topic Re: IMXRT1176 FBB_DISABLE Fuse is already set in i.MX RT Crossover MCUs

IMXRT1176 FBB_DISABLE Fuse is already set

bia-bonobo — Mon, 02 Mar 2026 08:59:55 GMT

Hello,

I have some fresh custom boards with MCU, when I check the fuses, which I expect them to be blank. All of them have the fuse FBB_DISABLE on address 0x870[4] set which disables the FBB. I was expecting that all fuses by default would not be set. Because it's not possible to unset it.

What's going on here?

Regards,

Adrian

Re: IMXRT1176 FBB_DISABLE Fuse is already set

Gavin_Jia — Wed, 04 Mar 2026 09:13:33 GMT

Hi @bia-bonobo ,

Thanks for your interest in NXP MIMXRT series!

FBB_DISABLE is factory-configured and is related to your chip's part number. It functions more like a flag bit. Please refer to the note in the datasheet/RM.

Best regards,
Gavin

Re: IMXRT1176 FBB_DISABLE Fuse is already set

bia-bonobo — Wed, 04 Mar 2026 10:11:21 GMT

@Gavin_Jia Thank you for your response. I understand.

I also had some boards where this fuse was not set. But it's possible, these were another part number.

Is there a list for which part numbers this fuse is set and for which not?

Re: IMXRT1176 FBB_DISABLE Fuse is already set

Gavin_Jia — Mon, 09 Mar 2026 08:12:46 GMT

Hi @bia-bonobo ,

A more precise description would be that FBB_DISABLE is specific to the chip itself and is therefore factory-configured. When the RT1170 needs to operate in overdrive mode, it must read FBB_DISABLE first and then determine whether to enable FBB.

There is no publicly available list corresponding to part numbers; instead, this depends on the specific characteristics of the process/chip itself. Therefore, as described in the datasheet, the software flow should first read FBB_DISABLE.

Best regards,
Gavin

Re: IMXRT1176 FBB_DISABLE Fuse is already set

bia-bonobo — Mon, 09 Mar 2026 08:32:21 GMT

I get it now, Thank you!