VBATMON Operating and Absolute Limits – L9678P

[Umesh_Kumar278]

Dear ST Support Team,

We are using the L9678P in an automotive design where the battery voltage is nominally 28 V.

From the datasheet, we understand the following for the VBATMON pin:

Absolute maximum voltage: 40 V

Operative maximum voltage: 18 V

We would like to confirm:

1. Can VBATMON be directly connected to a 28 V rail continuously, or is this outside the safe operating range?

2. Is it mandatory to use a voltage divider to reduce VBATMON below 18 V during normal operation?

3. Is VBATMON used only for battery voltage monitoring, or does it have a role in powering internal logic?

4. Does VBATMON directly influence wake-up and shutdown behavior of the IC?

We want to ensure safe operation and avoid long-term reliability issues.

Thank you in advance.

Best regards,

Umesh

[MJ_Pellegrini]

Dear Umesh,

if you don't use PSI5 sensors you can buy the L9678P part number:

About deployment trigger, you are right.

You can use:

1. FENH and FENL (from DIAG state to SAFING state)
2. ACL for end of life (from DIAG state to SCRAP state)

So the simple way to deploy is the following (reported also in paragraph 3.3 of AN5739, available on st.com):

1. Configure SAFESEL=1 in SYS_CFG register to select external arming
2.  Send watchdog override command in debug phase, or start to refresh the watchdog routine
3. Configure SYS_CTL register
4. Check POWER_STATE and FLTSR registers
5. Configure LOOP_MATRIX_ARMx and DCR_x registers
6. Check DSR_x registers
7. Move in SAFING state with the proper command (check SYS_STATE register)
8. Set FENH high and FENL low
9. Sent unlock command in SPIDEPEN register
10. Sent deploy command in DEPCOM register
11. Check deploy status in DSR_x registers

In alternative you can use ACL line, but usually it is used for end of life (deployment of all the channels) before the vehicle is scrapped.

Kind regards,

Jonathan

[Umesh_Kumar278]

Dear Jonathan,

Thank you for your previous clarification.

As a final confirmation, I’m considering that the minimal pin set required for deployment (in a scenario where low-power mode and sensors are not used) includes the following:

SPI interface:
-------------
Clock
NSS
MISO
MOSI

FENL
FENH
ACL (optional, but I would like to include it)

Could you please confirm if this list is correct, or let me know if anything is missing for  the deployment  ?

Thanks again for your support.

Best regards,
Umesh

[MJ_Pellegrini]

Dear Umesh,

yes, you are right.

Kind regards,

Jonathan