TCAN1043G-Q1: Query about TCAN1043GDMTRQ1 wakeup times

The second question is Do transceivers have lifespan related parameter indicators?

Wang,

Thanks for your question and patience. We will have a response to you by end of business tomorrow CST.

Regards,

Eric Hackett

Hi Wang,

For the first two questions, I have found a functional safety document on ti.com that describes different characteristics about the lifespan of the part here. I don't think we specifically conduct tests for your question 1, but the document might be of help.

wang lei said:

3.What is the definition of common mode voltage in the datasheet? Vcom=（Vcanh+Vcanl）/2 ?

The equation that you describe here is the common voltage shared between the CANH signal and the CANL signal. This is the voltage that CANH and CANL will roughly settle at when in a recessive bit state.

The common mode receiver voltage that you are pointing at in the datasheet is referring to the +/- 30V limit. This is generally saying that if there is a +/-30V ground shift in a system, the transceiver will still be able to operate correctly.

wang lei said:

4.How to understand bus fault protection: ±58 V in the datasheet? Is there any connection between this parameter and the common mode voltage parameter?

The +/-58V bus fault protection refers to the maximum voltage that can be present on a single CAN line (either CANH or CANL), and describes the differential voltage that can be present on the CAN bus. You can find these limits in the abs. max conditions in the datasheet. These limits do vary between the version of the device you have. The "H" suffix can withstand up to +/-70V. 

The common mode voltage parameter that you listed above where Vcom = (VcanH+VcanL) / 2 does not necessarily apply. The ground shifting however could. If the ground shift is large enough, this could potentially raise the potential on the CAN bus and put them close or over the +/-58V spec listed in the abs. max conditions. If the abs. max conditions are exceeded, there may be permanent damage to the device. 

wang lei said:

5.Is there any connection between the ground offset of the transceiver and the common mode voltage parameters?

The ground offset of the transceiver would shift the common mode voltage parameter between CANH and CANL. For example, if your GND is shifted up 2V, you would expect CANH and CANL to both be shifting up 2V, which would shift the common mode voltage between them up 2V. Your differential voltage between CANH and CANL would not be affected because both CANH and CANL signals were equally shifted by the same voltage potential. 

Regards,

Tyler

Hello Tyler,

    Thanks for your detailed reply.

For TCAN1043GDMTRQ1, common mode voltage is ±30V in normal mode and ±12V in sleep mode shown in the datasheet.

1.Does this mean TCAN1043GDMTRQ1 can withstand ±30V GND shift in normal mode and ±12V GND shift  in sleep mode?

2.If the max common mode voltage in our application is ±20V, both in normal mode and sleep mode:

(1) What will happen in sleep mode if we use TCAN1043GDMTRQ1? Will TCAN1043GDMTRQ1 be damaged?

(2)]From the perspective of cost and PCB space, we don't want to  add additional isolation devices(such as ISO7041-Q1) or use isolation CAN(such as ISO1042).  Base on above, what can we do to make TCAN1043GDMTRQ1 work normally in sleep mode in ±20V GND shift system?（such as  receiving wake-up signals Correctly  ）

Looking forward to your reply.

Best regards!

wang lei

Tyler Townsend said:

TCAN1043 is spec'ed for +/12V common mode in sleep mode. There is no changing this parameter for this device, the changes will need to come from a system perspective. I recommend that GND loops would be minimized as much as possible in order to reduce any large ground potential differences in your system. 

Hello Tyler,

    It's a good idea to minimize GND loops as much as possible.

Is there any other way to improve the common mode voltage in sleep mode of TCAN1043？such as adding some electronic component in transceiver circuit?

Below is our application. The right side（BMS in vehicle）is powered by 6V battery, the left side（DCDC charger） is powered by 26V DC power. The positive poles of the left and right are connected together while the negative poles are not connected together  because the low side switch is open. Under this condition, there will a 14V GND shift  between GND1 and GND2.

In extreme cases, the ground offset will reach 20V in our application.