• State TI Thinks Resolved
  • Locked Locked
  • Replies 9 replies
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 2365 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ24650: solar charge controller application

maruthirao hamsa
Prodigy 60 points
Part Number: BQ24650
Other Parts Discussed in Thread: TPS61041, PMP, BQ25505, BQ25570

Hello, 

 This query is regarding BQ24650, where this is used as a solar charge controller for Battery : Li-On 3.7 volts, 4400mAH.    (This is for ultrasonic flow water meter application.)

Primary charging source is through Solar panel : 3.5-9 volts

Min VCC of the BQ24560 is 5 volts and the battery voltage is 3.7 volts since TPS61041 is used in Boost topology. Attached is the schematic 

Please help to clarify on below queries:-

1.) Can we interface TPS61041 in boost topology to get required 5 volts from the battery which is only 3.7 volts and 4400 mAH, without hindering or disturbing the main features of the BQ24650 charge        controller. i.e battery detection, wake up, current sensing, and other important features of the controller?

2.) what is the optimal MPPSET value normally. As per the BQ24XX series battery charger calculation tool , it says 1.2volts optimal fixed , Please clarify

3.) Maximum currents during charging of the battery from the solar panel for the attached circuit will draw current continuous or intermittent ?

4.)Current drawn during the sleep, wakeup and reconnect. Can we still control all these features in the attached schematic?

5.)Please suggest optimization points for the schematics which would support 3.7 volts, 4400 mAH Li Ion battery(3.7 volts 2200mAh 2cells in parallel ), which has built-in all the safety features like overcharge protection, deep discharge protections,  etc. Or can we use a simple battery without these inbuilt safety features?

6.)Can we control the TERM_EN using external microcontroller to shut down or control the controller as per our need or can we control it optimally in any other way?

7.)optimization of R9-R10, R3-R4, R1-R2 for the above battery specification and best suitable solar panel ? What does solar cell, HALF PANEL mean?

8.)  Thermistor pack is optional or mandatory ? which could optimize the entire schematic without compromising on the features ?

 

 

solar charge controller (002).pdf

  • 0
    TI__Intellectual 2320 points
    Hi,
    1. It is Ok for BQ24650.
    2. MPPSET regulation voltage is 1.2V. Normally VMPPT = 70~80% floating voltage. please check your solar panel' Spec.
    3.Continuous
    4.Yes, but you should disable the boost converter.
    5. What is the termination voltage of the battery? 4.2V? If yes please set FB resistor network to 4.2V.
    6. You can control the Q3 to shut down.
    7.R1-R2 What is the termination voltage of the battery? 4.2V? If yes please set FB resistor network to 4.2V. R3-R4 Please provide the VMPPT of the solar panel. R9-R10 is OK
    8.If you don't have thermal protection for battery it is mandatory, If yes it is optional.
    Alen
  • 0 in reply to Alen%2520Chen
    Intellectual 520 points
    Hi Alen,

    Thanks for your clarifications. We are pursuing BQ24650 because we could not get any other charge controller IC that can work with lower VCC (3V or so). We want to power the charge controller IC (BQ24650) through the Battery (and Boost regulator) rather than through Solar Panel. Solar panel cannot generate the required voltages and currents due to various environmental conditions. Also the panel that we are considering is of very low wattage (Pmp<1W approx; Vmp=4.8V, Imp=200mA) and hence it will generate very low currents under normal lighting conditions. In low light conditions, the panel will generate much lower currents (less than 5mA). Hence we would like to power BQ24650 through the Battery and Boost regulator, that can supply voltage continuously for its working, and we will have better control as we need.

    We are designing the system (including charge controlling circuitry) for life time of at least 10years. Considering these product requirements, can you clarify our below doubts?

