Principle of charging a car using a wideband VIN integrated buck and LDO

In recent years, automotive electronics have become increasingly important in automotive system design. You may also often hear that cars have more and more convenient functions, more advanced infotainment, driver assistance systems, and great progress in the field of driverless cars. To promote innovation in automotive systems, the size of each new device must be optimized to meet increasingly stringent design requirements. But what does this mean for the power tree that powers various devices?

In this article, I’ll explore how innovation is changing the automotive electronics market and how TI is helping solve a common design problem in this space by integrating a buck converter and LDO.

Most electronic control units (ECUs) require at least two regulated rails to efficiently power the system components. Although two rails are required, the current requirements of these two rails are very different.

Take, for example, an LED ceiling light with haptic feedback. The power supply system for this device requires a 5V rail to power both the LED driver and the haptic driver that controls the deflection mass motor (ERM). Both the LED and haptic driver are current intensive devices, requiring approximately 2A of current. A buck converter is the best choice to provide this current, as it can achieve efficient current conversion to ensure that the system does not heat up under this load. The core component of the automotive ECU is a microcontroller (MCU) that operates at 3.3V but requires only 150mA of current. When the car is turned off, although the MCU can switch to standby power saving mode, it cannot be completely shut down because it also handles communication and wake-up functions.

For these applications, you can choose to use a low dropout regulator (LDO). As the most cost-effective electronic component, LDO can provide a low current and a clean power rail for the noise-sensitive microprocessor. But in standby mode, the LDO will be directly connected to the car battery, which will cause a significant voltage drop. Since LDO is not the most efficient way to power the microcontroller, can you suggest some optimization solutions for the total power consumption?

With the TPS65320C-Q1, you can power your system in this way directly from a battery. It accepts input voltages from 3.6V to 36V and has two output rails: a 3.2A buck converter that can achieve frequency conversion from 100kHz to 2.5kHz with 10% conversion accuracy; and a 289mA LDO. Both rails are integrated into a small 14-pin thin small outline package (HTSSOP).

For example, in the case of an LED ceiling light in a car, you can use a buck converter to power the 5V rail and an LDO to power the 3.3V rail, as shown in Figure 1. Integrating the two rails into a small chip not only saves space, but also adds a function that improves system power efficiency: LDO automatic power. When the buck converter starts working, the switching regulator will switch the output power to the LDO, which can minimize voltage drop, power loss and heat dissipation.

Figure 1: Working module diagram of the car interior ceiling light in working state

When the buck converter is not in operation, the LDO will still be in operation and automatically switch to the battery voltage to keep the MCU working while the rest of the system is shut down. The principle is to obtain a typical quiescent current of less than 35µA from the LDO, as shown in Figure 2:

Figure 2: The working module of the car interior ceiling light in standby mode

You can see similar use cases in almost all in-vehicle devices, including infotainment, advanced driver assistance systems (ADAS), instrument clusters, and body electronics systems.

Do you have the exact opposite requirement: 100mA on a 5V rail, but 2A on a 3.3V rail? Stay tuned for the next part of this article, where I’ll discuss how wide VIN integrated buck converters and LDOs can power your automotive systems.