Spread Spectrum on AM62

Hello!

I am working on a product for which low EMI is paramount. I read the documentation for the PMIC used on the Verdin AM62-based modules, the TI TPS65219, and it mentions setting the BUCK_SS_ENABLE and BUCK_FF_ENABLE bits in order to enable spread spectrum operation of the buck converters.

Are these bits set by default in the U-Boot/Linux images released by Toradex? If not, how do we go about enabling spread spectrum operation?

Thank you for your time and consideration of my questions!

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Hello!

For the Verdin AM62-based modules, the spread spectrum settings for the buck converters, controlled by the BUCK_SS_ENABLE and BUCK_FF_ENABLE bits in the PMIC (TI TPS65219), are not enabled by default in the U-Boot or Linux images provided by Toradex. Enabling spread spectrum operation can help reduce electromagnetic interference (EMI), which is crucial for applications where low EMI is a priority.

To enable spread spectrum operation on the buck converters, you will need to modify the device tree used by U-Boot and/or the Linux kernel. This involves setting the appropriate bits in the PMIC registers. Here’s a general approach to achieve this:

  1. Identify the PMIC Device Tree Node: First, locate the device tree node for the TPS65219 PMIC in your device tree source files. This node will be part of the I2C bus it’s connected to.

  2. Modify the Device Tree: Within this PMIC node, you’ll need to add or modify the register settings to enable the BUCK_SS_ENABLE and BUCK_FF_ENABLE bits. This might involve adding a reg property that targets the specific register addresses controlling these bits and setting them accordingly.

  3. Recompile the Device Tree: After making the necessary modifications, recompile the device tree blob (DTB) using the appropriate toolchain for your project.

  4. Deploy the Modified Device Tree: Replace the existing device tree blob on your device with the newly compiled version that includes the modifications for spread spectrum operation.

  5. Testing and Verification: Once the device boots with the modified device tree, verify that the spread spectrum settings are applied correctly. This might involve reading back the PMIC register settings under Linux or using oscilloscope measurements to observe the changes in the power supply noise spectrum.

Please note, the exact register addresses and bit settings depend on the PMIC’s datasheet and might require consulting the TI TPS65219 documentation for precise details.

Remember, while adjusting PMIC settings can help reduce EMI, it’s also important to consider other factors such as PCB layout, component placement, and shielding in your overall EMI reduction strategy.

Best regards,
Toradex AI Assistant

Please, also check if these links can help you solve your problem:

SPI (Linux) | Toradex Developer Center.

The BUCK_SS_ENABLE and BUCK_FF_ENABLE bits are set to 0 by default. They are preprogrammed into the PMIC’s internal EEPROM during manufacturing. Technically, you can change them, but the TPS65219 datasheet has a warning:


Modifying the BUCK_SS_ENABLE and BUCK_FF_ENABLE bits may cause module damage and is not recommended.

Hi @MBKEA ,

Have you conducted any EMI measurements? According to our hardware team, enabling Spread Spectrum mode on the PMIC may require hardware changes on the module. Therefore, we would like to avoid it if possible.