Table of Contents
Advertisement
BQ76952
SLUSE13A – JANUARY 2020 – REVISED MAY 2021
used by the ADC, and the input range of the ADC is limited to the REG18 pin voltage. The digital fullscale range
of the ADC is effectively 1.6667 × VREF1, which is approximately 2.08 V during normal operation.
The BQ76952 device also reports the raw ADC counts when a measurement is taken using the TS1 pin. This
data can be used during manufacturing to better calibrate the ADCIN functionality.
10.3 Coulomb Counter and Digital Filters
The BQ76952 device monitors pack current using a low-side sense resistor, which connects to the SRP and
SRN pins through an external RC filter, which should be connected such that a charging current will create
a positive voltage on SRP relative to SRN. The differential voltage between SRP and SRN is digitized by an
integrated coulomb counter ADC, which can digitize voltages over a ±200 mV range and uses multiple digital
filters to provide optimized measurement of the instantaneous, averaged, and integrated current. The device
supports a wide range of sense resistor value, with a larger value providing better resolution for the digitized
result. The maximum value of sense resistor should be limited to ensure the differential voltage remains within
the ±200 mV range for system operation when current measurement is desired. For example, a system with
maximum discharge current of 200 A during normal operation (not a fault condition) should limit the sense
resistor to 1 mΩ or below.
The SRP and SRN pins can also support higher positive voltages relative to VSS, such as may occur during
overcurrent or short circuit in discharge conditions, without damage to the device, although the current is not
accurately digitized in this case. For example, a system with a 1 mΩ sense resistor and the Short Circuit in
Discharge protection threshold programmed to a 500 mV level would trigger an SCD protection fault when a
discharge current of 500 A was detected.
Multiple digitized current values are available for readout over the serial communications interface, including two
using separate hardware digital filters, CC1 and CC2, as well as a firmware filter CC3.
The CC1 filter generates a 16-bit current measurement that is used for charge integration and other decision
purposes, with one output generated every 250 ms when the device is operating in NORMAL mode.
The CC2 filter generates a 24-bit current measurement that is used for current reporting, with one output every
3 ms when the device is operating in NORMAL mode (which can be reduced to one output every 1.5 ms based
on setting, with reduced measurement resolution). It is reported in 16-bit format, and the 24-bit CC2 data is also
available as raw coulomb counter ADC counts, provided in a 32-bit format (with the data contained in the lower
24-bits and the upper 8-bits sign-extended).
The CC3 filter output is an average of a programmable number of CC2 current samples (up to 255), based on
the configuration setting. The CC3 output is reported in 32-bit format.
The integrated passed charge is available as a 64-bit value, which includes the upper 32-bits of accumulated
charge as the integer portion, the lower 32-bits of accumulated charge as the fractional portion, and a 32-bit
accumulated time over which the charge has been integrated in units of seconds. The accumulated charge
integration and timer can be reset by a command from the host over the digital communications interface.
10.4 Synchronized Voltage and Current Measurement
While the cell voltages are digitized sequentially using a single muxed ADC during normal operation, the current
is digitized continuously by the dedicated coulomb counter ADC. The current is measured synchronously with
each cell voltage measurement, and can be used for individual cell impedance analysis. The ongoing periodic
current measurements can be read out through the digital communication interface, while the measurements
taken that were synchronized with particular cell voltage measurements are stored paired with the associated
cell voltage measurement for separate readout. These values can be read using a block subcommand, which
ensures the synchronously aligned voltage and current data are read out together.
10.5 Internal Temperature Measurement
The BQ76952 device integrates the capability to measure its internal die temperature by digitizing the difference
in internal transistor base-emitter voltages (delta-V
measurement loop and is processed to provide a reported temperature value available through the digital
38
Submit Document Feedback
). This voltage is measured periodically as part of the
BE
Product Folder Links:
BQ76952
www.ti.com
Copyright © 2021 Texas Instruments Incorporated
Advertisement
Table of Contents
