Tool/software:
Could you please help to check that how to calculate the Icc for TCAN1057A-DRBQ1(no VIO)?
I see in the datasheet that there are have different supply current for dominant and recessive state. And the test conditions also different. In the dominant state, test condition is RL=60Ω and RL=50Ω，
But in the recessive state, the test condition only have RL=50Ω.
Question 1: Does the RL is meaning the CAN terminal resistor?
Question 2: In our design, the CAN terminal resistor is 120Ω, so how to calculate the actual current consumption on VCC pin?
Question 3: As below is my understanding and calculation, does it correct or not?
- About why including the Irecessive in the calculation, the reason is in recessive state, Vdiff = VCANH-VCANL=0V, so the current on the RL is 0mA, but the Icc_recessive=7.5mA≠0mA, so, we can think the current consumption is the device internal logic unit needed.
- See as below diagram block from datasheet and schematic, we know that the device that we selected there is no VIO pin, So the internal logic unit is also supply by VCC. Hence, the total current consumption Icc should be calculated like: Icc =Icc_internal logic+IL.
- In the datasheet, we can not clearly know how much is the Icc_internal logic, but we can estimate it by step 1 above.
- In our design, the load resistor on CANH and CANL are two 60R4 resistors which tolerance is 1%, we use the 3% tolerance to calculate for WCCA, so, RL_MIN=60,4*(1-0,03)*2=117,176Ω
- From datasheet figure 8-1, we can know CAN transceiver have normal mode and silent mode. And in the normal mode, there have dominant state and recessive state. They are all working state for this transceiver. We also can know that form chapter 6.6, Icc_silent_max =2,1mA, Icc_recessive_max=7.5mA, Icc_dominant_max=70mA. Both in the recessive state and silent mode, there are no current flow to the RL. But they are still have the current consumption, so the only explanation is the internal logic unit are still working, hence, we can estimate the internal logic current consumption with Icc_silent or Icc_recessive. But in the silent mode, maybe some internal logic are not working, so for safety reasons, we can think that the current consumption in recessive state is the current consumption for internal logic unit.
- According to step4/ 5 above, we can estimate that the current consumption in dominant state with our design. Namely, Icc_dominant=(70mA*60Ω)/117,176Ω≈35,8mA.
- In summary, we can calculate the Icc_normal mode_max=Icc_dominant+Icc_internal logic = Icc_dominant+Icc_recessive = 35,8mA+7,5mA=43,3mA for WCCA.
