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RM44L920: Safety Power Circuit

Yun Hoseong
Prodigy 100 points
Part Number: RM44L920


Hi, I'm Hoseong Yun from RSautomation.

I have a question about core voltage and IO voltage.

Our circuit use regulator for 5V to 1.2V, 3.3V.

On circuit, there is just 5V UV/OV detection IC.

I found "Voltage Monitor reset" on technical reference.

Because Hercules has internal VMON, I think i don't need to 1.2V,3.3V UV/OV detection IC. 

Is it correct? if you recommend using UV/OV detection IC, do you have any references?

thank you

  • 0
    TI__Guru**** 197566 points

    Hi Yun,

    The VMON's main function is to eliminate the requirement for a strict power up/down sequence between the core (Vcc) and I/O (Vccio) power supplies. The job of monitoring the power supplies (Vcc and Vccio) and asserting power-on reset must be done by an external supervisor.

    Below 1.14v, the core voltage is out of range, but the VMON circuit will not take action.  

    Please refer to TPS65381 which is designed for TMS570 devices.

  • 0 in reply to QJ Wang
    Prodigy 100 points

    Hi QJ Wang,

    So these are what i understand. Am i understand right?

    1. If Hercules MCU's status is operational and Core voltage get lower than 1.14V, VMON couldn't take action.

    2. If I wanna check Vcc and Vccio, I should use external safety regulator.

    thank you.

  • 0 in reply to Yun Hoseong
    TI__Guru**** 197566 points

    The VMON is primarily intended to simplify power supply sequencing and the coarse overvoltage/ undervoltage detection is a secondary benefit. It is expected that the customer utilizes a more fine-grained voltage supervisor circuit to ensure the voltage is in proper ranges.

    Between 1.0 and 1.14v, the core voltage is out of range but the VMON circuit will not take action. Action should be taken by the customer's external voltage supervisor.