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Linux/TMDXEVM3358: GPIO voltage

user6010090
Prodigy 20 points

Part Number: TMDXEVM3358
Other Parts Discussed in Thread: AM3358,

Tool/software: Linux

Hello,

I need to design a core module use AM3358 processor, I decided to revise and simplify it by referring to the schematic diagram of TMDXEVM3358.

But now, one problem I encountered was that my GPIO voltage should be 1.8V, but the reference design is 3.3V. After consulting the datasheet of TPS65910A31, I realized that the output voltage of a LDO can be controlled by modifying the value of the register. This could solve my problem, but then I encountered a new problem. According to the datasheet, I understand that I need to modify the value of registers through the I2C interface to control the output voltage. But when I can operate the I2C interface, the processor should have actually completed the power-on and initialization. 3.3V is the default output voltage of LDO used by VDDSHVx. This also means that the voltage of GPIO exceeds the allowable range of my design, which may damage peripheral devices.

So I want to know when I should operate the registers of the PMIC to modify this parameter (I found the PMIC-related code in uboot, but I think it's too late to modify the voltage in uboot)? Can you tell me where to modify or insert codes? And do I need to change my hardware design?

Thank you for your help!

  • 0
    TI__Guru**** 393215 points

    Hi,

    These are entirely hardware connections, you should not try to modify the PMIC voltages. You simply need to tie the relevant VDDSHVx power rails to 1.8V. You should also note that multiple I/O cells are powered from a common VDDSHVx voltage rail. This means that all I/O cells that are powered from the same VDDSHVx will work at the same voltage level - either 1.8V or 3.3V. You will find corresponding VDDSHVx for each I/O cell in Table 4-2 from the AM335x Datasheet Rev. K.

  • 0 in reply to Biser Gatchev-XID
    Prodigy 20 points

    Hello, thank you very much for your patience. If VDDSHVx is connected directly to 1.8V, will it lead to an excess of the maximum current allowed? Because after reading the PMIC datasheet, I understand that each LDO output is allowed to have a maximum current limit (e.g. 300 mA). If I connect the VDDSHVx directly to the existing 1.8V output, the original 3.3V output is no load now, but the original 1.8V output needs to withstand more current. Will this cause a problem?

    Best Regards

    Harris

  • 0 in reply to user6010090
    TI__Guru**** 393215 points

    You must sum expected current on each GPIO on the same VDDSHVx, and also confirm that total current does not exceed the VDDSHVx max. rating (Table 5-10 in the datasheet).