Intelligent Power Switches Augment Vehicle Performance and Comfort
Automotive electronic modules play a critical role in modern vehicles, providing a wide range of functions beyond reliability, comfort, and safety features. These modules are responsible for controlling various aspects of the vehicle, such as the engine, transmission, braking, as well as entertainment and communication systems, and they face several stringent challenges to adhere to international rules or standards.
This requires specialized design considerations and solutions to fulfill the additional demands addressed by the traditional 12V power system, to ensure numerous connectivity options along with the capability to support multiple cameras and sensors even in harsh conditions. This enhances the safety and comfort of the vehicle’s occupants and also improves the overall durability and longevity of the system.
An alternator’s severe high-energy transients and the ignition system’s low-level noise are examples of dynamic hazards for automotive power supplies. One of these extreme conditions is the cold crank, which occurs when the battery attempts to power the engine starter, and its voltage drops to a fraction of the normal level, typically below 3 V, due to heavy current draw. Start-stop technology makes checking cold crank operations even more difficult due to the large number of events, and cold temperatures make the problem worse as it further reduces the battery voltage. Another challenge that automotive electronic modules face is the need to be as efficient as possible to minimize power consumption and extend the life of the vehicle’s battery.
All this requires smart solutions for specialized power management circuits and protections that help to mitigate the effects of these hazards while ensuring high-end functionality, performance, and ruggedness.
An effective solution for distributed intelligence in battery management uses High Side Driver (HSD) circuits, which electrically turn the loads on and off.
Power Management in Automotive Systems
STMicroelectronics has developed VIPower M0-9 technology, which allows for the design of HSD circuits with advanced features and functions to manage automotive-system power.
The high side configuration is preferred for two main reasons. First, it protects against continuous operation in case of a short circuit to the ground which could result in load failure. Second, it prevents electrochemical corrosion that can occur in traditional 12V lead batteries due to harsh environmental conditions such as high temperatures, humidity, and salty atmosphere. The HSD is connected between the load and the positive power source, as shown in Figure 1.
This configuration ensures that the electrical components are at the lowest potential when not powered, which is the majority of the car’s lifetime. This helps prevent electrochemical corrosion.
The HSDs integrate a Serial Peripheral Interface (SPI) or a standard parallel interface with single, dual, and quad channels, helping scale circuit designs. The M0-9 HSDs also integrate complete digital and/or analog control circuits that can drive a vertical power transistor in the same chip, simplifying the design and reducing the overall size and cost of the systems. These smart switches can handle high currents and voltages up to about 40V and come with built-in protection against over-current and over-voltage. They also offer thermal shutdown and sophisticated diagnostics for optimal functionality, performance, ruggedness, and durability (Figure 2).
Overall, smart switches play a critical role in providing stable and reliable power to a broad range of automotive loads, including resistive, inductive, and capacitive loads. They can handle sudden surges of current and extra-energy transient events that occur when load current is switched off. This helps maintain optimal wire harness performance and protects local DC-DC converters. Furthermore, smart switches can charge capacitors of up to several millifarads, making them an excellent option for powering Electronic Control Units (ECUs) in Advanced Driver Assistance Systems (ADAS).
Distributed Intelligence in Smart Switches
The incorporation of logic and control sections that can receive microcontroller command signals enables smart switches to follow instructions that cover application requirements. By also incorporating sensors directly into the switch, the switch can monitor and respond to changes in the vehicle’s environment, including changes in temperature and anomalies in current absorption or voltage settlement. As a result, the switch can operate autonomously and make decisions without the need for a hub or central controller. This increases the system’s versatility and capability for use in automotive applications, as well as its efficiency and dependability.
Logic Section
The block diagram of the logic section of smart dual-channel M0-9 HSD is shown in Figure 3.
The smart dual-channel switch is a device that can control two independent channels with high accuracy and low power consumption. It has four input pins that can receive microcontroller command signals to follow the instructions that cover the application requirements. These input pins are compatible with 3.3V and 5V logic inputs. The datasheet specifies the pin names and functions:
- INx (IN0 and IN1) pins control and activate the output switch states
- SEx (SEn and SEL) pins are enablers for the multiplexer (MUX).
Additionally, a dedicated pin (FaultRST) is available to reset any fault condition and arrange the protection strategy between auto-restart and latch-off. Diagnostic feedback on a current sense pin (CS) allows for efficient and reliable system troubleshooting.
M0-9 devices exhibit the significant capability to automatically restore full functionality once the faulty condition is eliminated. This means that the device can recover from a fault condition without external intervention, reducing downtime and improving system reliability. All logic and control functions of the intelligent HSD are powered by an integrated power supply, which is divided into two subsections: the first section is always active and feeds the basic functionality of the logic and control circuits, while the second section is only active when the input is high to deliver the target power level.
This design approach is an effective solution to reduce power consumption in idle mode by ensuring that only the essential parts of the chip are active. As a result, the HSD can operate more efficiently and with less energy consumption, resulting in a significant improvement (about 20% at higher temperatures) over alternate devices (Figure 4).
This makes it an even more attractive option for applications that require high performance and low power consumption. In addition to its power-saving features, the driver also incorporates an undervoltage lockout circuit that safeguards the device from damage and ensures stable operation, even when driving inductive loads. This circuit prevents any significant voltage drop below the lockout threshold (typically 2.1V) during transient phases, making it an ideal solution for challenging conditions.
