introduction
In today's cars, systems for seat heating, air conditioning, navigation, infotainment, driving safety and the like are designed to improve comfort and driving experience. From these systems, it is easy to understand the electronic systems that power various functions in the car The Benefits Now it's hard to imagine a mere 100+ years ago when there was not one electronic component in a gas powered vehicle.At the turn of the century the car started to have a crank and the headlights were illuminated with acetylene gas, You can also use the ringtones to send a message to pedestrians.Nowadays cars are at the junction of electronic systems, minimizing the use of mechanical systems and becoming the largest and most expensive 'digital tool' in people's lives. Availability and environmental reasons, as well as increased demand for internal combustion, hybrid and all-electric car driving safety, the market has gradually reduced its dependence on gasoline, which is the driving force behind the "digital" shift.
As more and more mechanical systems are replaced by electronic systems, power consumption and how to monitor power consumption are becoming more and more important. Accurately monitoring the power consumption of an electric vehicle will ultimately make the driver more realistic. All-electric cars are likely to worry about driving distance because car batteries may run out of fuel before arriving at their destination. Hybrid-electric car owners have the advantage of relying on a gasoline-powered engine to drive home, The car can only be charged at the charging station, nowadays the charging station is scarce, and it takes a few hours before the battery can be fully charged.Therefore, it is important to monitor the power consumption of each electronic subsystem continuously and accurately.On the basis of monitoring information, You can also advise drivers who are on the road to conserve battery power to extend travel distance Disconnecting idle modules from the power bus further reduces power consumption Monitoring subsystem currents and power can also reveal any anomalies in the long term performance of the vehicle Trend, predict failure to prevent failure, mark the service request that needs to be sent to car repair shop, diagnosis system In order to benefit from the power and energy monitoring, access via wireless data and fault recording, you can quickly debug and reduce repair costs and downtime.
Several ways to monitor and control power consumption
To monitor the power consumption of an electronic system, it is necessary to measure the current and voltage continuously. The voltage can be directly measured with an analog-to-digital converter (ADC). If the ADC input range is less than the voltage being monitored, a resistor divider may be required ) To measure the current, a sense resistor needs to be placed in the power path to measure its voltage drop. As shown in Figure 1, the transconductance amplifier converts the high side sense voltage into a current output that flows through the gain setting resistor To produce a ground-referenced and load current proportional and suitable for feeding the ADC voltage in order to minimize power consumption, full-scale detection voltage limit of tens of millivolts Therefore, the amplifier input offset needs to be lower than 100μV. To calculate power, a microcontroller or processor that accesses the ADC data through the ADC's digital interface must be used to multiply the voltage and current readings. To monitor power consumption, it is necessary to accumulate (add) power readings over time .
In order to switch the power supply, electromechanical relays are generally used in automotive circuits. In order to save space, solid-state switches such as N-channel and P-channel MOSFETs replace the relays to produce all the components on the same circuit board. The PCB design of the solder-flow process assembly P-channel MOSFET turns on by pulling its gate low and is turned off by connecting the gate to the input voltage As compared to N-channel MOSFETs, the P-channel MOSFET leads With the same resistance, the cost is higher and the choice is narrow, limited to higher current levels (above 10A). N-Channel MOSFETs are the best choice for high currents, but charge pumps are needed to increase the gate voltage For example, a 12V input requires a gate voltage of 22V, which means the MOSFET gate is 10V above the input. Figure 2 shows the implementation of a power switch circuit.
Common power buses also need protection against short-circuits and overload faults that may occur on any board or module. To achieve the circuit breaker function, you can compare the output of the amplifier in Figure 1 with an overcurrent threshold to break Drive the gate driver in Figure 2. This solution replaces the fuses because the fuses react slowly and have too wide tolerances and need to be replaced after fusing.In order to save board space it is desirable to switch between protecting and monitoring the automotive power bus The power flow, the use of integrated solutions.
