CS2300-OTP_09 Datasheet, PDF (11/26 Pages) Cirrus Logic – Fractional-N Clock Multiplier with Internal LCO

5. APPLICATIONS
CS2300-OTP
5.1 One Time Programmability
The one time programmable (OTP) circuitry in the CS2300-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 14 on page 19). 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 23 for more details.
Parameter Type
Modal
Global
M[1:0] pins = 00
Configuration Set 0
Ratio 0
M[1:0] pins = 01 M[1:0] pins = 10
Configuration Set 1
Ratio 1
Configuration Set 2
Ratio 2
Configuration settings set once for all modes.
M[1:0] pins = 11
Configuration Set 3
Ratio 3
Table 1. Modal and Global Configuration
5.2 Timing Reference Clock
The internal LC oscillator is used to generate the timing reference clock. A single 0.1 µF cap must be con-
nected between the FILTP and FILTN pins and FILTN must be connected to ground as shown in Figure 7.
FILTN
FILTP
0.1 µF
Figure 7. External Component Requirements for LCO
5.3 Frequency Reference Clock Input, CLK_IN
The frequency reference clock input (CLK_IN) is used by the Digital PLL and Fractional-N Logic block to
dynamically generate a fractional-N value for the Frequency Synthesizer (see “Hybrid Analog-Digital PLL”
on page 10). The Digital PLL first compares the CLK_IN frequency to the PLL output. The Fractional-N logic
block then translates the desired ratio based off of CLK_IN to one based off of the internal LCO. This allows
the low-jitter internal LCO to be used as the clock which the Frequency Synthesizer multiplies while main-
taining synchronicity with the frequency reference clock through the Digital PLL. The allowable frequency
range for CLK_IN is found in the “AC Electrical Characteristics” on page 7.
5.3.1
Adjusting the Minimum Loop Bandwidth for CLK_IN
The CS2300 allows the minimum loop bandwidth of the Digital PLL to be adjusted between 1 Hz and
128 Hz using the ClkIn_BW[2:0] global parameter. The minimum loop bandwidth of the Digital PLL direct-
ly affects the jitter transfer function; specifically, jitter frequencies below the loop bandwidth corner are
passed from the PLL input directly to the PLL output without attenuation. In some applications it is desir-
able to have a very low minimum loop bandwidth to reject very low jitter frequencies, commonly referred
DS844F1
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