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Communicating w/ BQ77910 Help

Joel Jacobs
Prodigy 20 points

I have a BQ77910 chip and having difficulty communicating with it.  I purchased the chip, not the EVM.  I got a breakout board made so I can test it on a breadboard, and I have already checked that there are no shorts or opens.  I also purchased the USB-GPIO Module and updated it accordingly.  I'm using a 64-bit Win 7 machine.

My difficulty is what to do next.  I have not found an explicit set of insturctions to plug in and communicate with the chip directly.  Generally, I have all the GND, VSS, and GPIO GND all tied together, BAT and CHGSTS about 12V, DATA and CLK tied directly to the GPIO lines, and ZEDE tied directly to the GPIO line. 

The version of the software I have is defaulted to communicate with BQ77908, and it always says Cannot Find Target BQ77908.  But, the software won't let me select the BQ77910 option. 

Also, I've noticed a 'Comm Status: Driver Error' at the bottom status line when its searching for the target.

Outside of recheck your wires, does anyone have some suggestions or recommendations?

  • 0
    Prodigy 20 points

    Update:

    I called TI support, and they offered a few suggestions.  I implemented those suggestions, but the outcome is still the same.  One suggestion was to copy the external resistors shown in the circuit diagram in the BQ77910EVM manual.  I did that for the ZEDE, CLK, DATA, and GND lines.  I also switched machines and used a 32-bit Windows XP machine.

    Still no luck.  Right now I'm thinking either the software is still only looking for the BQ77908, or my chip is bad.  Besides the Vreg output pin, what would be a good way to test to see if the chip is still functional?  I don't want to connect my LI batteries to a potentially dangerous chip.

  • 0 in reply to Joel Jacobs
    TI__Guru 54715 points

    The bq77908 and bq77910 devices have the same address and register space. The device is selected by the user but the software does not allow it to be selected until the "target" is found.  Some suggestions:

    1. Be sure the interface status in the bottom left corner of the GUI shows "USB-TO-GPIO Version: 2.0.19".  If it shows something else, the GUI and interface will likely not be able to communicate with the part.
    2. If the device is not found, the communication status area should say "bq779xx Target Not Found" after you have acknowledged error boxes, where xx is the device selected.  You can not change the device selected until it finds a device.  If there is a different message, the issue may be a software installation or compatibility error. 
    3. Assuming the software is working correctly, look for a hardware cause for the communication error in the next steps.
    4. Be sure the device is on.  BAT at 12V is above the minimum start-up voltage and should be fine.  CHGST at 12V is well above the minimum threshold and should also be fine.  Be sure the VREG output is at 3.3V indicating the part is on.
    5. Next, be sure the communication lines are reaching the IC.  Monitor SCLK and SDATA with an oscilloscope and see that they toggle correctly on a Find Target attempt.
    6. The communication interface for the device is enabled by ZEDE.  The IO line from the USB-TO-GPIO used for this, pin 4, has very low drive strength.  It will not drive much more than the 100k pull-down shown on the EVM schematic.  Monitor this signal at the IC and be sure the line is going high during the communication attempt.
    7. If ZEDE is high during the Find Target communication attempt, be sure the device ACKs its address. If it does, the software should recognize the device. If not, the signal may be corrupted on the way back to the adapter.  Be sure you do not have excessive cable length, noise, or crosstalk on the signals.  If connections have been uncertain during the test attempts, the interface may have been damaged.
    8. Once the GUI finds the device, you can select the bq77910 button.  Instructions for the software are in the EVM user guide.

    You are wise not to connect cells to an unproven circuit, whether one using this IC or any other circuit.  Some suggestions for checking the part without software working might be:

    1. A basic checkout of the part would be similar to section 3 of the EVM user guide.
    2. Connect resistors to simulate cells and power these with a power supply.  If individual power supplies are available, this is better.If you do not have multiple supplies, you may get a similar effect with adjustable resistors, but there will be interaction.  Resistors in the 100 to 1k range with appropriate power ratings may be suitable.
    3. Apply normal simulated cell voltages and wake the part.  Observe that it powers up (VREG) and remains on. Check the FET control outputs DSG and CHG. If you have a test current, you can check your control devices (FETs). Note that if you are using less than the default number of cells, the unused inputs will be undervoltage and the DSG output will not come on. To get proper operation you will need to program the device correctly, so the communications must work.
    4. Adjust the simulated cell voltages to get an OV condition.  Observe the CHG output go low.
    5. Adjust the simulated cell voltages to get an UV condition.  Observe the DSG output go low.
    6. Note the device will shut down after 8s of UV in default mode.
    7. Check all inputs, particularly after programming.  You do not want to leave cells unprotected due to an assembly or programming error.
    8. Check current protection similarly whether with a power supply in CC mode or with a voltage on the sense pins.  Some test to be sure the device actually recognizes the current is critical.
    9. Another good check is the operating current of the IC.  The typical application has a resistor in the BAT input line.  Check the supply current by checking the voltage on this resistor.  Currents outside the operating current in the datasheet may indicate the device has been damaged in assembly or prior testing.  Be sure to consider leakage of any capacitors and diodes, and the test conditions for the device when comparing system currents to the datasheet limits.