    1) Kindly let us know whether powering through Battery and Boost regulator must be avoided, and it should be powered through solar panel only.
    2) As you know, solar power will be zero during night times everyday. If BQ24650 is powered from the solar panel as shown in application diagram, then BQ24650 is powered-up every day in the morning. Also it may be powered-off whenever there is low light to the panel (during night/cloudy conditions, etc). Is my understanding correct? Is it fine to power-up BQ24650 everyday in the morning (at 6AM or so) and power-down in the evening (at 6PM or so)?
    3) As you know, we are using Li-Ion Battery with 3.7V, 4400mAh specs. It can charge up to 4.2V only. So, we cannot directly power BQ24650 from a 3.7V battery, and hence using a Boost regulator TPS61041. Kindly suggest whether this connection methodology is correct. Is there any better charge controller and Boost regulator that we can pursue?
    4) Can you suggest any other charge controller that can power itself from a 3V source? This way, we can avoid the boost regulator and hence increase overall power efficiency.
    5) As shown in application diagram of the datasheet, why a 10uF is needed between the SRN and GND?
    6) In the datasheet, why does it mention I(BAT) battery discharge currents? What are these currents exactly? As per the the application diagram, Battery is not powering BQ24650. So, why the battery has to provide these currents?
    7) In the datasheet, IAC=25mA. This is very high current consumption by the BQ24650 circuitry. What does Qg_total = 10nC [1] mean? We will not be able to provide 25mA continuous current from the battery throughout the day time everyday. Kindly suggest how to reduce this current.
    8) In our schematic, BQ24650 is taking power from the battery. How much currents (approx) does entire BQ24650 circuitry take during charging and sleep conditions?
    9) We are worried about the BQ24650 circuitry consuming higher power. Can you suggest how it can be lowered?
    10) Are the designed L0 (22uH) and C0 (10uF) values correct for charging currents of 0.5A?
    11) As I understand, VFB decides VREG (Regulation voltage). Also VRECH = 4.15V (~50mV less than VREG of 4.2V). If VFB > VRECH, then it means battery is already charged to maximum possible voltage. So, why does flowchart (Figure 14 in datasheet) indicates as FAULT when battery is not able to precharge? I could not understand FAULT condition. Section 8.3.4 indicates something different in comparison with this flowchart. Can you clarify this?
    12) Do we require 2.2uF and 2ohm parts at the input side for our application? We will be connecting solar panel at the input and BQ24650 is powered through the Battery and Boost regulator.

    Thanks & Regards,
    Vikas Chandra Rao.
  • 0 in reply to Vikas Thukuntla75
    TI__Intellectual 2320 points
    Hi Vikas,

    Good questions!
    Base on your description, I think our energy harvesting charger bq25570/bq25505 is better. Because in low light conditions, the power consumption of BQ24650 would be higher than charging. Battery energy would be decrease with charging. And you need an additional controller to disable boost converter during night.

    You can clamp Vin with a 5V enough capacity zener diode. Energy harvesting charger will bring low IQ, low start voltage and high efficiency in low light . You can see the datasheet on our official website.
    Can you provide the solar panel's technical document?

    Alen Chen
  • 0 in reply to Alen%2520Chen
    Intellectual 520 points
    Hi Alen,

    Thanks for your suggestion.

    It looks like BQ25505 needs two different batteries, and we think it will be an overkill for the product. Hence we checked BQ25570 only, and it looks like it Quiescent currents are less than 1uA which is good. We have few other below doubts about this IC. Kindly clarify the same.

    1) BQ25570 has input max voltage up to 5.1V. Whereas the panel can generate more voltage depending on Light conditions. As per your suggestion, we can have a Zener diode at input side. But we are concerned that the voltage is so close to the Panel's Vmp voltage of 4.8V. Due to tolerances (with temperature, etc), there can be some issues in the input side circuitry operation. Kindly suggest how to overcome these issues.
    2) I think BQ25570 needs VBAT_OV setting to be more than VIN_DC (as per section 6.3 note 2 of the datasheet). For our application, VBAT_OV = 4.2V whereas VIN_DC can go up to 4.8V. How can we set VBAT_OV in this IC?
    3) It looks like the max input power range is 510mW. However the solar panel can generate more than this power if it is exposed to good sunlight. I have attached datasheet of the solar panel that we are pursuing. Kindly suggest how we can use this solar panel with BQ25570.
    4) What is the max charging current that we can use with BQ25570, with Vmp=4.8V?

    Can you keep this discussion confidential (and not available to public), as we will be sharing more and more about our product/functionality further?

    Thanks & Regards,
    Vikas Chandra Rao T.
  • 0 in reply to Vikas Thukuntla75
    Intellectual 520 points

    Hi Alen,

    Attached are the specsheet and IV curves of the solar panel. We are pursuing using two such panels in parallel so as to get more power from the sunlight, and hence recharge our 3.7V, 4400mAh Li-Ion battery sufficiently.

    We need to have the charge controller that can work with this solar panel. We will be installing the product in the areas where there can be low sunlight (due to shady areas, cloudy regions, etc), or there can be high sunlight (in sunny regions, etc).

