TJA1085G VBUF Supply

[Mayur_M_Bharadwaj]

Dear team,

For TJA1085G, 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!

[TomasVaverka · Accepted solution]

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

[Mayur_M_Bharadwaj]

Hello Tomas,

Thanks for the feedback.