TCAN1044AV-Q1: CAN Transceiver Wakeup

Kantha,

The actual falling undervoltage threshold UVCC on a particular device could be as low as 3.5 V, so it is possible that testing with 4 V will not trigger a UV_CC condition.

To your other question, however, you do not need to have V_CC < UV_CC to have wake-up working. The table that you've shown above in your post is from a section specifically describing device behavior during undervoltage conditions on V_CC and/or V_IO. The distinction you highlighted above is specifically showing that there are two different possibilities when V_CC < UV_CC and V_IO > UV_IO based upon the state of STB. Keeping V_CC and V_IO present is fine and even expected in application.

The more relevant table from the data sheet would be Table 9-4, which shows the operating modes of the device. Note specifically that WUPs are monitored when STB = HIGH.

Best,

Danny

Kantha,

The device will wake up and begin reflecting a filtered signal on RXD per the figure you included above after a valid WUP has been generated. This effectively occurs after a second dominant bit appears on the CAN bus. In many applications, the beginning of CAN communication serves as the wake event.

In your case, the device is likely passing filtered signals from CAN to RXD in the same fashion as the figure you've shown above. Note that tWK_FILTER is much smaller than your horizontal resolution appears to allow on the oscilloscope, so it may not be appearing clearly from the view you've shown.

Basic CAN transceivers do not fully ignore CAN communication when it occurs. If you'd like a device that can selectively wake up only when specifically addressed, you'd need to use a partial networking device such as TCAN1145-Q1.

Best,

Danny

Kantha,

Kantha Urs said:

1. Assume we have 3 CAN nodes on the same bus; 1 of the CAN node (ECU) being receiver, 1 CAN node transmitting the CAN messages at regular intervals and other CAN node is in standby mode (STB pulled high).

The CAN node which is standby mode has to wake up only when ECU which is being receiver all the time sends a wakeup pattern / message.

Is the above achievable with TCAN1044AV-Q1 or we need TCAN1145-Q1?

If there is any activity on the bus aside from one single dominant bit, then the transceiver will initiate a wake-up request as discussed above. This is the case for any transceiver without partial networking. TCAN1145-Q1 has partial networking, which allows you to program the device via SPI to only wake up when a specific frame is received. If the CAN bus remains silent, then devices will remain in their low-power states.

Kantha Urs said:

2. Assume we have 2 CAN nodes on the same bus; 1 of the CAN node (ECU) being receiver and other CAN node is in standby mode (STB pulled high).

when ECU which is being receiver all the time sends an CAN message and as the other CAN node is in standby mode, the bus sees the error frame. Need to switch off the standby mode (drive STB pin low) without seeing any error frame. 

Bringing STB low does not prevent the device from reacting to CAN frames. You can implement partial networking to ignore particular frames, but using the TCAN1044AV-Q1, you'd only be able to prevent the CAN → RXD pathway by completely removing the device's supply input.

Best,

Danny