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BQ76PL455A-Q1: BQ76PL455A-Q1_ help required

Pratik Das
Prodigy 160 points
Part Number: BQ76PL455A-Q1
Other Parts Discussed in Thread: INA282-Q1, BQ76940, BQ78350-R1

Dear Support team,

I am using the TI chip no. bq76PL455A-Q1 to make my BMS. I have few questions regarding that.

Is this chip supporting current measurement? i could not find the information in the reference design.

In the reference design there is no information about the temperature measurement. Is there a port for thermistor connection to the chip?

I am also not able to find a complete reference design with all the components and batteries included like give in other TI chip data sheet.

 

Please provide me there information’s.

 

With kind regards,

Pratik

  • 0
    TI__Genius 11480 points
    Hello Pratik,

    The chip itself does not support current measurement. To do this, you will likely need a sense resistor, INA, and possibly signal conditioning depending on what performance you require. There are many solutions that we can provide, ranging from simple and low performance ("good enough") to complex and high performance.

    For hobby level projects, reporting the sense amplifier to the AUX pin can be "good enough", even though the protection for OC/UC will be relatively slow. It would be faster to report to an MCU based ADC, or a dedicated current sense solution (TI has many current sense solutions on the web...its a matter of finding one close to your requirements and adapting it). Something like the TIPD-121 reference design may be what you want (www.ti.com/.../tipd121)

    For OEM or professional grade projects, system performance will likely dictate a more complicated approach. Something like TIDA-03040 (www.ti.com/.../TIDA-03040) may be better for you.

    On our EVM (TIDA-00717: www.ti.com/.../TIDA-00717), header J2 connects to the AUX pins. These are typically used for thermistor connections.
  • 0 in reply to David Wiest Jr
    Prodigy 160 points
    Hey David,
    Thank you for the reply. It's really helpfull. Actually, I found some fererence design for the chip i am using in this link.
    www.ti.com/.../TIDA-00717 Documents

    However, I am not able to find a schematic of the complete design which i can modify for the temperature sensor and current measurement. could you plese help me out with that?

    With kind regards,
    Pratik
  • 0 in reply to Pratik Das
    Prodigy 160 points
    Hey David,
    I have coosen this INA (INA282-Q1) from the TI samples. I want to take a sence resistor of 1mOhm. with the sence resistor i am using capacitance resistance arrengment like shown in chip bq76940. I am using the same resistance and capacitance values. Could you plese have a look at the design and let me know if I have to change something. (If i am usung a INA do I need the resistance, capacitance arrangement?)

    With kind regards,
    Pratik
  • 0 in reply to David Wiest Jr
    Prodigy 160 points
    Hey David,
    I have another question regarding the chip bq76PL455A-Q1 hat i am using to make my BMS. I want to make a BMS for 48V 100Ah system (13 cells in series). I have taken the reference design and BOM from the demo board made from the chip (all data available in the website). My question is what kind of changes in components i need to make if i am designing for 100 Ah system, assuming that the demo board is designed for 16S1P (16 series, 1 parallel) system.

    Thank you.
    With kind regards,
    Pratik
  • 0 in reply to Pratik Das
    TI__Genius 11480 points

    Hi  Pratik,

    The monitor should not "see" the high current due to the system. It only measures cell voltages (so, parallel cells = 1 "actual" cell). From a  monitor point of view - 1Ah or 100 Ah is  more or less the  same, we  watch cell OV/UV and OT/UT.

    The current sense  solution seems okay... the capacitors you are speaking  of are a differential filter (the cap in parallel with  sense resistor) and common mode  filters  (the two caps two GND on either side of the resistor). If anything, I would say include the footprint in a pcb so that you can populate them if needed.

    I would give you  a few words of caution... be very careful with this system, as it is high enough power to cause serious damage. Make sure you don't  connect a relatively "dead" cell in parallel with a moderately "full" cell, as it will dump the current into the lesser charged cell and could  be dangerous.

    Also, make sure your sense routes for the sense resistor are matched, as short as possible, and away from sources  of noise. They have an example in the datasheet of the INA you chose, I believe.

    If you know more about your system requirements (high side/low side, accuracy requirements, bandwidth requirements, min/max  charge/discharge current etc), I think it  would be worth heading over to this forum (e2e.ti.com/.../931 ) and asking the team over there. I believe this is the correct forum, and they should have much more experience with these parts, which means  they should be able to help you better than I can.

     

  • 0 in reply to David Wiest Jr
    Prodigy 160 points
    Hey David,
    Thank you for the reply. Can you elaborate your suggestion on connecting the relatively good cell in parallel with relatively dead cell?
    I have read somewhere that, the good and bad cell will balance out and the effective voltage will appear as the total voltage of the parallel string. do you have some literature or more information regarding it?

    Another thing, I found a TI chips, there is a chip which does voltage, current and temperature measurements simultaneously. It also has passive balancing (www.ti.com/.../toolssoftware). This is what i was exactly looking for. Could you confirm if my understanding is correct?
    In this chip the maximum output current is given as 20A (schematic/block diagram). However the MOSFET ratings are more than 200A. I would like to have an output of 50A. is there any design changes i should do to achieve it?

    With kind regards,
    Pratik
  • 0 in reply to Pratik Das
    TI__Genius 11480 points
    Pratik,

    Think of it like this, in a somewhat over-simplified way:

    You have two voltage sources, 1 at 3.8V, and 1 at 3.6V. If you connect the two directly in parallel, you have the potential for very high currents, as only the connector resistance would be between the two. It is possible that this current exceeds what is safe for the cell.


    Do you have a part number? The link appears to be broken.
  • 0 in reply to David Wiest Jr
    Prodigy 160 points

    Dear David,

    Thank you very much for the reply. 

    the chip is described as : bq78350-R1 CEDV Li-Ion Gas Gauge and Battery Management Controller Companion to

    the bq769x0 Battery Monitoring AFE

    WIth kind regards,

    Pratik

  • 0 in reply to Pratik Das
    TI__Genius 11480 points

    Hi Pratik,

    One thing that I noticed is that the AFE family only supports up to 15S. If you are willing to reduce your cell count to meet that, i think this chipset will fit your needs  reasonably well.

  • 0 in reply to David Wiest Jr
    Prodigy 160 points
    Hey David,
    Thats correct. I am using 13S cells. Everything is fine. i still have a question i asked previously, In this chip the maximum output current is given as 20A (schematic/block diagram). However the MOSFET ratings are more than 200A. I would like to have an output of 50A. is there any design changes i should do to achieve it?

    With kind regards,
    Pratik
  • 0 in reply to Pratik Das
    TI__Genius 11480 points

    Pratik,

    The  reasoning behind  the FET choices  is  that they should  have an  extremely low  RDSon, which gives  rise to a  large current rating. Lower RDSon means  that there is  less efficiency loss  in  the  protector FETs, and that the  "ground" of  the  battery more  closely matches the ground of the system (less  impedance  between potentials).

    This  is not a  part  that I have supported, but it appears  that  the current measurement is  done  through  a Coulomb Counter, so as  long  as  your sense resistor and  current does  not  violate the maximum input ratings of the  CC, I see no reason why you could  not scale  your  sense resistor. I think  that  is  a  topic  for its own post, though, so that  you can get support from an engineer more familiar  with the device.

  • 0 in reply to David Wiest Jr
    Prodigy 160 points
    Hey David,
    Thank you for the reply. yes, I think the sense register can be adjusted to our requirement and it should be working. I can put separately a topic for this to get some other prospective if we are missing something.

    With kind regards,
    Pratik