73M1903C-EVM Maxim Integrated Products, 73M1903C-EVM Datasheet - Page 47

• Manufacturer Part Number: 73M1903C-EVM
• Description: BOARD DEMO 73M1903C WORLDWIDE
• Manufacturer: Maxim Integrated Products

Specifications of 73M1903C-EVM

• Main Purpose: Interface, Analog Front End (AFE)
• Utilized Ic / Part: *
• Primary Attributes: *
• Secondary Attributes: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Embedded: -

DS_1903C_033
PLL NCO: From Nnco2/Dnco2 = 5/96,
Ndvsr = Integer [ Dnco2/Nnco2 ] = 19;
Nrst[2:0] = Nnco2 – 1 = 4;
Dnco2/Nnco2 = 19.2 suggests a divide sequence of {÷19, ÷19, ÷19, ÷19, ÷20}, or
Nseq = {x,x,x,0,0,0,0,1} = x1h.
Example 4
Crystal Frequency = 24.576 MHz; Desired Sampling Rate, Fs = 16.0 kHz
Step 1. First compute the required VCO frequency, Fvco, corresponding to
Fs = 2.4 kHz x 20/3 = 16.0 kHz.
Fvco = 2 x 2304 x Fs = 2 x 2304 x 2.4 kHz x 20/3 = 73.728 MHz.
Step 2. Express the required VCO frequency divided by the Crystal Frequency as a ratio of two integers.
This is initially given by:
After a few rounds of simplification this reduces to:
The ratio, Nnco1/Dnco1 = 1/1, is used to form a divide ratio for the NCO in prescaler and Nnco2/Dnco2
=1/24 for the NCO in the PLL.
Pre-scaler NCO: From Nnco1/Dnco1 = 1/8,
Pdvsr = Integer [ Dnco1/Nnco1 ] = 8 = 08h,
Prst[2:0] = Nnco1 – 1 = 0; this means NO fractional divide. It always does ÷8. Thus, Pseq becomes
“don’t care”.
Pseq = {x,x,x,x,x,x,x,x}= xxh.
PLL NCO: From Nnco2/Dnco2 = 1/24,
Ndvsr = Integer [ Dnco2/Nnco2 ] = 24 = 18h,
Nrst[2:0] = Nnco2 – 1 = 0; this means NO fractional divide. It always does ÷24. Thus, Nseq becomes
“don’t care”.
Nseq = {x,x,x,x,x,x,x,x} = xxh.
Rev. 5.0
Fvco
=
Fvco
/
Fxtal
/
Fxtal
=
(
Nnco1
Dnco1
Nnco2
Dnco2
=
24
1
2
)
•
•
2304
(
=
24
•
.
1
8
576
2.4kHz
MHz
)
24
1
8
1
•
20/3
.
73M1903C Data Sheet
47