TJA1145 under voltage detection time and INH disable time

[smichael]

I have two questions on TJA1145.

1.In TJA1145 Under voltage detection time 54µs(mentioned on Datasheet) and under voltage detection to sleep mode time 200mS(as mentioned on datasheet), What will happen if TJA1145 is getting the VCC&VIO in between 54us to 200ms? Will it come back to normal(active) mode or it will go to under voltage detection(sleep) mode?

2.After gettnig the sleep command, How much time  TJA1145 will take to disable the INH pin(to enter active to sleep mode)@ 

[TomasVaverka]

Hi Michael,

1. Td(uvd): 6 to 54μs, is the time needed to detect under voltage condition of VCC or VIO. Some sample may detect under voltage in 6μs and all samples detect under voltage until 54μs.

Td(uvd-sleep): 200 to 400ms, is the time to enter Sleep mode by VCC under voltage detection. Some sample may enter Sleep mode in 200ms and all samples enter Sleep mode until 400ms.

In VCC under voltage condition, TJA1145 is forced to enter Sleep mode to reduce current consumption.

If VCC under voltage was detected in Normal mode, TJA1145 enters Sleep mode in 200ms to 400ms. Until then, Normal mode is kept. CAN mode is immediately changed to CAN Offline Bias or CAN Offline after under voltage detection if CAN Active mode by CMC[1:0]=01 was selected.

2. I received a feedback from the product group that mode change is done in 16μs (maximum) after SPI command (MC[2:0] bits) reception (count from SCSN high) if condition was fulfilled (no CAN input signal), but no information about time for INH pin switching to floating (if there was delay for action of INH pin). I will update this thread if I get this information.

Best regards,

Tomas

[smichael]

Thank You TomasVaverka

2nd question cleared. 

I have doubt in 1st question I will explain the scenario kindly clarify that

 TJA1145 is in sleep condition Only VBAT(12V) is given, remaining VCC and VIO is low when we give the wake up signal to TJA1145, It's woke-up and INH switch on the VCC and VIO regulators, after 200mS those regulators giving the corresponding voltage to the VCC and VIO pins,

After that will it work on normal mode?

[TomasVaverka · Accepted solution]

Hi Michael,

After (remote) wake up by CAN wake-up pulse input, TJA1145 goes in Standby mode (INH pin is connected to VBAT internally, as you described) automatically.

Thenyou need to send SPI command (MC[2:0] = 0b111), to move to Normal mode.

Sleep mode should be controlled by TJA1145 with MC[2:0] = 0b000 and INH voltage should switch VCC & VIO OFF.

If VCC was dropped in Normal mode, TJA1145 can enter to [Forced] Sleep mode after Td(uvd-sleep) from under voltage detection.

However, in Forced Sleep mode by under voltage, some SPI bits can behave different as shown in Table 31 of the datasheet.

So, it is strongly recommended to switch VCC & VIO by MC[2:0] bits of TJA1145.

Best regards,

Tomas

[smichael]

Thank you TomasVaverka