“Automotive infotainment systems contain a complex combination of Electronic components such as consumer electronics: high-performance microcontrollers, memory, interface and driver ICs. Power supply design is equally complex, as each component may require various low-voltage power rails with wide-ranging power requirements. Such complexity is not limited to infotainment systems. Vehicle performance, fuel efficiency, and driver ease of control all require more advanced electronic systems.
The integration of technology into every aspect of our lives has led to a common connected, media-driven lifestyle, and new lifestyles are driving further advances in technology, including today’s highly integrated automotive infotainment systems.
Automotive infotainment systems contain a complex combination of electronic components such as consumer electronics: high-performance microcontrollers, memory, interface and driver ICs. Power supply design is equally complex, as each component may require various low-voltage power rails with wide-ranging power requirements. Such complexity is not limited to infotainment systems. Vehicle performance, fuel efficiency, and driver ease of control all require more advanced electronic systems. Power systems also need to face both sensitive electronic systems and harsh automotive operating conditions: wide voltage ranges and predictable transient battery environments. A well-designed power system must both power and protect electronic systems, even when features such as start-stop technology make the automotive environment unsuitable for use by manufacturers.
Start-stop technology exacerbates the extreme conditions that electronic systems have to face, especially when the engine is cranked repeatedly. Cars with start-stop technology repeatedly restart the engine, each time causing the battery power to experience a cold start, and even then critical systems must remain functional.In another case, such as the sound of car music
Sudden stops and the driver turns into a cappella a cappella is an experience that, while not disastrous, doesn’t lead to positive reviews either.
On the other hand, ultra-low quiescent current is a key requirement for automotive power systems. A car may be left idle for a month or more, and while some critical electronic systems are always on and running quietly, it must be guaranteed not to drain the battery.
The LTC3372 all-in-one high-voltage controller can withstand extreme voltage changes brought about by the automotive battery environment and maintain regulation. Thanks to its ultra-low quiescent current, it keeps always-on components running without draining the battery. The LTC3372 features four configurable monolithic voltage regulators that provide up to five output channels for infotainment or other electronic systems.
Automotive multi-channel power supply
The LTC3372 significantly reduces the number of components required to create multiple power rails. It combines proven high-voltage automotive controller technology with four configurable monolithic buck regulators to create a space- and cost-saving automotive multi-channel power supply solution.
The high-voltage buck controller input can withstand input surges up to 60V (such as seen during load dump), and can also operate from input voltages as low as 4.5V in a standard buck configuration, using Input voltage as low as 3V in SEPIC configuration. This input operating range provides uninterrupted power for sensitive electronic systems when exposed to significant transients. The LTC3372’s four low-voltage step-down regulators can be individually configured in a combination of eight 1A power stages. The power requirements of each regulator are met by combining power stages, with 8 possible unique 4-output channel configurations, all directly from the car battery supply.
One advantage of a monolithic IC multi-channel power solution is the sharing of internal reference and bias supplies. This bias sharing results in lower per-channel IQ values for multi-channel power supplies compared to separate multiple ICs. For an always-on single-channel supply, the VIN reference bias IQ is a typical value of 23µA and a maximum value of 46µA (at 150µC). When all five channels are regulated in Burst Mode™ of operation, the typical bias current is only 60µA in total, or 12µA per channel. Since the total bias IQ of the LTC3372’s 5 channels is comparable to a single channel using older technology, new always-on automotive applications are supported.
Single-Chip Controller and Voltage Regulator
The LTC3372 includes a front-end 60 V high-voltage (HV) buck controller and four low-voltage (LV) 5 V monolithic step-down regulators that support low-IQ burst mode operation. By integrating the controller and monolithic regulator, the LTC3372 can provide up to five independent power rails from high input voltages at low cost and in a compact size. The output voltage of the high-voltage controller can be selected to be 3.3 V or 5 V, depending on the level of the VOUTPRG pin; the output voltage of the low-voltage regulator is individually configurable through the FB1 to FB4 pins using external resistors.
Figure 1. Typical application of the LTC3372 60 V input. The high voltage controller feeds four 2A, 1 V/1.2 V/1.8 V/2.5 V low voltage regulators. 3.3 V/5 V high voltage controller output can be used as an additional 3 A current rail
Figures 1 and 2 show the efficiency of a high voltage controller in a typical application. While high voltage controllers are typically used to feed low voltage regulators, each regulator can operate independently through the enable and input pins of each channel. Eight power stages provide more flexibility. Eight switches can be distributed among the low-voltage regulators, digitally configured via the C bits (C1, C2, C3) in combination to meet the large current limits of a particular supply rail. Table 1 shows the C-bit settings and high output current limit configuration for each regulator number. Figure 3 shows how the efficiency varies with the number of parallel switches.
Figure 2. Burst-mode operating efficiency versus high-voltage controller output current in Figure 1.High output current up to 10 A, enough to feed 4 fully loaded low voltage regulators and a 3 A, 3.3 V/5 V load
Figure 3. Burst-mode operating efficiency versus low-voltage regulator output current. 1 A, 2 A, 3 A, and 4 A buck regulators represent configurations with 1, 2, 3, and 4 switches connected in parallel, respectively
Table 1. Low-Voltage Regulator Configuration Set by C1, C2, and C3 Code; With Any Configuration With Less Than 4 LV Regulators, Unused Regulator Enable and Feedback Pins Are Connected to land
The LTC3372 also provides on-chip temperature sensor and watchdog timer functions. The temperature sensor allows the user to closely monitor the die temperature when the LV regulator is enabled. The watchdog timer issues a reset signal if the microprocessor fails to clear the timer in the event of a fault.
