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TCAN1044A-Q1: Standby mode configuration

chee hua how
Prodigy 60 points
Part Number: TCAN1044A-Q1

Hi I am studying the possibility of using TCAN1044A into my design.

Just to ensure I understand the standby and wakeup sequence of such chip correctly, let me know if any of my understanding below is incorrect:

  1. To put the chip into standby is by setting STB pin from low to high logic.
  2. To wake up the chip I have to
  3. Put STB pin from “1” back to “0” and
  4. Generate the wake-up pattern (WUP) pulses as described by section 4.3.1 in order to drive RXD from high to low transition.

 

Sorry I am a bit confuse with item (b) (ii) above. If there is a dedicated STB pin for standby control, why we can’t wake the chip by simply just pulling STB pin back to 0s instead need the additional WUP sequence?  

  • 0
    TI__Guru 53575 points

    Hi Chee Hua,

    The TCAN1044A mode is solely controlled by the STB pin state. The MCU that is connected to the transceiver is responsible for putting the transceiver into normal mode when CAN transmission/reception is needed and putting the device into standby mode when the system goes into a low power state. This is all done using the STB pin. The WUP function has no direct impact on the transceiver's mode. 

    When the transceiver is in standby mode, the high speed CAN receiver is disabled to save power. This means that the MCU cannot receive CAN communication and would therefore not be able to tell when the system needs to return from a low power state. Therefore, TCAN1044A activates a low power receiver during standby mode in order to monitor the CAN bus for activity. When the CAN bus is idle, the transceiver does not react and the system remains in a low power state. However, when any CAN communication appears on the bus, the WUP requirement of the transceiver will be met and the TCAN1044A will indicate this activity to the MCU by driving the RXD pin low. This edge on RXD should trigger an interrupt in the MCU to bring it out of low power mode. Once its ready, the MCU can then drive the STB pin low to enable to transceiver and it will be able to interface with the CAN bus. 

    Let me know if you have any more questions. 

    Regards, 
    Eric Schott