What should I pay attention to when using the AM335x series chip?

The road developed by ARM is long and interesting. The well-known development advantages and the problems in the face of problems make people love and hate ARM. What kind of plot do you have with ARM?

At present, embedded ARM is widely used in industrial control systems, such as industrial process control, power system, petrochemical, CNC machine tools, etc. The development of ARM embedded systems has promoted the automation of industrial control.

The AM335x microprocessor is based on the ARM Cortex-A8 processor and is enhanced with image, graphics processing, peripherals, and industrial interface options such as EtherCAT and PROFIBUS. The 800MHz clocked Cortex-A8 core is far superior to ARM9, providing fast data processing and smooth interface switching.

Figure 1 AM335x functional block diagram

With its 6-way UART, 2-way CAN-Bus, 2-way USB OTG, support for 2 Ethernet interfaces, and other powerful communication functions, as well as industrial-grade performance guarantee, it has been widely used in portable navigation systems, industrial automation, and human-machine interfaces. And many other industries.

With the widespread use of the Cortex-A8 processor, the customer base is rapidly increasing, and the problems encountered by customers are also very strange. Today, we will understand how the inexplicable burnout of the Cortex-A8 processor with customers is going on.

In order to find out the cause and solve the problem, Zhiyuan R&D engineers made a lot of analysis on the burnt out module and found that the burnt out module is burned out in the power domain. What causes the power domain to burn out?

Will the R&D staff analyze whether the IO port of the module is over-pressurized or the current is drained, causing the IO port to burn out, which is serious and burns the CPU? With the direction of analysis, the next step is to review the data and confirm the experiment.

Figure 2 IO voltage range specified in the TI official website M335x data sheet

Figure 3 IO voltage range specified by the Freescale i.MX28 series chip

In order to further confirm the difference between the two, the R&D personnel conducted a comparative experiment on the module. After several tests, the IO withstand voltage of the Freescale ARM9 chip CPU is up to 5V, and TI's Cortex-A8 platform M335x series chip CPU IO The withstand voltage is only 3.6V! I believe this is also an important reason for the CPU burnout of the Cortex-A8 platform.

So what should we pay attention to when using the AM335x series of chips?

1, IO use precautions

When using GPIO as an input, ensure that the maximum voltage does not exceed 3.3V and the minimum voltage must not be lower than -0.2V. When GPIO is used as output, due to the limited driving capability of IO, the maximum output of single IO is 4mA, and the maximum IO is less than 50mA. It is recommended to add a triode or MOS tube when driving power devices such as LEDs, optocouplers and relays. It can also be designed as a sink current output mode when driving small power devices such as LEDs and optocouplers.

It is recommended to add a 100R current limiting resistor when using Cortex-A8 IO, especially the reserved GPIO.

2, power supply design considerations

After the 3.3V power supply of the core board is powered on, the 3.3V power supply output of the backplane is enabled. When the core board is powered down, the 3.3V of the backplane affects the power-on timing of the core board, causing the core board to fail to start or be damaged.

Figure 4 CPU power-on timing description

It is recommended that the backplane power supply 3.3V use a power supply with an enable terminal, connect the enable terminal to the PWR_OK of the core board (PWR_OK is connected to the core board 3.3V power supply) or use GPIO for enable control. A pull-down resistor should be added to disable the power supply and prevent the system from malfunctioning due to the IO port status being undefined during power-on.

3, start settings precautions

EMU0 ~ EMU4 are the startup configuration pins and can be used as normal GPIOs. However, when power-on, these two pins should be in a floating or high-impedance state. The wrong configuration will cause the system to fail to start. Therefore, it is recommended not to use as an input pin during design.

Ld_data[0..15] of the M335x and A335x core boards is the boot option selection pin of the AM335x processor. If these pins are not used as the lcd data line, it should be noted that the state at power-on cannot affect the startup of the processor. It can only be used as an output pin.

The GPMC_D[7..0] data bus has been used internally by NAND Flash. When the external GPMC bus is used, the GPMC communication protocol must be strictly observed to prevent system startup.

These three points are the places that are easy to make mistakes in the system application. Here we will introduce them to you, and hope to provide reference for everyone in the future design.

ZLG Zhiyuan Electronics has been committed to the research of various technologies in the fields of high-end measurement and analysis instruments, embedded industrial control and Internet of Things, and has been working hard to provide you with good products and high-quality technical services.

Figure 5 ZLG Zhiyuan Electronic Industry Internet Intelligent Control Solution