73M1903-IVT/F Maxim Integrated Products, 73M1903-IVT/F Datasheet - Page 46

• Manufacturer Part Number: 73M1903-IVT/F
• Description: IC MODEM AFE V.22BIS 20-TSSOP
• Manufacturer: Maxim Integrated Products

Specifications of 73M1903-IVT/F

• Number Of Channels: 2
• Voltage - Supply, Analog: 3 V ~ 3.6 V
• Voltage - Supply, Digital: 3 V ~ 3.6 V
• Package / Case: 20-TSSOP (0.173", 4.40mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power (watts): -
• Number Of Bits: -

73M1903 Data Sheet
Example 3:
Crystal Frequency = 27 MHz; Desired Sampling Rate, Fs = 7.2 kHz
Step 1. First compute the required VCO frequency, Fvco, corresponding to
Fs = 2.4 kHz x 3 = 7.2 kHz.
Fvco = 2 x 2304 x Fs = 2 x 2304 x 2.4 kHz x 3 = 33.1776 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 two ratios are not unique and many other possibilities exist. But for this particular application, they
are found to be the best set of choices within the constraints of Prst and Nrst allowed. (Nnco1, Nnco2
must be less than or equal to 8.)
The ratio, Nnco1/Dnco1 = 8/125, is used to form a divide ratio for the NCO in prescaler and Nnco2/Dnco2
=5/96 for the NCO in the PLL.
Pre-scaler NCO: From Nnco1/Dnco1 = 8/125,
Pdvsr = Integer [ Dnco1/Nnco1 ] = 15;
Prst[2:0] = Nnco1 – 1 = 7;
Dnco1/Nnco1 = 125/8 = 15.625 suggests a divide sequence of {÷16,÷16,÷15,÷16,÷16,÷15,÷16,÷15}, or
Pseq = {1,1,0,1,1,0,1,0} = DAh.
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.
46
Fvco
=
Fvco
/
Fxtal
/
Fxtal
=
(
Dnco2
Nnco1
Dnco1
Nnco2
=
125
8
2
)
•
•
(
2304
=
27
96
•
5
MHz
2.4kHz
)
125
96
8
5
•
3
.
DS_1903_032
Rev. 2.1