Fan

The phyCORE-AM62Ax development kit provides fan connectivity via a 4-pin Hirose connector at X16 (VCC_5V0_SW rail). The fan is intended to be mounted directly to the processor heat sink for thermal management. The regulated 5V output is enabled by driving a GPIO0 low (0), turning the fan on. When the GPIO0 is pulled high (1), the 5V supplied to the fan connector will be turned off. This guide will demonstrate how to test your connections to the header x16. To learn more information about the phyCORE-AM62Ax thermal management and fan utilization, please see section 4.9 in the Hardware Manual .

Requirements

The phyCORE-AM62Ax development kit does not include a heat sink and fan. The below are the two fans that were tested on the PHYTEC hardware:

Item	Description	Link
Heat Sink	(29mmx29mmx9.5mm)	Digikey link (heat sink)
Fan	DC axial fan, 30mm square x 10mm	Digikey link (fan)
Female Connector	PCB 1576.2 version 4xpin keyed header	Digikey link (female connector for 1576.2)
Crimping Terminals	4x crimping jackets	Mouser link

Recommended Header Configuration

Pin	Signal	Wire Color
1	VCC_5V0_SW	Red
2	GND	Black
3	FAN_FG	Yellow
4	PWM	Blue

Hardware Setup

• Connect fan to the 4-pin Hirose connector located at X16.

Enabling the Overlay

• Power on the development kit and stop in U-boot.

• Load the device tree overlay required for exporting the GPIO signal that controls the fan and then boot the board.

  Target (U-boot)

  setenv overlays k3-am62-phyboard-lyra-gpio-fan.dtbo
  boot
  

Note

For more information about overlays see chapter Configuring the Bootloader.

• Verify that the “gpio-fan” was exported properly to gpio-460.

  Target (Linux)

  cat /sys/kernel/debug/gpio
  

  Expected Output

  root@phyboard-lyra-am62axx-2:~# cat /sys/kernel/debug/gpio
  gpiochip2: GPIOs 360-367, parent: i2c/1-0021, pcf8574, can sleep:
  gpio-360 (GPIO0_HDMI_RST      |reset               ) out hi ACTIVE LOW
  gpio-361 (GPIO1_CAN0_nEN      |standby             ) out lo
  gpio-362 (GPIO2_LED2          |led-2               ) out lo
  gpio-363 (GPIO3_LVDS_GPIO     )
  gpio-364 (GPIO4_BUT2          |menu                ) in  lo IRQ
  gpio-365 (GPIO5_LVDS_BKLT_EN  )
  gpio-366 (GPIO6_ETH1_USER_RESE)
  gpio-367 (GPIO7_AUDIO_USER_RES)
  
  gpiochip1: GPIOs 368-419, parent: platform/601000.gpio, 601000.gpio:
  gpio-391 (                    |home                ) in  lo
  
  gpiochip0: GPIOs 420-511, parent: platform/600000.gpio, 600000.gpio:
  gpio-433 (                    |green:heartbeat     ) out lo
  gpio-452 (                    |led-1               ) out lo
  gpio-460 (                    |gpio-fan            ) out lo ACTIVE LOW
  

Toggling the Fan

• Turn the fan ON.

  Target (Linux)

  echo 1 > /sys/class/thermal/cooling_device0/cur_state
  

Note

Run the command above 3-4 times to have the fan stay ON consistently.

• Turn the fan OFF.

  Target (Linux)

  echo 0 > /sys/class/thermal/cooling_device0/cur_state
  

Enabling a proper Thermal Governor

If your application includes a GPIO-based fan, PHYTEC recommends enabling the bang-bang thermal governor as the default setting. This governor uses hysteresis to manage fan state transitions, preventing abrupt on/off cycling and enabling smoother control for fans that only support binary on/off operation, rather than variable speed throttling.

Update the current thermal governor strategy to bang-bang using the command below:

Target (Linux)

echo bang_bang > /sys/class/thermal/thermal_zone0/policy

Note

To enable the bang-bang thermal governor by default, recompile the kernel with CONFIG_THERMAL_DEFAULT_GOV_BANG_BANG=y in the menuconfig configuration. For further details, please refer to the guide: Modify The BSP.