FS26 datasheet(111/156 Pages) NXP

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NXP Semiconductors

FS26

Safety system basis chip with low power for ASIL D/ASIL B

19 System enhancement functions

19.1 Clock management of the Main domain

The main clock management block is comprised of one high-frequency oscillator, one low-frequency system

oscillator, and multiple dividers to generate clocking for the internal main digital state machine, for the low power

clock, and for the switching regulators.

The low-frequency oscillator runs at 98 kHz. This oscillator is used for the Long Duration Timer (LDT) and

remains ON in Low-power modes to filter the wake-up sources.

The high-frequency oscillator runs at 18 MHz by default. The frequency and the spread spectrum can be

configured by SPI to reduce the emission of the oscillator fundamental frequency. The oscillator is used for the

SMPS regulators and all the main domain timings. This oscillator is OFF in Low-power modes to reduce the

current consumption.

Two frequency dividers provide lower frequency clocks for the switching regulators:

• CLK1 is set at the high-frequency oscillator divided by 8.

• CLK2 is set at the high-frequency oscillator divided by 40.

The frequency of the switching voltage regulators is assigned as shown in Table 111.

Regulator

CLK1

CLK2

VBST

Yes

VCORE

Yes

VPRE

VPRE_CLK_OTP = 1

VPRE_CLK_OTP = 0

Table 111. Switching clock assignment

aaa-045471

18 MHz INTERNAL

OSCILLATOR

(SPREAD SPECTRUM)

CLK2

CLK1

DIVIDER 2

/40 (OTP)

CLK_HIGH

DIVIDER 1

/8 (OTP)

PHASE

SHIFTING

PHASE

SHIFTING

Figure 34. Clock management block diagram

19.1.1 Manual frequency tuning

The internal oscillator frequency runs at 18 MHz by default, and it is configurable via OTP from 16 MHz to 19

MHz with a 1 MHz frequency step. NXP recommends using 18 MHz as a reference value.

CLK_FREQ_OTP[1:0]

High-frequency oscillator

CLK1

CLK2

16 MHz

2.000 MHz

400 kHz

17 MHz

2.125 MHz

425 kHz

10 (default)

18 MHz

2.250 MHz

450 kHz

19 MHz

2.375 MHz

475 kHz

Table 112. Manual frequency tuning configuration

FS26_SDS

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

Product short data sheet

Rev. 6.0 — 12 December 2025

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