boosts the voltage and not the current so I'm not sure if it will be able to boost the 45W to 100W in my application. Can you provide some insight on how I could implement pass through charging and whether or not there is a way to do so using a 45W USB-C PD PPS charger?

    For the power path management, will a mux and the MCU as the host work or is there another part that would simplify this design? Also, is the BQ25890 a suitable charge controller for the BQ25970 or does it limit the current to 5A?

    I appreciate your help!

    Best,

    Ben

  • 0 in reply to Ben Rosenberg
    TI__Mastermind 25800 points

    Hey Ben, 

    Thanks for your patience:

    I think where I am getting confused is that you want to output 100W on one of the input ports to the right, or 70W to both ports on the right. This would be sourced from the battery, through the charger, to one (100W) or both (70W) of those ports, correct? 

    However, you then mention the following:

    Ben Rosenberg said:
    I am trying to implement pass through charging with a system that outputs 100W for the load and inputs 45W to the battery.

    So you want to be able to provide 100W to one of the outputs, and also provide 45W to charge the battery; am I correct in saying this? 

    If so, the implementation you have now in your block diagram would be correct, but if I may, I will outline the flow of current: 

    The blue trace would indicate charging (both through the BQ25713 and the BQ25970 flash charger, which would be from your 45W source, and the red trace would be in OTG mode providing your 100W output. It is important to note two things about this configuration: 1) It is likely that all of your charging current will actually come back and flow through the second BQ25713 and provide that current through the red trace and 2) you can have 2x 70W ports because one port is consumed in charging.

    One other thing to note is that you will need a PPS as your 45W power supply (which sources the blue trace) in order to use it with the BQ25970. The buck-boost charger cannot regulate an input voltage for the BQ25970 Flash Charger while also charging, so that will need to come from the USB Type-C adapter from the blue trace.

    Obviously, if there is no blue trace, you can have 2x70W outputs by driving both BQ25713's in OTG mode.

    Regards,

    Joel H