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NXP Semiconductors

FS23

Safety system basis chip (SBC) with power management, CAN FD and LIN transceivers

13.1.2 HVBUCK clock management

13.1.2.1 Description

The HVBUCK 450 kHz or 2.2 MHz clock is generated from a 20 MHz internal oscillator.

A triangular and a pseudo-random spread spectrum feature can be activated and configured by OTP and SPI/

I2C to reduce the emission of the oscillator fundamental frequency.

13.1.2.2 Spread spectrum

The internal oscillator can be modulated around the oscillator frequency. The spread spectrum feature can

be activated by SPI/I2C with the MOD_EN bit and the carrier frequency can be selected by SPI/I2C with the

MOD_CONF bit. By default, the spread spectrum is disabled, unless configured differently by OTP.

The main purpose of the spread spectrum is to improve the EMC performance by spreading the energy of the

internal oscillator and HVBUCK frequency on VBAT frequency spectrum.

It is recommended to select the triangular spread spectrum for the best performance.

MOD_EN

MOD_CONF

Spread spectrum

Disabled

Triangular (19 kHz)

Pseudo-random triangular

Table 14. Spread spectrum configuration

Triangular spread spectrum

The triangular spread spectrum is activated in M_SYS_CFG SPI/I2C register by setting MOD_EN bit high and

MOD_CONF bit low. In this configuration, the internal oscillator is modulated with a triangular carrier frequency

of 19 kHz with -10 %/0 % deviation range of the nominal oscillator frequency.

aaa-051444

No modulation

-10 %

∆f = 10 %

19 kHz (52.6 µs)

Figure 19. Triangular spread spectrum

Pseudo-random triangular spread spectrum

The pseudo-random triangular spread spectrum is activated in M_SYS_CFG SPI / I2C register by setting

MOD_EN bit high and MOD_CONF bit high. In this configuration, the internal oscillator is modulated with a

triangular carrier frequency of 19 kHz with -10 %/0 % deviation range of the nominal oscillator frequency, but

two random commutations on the carrier slope are added in each half period to increase the spectrum content.

FS23

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Product data sheet

Rev. 7.0 — 16 October 2024

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