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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
37 of 808
NXP Semiconductors
UM10360
Chapter 4: LPC17xx Clocking and power control
The PLL0 output frequency (when PLL0 is both active and connected) is given by:
F
CCO
= (2
×
M
×
F
IN
) / N
PLL inputs and settings must meet the following:
•
F
IN
is in the range of 32 kHz to 50 MHz.
•
F
CCO
is in the range of 275 MHz to 550 MHz.
The equation can be solved for other PLL parameters:
M = (F
CCO
×
N) / (2
×
F
IN
)
N = (2
×
M
×
F
IN
) / F
CCO
F
IN
= (F
CCO
×
N) / (2
×
M)
Allowed values for M:
At higher oscillator frequencies, in the MHz range, values of M from 6 through 512 are
allowed. This supports the entire useful range of both the main oscillator and the IRC.
For lower frequencies, specifically when the RTC is used to clock PLL0, a set of 65
additional M values have been selected for supporting baud rate generation, CAN/USB
operation, and attaining even MHz frequencies. These values are shown in
N
PLL0 Pre-divider value from the NSEL0 bits in the PLL0CFG register
(PLL0CFG NSEL0 field + 1). N is an integer from 1 through 32.
M
PLL0 Multiplier value from the MSEL0 bits in the PLL0CFG register
(PLL0CFG MSEL0 field + 1). Not all potential values are supported. See
below.
F
REF
PLL internal reference frequency, F
IN
divided by N.
Table 26.
Additional Multiplier Values for use with a Low Frequency Clock Input
Low Frequency PLL Multipliers
4272
4395
4578
4725
4807
5127
5188
5400
5493
5859
6042
6075
6104
6409
6592
6750
6836
6866
6958
7050
7324
7425
7690
7813
7935
8057
8100
8545
8789
9155
9613
10254
10376
10986
11719
12085
12207
12817
13184
13672
13733
13916
14099
14420
14648
15381
15564
15625
15869
16113
16479
17578
18127
18311
19226
19775
20508
20599
20874
21149
21973
23071
23438
23804
24170
Table 25.
PLL frequency parameter
Parameter
Description