TJA1043 Wake-up when VBAT < Vuvd(VBAT)

[SKY_YANG]

Hi NXP member,

I have a quesion about wake-up on VBAT status,

When VCC/VIO > Vuvd, then VBAT < Vuvd(VBAT), TJA1043 will go to stanby mode,

can we wake-up by these meoths as below?

1. local wake (the logic level on pin WAKE changes)

2. remote wake-up via CAB bus (wake-up pattern)

for meoth 2, in datasheet 7.2.2, "When UVBAT is set, the transceiver will try to enter Standby mode to save power and will disengage from the bus (zero load)." that's mean CAN bus disengage? so I can't remote wake-up via CAB bus, right? only meoth 1 OK?

[JozefKozon]

Hi Sky,

please refer to the Table 4. in the TJA1043 datasheet. If the UVBAT flag is set the, the TJA1043 will transfer to Standby mode. As long the UVBAT flag is set, you cannot wake-up the TJA1043. Non of the two methods will work. The voltage on the VBAT pin must recover, raise above 3.5V typically and then the TJA1043 will transfer to operating mode according to the STB_N and EN voltage levels. So you don't need to wake-up the TJA1043.

With Best Regards,

Jozef

[SKY_YANG]

Hi Jozef,
Thanks for your quick reply,

so that mean when VBAT < Vuvd(VBAT), it' not go to standby mode? like protected mode? and CAN bus can't TX/RX at that time(VBAT < Vuvd(VBAT)), right?

[JozefKozon]

Hi Sky,

actually the TJA1043 will switch to Standby mode when VBAT < Vuvd(VBAT). From the Table 4. when the UVbat flag is set, meaning that the VBAT < Vuvd(VBAT), the TJA1043 will switch to Standby mode.

But you under the condition VBAT < Vuvd(VBAT) you cannot wake up the TJA1043. 

With Best Regards,

Jozef

[SKY_YANG]

Hi Jozef,
Thanks for your quick reply,

Understood your reply, at last I want confirm about "7.2.2 UVBAT flag",

"When UVBAT is set, the transceiver will try to enter Standby mode to save power and will disengage from the bus (zero load)."

From my understanding , when :
VBAT < Vuvd(VBAT) ;
VCC > Vuvd(VCC) ;
VIO >Vuvd(VIO),

then :
1. TJA1043 will go to will try to enter Standby mode, but can't wake-up y any meoths.
2. TJA1043 will disengage from the CAN bus (zero load), so can't transmit and receive via CAN bus.

my understanding is corrent?

[JozefKozon · Accepted solution]

Hi Sky,

1. TJA1043 will go to will try to enter Standby mode, but can't wake-up y any meoths.
2. TJA1043 will disengage from the CAN bus (zero load), so can't transmit and receive via CAN bus.

Yes, both of these statements are correct. 

Have a nice day.

With Best Regards,

Jozef

[SKY_YANG]

Hi Jozef,
Thanks for your quick reply and support always.

Have a nice day.
BR
SKY