Furthermore, in the event of an operating supply voltage (VCC) short to ground (GND), the smart driver is designed to set the output current at a safe level to prevent damage caused by excessive current, ensuring the protection of the device.
Control and Diagnostic Section
The M0-9 smart driver features a control and diagnostic section that includes several important functions, as shown in Figure 5.
The charge pump in the gate driver subcircuit section is an important component that provides gate-source voltage for driving the power stage in high side configuration at controlled current slew rate, ensuring efficient and reliable operation. The output voltage clamping circuit is a crucial feature to protect the intrinsic power MOSFETs during turn-off in case of inductive load. The device can thereby avoid damage to the MOSFETs and other system components, even in the event of a load dump, by capping the additional voltage spikes at 36V.
The specific non-dissipative current sensing circuits are also essential components that allow for high precision detectability with 7% accuracy. By choosing a proper external sensing resistor and in line with the specific sensing voltage and minimum sensing current values of the device, a current mirror approach makes it possible to achieve a linear sensing reading covering the complete device current range all over the current and temperature range with a constant K factor. The current sense pins also have Electro-Static Discharge (ESD) protection up to 2kV, which helps ensure that the device can work in harsh automotive environments. Overall, these features demonstrate the device’s ability to provide reliable and safe operation in automotive applications while meeting industry benchmarks such as ISO and AEC Q100 standards.
The M0-9 technology introduces an additional feature to reduce power dissipation in case of reverse polarity. By connecting the specific input pins with a protection resistance of about 15kΩ as an interface versus the microcontroller, the internal logic can turn on the integrated power MOSFET, avoiding high power losses and forward biasing of the body drain diode. This is an effective way to improve the efficiency of power management systems.
As an example, consider the VND9012AJ power switch that is an M0-9 dual-channel HSD. The on-state resistance in reverse battery condition (RON_Rev) is the same as in normal on operation:
RON_Rev = RON = 12 mΩ
Then, the voltage drop (VDS) relevant to a load current IL = 4.75A is given by:
VDS = IL x RON_Rev = 0.06V
This value is significantly lower than the forward on-voltage of the MOSFET body drain diode, which is typically in the range of 1V.
Power Section
The device’s power stage includes integrated temperature sensing for fast and accurate detection. In the event of a load short circuit at start-up, the power MOSFET remains in linear mode until overtemperature detection turns off the device. When passive cooling and crossing of the protection threshold occur, the device resumes operation, resulting in a cycling working condition until the short circuit is removed. If the short circuit occurs when the internal MOSFET is already in full conduction mode with high gate-source voltage, then the current slew rate is controlled solely by the load itself. This results in a steady-state thermal condition and relevant thermal cycling up to the point when the short circuit is removed.
In the first case, by considering the HSD VND9012AJ with a battery voltage of 28V, as worst case for biasing voltage in AEC Q100 specification, the measured waveforms relevant to the short circuit condition are shown in Figure 6.
Where:
VDS is the drain-source voltage of the integrated power MOSFET
VOUT is the output voltage of the smart switch
IOUT is the output current of the smart switch
ENERGY is the dissipated energy calculated through the following equation:
ENERGY = (IOUT x VOUT x Dt) / 2
Being Dt the time duration of the short circuit event sustained by the driver.
According to the experimental data, the VND9012AJ smart dual-channel M0-9 switch can withstand a current of 33A for 60µs and sustain a dissipated energy of 26mJ when the battery voltage reaches 28V. Overall, the device’s temperature sensing and protection features help to ensure safe and reliable operation, even in the event of load short circuits.
Main Advantages in Automotive Applications
The automotive M0-9 drivers are designed to meet the stringent cold-cranking specification of the German car industry’s LV124 tests (Figure 7).
The parameter values for test pulses in case of a severe condition are listed in the following table (Table 1).
| Parameter | Severe Test Pulse |
| VB | 11.0V |
| VT | 3.2V +0.2 V |
| VS | 5.0V (0%, -4%) |
| VA | 6.0V (0%, -4%) |
| VR | 2.0V |
| tf | ≤ 1ms |
| t4 | 19ms |
| t5 | ≤ 1ms |
| t6 | 329ms |
| t7 | 50ms |
| t8 | 10s |
| tr | 100ms |
| f | 2Hz |
| Break between 2 cycles | 2s |
| Test cycles | 10 |
Compliance with this standard is a significant advantage of ST’s technology, as it ensures that the devices can operate reliably even in the most challenging conditions, providing the necessary functionality to the user. The minimum voltage specification of 2.7V (as maximum value) for cold cranking is the lowest in the competition ranking, providing a 10% improvement. This means that the M0-9 drivers are better equipped to handle the voltage drop that occurs during the cranking of a car’s engine.
Additionally, ST’s technology allows for operational and controlled outputs by the relevant input pins during this transition phase, when no diagnostic is required. This is a significant advantage for all automotive ecosystems, as it ensures that the device can be relied upon to perform its intended function, even in extreme conditions. Overall, ST’s technology offers superior performance and reliability, making it an excellent choice for automotive applications.
Conclusion
The M0-9 intelligent power switches offer improved automotive power management, enhancing vehicle safety and comfort. These switches feature integrated power MOSFETs, standby mode, and reverse polarity protection, all working together to reduce power consumption and boost efficiency. They also incorporate reliable current and temperature sensing for stable and safe operation, along with short-circuit protection to ensure system reliability and longevity. Additionally, they can operate effectively in low-voltage conditions, making them suitable for use in extremely cold weather, such as deep cold cranking scenarios.
