Figure 6 Data from Lookup Table Showing Resistance Drift with Temperature
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MODEL CSM2F HIGH POWER CURRENT
SENSE RESISTORS
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CURRENT SENSE RESISTORS
Figure 5. Accuracy of Bourns® Model CSM2F-8518 Shunt with
Current Sense Module
The data at several DC currents ranging from 10mA up to
20A was recorded, and the accuracy calculated (shown
on the graph in Figure 5). The accuracy tends to degrade
once the currents increase beyond 10 amperes, and
the shunt starts to heat up. The resistance value used
to calculate the current will drift as a result, which has a
negative impact on the accuracy of the measurements. To
further assist designers, Bourns has developed a look-up
table that shows the normalized increase or decrease
of the resistance with temperature. With this data, the
original value used for the resistance can be modified
by the factor shown in Figure 6 and correlated with the
temperature sensor reading.
Helping to Ensure BMS Safety and Long Life
Currents of several hundred amperes are measured by
BMS in various e-mobility applications during battery
charging and discharging. The ability to measure current
accurately provides critical
information for safety and ensures
long battery pack life. Using an
ultra-low resistance shunt resistor
and a precision AFE can provide
very accurate readings from
very high to very low current
levels with accuracy tolerances
of less than 0.01 percent. Also,
temperature sensing, and lookup
tables from Bourns, can improve
measurement accuracy as the
temperature increases.
This application note has provided a proven methodology
to measure the cell voltage, temperature, and current to
determine the state of health of a battery cell. Key in this
process are Bourns
®
current sense amplifiers featuring low
offsets and high common mode voltages that enable high
accuracy with the shunt being placed at the high end in 48V
applications.
Bourns
®
Model CSM2F Series shunt resistors are
manufactured in an International Automotive Task Force
approved facility certified to build components for certain
harsh environment applications such as in high energy
BMS used in HEVs and BEVs. ■
