3 pll, 3 clocking, 3 pll -12 – Cirrus Logic CS4953xx User Manual

Page 100: 3 clocking -12, Figure 9-9. pll filter topology -12, Table 9-5. pll filter pins -12, Table 9-6. reference pll component values -12, Cs497xx

Clocking

CS4953xx Hardware User’s Manual

DS732UM10

9-12

9.2.3 PLL

The internal phase locked loop (PLL) of the CS4953xx requires an external current reference resistor. The
resistor is used to calibrate the PLL and must meet the tolerances specified below. The layout topology is
shown in the typical connection diagrams. Care should be taken when laying out the current sense
circuitry to minimize trace lengths between the DSP and resistor, and to keep high-frequency signals
away from the resistor. Any noise coupled onto the these traces will be directly coupled into the PLL,
which could affect performance. Please see tables below for pin numbers and external component values.

Figure 9-9. PLL Filter Topology

9.3 Clocking

The CS4953xx incorporates a programmable phase locked loop (PLL) clock synthesizer. The PLL takes
an input reference clock and produces all the clocks required to run the DSP and peripherals.

In A/V Receiver designs that require low-jitter clocks, the XTI pin is typically connected to an external
12.288 MHz or 24.576 Mhz oscillator that is used throughout the system.

The CS4953xx has a built-in crystal oscillator circuit. A parallel resonant-type crystal is connected
between the XTI and XTO pins as shown in

Figure 9-10

. The value of C1 is specific to each crystal. The

CS4953xx data sheet specifies acceptable crystal parameters (including C

and ESR). When a crystal is

used, XTAL_OUT is used to clock other devices in the system such as the S/PDIF receiver.

The PLL is controlled by the clock manager in the DSP O/S application software. AN288, “CS4953xx
Firmware User’s Manual” should be referenced regarding what CLKIN input frequency and PLL multiplier
values are supported.

Table 9-5. PLL Filter Pins

LQFP-144 Pin

LQFP-128 Pin

Pin Name

Pin Type

Pin Description

128

PLL_REF_RES

Input

Current Reference Resistor for
PLL filter

Table 9-6. Reference PLL Component Values

Symbol

Reference Value

5.1 k

Ω,

PLL_REF_RES

GNDA

CS497xx

VDDA

3.3V

Bead

10u

0.1u