STM32F446VC datasheet(111/202 Pages) STMICROELECTRONICS

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STM32F446xC/E

Electrical characteristics

175

Equation 1

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

MODEPER

round fPLL_IN

4fMod

()

⁄

[]

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 10

410

()

⁄

[]

250

Equation 2

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

INCSTEP

round

–

() md PLLN

()

100

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

–

() 2240

()

100

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

()

–

() PLLN

()

⁄

As a result:

mdquantized%

250

126

100

()

–

() 240

()

⁄

2.002%(peak)

Table 46. SSCG parameters constraint

Symbol

Parameter

Min

Typ

Max(1)

Unit

fMod

Modulation frequency

KHz

Peak modulation depth

0.25

MODEPER * INCSTEP

215

−1-

1. Guaranteed by design.

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