5V49EE704NDGI8

更新时间： 2024-02-16 16:39:37

品牌	Logo	应用领域
艾迪悌 - IDT		时钟发生器可编程只读存储器电动程控只读存储器电可擦编程只读存储器
页数	文件大小	规格书
30页	651K
描述
EEPROM PROGRAMMABLE CLOCK GENERATOR

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5V49EE704NDGI8 数据手册

IDT5V49EE704

EEPROM PROGRAMMABLE CLOCK GENERATOR

CLOCK SYNTHESIZER

to enhance the profile of the spread spectrum waveform.

Tssc = 14 + 2 = 16

Profile:

Waveform starts with SS_OFFSET, SS_OFFSET + SDJ,

SS_OFFSET + SD^J+1, etc.

Nssc = 6 * 2 = 12

Spread Spectrum Using Sinusoidal Profile

Nssc * Tssc = 192

Use Eq.10 to determine the value of the

sigma-delta-encoded samples.

2% = (Σ∆ * 100)/(64 * 48)

Σ∆ = 61.4

Either round up or down to the nearest integer value.

Therefore, we end up with 61 or 62 for sigma-delta-encoded

samples. Since the sigma-delta-encoded samples must not

exceed 63 with SS_OFFSET set to '0', 61 or 62 is well within

the limits. It is the discretion of the user to define the shape

of the profile that is better suited for the intended application.

Using Eq. 9 again, the actual spread for the

sigma-delta-encoded samples of 56 and 57 are 1.99% and

2.02%, respectively.

Use Eq.10 to determine if the X2 bit needs to be set;

Amplitude = 48 * (1.99 or 2.02) / 100/2 = 0.48 < 1

Example

FIN = 25MHz, FOUT = 100MHz, Fssc = 33KHz with center

spread of 2%. Find the necessary spread spectrum

Therefore, the X2 = '0 '. The dither bit is left to the discretion

of the user.

The example above was of a center spread using spread

spectrum. For down spread, the nominal M value can be set

one integer value lower to 47.

Since the spread is center, the SS_OFFSET can be set to

'0'. Solve for the nominal M value; keep in mind that the

nominal M should be chosen to maximize

Note that the IDT5V49EE704 should not be programmed

with TSSC > '0', SS_OFFSET = '0', and SD = '0' in order to

prevent an unstable state in the modulator.

the VCO. Start with D = 1, using Eq.6 and Eq.7.

M^NOM= 1200MHz / 25MHz = 48

The PLL loop bandwidth must be at least 10x the

modulation frequency along with higher damping (larger

ωuz) to prevent the spread spectrum from being filtered and

reduce extraneous noise. Refer to the LOOP FILTER

section for more detail on ωuz. The A[3:0] must be used for

spread spectrum, even if the total multiplier value is an even

integer.

Using Eq.4, we arbitrarily choose N = 22, A = 3. Now that we

have the nominal M value, we can determine TSSC and

NSSC by using Eq.8.

Nssc * Tssc = 25MHz / (33KHz * 4) = 190

However, using Eq. 2 and Eq.3, we find that the closest

value is when TSSC = 14 and NSSC = 6. Keep in mind to

maximize the number of samples used

IDT® EEPROM PROGRAMMABLE CLOCK GENERATOR

IDT5V49EE704

REV F 022310

1...6 7 8910 11 12...30

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