BATTERIES
Automotive- shunts and matching evaluation electronics:
Intelligent battery sensor consisting of two key components Ralf Hickl, product sales manager, automotive business unit at Rutronik
B
attery monitoring plays an essential role in ensuring a reliable power supply for high-availability control units in assistance systems, as does sensor technology. Parameters such as battery current and voltage are measured to monitor the battery in the vehicle. The electronics use these parameters to calculate the residual energy stored in the battery, among other variables. Based on this, a control unit can decide which loads may be switched on or must be switched off to ensure that vital assistance functions remain available.
To measure the current, an important component in any battery sensor is the sensing element, such as shunt resistors. Their advantage is that they provide a simple linear relationship between the measurand and the output signal. According to Ohm’s law, the voltage drop across the shunt is proportional to its constant resistance and shunts suitable for DC and AC currents, as well as for both current directions. The sensitivity to interference with respect to temperature calculated if the actual temperature value is
One of the disadvantages is that the measurement signal of the shunt around a conductor, is at the potential of the current being measured. Therefore, current measurement in high-voltage systems still requires galvanic isolation of the measurement signal, which is an additional requirement. In addition, shunts dissipate power loss according to the formula Ptot=R·I2
heat up and transfer the heat to their surroundings.
Types of shunt resistors
Shunt resistors come in a variety of designs metal surface mount resistors. Compared higher pulse load capability.
Sizes for surface mount resistors range from 0603 to 5931. The higher the currents, the more
Figure 1: Thanks to its robust design, Vishay’s WSBR series tandem shunt provides greater functional safety.
with screw connectors. This is especially true in the range up to several hundred amps. The sensing element is made of a special alloy with the smallest possible temperature elements made of copper. The position of the sensing taps should be as close as possible to the sensing element with the smallest possible current path in the copper, ensuring the copper path with its higher temperature element and falsify the measurement result.
,
Tandem shunt from Vishay and a small thermoelectric voltage of up to 1.25 μV/°C. Since the power loss is proportional to the resistance of the shunt, the smaller allow higher currents to be measured. The tandem shunt (Fig.1) is its robust design with two independent measuring sections, which ensure high functional safety.
the voltage drops across the two independent measuring sections. In combination with appropriate evaluation electronics, can be achieved.
Evaluation electronics with
evaluation electronics with a two-channel
10 SEPTEMBER 2024 | ELECTRONICS FOR ENGINEERS
Figure 2: Block diagram of an intelligent battery
Automotive PSoC 4 HVPA (Fig.2). Its two differential input pairs can be interconnected measurement results of the same magnitude but with reversed sign.
The Automotive PSoC 4 HVPA has a LDO that can be connected directly to a 12V battery. Its
delta-sigma ADCs is suitable for input signals in the mV range. It communicates with a higher-level control unit via a LIN interface. The LIN transceiver is already integrated on the chip. Developed in accordance with ISO 26262, the microcontroller meets the requirements The combination of shunt and microcontroller can be tested with the
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