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TDA4VMXEVM: BUF_MCU_BOOTMODE4 signal design have risk that pull down can not be recognize as '0' for bootrom.

Tao Han
Expert 6415 points

Part Number: TDA4VMXEVM

Hi Experts:

Based on our latest E7 BUF_MCU_BOOTMODE4 at PROC078E7A(001)_SCH.pdf PAGE7. the signal combine two network. BOOT_EEPROM_WP and BUF_MCU_BOOTMODE4.

At main board schematic PROC079E3B(001)_SCH.pdf page 26. EVM board add fix 10K pull up resistor R311 at MCU_BOOTMODE4 pins.

When we select SW9 disable MCU_BOOTMODE04 pull up. R371 pull down 10K and R311 pull up 10K + R63 1K resistor will separate the 3.3V voltage to 1.72V. It have risk that ROM can not recognize 0 mode at BOOTMODE4 pins. I think maybe DNI R311 at reference design is better.

Please check the EVM board topology for this pins.

Best Regards!

Han Tao   

  • 0
    TI__Genius 17720 points

    Hi Han Tao,

    No issue with resistor divider network to worry about. BOOTMODE04 is actively buffered by U149, therefore the only divider network would be R311(10k) - R63(1k) during BOOTMODE04 = LOW, which is acceptable.

    I see other issue here. I think it was a bad decision to choose a BOOTMODE pin to be a WP output for EEPROM. We want EEPROM to be write-protected during resets (that's why is R311 for) , but at the same time WP can be overriden by BOOTMODE04 switch set to '0' by user (Write allowed to EEPROM).

    That is, the circuit we are discussing does the job. However, BOOT EEPROM will be unprotected from writes during resets if user selects BOTOMODE04=0. Even then, it is very unlikely a spurious write to happen and to corrupt the EEPROM for the short time it is unprotected, I think.

    Regards,

    Stan