topic TJA1085G VBUF Supply in In Vehicle Networking

TJA1085G VBUF Supply

Mayur_M_Bharadwaj — Thu, 10 Jul 2025 12:38:02 GMT

Dear team,

For , is it mandatory to connect VBUF to 5V Supply, or is it optional? InAH1001 Document,

In Section 4.1.2, it says VBUF is derived from VCC/VBAT
In Fig 27, there is no 5V connection to VBUF
In Fig 28, there is 5V connection to VBUF

If it is internally derived, we wanted to understand why it is connected in Fig 28. We do not have Wake-Up Requirement, and VBAT and VCC will be connected to 5V. So, we wanted to understand the connection of VBUF to 5V externally.

Thank you!

Re: TJA1085G VBUF Supply

TomasVaverka — Fri, 11 Jul 2025 06:54:20 GMT

Dear Mayur,

Figure 27 shows a system with wake-up support, where VBUF is separated and connected to a capacitor (CBUF) to allow wake-up signaling even when VCC is off.

Figure 28 shows a system without wake-up support, where VBAT, VCC and VBUF are all tied together to 5V. This simplifies the design and is acceptable when wake-up functionality is not needed.

So in your case, you can connect VBUF directly to 5V and you do not need a separate supply or buffer capacitor.

BRs, Tomas

Re: TJA1085G VBUF Supply

Mayur_M_Bharadwaj — Fri, 11 Jul 2025 12:27:55 GMT

Hello Tomas,

Thanks for the feedback.