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BQ77PL900: Life cycle status

Wim2532
Intellectual 330 points
Part Number: BQ77PL900
Other Parts Discussed in Thread: BQ76930, BQ77905

Dear,

One of my customers wants to start a new design, using the BQ77PL900. This is already a bit old device, so the question is if this part is still recommended for new designs? If not, which alternatives do you recommend which can work, like the BQ77PL900, stand alone? 

Are there any errata documents available of the BQ77PL900? If yes where can I find these?

Thanks in advance and kind regards,

Wim van der Steeg

Avnet Silica

  • 0
    TI__Guru 54715 points

    Hi Wim,

    The bq77PL900 is an older device but remains an active part.  It does not have a direct replacement, the bq76930 would offer a monitor function with balancing for systems which want MCU control, the bq77905 could be stacked for systems which want only standalone protection without balancing.  

    There is not an errata document for the part.  Generally documents are in the "technical documents" tab of the product folder or associated with the EVM in the "tools & software" tab.  The data sheet is the older TI format, but represents the part well.  You may find some common questions, concerns or confusions in the forum posts.  A few items which may be of interest:

    • The cell inputs are sensitive to abuse, don't exceed abs max.
    • The part measures the bottom cell with respect to GND, connecting VC11 and GND near the cell as shown in the characteristics table is preferred.
    • The basic circuit does not show a cap from VC11 to GND, but adding one will help prevent transients from pushing VC11 below GND.  Moving the cap connection for the bottom cell from VC11 to GND can also be beneficial, this topology is shown in the bq76930 schematics.
    • The cell voltage calibration described in the data sheet does not correct for the common mode effects of the cell sampling circuit, a per-cell calibraiton or compensation may be desirable in addition or in place of the data sheet technique.  Cell calibration is separate from BAT, PACK and current calibration which may be done.
    • The 10k input resistors shown in the cell balancing apnote are rather large and can show some sampling errors, 1k may be a more typical upper value.
    • Cell balancing and cell monitoring will interact since they are independent, the host should not measure cells during cell balaning.  The safety monitoring is duty cycled with the balanicing, but the host must duty cycle its measurement.
    • There is an internal resistance for the FET gate drive and a diode to the supply.  Do not attempt to switch the pin away from the FET source without also switching the gate.  For example if you attempt to switch off the PACK pin but leave CHG connected to the FET, the CHG pin will hold up the PACK pin and likely pull down the FET gate.
    • Be sure to set the hardware zero volt charge and the EEPROM zero volt charge to compatible settings. You do not want it to turn off your precharge FET when it wakes up.
    • The EEPROM is intended for factory configuration, not repeated writes. The EEPROM programming description in the data sheet with the cell balance FETs is not required for programming, it was offered as a technique requiring little support equipment.  Provide appropriate voltage for programming and keep the inputs within their specs during programming.