UJA113x SBC - Wake-up from Sleep Mode

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UJA113x SBC - Wake-up from Sleep Mode

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Contributor III

Hello,

We're developing a PCB with UJA113x SBC as CAN driver and voltage regulator. When we switch the SBC to Sleep mode, we need it to wake-up when CAN activity or undervoltage is detected.

Switching SBC to Sleep mode and SBC wake-up upon CAN activity detection works as expected (0x23:CVIE = 1).

For undervoltage wake-up, we have the following setup:

  • 0x1C:BMUIE = 1 - battery monitor undervoltage interrupt enabled.
  • 0x11:BMSC = 0 - voltage on BAT pin triggers an event. This should be correct, as we can read the plausible voltage value from registers 0x15:BMBCD and 0x16:BMBCD.
  • 0x12:BMUTC = 115 - undervoltage threshold = (115 / 255) * 20V = 9V

When we switch the SBC to sleep mode and lower the voltage on BAT pin below 9V however, SBC does not wake up. When we lower the voltage in normal mode, we can see the undervoltage interrupt triggering in both 0x62:BMUI and 0x1B:BMUVS, so it seems, the interrupt trigger event is correctly detected, but does not lead to a wake-up.

While experimenting, we also noticed a strange behaviour. When the BMUI interrupt flag was set to 1 and we sent the SPI command to switch the SBC to sleep mode, it does, even though the documentation says it can't, while any interrupt flags are set and not cleared (7.12.2 Sleep mode protection).

Thanks for advice!

Tomas

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NXP Employee
NXP Employee

Hi Tomas,

the internal battery monitor is not a wake-up source, because it is off in Standby or Sleep mode. See also data sheet section 7.8.2:

"In order to minimize quiescent current consumption, battery monitoring is only enabled

when the SBC is in Normal mode. When battery monitoring is deactivated, all related

functions are unavailable."

Best regards,

Peter

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NXP Employee
NXP Employee

Hi Tomas,

the internal battery monitor is not a wake-up source, because it is off in Standby or Sleep mode. See also data sheet section 7.8.2:

"In order to minimize quiescent current consumption, battery monitoring is only enabled

when the SBC is in Normal mode. When battery monitoring is deactivated, all related

functions are unavailable."

Best regards,

Peter

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Contributor III

Hello, Peter,

thank you for your reply! I got confused, but now I see it as well, since 7.12 says:

The SBC does not distinguish between wake-up and interrupt events.
All wake-up events (LIN, CAN and HVIO) generate interrupt requests and all interrupts
trigger a wake-up event when the UJA113x is in a low-power mode.

Therefore, CAN wake-up works as expected. Is there some recommended solution for low battery voltage wake-up, except for using a HVIO interrupt and some transistor circuitry? We are looking for the lowest possible current consumption when the SBC is in sleep mode.

Thanks!

Tomas 

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