STM32F756XX Datasheet, PDF (133/228 Pages) STMicroelectronics – ARM-based Cortex-M7 32b MCU+FPU, 462DMIPS, up to 1MB Flash/320+16+ 4KB RAM, crypto, USB OTG HS/FS, ethernet, 18 TIMs, 3 ADCs, 25 com itf, cam & LCD

STM32F756xx
Electrical characteristics
Equation 2
Equation 2 allows to calculate the increment step (INCSTEP):
INCSTEP = round[((2¹⁵ – 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[((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:
md_quantized% = (MODEPER × INCSTEP × 100 × 5) ⁄ ((2¹⁵ – 1) × PLLN)
As a result:
md_quantized% = (250 × 126 × 100 × 5) ⁄ ((2¹⁵ – 1) × 240) = 2.002%(peak)
Figure 36 and Figure 37 show the main PLL output clock waveforms in center spread and
down spread modes, where:
F0 is f_{PLL_OUT} nominal.
T_mode is the modulation period.
md is the modulation depth.
Figure 36. PLL output clock waveforms in center spread mode
&REQUENCY0,,?/54
MD
&
MD
TMODE
XTMODE
4IME
AI
DocID027589 Rev 4
133/228
196