STPM098C datasheet(41/110 Pages) STMICROELECTRONICS

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3.7.1

Spread spectrum modulation (SSM)

STPM098C clock generator implements a frequency modulation (spread spectrum modulation) feature to reduce

the main logic emissions around the main frequency by spreading the power spectrum over a larger frequency

range.

Figure 33. Clock spread spectrum modulation details

0.5/fm

1/fm

(1+δ)fc

(1-δ)fc

The carrier frequency fc (typ = 40 MHz) is modulated by means of a triangular modulating signal with frequency

fm and a spreading range δ.

Table 31. Clock spread spectrum electrical characteristics

Symbol

Parameter

Test condition Min Typ Max Unit

Notes

SSM_spreading

Spread spectrum modulation spreading

range

1.5

Application information

SSM_freq

Spread spectrum modulating frequency

9.7

kHz Application information

The clock spread spectrum modulation function can be enabled by a dedicated PMBus™ bit as follows:

Table 32. Clock spread spectrum enable bit

CLK_SSM_EN

Description

Clock SSM disabled (default)

Clock SSM enabled

Note:

•

When the clock spread spectrum is enabled, the internal digital timings are affected by a timing jitter equal

to the selected spread spectrum spreading range.

•

ICM timeout accuracy is valid only in case of sudden stuck fault. In case of progressive clock frequency

degradation, such an accuracy range is no more valid.

•

If no oscillator clock is available, the PMBus™ data processing cannot work properly: STPM098C delivers

always the latest answer.

STPM098C

Functional description

DS14440 - Rev 1

page 41/110

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