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SN65HVD251: if the Vih min. of D input can be lower to 3.3V, even to 2.0V?

Eric Li3
Prodigy 150 points
Part Number: SN65HVD251
Other Parts Discussed in Thread: TCAN1044V

hello, sir,

this is eric.li, an EE engineer from Advantech Co. Ltd.

we choose STM32F405 as CAN-MCU and SN65HVD251 as CAN transceiver.

the Voh of MCU's TX is 2.9~3.3V but the Vih of D input of CAN transceiver is 3.5V (0.7*VCC).

although the Voh of STM32F405 violates the min. Vih 3.5V of SN65HVD251, in our internal function and throughput test, it works fine as expected. see table.1

we wondered if SN65HVD251 can accept D input lower than 3.3V, even to 2V?

thanks a lot !

Regards,

Eric Li

Table.1 CAN bus throughput test result, for STM32F405 as CAN-MCU and SN65HVD251 as CAN transceiver

 

  • +1
    TI__Guru 53555 points

    Hi Eric,

    The input threshold for the digital logic is specified to be 0.7*Vcc minimum across all operating conditions. This means that an input voltage above this level will always be recognized as a valid high-level input as long as all other operating conditions are met. However, this threshold is often lower under normal conditions when no specification is nearing its limit. So at room temperature and nominal Vcc, it's quite normal for these thresholds to be compatible with lower logic voltages. However, this cannot be guaranteed across all conditions, so if this application is expected to handle operate in non-optimal conditions, this implementation may not be sufficient. 

    I would recommend a transceiver that is designed to work with different voltage levels such as TCAN1042V or TCAN1044V ('V' suffix denotes voltage integrated voltage translation). These devices have a Vio input which sets the digital logic voltage reference for the device so that 3.3V logic can be used with a 5V transceiver. Let me know if you would like to know anything more about these devices. 

    Regards,
    Eric Schott