How To Make Infotainment Equipment Not Reset When Using Car Start-stop System?

The start-stop system shuts down the engine when it stops, instead of idling, and then quickly restarts the engine when it needs to travel. If you need to stop and go during driving, you can reduce emissions and save fuel by avoiding engine idle for a long time.

For example, if you stop when you encounter a red light or train passing, the engine should not run; if the engine is not running, no energy will be wasted. Compared to cars that are not equipped with such systems, the fuel consumption of urban traffic is reduced by up to 8%.

Driving comfort and safety are not affected by the automatic start and stop function, as this function is only activated when the engine reaches the desired operating temperature. If the air conditioner has not yet brought the cabin to the desired temperature, the battery is not fully charged, or the driver is still turning the steering wheel, this function will not be activated.

The automatic start-stop function is coordinated by a central control unit that monitors data from all relevant sensors, including the starter motor and alternator. If comfort or safety is needed, the control unit will automatically restart the engine – for example, if the wheels start to roll, the battery level drops too low, or condensation on the windshield. In addition, most systems recognize the difference between temporary parking and the end of the trip. If the driver's seat belt is unlocked, or the door or trunk is open, the system will not restart the engine. If necessary, the automatic start and stop function can be completely disabled by pressing the button (at least for now).

However, when the engine is restarted, the 12 V battery may have dropped below 5 V, which may cause these systems to reset when the infotainment system is turned on or other electronic devices require voltages above 5 V. Some navigation and infotainment systems operate with input voltages of 5 V or higher. When the input voltage drops below 5 V during engine restart, these systems will reset if the DC-DC converter only has an input voltage buck function. Obviously, the reset of the music player or navigation system is unacceptable when the car is restarted in the start and stop state.

Solution:

Analog Devices Introduces Triple Output DC-DC Controllers Power by Linear LTC7815 This device integrates a boost controller and two buck controllers in a single package. The high-efficiency synchronous boost converter feeds two downstream synchronous converters to avoid output voltage differentials when the vehicle's battery voltage drops, which is a very useful feature in automotive start-stop systems. In addition, when the input voltage of the car battery is higher than its programmed boost output voltage, the boost controller operates at 100% duty cycle, passing the input voltage directly to the buck converter, minimizing power consumption. .

Figure 1 shows the schematic of the LTC7815's boost converter providing a 10V supply to the buck converter. In addition to powering the two buck converters (5 V/7 A and 3.3 V/10 A, respectively), the boost converter can also be used as a third output to provide an additional 2 A. The circuit maintains a 2.1 MHz operating frequency up to 28V VIN and operates at skip times above 28 V.

Figure 1. Schematic of the LTC7815 start-stop application with an operating frequency of 2.1 MHz.

The LTC7815 can operate from an input voltage of 4.5V to 38V during startup and remains operational after startup until the input voltage is as low as 2.5V. The synchronous boost converter can generate an output voltage of up to 60 V. When the input voltage is high enough, it allows the synchronous switch to be fully turned on to pass the input voltage for maximum efficiency. Two buck converters produce an output voltage from 0.8V to 24V, and the entire system can achieve efficiencies as high as 95%. The shortest on-time as low as 45 ns enables high step-down ratio conversion in 2 MHz switching operation, avoiding noise-sensitive critical bands such as AM radios, and using smaller external components.

The LTC7815 can be configured for Burst Mode® operation, reducing quiescent current to 28μA per channel (38μA when all three channels are turned on) while regulating the output voltage under no-load conditions, a feature that saves on continuous conduction systems. Battery runtime is useful. The powerful 1.1Ω built-in full N-channel MOSFET gate driver minimizes switching losses and provides an output current of more than 10A per channel, limited only by external components. In addition, the output current of each converter is sensed by monitoring the voltage drop across the inductor (DCR) or using a separate current-sense resistor. The LTC7815's constant frequency current mode architecture provides selectable frequencies from 320kHz to 2.25MHz or can be synchronized to the same range of external clocks.

Extend battery run time

Any battery-powered system must save battery power if it is required to always have a power-on bus when other parts of the system are turned off. This state is often referred to as sleep, standby, or idle mode and requires the system to have very low quiescent current. Low quiescent current to save battery energy is especially important for automotive applications, which may include multiple electrical circuits such as telematics, CD/DVD players, remote keyless entry, and multiple always-on bus circuits. The total current consumption of these systems in standby mode is as low as possible, and as automotive operations become more dependent on electronic systems, the pressure to conserve battery power continues to increase.

In sleep mode, the LTC7815 consumes only 28 μA when the boost converter and one of the buck converters are turned on. When all three channels are in sleep mode, the LTC7815 consumes only 20 μA, which significantly increases battery run time in idle mode. This is accomplished by configuring the LTC7815 in an efficient Burst mode that provides a short burst of current to the output capacitor and then enters a sleep period during which the output power is only delivered to the load through the output capacitor. Figure 2 is a conceptual timing diagram of this mode of operation.

Figure 2. Burst mode operating voltage diagram for the LTC7815

In sleep mode, most of the internal circuitry is turned off except for the critical circuitry required for fast response. When the output voltage drops enough to activate the sleep signal, the controller resumes normal Burst mode operation by turning on the external MOSFET at the top. Or, in some cases, the user wishes to operate in a forced continuous or constant frequency pulse skip mode at light load currents. Both modes are easy to configure and have a higher quiescent current.

Efficiency / solution size

The 5 V output efficiency shown in the schematic of Figure 1 is approximately 90% (as shown in Figure 3). If the operating frequency is reduced from 2.1 MHz to 300 kHz, the efficiency can be increased by 3% to 4%.

Figure 3. Efficiency and load current of the LTC7815 in different converter sections

Figure 4 shows the LTC7815 demo board (shown in Figure 1) with a widest part of 48 mm

Figure 4. Size and layout of the top and bottom layers of the LTC7815 demo board

Protection characteristics

The LTC7815 can be configured to sense the output current by using a DCR (inductor impedance) or current-sense resistor. The choice between the two current sensing schemes is primarily a trade-off between cost, power consumption, and accuracy. DCR detection is becoming increasingly popular because it eliminates expensive current sense resistors and is more power efficient, especially in high current applications. The current-sense resistor is a more accurate method of current detection.

The on-chip comparator monitors the buck output voltage and issues an overvoltage condition signal when the output is greater than 10% of the nominal value. When this is detected, the top MOSFET turns off and the bottom MOSFET turns on until the overvoltage condition is cleared. As long as the overvoltage condition continues, the bottom MOSFET is continuously turned on. If the output voltage returns to a safe level, normal operation resumes automatically.

The overtemperature shutdown circuit turns off the LTC7815 when the temperature is high or internal power dissipation causes excessive self-heating on-chip. When the junction temperature exceeds approximately 170°C, the overtemperature circuit disables the on-chip bias LDO, which reduces the bias supply to 0 V and effectively shuts down the entire LTC7815 in sequence. Once the junction temperature drops back to approximately 155 ° C, the LDO is turned back on.

In conclusion

The car start-stop system saves fuel and continues to evolve over the next few years. Care must be taken to power onboard infotainment systems and navigation systems that require voltages of up to 5 V or even more than 5 V. When the engine is restarted, these systems may reset if the car battery voltage drops below 5 V. The LTC7815 solves this problem by raising the battery voltage to a safe operating level. This feature, combined with two step-down controllers, is ideal for powering many automotive electronics in cars with start-stop systems.