STA538B 查看數據表（PDF） - STMicroelectronics

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STA538B

2 x 1.3 W class-D amplifier with analog or digital input 2.0 multichannel digital audio processor with FFX

STMicroelectronics 

PLL

STA538

PLL filter

Figure 5 shows the PLL filter scheme. Recommended values are R1 = 12.5 kΩ,

C1 = 250 pF, and C2 = 82 pF.

Figure 5. PLL filter scheme

Vc

R1

C2

C1

Ground

Table 10 on page 14 gives a typical lock time value for the PLL.

5.2

Configuration examples

The STA538 PLL can be configured in two ways:

● default startup configuration

● direct PLL programming

The default startup configuration reads the device’s defaults. With this configuration, it is not

necessary to program the PLL dividers directly as some presets are used. In this mode, the

oversampling ratio between pins XTI (or MCLK33) and LRCLKI is fixed to 256.

The direct PLL programming bypasses the automatic presets allowing direct programming

of the PLL dividers.

The output PLL frequency can be determined as following:

Output division factor:

ODF = 2

Relation between input and output clock frequency:

FINFIN = FXTI / IDF

If register bit PLLCFG0.FRAC_CTRL = 1

FVCO = FINFIN * (LDF + FRACT/216 + 1/217)

FPHI = FVCO / ODF

When register bit PLLCFG0.DITHER_DISABLE[1] = 1, the 1/217 factor is not in the

multiplication. This is recommended in order to keep register bit

PLLCFG0.DITHER_DISABLE[1] = 0, otherwise there can be spurious signals in the output

clock spectrum.

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