STM32F205XX_12 STMICROELECTRONICS [STMicroelectronics], STM32F205XX_12 Datasheet - Page 89

• Manufacturer Part Number: STM32F205XX_12
• Description: ARM-based 32-bit MCU, 150DMIPs, up to 1 MB Flash/128+4KB RAM
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

STM32F20xxx
5.3.11
Table 34.
1. Guaranteed by design, not tested in production.
MODEPER * INCSTEP
Symbol
f
md
Mod
PLL spread spectrum clock generation (SSCG) characteristics
The spread spectrum clock generation (SSCG) feature allows to reduce electromagnetic
interferences (see
SSCG parameters constraint
Equation 1
The frequency modulation period (MODEPER) is given by the equation below:
f
As an example:
If f
1:
Equation 2
Equation 2 allows to calculate the increment step (INCSTEP):
f
With a modulation depth (md) = ±2 % (4 % peak to peak), and PLLN = 240 (in MHz):
An amplitude quantization error may be generated 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:
As a result:
PLL_IN
VCO_OUT
PLL_IN
INCSTEP
and f
= 1 MHz and f
must be expressed in MHz.
md
md
Mod
INCSTEP
quantized
quantized
must be expressed in Hz.
=
Table 40: EMI
round
%
MOD
%
=
[
(
=
Peak modulation depth
MODEPER
(
=
Modulation frequency
round
2
MODEPER
(
= 1 kHz, the modulation depth (MODEPER) is given by equation
15
(
250
MODEPER
–
Doc ID 15818 Rev 9
Parameter
[
1
×
(
)
(
characteristics). It is available only on the main PLL.
126
2
×
15
2
–
×
=
×
=
1
240
100
round 10
) md
×
round f
×
INCSTEP
)
×
⁄
(
5
[
100
)
[
×
⁄
PLL_IN
PLLN
(
6
(
×
⁄
2
(
5
15
4 10
×
×
×
–
100
)
⁄
250
1
⁄
(
(
4
) 240
100 5
3
×
×
×
)
)
]
]
0.25
f
5
Min
Mod
=
=
)
×
-
-
⁄
)
(
250
126md(quantitazed)%
)
(
×
]
2
=
Electrical characteristics
15
MODEPER
2.0002%(peak)
–
Typ
1
-
-
-
) PLLN
×
Max
2
)
15
10
]
2
−1
)
(1)
Unit
KHz
89/177
%
-