Datasheet
Electrical characteristics STM32F20xxx
98/184 DS6329 Rev 16
6.3.11 PLL spread spectrum clock generation (SSCG) characteristics
The spread spectrum clock generation (SSCG) feature allows to reduce electromagnetic
interferences (see Table 42: EMI characteristics). It is available only on the main PLL.
Equation 1
The frequency modulation period (MODEPER) is given by the equation below:
MODEPER round f
PLL_IN
4f
Mod
×()⁄[]=
f
PLL_IN
and f
Mod
must be expressed in Hz.
As an example:
If f
PLL_IN
= 1 MHz and f
MOD
= 1 kHz, the modulation depth (MODEPER) is given by equation
1:
MODEPER round 10
6
410
3
×()⁄[]250==
Equation 2
Equation 2 allows to calculate the increment step (INCS
TEP):
INCSTEP round 2
15
1–()md PLLN××()100 5× MODEPER×()⁄[]=
f
VCO_OUT
must be expressed in MHz.
With a modulation depth (md) = ±2 % (4 % peak to peak), and PLLN = 240 (in MHz):
INCSTEP round 2
15
1–()2240××()100 5× 250×()⁄[]126md(quantitazed)%==
An amplitude quantization error may be generate
d because the linear modulation profile is
obtained by taking the quantized values (rounded to the nearest integer) of MODPER and
INCSTEP. As a result, the achieved modulation depth is quantized. The percentage
quantized modulation depth is given by the following formula:
md
quantized
% MODEPER INCSTEP× 100× 5×()2
15
1–()PLLN×()⁄=
As a result:
md
quantized
% 250 126× 100× 5×()2
15
1–()240×()⁄ 2.0002%(peak)==
Table 36. SSCG parameters constraint
Symbol Parameter Min Typ Max
(1)
1. Guaranteed by design, not tested in production.
Unit
f
Mod
Modulation frequency - - 10 KHz
md Peak modulation depth 0.25 - 2 %
MODEPER * INCSTEP - - - 2
15
−1-
Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.