ICS841S012DI datasheet(12/24 Pages) RENESAS

12 / 24 page

841S012DI Datasheet

January 4, 2016

SPREAD SPECTRUM

Spread-spectrum clocking is a frequency modulation technique for

EMI reduction. When spread-spectrum is enabled, a 32kHz triangle

waveform is used with 0.6% down-spread (+0.0% / -0.5%) from

the nominal output frequency. An example of a triangle frequency

modulation proﬁle is shown in Figure 4A below. The ramp proﬁle

can be expressed as:

Fnom = Nominal Clock Frequency in Spread OFF mode

Fm = Nominal Modulation Frequency (30kHz)

δ = Modulation Factor (0.6% down spread)

The 841S012DI triangle modulation frequency deviation will not

exceed 0.7% down-spread from the nominal clock frequency (+0.0%

/ -0.5%). An example of the amount of down spread relative to the

nominal clock frequency can be seen in the frequency domain,

as shown in Figure 4B. The ratio of this width to the fundamental

frequency is typically 0.4%, and will not exceed 0.7%. The resulting

spectral reduction will be greater than 5dB, as shown in Figure 4B. It

is important to note the 841S012DI 5dB minimum spectral reduction

is the component-speciﬁc EMI reduction, and will not necessarily

be the same as the system EMI reduction.

FIGURE 4B. 200MHZ CLOCK OUTPUT IN FREQUENCY DOMAIN

(A) SPREAD-SPECTRUM OFF (B) SPREAD-SPECTRUM ON

FIGURE 4A. TRIANGLE FREQUENCY MODULATION

(1 -

δ) fnom + 2 Fm x δ x Fnom x t when 0 < t < ,

(1 -

δ) fnom - 2 Fm x δ x Fnom x t when

< t <

2Fm

➤

1/fm

0.5/fm

Fnom

(1 -

δ) Fnom

Time

Δ − 10 dBm

δ = .6% ➤

ICS841S012DI Datasheet(PDF) 12 Page - Renesas Technology Corp