Integrated power control and telemetry solutions
The LTC4282 is a hot-pluggable controller and circuit breaker that provides energy telemetry and EEPROM (Figure 3) to meet the needs of high-current applications with innovative dual-current path features that control the external N The trench MOSFET, which smoothly powers the bulk capacitor, avoids input power interference and current damaging levels, ensuring that the power supply can be safely turned on and off in the 2.9V to 33V range. The LTC4282 is located on the way to the circuit Board Power Entry with Accuracy of 0.7% 12-Bit or 16-Bit ADCs Report Board Voltage, Current, Power and Energy Consumption via an I2C / SMBus Digital Interface Internal EEPROM Provides Register Setup and Fault Logging Data with Non-Volatile Sexual Storage, which accelerates debugging and failure analysis during development and on-site operation.
The LTC4282 features a current limit circuit breaker with 2% accuracy to minimize overcurrent design, which is even more important at high power. In the event of overcurrent, the LTC4282 snapback current limit maintains for an adjustable timeout period Constant MOSFET power consumption. The circuit breaker opens the connection between the faulty module and the utility power bus after the timer expires. The idle module also disconnects the power bus to save power. A circuit breaker that can be configured digitally The threshold is allowed to be dynamically adjusted as the load changes, facilitating the selection of small resistance detection resistors The minimum and maximum values of the monitored electrical parameters are recorded and a warning signal is issued when the adjustable threshold is exceeded 8. In order to prevent Circuit boards cause catastrophic damage. These MOSFETs are continuously monitored to detect abnormalities such as low gate voltage and drain-to-source shorts or large voltage drops.
SOA shared path
Although the LTC4282 controls a single power supply, it provides two parallel current-limiting paths for load current.A large current board with a traditional single controller uses multiple MOSFETs in parallel to reduce the on-resistance, but all of these MOSFETs require Has a large safe operating area (SOA) to safely withstand over-current faults because it can not be assumed that shunted MOSFETs share current during current limiting In addition, the choice of MOSFET narrows at higher current levels and the price increases, And SOA levels can not keep up with the RDS (ON) drop. By separating the current into two precisely matched current-limit paths, the LTC4282 ensures that both MOSFETs will share the current even under overload conditions. For 100A applications , Each with a design current limit of 50A, reducing SOA requirements in half, broadening the choice of MOSFETs and reducing their cost is called a 'match' or 'parallel' configuration because the two The path is designed using similar MOSFETs and sense resistors.
In addition, the dual current paths of the LTC4282 are used to decouple the MOSFET SOA requirements from the on-resistance Large SOA is important for situations where there is significant stress in starting surges, current limits, input voltage steps, etc. When the MOSFET gate Low on-resistance reduces voltage drop and power loss during normal operation when switched on completely, but these are conflicting requirements as MOSFET SOA typically degrades as the on-resistance improves. The LTC4282 allows one Has a path that can handle stress MOSFETs and another path that has a low on resistance MOSFET This is referred to as a staged start-up configuration Generally, stress handling during startup, current limit, and input voltage steps The path is on while the RDS (ON) path remains off. The RDS (ON) path is turned on during normal operation to bypass the stress path, providing a low on-resistance path to the load current, reducing voltage drop and power Loss Depending on the size of MOSFET stress at start-up, there are two staged start configurations, low stress (Figure 4) and high stress. Current levels below 50A and parallel and low-stress staging configurations are recommended for applications up to 50 A. The lowest MOSFET cost is provided by a low-stress staging configuration compared to a single-path design, at the expense of transient conditions The ability to run uninterrupted is limited and can not be started with load current Parallel and high-stress staged configurations can initiate a load and provide longer time-out fault timers that operate over longer duration of overload conditions and inputs Voltage stepless operation without interruption.
in conclusion
In the past two decades, the number of electronic systems used in automobiles has been rapidly increasing driven by functions such as power steering, ABS brakes, convenience, driving safety, and entertainment, etc. As cars move toward full connectivity and full autonomy, The proliferation of electronic systems is also accelerating, increasing the need for precious battery power. Careful power monitoring coupled with the shutdown of idle systems are expected to increase battery efficiency. The LTC4282 circuit breaker relieves the need for circuit-level electrical data Measuring the power and energy consumption of each subsystem, thereby reducing the measurement burden on the overall vehicle power and energy consumption.The LTC4282 greatly facilitates the high current kilowatt-scale circuits with its novel dual-current path that can be configured in a variety of ways The board design allows for both large SOA and small on-resistance in the same design.