Automotive MCU Low Power Solution

With the development of the automobile industry, the number of electronic control systems on automobiles has increased exponentially. The on-board electronic control system with ECU as the core has gradually replaced passive devices and mechanical systems, and also completed most of the measurement, drive and control functions.

Due to the increase in new on-board electronic control systems in vehicle applications, the power load is increasing at a rate of about 100W per year. The biggest challenge currently faced is to find new ways to ensure the continuous increase in the number and functions of automotive electronic devices under the same battery power conditions. Therefore, in practical applications, the power consumption of MCUs needs to be continuously reduced.

In addition, the maximum power consumption of digital circuits is closely related to reliability issues, such as device aging caused by electromigration and hot carriers. Thermal stress caused by chip heat dissipation is also one of the main issues related to reliability. Therefore, reducing power consumption is also crucial to improving chip reliability.

In order to meet the growing demand for low power consumption, Freescale's Qorivva series of 32-bit MCUs adopts a special design to reduce overall power consumption. In addition to improved device characteristics and smaller process size, circuit-level and system-level measures also greatly reduce power consumption.

Freescale's Qorivva series MCUs based on the 32-bit Power Architecture are designed specifically for embedded automotive applications. This series of MCUs uses a variety of low-power designs to reduce dynamic and static power consumption, including:

• Multiple working modes

• Gated power supply

• Clock gating

Multiple working modes

Figure 1 shows the different operating modes of the Freescale Qorivva MPC560xB series.

 

 

Figure 1 Qorivva MPC560xB working mode

The Qorivva MPC560xB series MCUs include three low-power modes: HALT, STOP, and STANDBY. Users can combine different working modes according to actual conditions.

In HALT mode, system activity is reduced, the core clock is turned off, and modules such as the phase-locked loop, flash memory, and analog-to-digital converter can be turned off to reduce power consumption. This mode can be used for LIN low-speed transmission and reception.

Compared with HALT mode, STOP mode can further reduce the power consumption of MCU by configuring to shut down most peripherals. This mode retains the power supply of the entire MCU, so it has a shorter recovery time than STANDBY mode. STOP mode can be configured to shut down all clock sources and retain the current state. In this mode, the phase-locked loop is always in the off state. When exiting STOP mode, the system will use the high-speed internal clock until the specified clock is stable.

In STANDBY mode, the core is stopped, the flash memory and most peripherals are turned off, and most of the chip power is cut off, thereby achieving the minimum possible power consumption. At this time, the MCU can be awakened by an external pin, reset, or a periodic wake-up source using a low-power clock.

Table 1 lists the power consumption of Qorivva MPC5602B in different operating modes at room temperature:

Table 1 Current of Qorivva MPC5602B in different modes

Mode Clock Current

RUN(RAM)64MHz57mA

RUN(FLASH)64MHz66mA

HALT128KHz IRC8mA

STOP128KHz IRC228 μA

STANDBY(32KB)128KHz IRC30 μA

STANDBY(8KB)128KHz IRC20μA

Gated Power

The Qorivva MCU is divided into three different power domains, and different peripherals belong to different power domains. The power control unit allows the user to power on or off a power domain in different modes. When switching modes, the finite state machine is responsible for turning on or off the power supply of each power domain according to the user's configuration to ensure that the state switching is smooth and safe. For example: entering the STANDBY mode will cut off the power supply of the core, most peripherals, clock and other modules, thereby saving the most power consumption.

 

 

Figure 2 Qorivva MPC560xB gated power supply

Gated Clock

The power consumption of MCU is directly related to the working clock, which means that more gate flips per unit time will bring greater power consumption. Qorivva MPC560xB series MCU adopts a variety of methods to reduce the dynamic power consumption caused by gate flips. Including: 1. Stop the core clock. In low power mode, disconnecting the core clock can effectively reduce the power consumption of the core. 2. Peripheral clock division. For some peripherals that do not need to run at high speed, the peripheral clock can be reduced to reduce dynamic power consumption. 3. Disconnecting some peripheral clocks that are not used can effectively reduce the dynamic power consumption caused by the peripherals.

 

 

Figure 3 Qorivva MPC560xB gated clock

A typical low-power application based on Qorivva MPC5602B MCU

 

 

Figure 4 Qorivva MPC5602B low power application

As shown in Figure 4, a typical low-power application of Qorivva MPC5602B is shown. In the first stage, the MCU is in STANDBY mode for 16ms, and its current consumption is only 30 μA. At this time, it is automatically awakened by the internal timer. After waking up, the MCU is in RUN mode for 71μs in the second stage. At this time, a 2MHz system clock is used and the current consumption is less than 8mA. In the third stage, the MCU is in STOP mode for 64μs, and the RTC is set to wake up after 64μs. At this time, the current consumption is less than 300 μA. After waking up, the fourth stage returns to RUN mode in 57μs. The average current consumption of the MCU in these four stages is only 94 μA. It can be seen that intermittently putting the MCU in low-power mode under certain conditions can significantly reduce system power consumption.

Summarize:

In addition to using devices with better features and more advanced process sizes, Freescale's Qorivva series MCUs also provide low-power solutions at the application layer. Users can reduce system power consumption and meet low-power challenges by combining different working modes.