Clarifications required for SBCFS26 FCCU External pullup configuration

[Sivahari]

Hi NXP,

We are using MFS2613AMDA6 IC in our motor controller project.

We have gone through the product data sheet to Implementation FCCU with bi stable protocol configuration(default).

we found figure 54. In that we understood external pull up/pull down is not required for bi stable protocol configuration.

IS that Correct?

but it was contradicting when referring configuration for FCCU12_FLT_POL = 1.

If Fault Condition is FCCU1 = 1 and FCCU2 = 0 level, then what is the purpose to connect pull up resistor at FCCU 1 and pull-down resistor at FCCU2? 

Is this Pull-up/pull-down for NO Fault Condition or Fault condition?

Thanks for Support.

[TomasVaverka]

Hi Siva,

The 5.1 kΩ and 22 kΩ resistors are external resistors required specifically when using FCCU Polarity 1 (FCCU12_FLT_POL = 1).

The FS26 has weak internal resistors (FCCU1: ~800 kΩ pull-down; FCCU2: ~200 kΩ pull-up). The system must be designed so that if the MCU pins enter a High-Z (tri-state) condition, the SBC detects a Fault state.

• Polarity 0 (Normal = H/L): If the MCU goes High-Z, the internal resistors pull the pins to L/H, which the FS26 correctly interprets as a Fault. No external resistors are needed.

• Polarity 1 (Normal = L/H): If the MCU goes High-Z, the internal resistors would pull the pins to L/H, which the FS26 interprets as Normal. This is unsafe.

So For Polarity 1, you must add stronger external resistors to override the internal ones and force a Fault state during High-Z:

• FCCU1: 5.1 kΩ external pull-up to VDDIO.

• FCCU2: 22 kΩ external pull-down to GND.

BRs, Tomas