TCAN1146-Q1: life time @CANH=12V

Our customer has come up with a new application scenario. When this product does not use CAN communication, CANH will be connected to the car KL.15 power supply (supply voltage 9-16V), and CANH will be used as the product wake-up signal.

Hi Sean，

There's  two application scenarios need to be consulted：

1、If we connect the CANH to 16V for long time, if this will influence the life time of TCAN1146；

2、if we connect the CANH to 16V in serial with a 4.7k resistor， and we guarantee the  inject current wil never exceed the TCAN1146's max current(±115mA), if it's ok?

Thank you!

Hi Jie,

1. No, lifetime will not be degraded, 16V is still OK.

2. It's OK, however, I won't recommend to connect such a large load in series, or you need to make sure the power rating of resistor is appropriately selected.  Due to the short-circuit current limiting, the maximum allowable output current when pulling dominant will be 115mA on TCAN1146 in the fault case you describe here (16V across a 4.7K Ohms load), each resistor should be rated to survive this short circuit current for a few µs. Once the CAN controller is able to identify the fault (transmission will likely be interrupted with such a fault), it will stop attempting to drive the CAN bus and the receiver will remain in a idle recessive state, so the transceiver and the resistors do not need to withstand the fault current for a prolonged period of time. The most conservative approach would be 0.115^2*4.7K= 62.15W which will allow for a CANH or L short to the power supply and the other bus pin to GND. But a more realistic case is really looking at most networks are designed for only about 50-60% bus loading and then 50% dominant vs recessive bits would give you closer to 18W, that would still be a problem when you choosing resistor package which takes PCB space and extra money. 

Regards,

Sean

In our application, the Tranceiver won't be worked in normal CAN communication, and no message will be transimited or received.

It just be used as a way to wake-up the INH signal， and the LP Receiver will be work.

The max current 115mA is for CANH or  CANL connected to -3V~18V directly. With a 4.7K resistor in serial  ,max current won't be reach.

Suggest CANH as 0V, the max power is 16^2 / 4700 = 0.05w，The regular rated power of resistor with package  0603  is 0.1W. So I think it's OK.

Thank you.

Hi Jie,

Ok, understood. So the bus will not actually drive dominant. In that case it will be fine to use 0.1W rating.

Regards,

Sean