MFS2401AVBA0ES datasheet(51/151 Pages) NXP

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NXP Semiconductors

FS2400

Fail-safe system basis chip with SMPS and LDO, CAN FD transceiver

The LDT_SEL bit allows the MCU to read the value of the 24-bits LDT counter in the LDT_WUP_H[7:0] and the

LDT_WUP_L[15:0] bits.

• When LDT_SEL = 0, the MCU reads or writes the wake-up value in the LDT_WUP_H[7:0] and the

LDT_WUP_L[15:0] bits.

• When LDT_SEL = 1, the MCU reads the counter current value.

The LDT_EN bit shall be provided to start the LDT timer operation:

• When LDT_EN = 0, the LDT is disabled.

• When LDT_EN = 1, the LDT starts counting as defined in the M_LDT_CTRL and L_LDT_CFGx registers.

The LDT2LP bit selects which Low-power mode (LPON or LPOFF) it needs to go once the after-run timer is

expired, when timer function 2 or 3 is selected.

• When LDT2LP = 0, the device goes into LPON mode when the after-run timer expires.

• When LDT2LP = 1, the device goes into LPOFF mode when the after-run timer expires.

• When timer function 4 or 5 is selected and the LDT_EN = 1, the LDT does not start any count until the device

enters the corresponding Low-power mode.

17.1 Calibration procedure

The calibration procedure consists of the MCU activating the counter for a specific duration. Once the timer

expires, the MCU reads back the timer final value, compares it with its own accurate time of activation to

calculate a time offset. It is recommended to perform the calibration between -20 °C and +85 °C.

Calibration example:

• Set the Timer mode to short count and select the timer function 1. Set the after-run value at max value

0xFFFF (~8.39 s).

• Start the counter.

• Read the counter when the MCU RTC reaches 6 s.

• If the oscillator period is at the exact typical value (absolutely no deviation error), expected reading is 46875.

• The exact reading calculates the error correction factor ECF = exact_reading / expected_reading

• ECF < 1 if the oscillator is faster than the exact typical value.

• ECF > 1 if the oscillator is slower than the exact typical value.

• After calibration, the new after-run or wake-up values to set the counter are “after run x ECF” and “wake-up x

ECF”.

17.2 Timer functions

LDT_FNCT[2:0]

LDT Function

000

Function 1: In Normal mode, count and generate a flag or an interrupt when the counter

reaches the after-run value.

001

Function 2: In Normal mode, count until the counter reaches the after-run value and enters

Low-power mode.

010

Function 3: In Normal mode, count until the counter reaches the after-run value and enters

Low-power mode. Once in Low-power mode, count until the counter reaches the wake-up

value and wakes up.

011

Function 4: In Low-power mode, count until the counter reaches the wake-up value and

wakes up.

100

Function 5: In Low-power mode, count and do not wake up unless the counter overflow

occurs or if the device wakes up by wake-up input source.

Table 23. LDT functions

FS2400

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 4 — 23 October 2024

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