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BQ78350-R1: Questions about Configuring the Hardware of bq78350-R1, bqstudio and battery chemistry

Paul K52
Intellectual 640 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQSTUDIO, BQ76920

Hardware Configuration-

Refering to the Datasheet of the BQ78350-R1:

Q0: KEYIN: A low level indicates application key-switch is inactive on position. A high level causes the DSG protection FET to open. If this pin is not used, then it should be tied to VSS.

Can the system only turn the DSG-FET on and off, only I use the function of KEYIN?

So when I connect the KEYIN-Pin to Ground, the DSG-Fet will always be in on-state?

Q0b: If the answer to question 0 is yes: Is there also a pin to control the state of the CHG-Fet to turn of or on?

Refering to the Technical Refernce of the BQ78350-R1:

Q1: !PRES: The bq78350-R1 has the capability to detect the presence of a system and/or a charger through the stateof the PRES pin. This can be used to disable the battery output when the bq78350-R1 detects the battery has been removed from the system or charger.

My question refers to the second sentence: When the battery has been removed, the battery ouput is disabled eitherway. Can you get in more detail, what do you mean?

What kind of hardware should I connect to the PRES-Pin, if I want to use the fuction? 

Q3: If I want to choose the right Battery-Chemistry-ID, is it said that I have to log the discharge behavior of the battery by 0 °C. 25 °C, and 40 °C with average max discharge and half of average max discharge

How do you simulate these temperatures by a discharge process?

What do you mean with max discharge? Is the max discharge refering to the current, during discharge?

Thanks for help

VAUX,PRES

Log-Files- Temperature: 0 °C, 25 °C, 40 °C

  • 0
    TI__Guru 54715 points

    Hi Paul,

    Q0: KEYIN will turn off the Discharge FET when other conditions would alllow it on. It does not toggle
    There is not pin to turn off the charge FET. There is the Host FET Control command which works on a 4 sec cycle, but it is not a pin, it is a command. KEYIN does not have the internal pull up feature and needs an external pull up resistor.
    Q1: PRES can turn off both FETs and recover from faults. See the technical reference manual for options. The pin has an internal pull up which is pulsed to reduce power. It is grounded when in the system and FETs should be on. When the battery is removed the pin can be pulled high and the FETs will turn off. If PRES is used you don't need a pull up but will likely want an ESD protection on the signal since it will go to the external world.
    Q3: Yes, max discharge is the current during discharge. Max discharge would be the maximum expected discharge for the system. If your cell can support 2C but your system will only support 1C in its maximum current mode the maximum would be the 1C value. If you have a 2500mAh cell that would be a 2500 mA load. Adjust the maximum rate as needed for your system and of course don't exceed the limits of your cells. The other test load would be half that current.
    The temperature sensor must be on the cells for proper chemistry match, it should not be simulated

  • 0 in reply to WM5295
    Intellectual 640 points
    To Q1: Example Szenario: The battery is used and is discharging. It is noticed that the battery is not in safety conditions( undervoltage-threshold is exceeded) It has to be disconnected from the system. Im not using the KEYIN fuction( the pin is connected to Ground).

    Will the batterymanagmentsystem turn off the DSG-FET to disconnect the battery from the system, even im not using the purpose of the KEYIN pin?





    To Q3:"The temperature sensor must be on the cells for proper chemistry match".

    Okay, in other words:

    So, I need 6 log files. This log-files will have informations about the discharge cycle of the battery. The discharge cycle have two paramters
    which can vary. This parameters are current and temperature.

    I need six log-Files which contains the discharge process with 0,25,40 degree and the maximum discharge current and
    with a half of the maximum discharge current.

    So the battery has to be in different conditions during discharge. The environent where the battery has to be during discharge
    has to be 0 degree in one case. So the temperature sensors has to measure 0 degree.

    How do you simulate 0 degree in the environment?
  • 0 in reply to Paul K52
    TI__Guru 54715 points
    Q1: Yes, UV can protect if KEYIN is not used. UV must be enabled (it is enabled by default), see section 3.1 of the technical reference manual. Many things can turn off the FETs, they can only turn on if conditions are acceptable.