Typically, we evaluate DC/DC converters in terms of efficiency, so designing to maximize their efficiency, but optimizing DC/DC converters in terms of power consumption (not just efficiency) is often achieved in high-power applications Higher performance returns. For multi-level converter systems such as those built with the LTC3372), efficiency measurements can be misleading when part of the efficiency comes from the combined action of the high voltage controller and low voltage regulator.
Remember, power optimization is not simply about keeping the total power consumption very low, it is about balancing the loss distribution among the devices. A good approach is to start with low voltage regulators, since most of the losses in the LTC3372 system are the total power dissipation from all low voltage regulators. By considering all applicable low-voltage regulator configurations, designers can compare a large number of power consumption options. Table 2 lists all applicable configurations and corresponding power consumption in 1.2 V, 1.8 V, 2.5 V applications and at 3 A, 3 A, 0.5 A heavy loads. The difference in power consumption between the very good and the bad configuration is 0.432 W. Under normal circumstances, recursively assigning the most likely switches to very high power channels produces good results.
Table 2. 1.2 V (3 A), 1.8 V (3 A), 2.5 V (0.5 A) Low Voltage Regulators Total Power Consumption in Burst Mode Operation in Various Configurations; VINACH is 3.3 V and switching frequency is 2 MHz; good configuration produces 0.332W less power consumption than poor configuration
The high-voltage controller can employ a more general efficiency optimization procedure. A slight difference is that the full/partial load of the high voltage controller becomes the input current of the low voltage regulator. When the low voltage regulator is its only load, even if each low voltage regulator is fully loaded, it is only a moderate load to the high voltage controller. The designer should focus on the target range of operating current, rather than blindly selecting low RDS FETs or pursuing high peak efficiency. Efficiency versus output current curves for 3 FETs with different RDS are shown in Figure 4. For the low-voltage regulators in Table 2, using FETs with high RDS but low QG yields high efficiencies below very large loads (3.759 A in a good configuration).
Figure 4. Burst-mode operating efficiency versus output current with 3 different FETs in a high-voltage controller. The same FETs are used for the high side and the low side. The graph is zoomed in for the 1 A to 6 A portion of the curve to clearly see the intersection, which determines the best FET for the low voltage regulators in Table 2. 3.759 A is a large load current for the low voltage regulator at full load. It turns out that a good choice is a FET with high RDS but low QG (BSZ099N06LS5)
Cold cranking has always been a challenge for DC/DC converters in automotive applications. If the output voltage is higher than the input voltage during cold cranking, the buck converter is forced to operate in dropout. Using the resources available in the LTC3372’s high-voltage controller, two front-end topologies (ie, boost and SEPIC) can be implemented to avoid operating in dropout conditions.
Even if the boost is simpler, it will pass any high voltage input surge to the next buck stage. This prevents high-efficiency, low-voltage buck regulators from being used as secondary buck stages. In Figure 5, we configure the LTC3372 high-voltage controller in an asynchronous SEPIC topology. The SEPIC converter generates a 5V intermediate supply rail to power two 3.3V/4A low voltage regulators, enabling continuous operation of the high voltage controller.
Figure 5. A non-synchronous high voltage SEPIC converter from 4.5V to 50V input feeds two 3.3V/4A low voltage regulators. After startup, when the two low-voltage regulators are fully loaded, the SEPIC converter can keep VOUT at 5V and VIN as small as 3V. A small value of VIN can be reduced to 1.5V if the load on the SEPIC is reduced. When VIN is below 5V, the output of the SEPIC must be set to 5V to maintain continuous operation. DIN and a 1µF capacitor need to be connected to IC VIN to prevent reverse current flow and transient spikes. A differential current sense scheme and low inductance sense resistor are recommended to provide a clean signal at the current comparator input. Low inductance (LHV1 and LHV2), large switching frequency, and low bandwidth are the result of a trade-off between right half-plane zero and current ripple.
When the two 4A low voltage regulators are fully loaded, the current output from the SEPIC is greater than 5A. Since the switch current is the sum of the two Inductor winding currents, the peak current through the sense resistor can easily exceed 10A. Considering that the sense resistor is inside the hot loop, it takes some effort to produce a clean waveform at the input of the current comparator. One solution is to use the differential filtering scheme shown in the SEPIC schematic and use a low-inductance resistor fabricated in reverse packaging.
Figure 6 and Figure 5 show the relationship between the burst mode working efficiency and the output current of the asynchronous SEPIC controller.High output current up to 6A, enough to feed two fully loaded 3.3V/4A low voltage regulators
Figure 6 shows the SEPIC efficiency during burst mode operation, and Figure 7 shows the SEPIC output voltage when a transient voltage of 12V to 3V is applied to the input. Designers should also not ignore the heat generated by circulating diodes during PCB design. Thermal constraints can be met by reserving extra space for relatively large diodes and using thicker copper pours. Another diode and filter capacitor are connected to the VIN pin to avoid reverse current and sudden voltage spikes due to input transients.
Figure 7. The SEPIC’s output response to input transients is similar to that of a cold crank condition. The input drops from 12V to 3V in 2ms and stays at 3V for 1 second before returning to 12V. Greater ripple is observed during 3V transients, caused by the higher peak current flowing through the loop diode to the output capacitor. This is the waveform with two fully loaded 3.3V/4A low voltage regulators at 500kHz SEPIC switching frequency.
The LTC3372 provides a single-chip solution for high voltage multichannel buck converters. Its low IQ operation and low cost per channel make it ideal for always-on systems in automotive applications.