STM32F217RGT7 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

STM32F217RGT7

ARM-based 32-bit MCU, 150DMIPs, up to 1 MB Flash/128+4KB RAM, crypto, USB OTG HS/FS, Ethernet, 17 TIMs, 3 ADCs, 15 comm. interfaces & camera

STMicroelectronics 

Electrical characteristics

STM32F21xxx

5.3.11

PLL spread spectrum clock generation (SSCG) characteristics

The spread spectrum clock generation (SSCG) feature allows to reduce electromagnetic

interferences (see Table 39: EMI characteristics). It is available only on the main PLL.

Table 33. SSCG parameters constraint

Symbol

Parameter

fMod

md

MODEPER * INCSTEP

Modulation frequency

Peak modulation depth

1. Guaranteed by design, not tested in production.

Min

-

0.25

-

Typ Max(1) Unit

-

10

KHz

-

2

%

-

215−1

-

Equation 1

The frequency modulation period (MODEPER) is given by the equation below:

MODEPER = round[fPLL_IN ⁄ (4 × fMod)]

fPLL_IN and fMod must be expressed in Hz.

As an example:

If fPLL_IN = 1 MHz and fMOD = 1 kHz, the modulation depth (MODEPER) is given by equation

1:

MODEPER = round[106 ⁄ (4 × 103)] = 250

Equation 2

Equation 2 allows to calculate the increment step (INCSTEP):

INCSTEP = round[((215 – 1) × md × PLLN) ⁄ (100 × 5 × MODEPER)]

fVCO_OUT must be expressed in MHz.

With a modulation depth (md) = ±2 % (4 % peak to peak), and PLLN = 240 (in MHz):

INCSTEP = round[((215 – 1) × 2 × 240) ⁄ (100 × 5 × 250)] = 126md(quantitazed)%

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:

mdquantized% = (MODEPER × INCSTEP × 100 × 5) ⁄ ((215 – 1) × PLLN)

As a result:

mdquantized% = (250 × 126 × 100 × 5) ⁄ ((215 – 1) × 240) = 2.0002%(peak)

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Doc ID 17050 Rev 8

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