Datasheet

PLL_N_MODPLL_N
8
8 5
6'M
% N
% PVCO
0
% M
PLL_M
0.5-30 MHz
PLL_P
External Loop
Filter
40 to 60 MHz
250 x FS
7
4
0.5 < 5 MHz
Phase Comparator
and Charge Pump
N = 10..250 31/32
P = 1..8
P = 0,1 + 0/2 - >64
LM49370
www.ti.com SNAS356D –FEBRUARY 2007–REVISED MARCH 2012
The complete N divider is a fractional divider as such:
N = PLL_N + PLL_N_MOD/32
If the modulus input is zero then the N divider is simply an integer N divider. The output from the PLL is
determined by the following formula:
F
out
= (F
in
*N)/(M*P)
FURTHER NOTES ON PLL PROGRAMMING
The sigma-delta PLL Is designed to drive audio circuits requiring accurate clock frequencies of up to 30MHz with
frequency errors noise-shaped away from the audio band. The 5 bits of modulus control provide exact
synchronization of 48kHz and 44.1kHz sample rates from any common system clock. In systems where an
isochronous I
2
S data stream is the source of data to the DAC a clock synchronous to the sample rate should be
used as input to the PLL (typically the I
2
S clock). If no isochronous source is available, then the PLL can be used
to obtain a clock that is accurate to within 1Hz of the correct sample rate although this is highly unlikely to be a
problem.
Figure 14. PLL Overview
Table 10. Example PLL Settings for 48 kHz and 44.1 kHz Sample Rates in DAC MODE 00
F
in
(MHz) F
s
(kHz) M N P PLL_M PLL_N PLL_N_MO PLL_P F
out
(MHz)
D
11 48 11 60 5 21 60 0 9 12
12.288 48 4 19.53125 5 7 19 17 9 12
13 48 13 60 5 25 60 0 9 12
14.4 48 9 37.5 5 17 37 16 9 12
16.2 48 27 100 5 53 100 0 9 12
16.8 48 14 50 5 27 50 0 9 12
19.2 48 13 40.625 5 25 40 20 9 12
19.44 48 27 100 6 53 100 0 11 12
19.68 48 20.5 62.5 5 40 62 16 9 12
19.8 48 16.5 50 5 32 50 0 9 12
11 44.1 11 55.125 5 21 55 4 9 11.025
11.2896 44.1 8 39.0625 5 15 39 2 9 11.025
12 44.1 5 22.96875 5 9 22 31 9 11.025
13 44.1 13 55.125 5 25 55 4 9 11.025
14.4 44.1 12 45.9375 5 23 45 30 9 11.025
16.2 44.1 9 30.625 5 17 9 20 9 11.025
16.8 44.1 17 55.78125 5 33 30 25 9 11.025
19.2 44.1 16 45.9375 5 31 45 30 9 11.025
19.44 44.1 13.5 38.28125 5 26 38 9 9 11.025
19.68 44.1 20.5 45.9375 4 40 45 30 7 11.025
19.8 44.1 11 30.625 5 21 30 20 9 11.025
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