    Q3. Yes, 6 logs are needed as described for CEDV coefficients. The temperature ranges can be appropriate for the system environment. The temperature sensors must be attached to the cells to get the cell temperature during the test. This type of test is typically done in a temperature conditioning chamber where the system temperature can be raised or lowered to simulate the temperature where the system could be operated without having to transport the system to that environment and wait for the right conditions. You might do an internet search on "temperature chamber", "thermal chamber", "environmental test chamber" or similar search terms. Some labs use a temperature conditioning system with an appropriate enclosure.
  • 0 in reply to WM5295
    Intellectual 640 points

    To Q3: I dont have a thermal chamber, I dont have a possibility to simulate to simulate other temperatures.

    What I could do in this case? Is it okay to log the behavior with room temperature in all 6 cases?

    Q4: How long does it take to get an email with the right Chemistry-ID?

    Q5: Im working with a Lithium-Polymer Battery. I cant choose this type of battery, because this type (Lithium-Polymer) is not listed, as you can see.

    What can I do to be able to choose Lithium-Polymer Batterys?

  • 0 in reply to Paul K52
    TI__Guru 54715 points
    Hi Paul,
    This may start backward, but there are 2 things which may be getting confused here.
    First is the chemistry ID which can be loaded into the bq78350-R1 to estimate the state of charge from the voltage on wake up (boot). This can be picked from the Chemistry tab in bqStudio for the bq78350-R1. You can browse the list and select the cell or closest type of cell. You can also record a log and submit for matching the chemistry if desired. This is typical for impedance track gauges, but less critical with the bq78350-R1 since it is CEDV gauging. The tool for matching chemistry is http://www.ti.com/tool/GPCCHEM
    The second is the CEDV parameters. You have the packager tab displayed above. The compensation is for current and temperature. Data is collected at 2 currents and 3 temperatures (6 files) and is submitted to the tool www.ti.com/.../gaugeparcal which will send CEDV parameters for setting up the bq78350-R1.

    With that background, your questions:
    3: If you don't own a chamber and can't borrow or rent one, you might consider contracting the test or determining what you can improvise safely. If you live in a hot or cold climate you might allow nature to condition one temperature. If you can't meet the requirements of the technology it will not perform to its capability. If you don't have 3 temperatures to test, you can feed the tool the same 2 files for the other temperatures, but the result may not be good. When collecting the data, be sure the temperature sensor is on the cell, not the ambient temperature. The "C" in CEDV is for "compensated", or adjusting the EDV for load and temperature. If you can't prepare the temperature portion of the data, consider if you need to use the compensated feature or if a fixed EDV is suitable. With fixed EDV you can run 1 curve, calculate capacity and select the EDV2, EDV1 and EDV0 points.

    4. The web tool should email in a few minutes. I have not done it.

    5. As noted above, select the chemistry tool/tab and browse through the cell list. You could use the matching tool if desired.
  • 0 in reply to WM5295
    TI__Guru 54715 points
    On #4, It took about 1 minute to get the emailed results on a test today. Results may vary.
  • 0 in reply to WM5295
    Intellectual 640 points
    Q6: But my battery is not listed in the Chemistry section. I am using a Lithium-Polymer battery with 2400 mAh. Is it very important to choose the exact battery in the list or is it okay to choose a chemistry-ID, which is near by my battery?

    Q7: What do you mean with: "Be sure the temperature sensor is on the cell". On my Batterymanagmentsystem-Board I used a temperature sensor. I have connected it to the BQ76920, as described in the datasheet of the IC.

    Q8: Refering to the Data Memory section in the Subclass Fuel Gauging, there are coefficients like EMF, R0, T0, T1, TC, C1. Are this the CEDV coefficients which I will get from Ti by email?

    Q9: With fixed EDV you can run 1 curve, calculate capacity and select the EDV2, EDV1 and EDV0 points.
    What you mean is that I should choose a fixed End of Discharge Voltage (EDV), right?
    Which formula should I use for calculating the capacity?
  • 0 in reply to Paul K52
    TI__Guru 54715 points

    Hi Paul,
    6: For bq78350-R1 it is not critical that it be the exact battery. You can run a log and match to a chemistry if desired, but for this CEDV part the chemistry is used for estimating the capacity at reset.

    7: The sensor part of the thermistor should be mounted to the cell, you want the temperature of the cell, not of the board some inches away.

    8: Yes. You can see a sample report at step 3 of http://www.ti.com/tool/gpccedv . Note that there is some information in the report you won't need.

    9: Right. If you discharge from fully charged to the fully discharged voltage logging the time, current, and voltage you can calculate the passed charge as the sum of the current x time. When discharge stops you have the capacity of the battery. Calculate 93% and look at the voltage, that is EDV2, same for EDV1, and EDV0 is of course where you stop.