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Texas Instruments BQ75614-Q1 – The Highest Functional Safety Level and Performance for 48-V System Application notes
Application Report
SLUA990 – September 2019
BQ75614-Q1 – The Highest Functional Safety Level and
Performance for 48-V Systems
ABSTRACT
This application note showcases the benefits of using the BQ75614-Q1 14S Precision Battery Monitor,
with Current Sense and Hardware Protector for 48-V designs.
Several features are highlighted, such as
• Device-level ASIL-D rating
• Enhanced SoC and SoH estimates
• High measurement accuracy
• Bill of material (BOM) advantages
• "Family" approach to devices
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Contents
ASIL-D.........................................................................................................................
Enhanced SoC and SoH ...................................................................................................
Fuse and Relay Monitoring .................................................................................................
Accuracy ......................................................................................................................
BOM Advantages ............................................................................................................
BQ7961x-Q1 Family ........................................................................................................
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List of Figures
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BQ75614-Q1 With Integrated Current Sense ............................................................................ 3
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External Current Sense ..................................................................................................... 4
List of Tables
Trademarks
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ASIL-D
The BQ75614-Q1 is a pioneer in the battery monitor market with ASIL-D-rated current measurement. The
device uses a dedicated current sense, 16-bit, sigma-delta ADC and a redundant ADC to achieve this
feat.
The device also features the ASIL-D rated systems inherent to the BQ7961x-Q1 family:
• Communications
• Voltage
• Temperature measurement
All of the features listed above, along with the current sense ADC, allow for a device-level ASIL-D rating
with minimal software requirements from the host microcontroller.
The device also features the capability to complete FDTI within 100 ms by using several built-in
diagnostics. This significantly reduces the amount of processing and communications required by the host,
and frees up the host to complete other tasks during the diagnostics.
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Enhanced SoC and SoH
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Enhanced SoC and SoH
The BQ75614-Q1 has easy and helpful features for providing better SoC and SoH estimates.
2.1
Synchronized Voltage and Current Measurements
The BQ75614-Q1 allows for current and voltage measurements to have synchronized starts to allow for
improved SoC and SoH estimates. This can be done without the microcontroller having to manually
synchronize each measurement with precise timings.
2.2
Current Measurement Notification
The device optionally allows for a GPIO line to be used to notify the microcontroller when a conversion is
complete. This can act as an external interrupt for the microcontroller to assist with coulomb counting
calculations.
By combining these features, the developer is provided with the tools necessary to provide the best SoC
and SoH estimation possible.
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Fuse and Relay Monitoring
Using two additional voltage measurement channels on the device, the BQ75614-Q1 is capable of
monitoring the fuse and relay of a battery management system with no additional components. This allows
for simplified development and communications for the microcontroller, as the monitoring system for the
fuse and relay is integrated.
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Accuracy
4.1
Current Measurement
The current-sense ADC in the BQ75614-Q1 offers a high-accuracy integrated ADC.
Details:
• Full scale voltage range: ± 250 mV
• Temperature range: -40°C to 105°C
• LSB resolution: 7.63 uV
• Conversion time options from 1 ms to 25 ms
These features allow for consistent and accurate SoC measurements for the battery system.
4.2
Voltage Measurement
The SAR ADC cell voltage measurement channels inherited from the BQ7961x-Q1 family allow for high
post-solder accuracy across temperature on all 14 channels. These channels have integrated front-end
RC filters, which assist in achieving this accuracy. The integrated filters also:
• Eliminate the need for external ESD diodes
• Allow for significantly reduced external RC filter requirements
The customizable, post-ADC, low-pass filters (with cutoff frequencies as low as 6 Hz) further assist in
accuracy and noise suppression.
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BOM Advantages
The BQ75614-Q1 provides several features that reduce the overall BOM cost of the device.
5.1
Current Sense Cost Advantages
By integrating the current sense ADC into the device, significant cost savings are available. These cost
savings (when compared to a stand-alone current sense ADC) come in many forms:
• Reduced quantity of components (no external current sense ADC or redundant ADC)
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BQ75614-Q1 – The Highest Functional Safety Level and Performance for 48V Systems
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BOM Advantages
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PCB area required reduced significantly
No additional UART or SPI lines required from microcontroller to current-sense ADC
Development time significantly reduced (only need to program one device)
Voltage and current sense ADCs easily synchronized for simplified SoH and SoC estimations (see
Section 2)
Device-level ASIL-D rating assists with further reduced development time
The difference in required components can be easily seen by a system-level block diagram comparison
between integrated current sense and external current sense:
Figure 1. BQ75614-Q1 With Integrated Current Sense
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BOM Advantages
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Figure 2. External Current Sense
5.2
Voltage Measurement Cost Advantages
The voltage measurement channels inherited from the BQ7961x-Q1 family maintain the highly costeffective features of the rest of the product family:
• Integrated ADC filters for significant reduction in size and quantity of components
• Easy diagnostic checks for fewer components (external redundant ADCs not needed for ASIL-D) and
simplified software development
• Integrated passive balancing FETs for cost savings and smaller footprint (reducing PCB cost)
• Internal LDO can support 10 mA loads for digital isolators, to remove the need for additional PMIC
These features, among many others found in the BQ7961x-Q1 family, assist in overall BOM and
production cost reduction.
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BQ75614-Q1 – The Highest Functional Safety Level and Performance for 48V Systems
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BQ7961x-Q1 Family
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6
BQ7961x-Q1 Family
With a “family” approach to devices, TI is able to deliver additional development time reduction. The ASILD BQ7961x-Q1 family (including the 16S, 14S, and 12S monitors for HV systems) share several features
with the BQ75614-Q1, including the same:
• Package
• Pinout
• Functional control
• Register map
Development for one device is easily ported to other devices in the family. This allows for similar firmware
between high voltage and 48V systems.
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