CS2000-OTP

10

DS758PP1

5. APPLICATIONS

5.1

One Time Programmability

The one time programmable (OTP) circuitry in the CS2000-OTP allows for pre-configuration of the device

prior to use in a system. There are two types of parameters that are used for device pre-configuration: modal

and global. The modal parameters are features which, when grouped together, create a modal configuration

set (see Figure 16 on page 23). Up to four modal configuration sets can be permanently stored and then

dynamically selected using the M[1:0] mode select pins (see Table 1). The global parameters are the re-

maining configuration settings which do not change with the mode select pins. The modal and global pa-

rameters can be pre-set at the factory or user programmed using the customer development kit, CDK2000;

Please see “Programming Information” on page 28 for more details.

Table 1. Modal and Global Configuration

5.2

Timing Reference Clock Input

The low jitter timing reference clock (RefClk) can be provided by either an external reference clock or an

external crystal in conjunction with the internal oscillator. In order to maintain a stable and low-jitter PLL out-

put the timing reference clock must also be stable and low-jitter; the quality of the timing reference clock

directly affects the performance of the PLL and hence the quality of the PLL output.

5.2.1

Internal Timing Reference Clock Divider

The Internal Timing Reference Clock (SysClk) is limited to a lower maximum frequency than that allowed

on the XTI/REF_CLK pin. The CS2000-OTP supports the wider external frequency range by offering an

internal divider for RefClk. The RefClkDiv[1:0] global parameter should be configured such that SysClk,

the divided RefClk, then falls within the valid range as indicated in Figure 5.

It should be noted that the maximum allowable input frequency of the XTI/REF_CLK pin is dependent

upon its configuration as either a crystal connection or external clock input. See the “AC Electrical Char-

acteristics” on page 7 for more details.

Parameter Type

M[1:0] pins = 00

M[1:0] pins = 01

M[1:0] pins = 10

M[1:0] pins = 11

Modal

Configuration Set 0

Ratio 0

Configuration Set 1

Ratio 1

Configuration Set 2

Ratio 2

Configuration Set 3

Ratio 3

Global

Configuration settings set once for all modes.

Referenced Control

Parameter Definition

RefClkDiv[1:0] .......................“Reference Clock Input Divider (RefClkDiv[1:0])” on page 25

Figure 5. Internal Timing Reference Clock Divider

N

Internal Timing

Reference Clock

PLL Output

Fractional-N

Frequency

Synthesizer

Timing Reference

Clock Divider

XTI/REF_CLK

RefClkDiv[1:0]

8 MHz < SysClk < 18.75 MHz

8 MHz < RefClk <

Timing Reference Clock

50 MHz (XTI)

75 MHz (REF_CLK)