BQ76940: bq78350-r1

Hi Pavani,

It sounds like the part or a support component was damaged during cell removal or connection.  Check for supply to the REGSRC pin and current into the pin.  REGSRC supplies the REGOUT regulator and FET drive as well as some internal circuitry.

For diagrams see the block diagram in the data sheet http://www.ti.com/document-viewer/BQ76930/datasheet/functional-block-diagram-slusbk22474#SLUSBK22474 or various diagrams in http://www.ti.com/lit/pdf/slua749  

Hi Pavani,

A damaged part may have various resistive paths inside the circuit which could allow the part to regulate at the low voltage or limit at that voltage.  I expect you have already checked the net for contamination or unexpected conductors on the net, but an external short could also limit the voltage.  You might try lifting the REGOUT pin before replacing the IC to confirm if it is internal or external.

If the IC is damaged I don't know of a way it might be used.  While the IC is removed be sure to check for unusual voltages present or shorts on nets or components.  Other than a short of REGOUT to GND or a high voltage, short of the REGSRC to high voltage including shorting of the source follower FET might be suspected.

Hi Pavani,

"Lifting the pin" would be to de-solder the pin and bend it up slightly off the trace to see if the short is internal to the IC or on the remaining net. Sometimes this will remove a solder short under the IC pin and both the IC and the net will look normal.  With the pin lifted you can see if the REGOUT goes to its normal voltage and the IC has a normal temperature.  If it does the part may not work well since it does not have a capacitor on the REGOUT.  Similarly you can see if the REGOUT net on the board has an unusual resistance, or draws unusual current when powered by an test source at its normal value.

When you set the FET_EN bit in the Mfg Status Init parameter, after the checks for normal conditions at power up the BQ78350-R1 will turn on the FETs.  If you leave the FET_EN bit low the part will not turn on FETs after the power up checks even though things are normal and FETs will not come on until the ManufacturerAccess command 0x0022 is sent.  Notice though in table 17-2 of the technical reference manual http://www.ti.com/lit/ug/sluubd3d/sluubd3d.pdf  that command 0x0022 is not available when the pack has been sealed.  The commands are good for testing in evaluation or during manufacturing, but the settings read from the Mfg Status Init parameter are best for the final product.

The bits in Mfg Status Init are additive, the BQStudio tool will allow setting a single bit.  This can also be done with your own production system using a read/modify write to change 0x0010 to 0x0210.  See the technical reference section 12.1.1.  Another way to describe this may be that the Mfr Status Init parameter in data memory is copied to the Manufacturing Status register at reset.  The part behavior is controlled by the Manufacturing Status register which can be modified by various commands before the part is "sealed".

Hope this helps.

Hi Pavani,

The BQ78350-R1 describes power modes in the technical reference manual http://www.ti.com/lit/pdf/sluubd3  section 8 as normal, sleep and shutdown.  In shutdown it puts the BQ76940 in its ship mode to turn off power. 

Ship mode is a power state where the BQ78350-R1 is turned off, and most of the BQ76940 is turned off except the boot detector. 

To get out of ship mode boot the BQ76940 with the rising edge to TS1.

Seal mode of the BQ78350-R1 is a security state where many commands are not allowed and configuration can not be changed.  This protects the settings in the battery.  See section 11.5 for information on security modes.  Once the BQ78350-R1 (or the battery) is sealed it is more difficult to make changes since the key must be entered after each reset.  As the designer of the battery you can enter your own key and make changes, and but normally the key is entered at the end.  The keys can be confusing so it is advisable to work with one to get a good understanding of how to work with it using the default key and how it will work for your situation with your own key and a part you can discard if needed.

To get out of seal mode send the key as described in section 11.5.2 and 11.5.3, but it will return on reset.  You can reprogram the part with the firmware to get out of sealed mode but you will need to re-enter your parameters.

Hi Pavani,

1. I don't know, you will need to figure out why.    In the figure somthing is not right since the device number shows fff...  this should read 1e9b..., see the EVM user guide http://www.ti.com/lit/pdf/slvu925 figure 10.  Re-start BQStudio and see if it is correct.

2. The data looks wrong.  If it is not showing actual cell voltages, you are not getting current data. 

3. Yes, the device has body diode protection.  If you have charged to a COV condition and the charge FET is off, the charge FET will turn on again with sufficient discharge current.   It takes the part time to recognize the current and respond with FET control.  Your system should prevent charge or discharge, if you connect both and they can cycle, you can trick the part into charging periodically as your discharge tricks the battery into turning on the body diode protection.

Hi Pavani,

BQStudio talks to the BQ78350-R1.  In a system with BQ78350-R1,  it controls all features of the BQ76940.  There is no ADC_EN available, the BQ78350-R1 controls it as needed for operation.  Any time voltage is read by the gauge ADC_EN will be set.

Hi Pavani,

If you have cells set in the AFE Cell Map, which you do, they should be measured.

The BQ76940 monitor does not provide voltages if it has an XREADY fault. If the monitor has a fault the gauge will quietly try to fix it and you may not know unless you have enabled observation.  

You might look for the AFE_XRDY bit in the ManufacturerAccess() 0x0052 PFAlert, or read the status register from the monitor using ManufacturerAccess() 0x0058 AFEStatus, see the TRM.  If you have a XREADY fault, find the problem with the power and correct it.

Hi Pavani,

Your gg file reads voltages fine in an EVM, voltages change when the supply is adjusted.  If the file is not operating on your board perhaps the issue is in calibration data which is not normally copied from part to part.

If you think your gg file has caused some problem, restore defaults to confirm operation of the board, then add back the settings until you find something which stops the ADC.

You will need to determine if the settings are appropriate for your design.

Hi Pavani,

If you are looking at BQStudio be sure you are scanning.  A log will start scanning, so if you are seeing voltages not change in a log then the gauge is not seeing them.

You might see if the I2C pull up resistors have been lost so that the gauge no longer can talk to the BQ76940, but often this will cause loss of SMBus communication.

If the BQ76940 has an XREADY fault it will not update voltages.   XREADY is caused by missing voltage on the CAPn capacitors or excessive noise on the system.  If one is occurring, fix the problem. While it is disruptive to the gauge you may need to read the BQ76940 status register during operation to see if XREADY has occurred.  If yes, fix the problem.

Hi Pavani,

The part works when implemented and installed correctly.  Beyond the causes mentioned I don't know why it would not work.  Check workmanship on connections, check the design based on the data sheet, EVM, and various reference documents.  Be sure power is remaining on and that the part is communicating.  Inspect the SMBus lines and I2C lines to determine what is the problem.  Be sure the PC has not become busy and ignoring the BQ78350-R1 or interface.

Hi Pavani,

IFC is a permanent fail condition.  See the technical reference manual http://www.ti.com/lit/pdf/sluubd3 section 4.1 

Notice that the FETs are turned off when this condition is detected and charge or discharge should be prohibited. 

If the instruction flash is corrupt, the part will not be able to operate.  To recover from this condition reprogram  the gauge.