FS5600 datasheet(42/111 Pages) NXP

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NXP Semiconductors

FS5600

Automotive buck regulator and controller with voltage monitors and watchdog timer

During the initialization phase (INIT_RUN), the MCU can send the seed for the LFSR

by writing to the WD_SEED register, or use the default LFSR value generated by the

FS5600 (0x5AB2). It is not possible to write 0x0000 to the WD_SEED register when in

the challenger mode. The I2C_REQ_ERR bit is set when writing a 0x0000 is attempted.

Using the seed value, the MCU should perform a simple calculation based on the formula

below, and send the results in the WD_ANSWER register in the OPEN window for a valid

watchdog refresh.

aaa-031017

WD_SEED[23:8]

WD_ANSWER[23:8]

NOT

Figure 13. Challenger watchdog formula

17.3.3 Watchdog error counter and error impact

The watchdog error counter is available for the Challenger and Simple watchdog

schemes. The watchdog error counter is used to count the number of bad watchdog

refreshes (data and temporal errors).

Each time a watchdog failure occurs, the device increments this counter by 2. The

watchdog error counter decrements by 1 each time the watchdog is correctly refreshed.

This principle ensures that a cyclic ’OK/NOK’ behavior converges to a failure detection.

To allow flexibility in the application, the maximum value of this counter is configurable

with the WD_ERR_LIMIT[1:0] register as shown in the table below.

WD_ERR_LIMIT[1:0]

Watchdog error counter value

01 (reset value)

Table 40. Watchdog error counter

The watchdog error counter value can be read by the MCU for diagnostic with the

WD_ERR_CNT[3:0] register.

When the watchdog error counter reaches or exceeds its maximum value, the counter

resets to “0” value and induces a system reaction based on WD_FAIL_IMPACT[1:0]

configuration. The initial value of WD_FAIL_IMPACT[1:0] is loaded from

OTP_WD_FAIL_IMPACT[1:0]. Use WD_FAIL_IMPACT[1:0] = 01 or 10 only if

OTP_WD_PGOOD1/2 = 1.

WD_FAIL_IMPACT[1:0]

Watchdog failure reaction

Stay in NORMAL STATE

Transition to INIT_RUN state or Remain in INIT_RUN

Transition to DEEP FAIL-SAFE state

Stay in NORMAL STATE

Table 41. WD_FAIL_IMPACT[1:0] description

FS5600

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

Product data sheet

Rev. 3 — 2 August 2022

42 / 111

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