Texas Instruments | bq40z60 Charging Voltage Compensation | Application notes | Texas Instruments bq40z60 Charging Voltage Compensation Application notes

Texas Instruments bq40z60 Charging Voltage Compensation Application notes
Application Report
SLUA750 – June 2015
bq40z60 Charging Voltage Compensation
Thomas Cosby
Battery Management Solutions
ABSTRACT
The bq40z60 integrated charger is a NVDC buck architecture and the charging voltage
range is set by the feedback resistors and a set of charging parameters. If you find that
the charging voltage is not accurate, then you can use this document to adjust parameters
to improve the accuracy.
Hardware Configuration:
The charger feedback resistors set the maximum output voltage for the charger. The charger is
an NVDC architecture, so the gauge dynamically adjusts the feedback voltage from 610 mV to
1220 mV as the cells charge.
The equation to set the feedback voltage is: Maximum output voltage = 1220 mV × (1 + R1 / R2)
Figure 1.
bq40z60 Charger
1
SLUA750
Firmware Configuration:
The bq40z60 firmware charging algorithm sets the charging voltage range. You do not have to
change the feedback resistors to reduce the charging voltage. The device can adjust for this, but
there is a resolution issue that we have to compensate. The issue is that the Voltage
Resolution register accepts an integer, so the calculated value must be rounded.
Charging Voltage
Sets the maximum pack charging voltage. Multiply the data flash Voltage parameter by the
number of series cells.
Minimum Output Voltage
Sets the minimum voltage for NVDC charging voltage range.
Voltage Resolution
Sets the step size that the firmware uses for the NVDC charging voltage.
Assumptions for this example:
Cell configuration: 3S
Desired Charging Voltage: 12300 mV (4100 mV per cell)
The formula for the Minimum Output Voltage = 610 mV × (1 + R1 / R2), where we set
R1 = 332 kΩ and R2 = 35.7 kΩ for a 3S configuration. So, the Minimum Output Voltage = 6283
mV
The formula for the Voltage Resolution = (610 mV × (1 + R1 / R2)) / 256.
So, Voltage Resolution = 6283 mV / 256 = 24.54 mV
The device only accepts an integer for the Voltage Resolution, so we enter 24 mV to be
conservative. This is the firmware limitation that causes a mismatch between the desired
maximum Charging Voltage and the actual maximum charging voltage. The Voltage
Resolution parameter will be set in µV in the next firmware revision to allow better resolution.
The charger has an internal Voltage Register that sets the number of Voltage Resolution steps
required to reach the Charging Voltage. The full-scale range of the Voltage Register is 256
steps.
Charging Voltage = Minimum Output Voltage + Voltage Resolution × Voltage Register
12300 mV = 6283 + 24 × Voltage Register
Voltage Register = (12300 – 6283) / 24 = 250.7 ⇒ 250
This is where the Voltage Resolution data entry limitation affects the results.
The desired maximum Charging Voltage = 6283 + 24 × 250 = 12283 mV, but the hardware
control loop uses the actual voltage resolution of 24.54 mV. Therefore, the actual maximum
Charging Voltage = 6283 + 24.54 × 250 = 12418 mV, which exceeds the desired maximum
Charging Voltage.
2
bq40z60 Charging Voltage Compensation
SLUA750
The firmware should set it to 245, based on the true charging voltage range.
Voltage Register = (12300 – 6283) / 24.54 = 245.2 ⇒ 245
Charging Voltage = 6283 + 24.54 × 245 = 12295 mV
The device will use the entered Voltage Resolution setting (24 mV) to set the internal Voltage
Register.
We need to set the Charging Voltage lower to force the Voltage Register to 245 to match the
hardware control loop.
Therefore, you should reduce the Charging Voltage parameters to compensate for this
mismatch.
Charging Voltage = 6283 + 24 × 245 = 12163 mV
Therefore, set the data flash Voltage (cell based) to 12163 mV / 3 = 4054.3 mV ⇒ 4054 mV.
If we set the Voltage to 4054 mV. (12162-mV stack), then the device will set the Voltage
Register to (12300 – 6283) / 24.54 = 245.2 ⇒ 245.
This should allow the control loop voltage range to be 6283 mV to 12295 mV (6283 + 24.54 ×
245). The pack should switch to CV mode at this voltage and taper the current. You can follow
the same process, if you want to set the peak charging voltage slightly higher.
bq40z60 Charging Voltage Compensation
3
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other
changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest
issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and
complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale
supplied at the time of order acknowledgment.
TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms
and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary
to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily
performed.
TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and
applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information
published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or
endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration
and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered
documentation. Information of third parties may be subject to additional restrictions.
Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service
voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.
TI is not responsible or liable for any such statements.
Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements
concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support
that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which
anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause
harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use
of any TI components in safety-critical applications.
In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to
help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and
requirements. Nonetheless, such components are subject to these terms.
No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties
have executed a special agreement specifically governing such use.
Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in
military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components
which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and
regulatory requirements in connection with such use.
TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of
non-designated products, TI will not be responsible for any failure to meet ISO/TS16949.
Products
Applications
Audio
www.ti.com/audio
Automotive and Transportation
www.ti.com/automotive
Amplifiers
amplifier.ti.com
Communications and Telecom
www.ti.com/communications
Data Converters
dataconverter.ti.com
Computers and Peripherals
www.ti.com/computers
DLP® Products
www.dlp.com
Consumer Electronics
www.ti.com/consumer-apps
DSP
dsp.ti.com
Energy and Lighting
www.ti.com/energy
Clocks and Timers
www.ti.com/clocks
Industrial
www.ti.com/industrial
Interface
interface.ti.com
Medical
www.ti.com/medical
Logic
logic.ti.com
Security
www.ti.com/security
Power Mgmt
power.ti.com
Space, Avionics and Defense
www.ti.com/space-avionics-defense
Microcontrollers
microcontroller.ti.com
Video and Imaging
www.ti.com/video
RFID
www.ti-rfid.com
OMAP Applications Processors
www.ti.com/omap
TI E2E Community
e2e.ti.com
Wireless Connectivity
www.ti.com/wirelessconnectivity
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2015, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising