TCAN2451-Q1: Sleep mode current topology for TCAN2451-Q1

Hi Kalpak,

For your questions:

1. You have to configure the device to maintain those conditions - but it is possible. By default VCC1 and VCC2 are off in sleep mode - but VCC1 can be configured to stay on during sleep. Selective wake can be used for the CAN transceiver in this state - once it is configured - see steps below because they need to followed exactly for selective wake/partial networking to be implemented:

"""

To enter selective wake mode, the following conditions must be met:
• Selective Wake Configured, SWCFG, flag is set
– All Selective Wake registers must be written followed by a read to make sure the programming is correct
for the proper frame detection and selective wake configuration. Once configured, the SWCFG bit should
be set to 1b.
• Selective Wake Error, SWERR, flag is cleared
• Set Selective Wake Enable (SW_EN) = 1b, register 8'h10[7] = 1b

"""

But overall - your goal/intention is possible with this SBC.

2. In sleep mode it is going to depend on what functions you have enabled and the junction temperature of the device - assuming that you basically have everything off in sleep mode except VCC1 and partial networking the power supply current is going to be comprised of a few specifications. 

First you have the base current - which we call ISUP_SLP_xxC - where xx can either be 85C or 150C and represents the junction temperature. 

ISUP_SLP_85C is typically 18uA but can be up to 35uA

ISUP_SLP_150C is typically 18uA but can be up to 50uA - keep in mind that typical values are usually in nominal (room temp.) conditions as to why the typical is the same for both specs - the extra junction temperature adds to max current consumption. 

Since you have VCC1 on we have to add the extra leakage from that which will be typically 25uA but up to 31uA - we only have this characterized for junction temperatures up to 85C - so above that you could see >31uA - but we don't have a direct parameter for that. 

Since you want to have selective wake we need to also add current from the CAN transceiver since it will be wake capable which will be typically 7uA and up to 10uA. 

When a wake-up pattern has been detected the selective wake circuitry activates which is going to cause an 480uA typical increase in supply current but up to 550uA. 

Then we need to add the current consumption from the load on VCC1 - an approximate efficiency of about 75% would be a good estimation (there will be some differences due to the external components - but 75% is relatively reasonable) - so the 2.4mA number would be okay. 

That should be the main IC current consumption specs based on what you are wanting - so the total current would be:

Typically before wake up pattern detected: 18uA + 25uA + 7uA + 2400uA = 2.45mA (2450uA)

Typically after wake up pattern detected: 2.45mA + 480uA = 2.93mA (2930uA)

Max* (approximation could be worse as some specs are measured only at 85C when IC can handle 150C junction temps):

50uA + 31uA + 10uA + 2400uA = 2.491mA

Max* After wake up pattern detected: 2.491mA + 550uA = 3.041mA (3041uA)

So under our current specifications you are looking at being under the 3200uA - but there is some risk if there is a high junction temp - but I don't think the increase would cause a 160uA increase. Also this assumes that you hit the 75% efficiency - which based on our quick calculator is realistic but external components could cause that to be lower. So there definitely needs to be testing to ensure it works - but based on how the device operates and how it is spec'd - this seems like you should be able to get under the desired current budget with a bit of margin - most of the current is due to the load on VCC1. 

If you have any other feature turned on though - this could be different. Also passive components may also add to current load (i.e. if I measured our EVM sleep current right now it could be higher as we have some other passives in our design that consume current - so don't forget to account for that type of current consumption). 

In normal mode - you are basically looking at 8mA to 11mA of idle current + any loads you are powering from VCC2 + VCC1. 

 3. Your understanding seems to be correct - I don't see anything concerning in your process as described. The only thing I would hit on is to ensure that you know exactly what functions you want active during sleep mode because that is where other currents could be coming into play. 

4. Generally - VCAN is powered through VCC2 and by default VCC2 turns off in sleep mode (the selective wake uses the low power receiver which is powered through VSUP and not VCAN) - when the SBC/transceiver wake up VCC2 comes on and powers VCAN. If you want to power VCAN externally - that is possible and you don't need to supply anything to VCAN during sleep mode - but the external supply should apply voltage when the SBC wakes up if that method is used - and this is typically easier when connecting directly to VCC2 - but not impossible if you don't. 

Please let me know if you have any further questions and I will see what I can do!

Best,

Parker Dodson