    Considering these, kindly clarify above doubts.

    Thanks & Regards,
    Vikas Chandra Rao.Specs_MPT4.8-150.pdfMPT4_56310B2DDA7C2.pdf

  • 0 in reply to Vikas Thukuntla75
    TI__Intellectual 2050 points

    Vikas Thukuntla75 said:

     
    1) BQ25570 has input max voltage up to 5.1V. Whereas the panel can generate more voltage depending on Light conditions. As per your suggestion, we can have a Zener diode at input side. But we are concerned that the voltage is so close to the Panel's Vmp voltage of 4.8V. Due to tolerances (with temperature, etc), there can be some issues in the input side circuitry operation. Kindly suggest how to overcome these issues.

    The device is capable of handling the 4.8V. My concern is on the Open-Circuit voltage spec of the Panel. 6.4V is outside the Absolute Max spec for this device. This is a concern for the internal MPPT function of the IC. The device will take an open-circuit sample of the input for a brief time.

    To avoid this, you could disable the internal MPPT to either deactivate it or externally control the MPPT. More information can be found in section 7.3.1 of the datasheet.

    Vikas Thukuntla75 said:


    2) I think BQ25570 needs VBAT_OV setting to be more than VIN_DC (as per section 6.3 note 2 of the datasheet). For our application, VBAT_OV = 4.2V whereas VIN_DC can go up to 4.8V. How can we set VBAT_OV in this IC?

    Yes, VBAT_OV must be more than VIN_DC since this IC is designed for a Boost topology.

    VBAT_OV sets your over voltage setting, also this sets your ouput voltage on VBAT. This can be set with two external resistors, ROV1 and ROV2. See section 7.3.3 on page 15 of the BQ25570 datasheet.

    On this same page, please pay attention to the "CAUTION" note that decribes the condition when VIN > VBAT/VSTOR.

    Vikas Thukuntla75 said:


    3) It looks like the max input power range is 510mW. However the solar panel can generate more than this power if it is exposed to good sunlight. I have attached datasheet of the solar panel that we are pursuing. Kindly suggest how we can use this solar panel with BQ25570.

    I do not suggest inputing more power than the Absolute Max spec for this device. Functionality can not be guaranteed above the Abs Max specs. Let me think about this one further. You may want to consider using two of the BQ25570.

    Vikas Thukuntla75 said:


    4) What is the max charging current that we can use with BQ25570, with Vmp=4.8V?

    The datasheet shows the max cycle-by-cycle current limit for the charger to be 285mA. This is for VIN ranging from 0.5 to 4V. Output set to 4.2V. I would use this spec.

    Vikas Thukuntla75 said:


     Can you keep this discussion confidential (and not available to public), as we will be sharing more and more about our product/functionality further?

    This is a public forum, so if you would like to keep this more confidential then we should take this to an email discussion.

    Best Regards,

    Joe

    If your questions were successfully answered, please hit the "Vrify Answer" button below.

  • 0 in reply to Joe Stephan
    Intellectual 520 points

    Dear Joe,

    Thanks for your clarifications.

    1. It is not clear how the open-circuit voltage 6.4V of the solar panel can be handled momentarily. Also the issue is not just about the open-circuit voltage. Whenever there is high sunlight, the panel can generate voltages more than 5.1V. And the input protection zener diode cannot exactly take care of the max input voltage of 5.1V, due to various tight tolerances that we will be operating with. So, low tolerances of operation can damage BQ25570 under various operating conditions.
    2. Whenever there is good sunlight, VIN_DC (>4.8V) is always more than VBAT_OV (4.2V). And this happens for most of the day time. As per the Caution notice in the datasheet (7.3.3), it looks like battery will never be charged. This way, we will never be able to charge the battery. This is an issue.
    3. Ours is a cost sensitive application. We will not be able to consider two pieces of BQ25570, unless it is mandatory. Is there no other IC that can serve our needs?


    How can we take this discussion to an email discussion instead of public forum?

    Regards,
    Vikas Chandra Rao.

  • 0 in reply to Vikas Thukuntla75
    Intellectual 520 points

    Hi TI team,

    Can you respond to my above queries, at the earliest? Kindly let me know if you need any info from my side.

    Thanks & Regards,

    Vikas Chandra Rao T.

  • 0 in reply to Vikas Thukuntla75
    TI__Intellectual 2050 points
    This discussion has moved to off the forum. I will be closing this post.

    -Joe