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BQ34110EVM-796: Max cell voltage on eval board vs device maximum

howard banks
Intellectual 580 points
Part Number: BQ34110EVM-796
Other Parts Discussed in Thread: BQ34110

We recently purchased the BQ34110EVM-796 with a view to evaluating it on our battery packs.

It appears that the eval board only accepts a cell voltage to a maximum of 48V. The BQ34110 device looks good to 65V. 

Why is there a discrepency between the two maximum voltages? When we charge our cells we can see voltages upto 57V so i don't want to run the eval board in our system without some guidance as to what i need to do to ensure its safe.

Also, the datasheet mentions scaling to allow the capacity and currents measured to be extended, but i don't see any further reference to scaling. Is there any further information on the scalling required?

  • 0
    TI__Mastermind 25955 points

    Hi Howard,

    The 48 V limit is due to the external resistive divider on the board. With a jumper shorting pins 5 and 6 of J5 (the 48 V setting) the upper leg of the resistive divider is 900 K, and with a jumper shorting pins 5 and 6 and pins 7 and 8 of J2 (the >5V settings) with a lower leg resistance of 16.5 K. With 48 V stack voltage, this equates to 0.864 V seen at the BAT pin.

    An important design consideration here is to select a resistive divider that will bring your maximum stack voltage down to ~900 mV. With an appropriately sized external resistive divider, the device can operate well over 65 V, however, the maximum voltage the device can store before overflowing is 65535 mV because the value is stored as a 16 bit unsigned integer. This is where scaling comes to play. By utilizing a scale factor for voltage, the device may operate without going beyond the 65535 voltage limit imposed by a 16 bit unsigned integer.

    For more information on voltage, current and capacity scaling, please refer to this app note (this app note is written for the 34z100-g1, but the scaling methodology is similar): www.ti.com/.../slua760

    The EVM is rated for 3-5 V operation in 1S mode, and 6-48 V operation in multicell mode, for charge and discharge currents up to 7A.

    Please note: the current sense resistor is 10 mOhm. an important design parameter on the current sense resistor is a +/- 125 mV drop across the resistor. Please size your current resistor for your application.

    For more information on device operation and design considerations, please refer to the TRM: http://www.ti.com/lit/ug/sluubf7/sluubf7.pdf


    Sincerely,
    Bryan Kahler

  • 0 in reply to Bryan Kahler
    TI__Mastermind 25955 points
    Hi Howard,

    If the above response helped resolve your question, please click on the 'This Resolved my Issue' button below to improve the find-ability of this response for others that may have the same issue. Thanks!

    Sincerely,
    Bryan Kahler