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PDF PCK12429D Data sheet ( Hoja de datos )
| Número de pieza | PCK12429D | |
| Descripción | 25-400 MHz differential PECL clock generator | |
| Fabricantes | NXP Semiconductors | |
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INTEGRATED CIRCUITS
PCK12429
25–400 MHz differential PECL
clock generator
Product data
Supersedes data of 2002 Mar 15
2002 Jun 03
Philips
Semiconductors
1 page  
Philips Semiconductors
25–400 MHz differential PECL clock generator
Product data
PCK12429
BLOCK DIAGRAM
16 MHz
OE
S_LOAD
P_LOAD
S_DATA
S_CLOCK
+3.3 V
DIV 16
1 MHz
FREF
XTAL1
OSC
XTAL2
PHASE
DETECTOR
PLL_VCC
VCO
9-BIT DIV M
COUNTER
200–400
MHz
DIV N
(1, 2, 4, 8)
VCC0
LATCH
LATCH
0
9-BIT
SR
1
0
2-BIT
SR
1
LATCH
3-BIT
SR
VCC1
+3.3 V
9
M[8:0]
2
N[1:0]
+3.3 V
FOUT
FOUT
TEST
N[1:0] Output Division
00 1
01 2
10 4
11 8
SW00728
PROGRAMMING INTERFACE
Programming the device amounts to properly configuring the internal
dividers to produce the desired frequency at the outputs. The output
frequency can be represented by this formula:
FOUT = (FXTAL ÷ 16) × M ÷ N
(1)
Where FXTAL is the crystal frequency, M is the loop divider modulus,
and N is the output divider modulus. Note that it is possible to select
values of M such that the PLL is unable to achieve loop lock. To
avoid this, always make sure that M is selected to be 200 ≤ M ≤ 400
for a 16 MHz input reference.
Assuming that a 16 MHz reference frequency is used, the above
equation reduces to:
FOUT = M ÷ N
Substituting the four values for N (1, 2, 4, or 8) yields:
FOUT = M, FOUT = M ÷ 2,
FOUT = M ÷ 4 and FOUT = M ÷ 8
for 200 ≤ M ≤ 400
The user can identify the proper M and N values for the desired
frequency from the above equations. The four output frequency
ranges established by N are 200–400 MHz, 100–200 MHz,
50–100 MHz, and 25–50 MHz respectively. From these ranges the
user will establish the value of N required, then the value of M can
be calculated based on the appropriate equation above. For
example, if an output frequency of 131 MHz was desired, the
following steps would be taken to identify the appropriate M and N
values. 131 MHz falls within the frequency range set by an N value
of 2 so N [1:0] = 01. For N = 2 FOUT = M ÷ 2 and M = 2 × FOUT.
Therefore, M = 131 × 2 = 262, so M[8:0] = 100000110. Following this
same procedure a user can generate any whole frequency desired
between 25 and 400 MHz. Note that for N ≥ 2 fractional values of
FOUT can be realized. The size of the programmable frequency
steps (and thus the indicator of the fractional output frequencies
achievable) will be equal to FXTAL ÷ 16 ÷ N.
For input reference frequencies other than 16 MHz, the set of
appropriate equations can be deduced from equation 1. For
computer applications another useful frequency base would be
16.666 MHz. From this reference, one can generate a family of
output frequencies at multiples of the 33.333 MHz PCI clock. As an
example, to generate a 133.333 MHz clock from a 16.666 MHz
reference, the following M and N values would be used:
FOUT = 16.666 ÷ 16 × M ÷ N = 1.041625 × M ÷ N
Let N = 2, M = 256,
FOUT = 1.041625 × 256 ÷ 2 = 133.328 MHz
The value for M falls within the constraints set for PLL stability,
therefore N[1:0] = 01 and M[8:0] = 100000000. If the value for M fell
outside of the valid range a different N value would be selected to try
to move M in the appropriate direction.
The M and N counters can be loaded either through a parallel or
serial interface. The parallel interface is controlled via the P_LOAD
signal such that a LOW to HIGH transition will latch the information
present on the M[8:0] and N[1:0] inputs into the M and N counters.
When the P_LOAD signal is LOW the input latches will be
transparent and any changes on the M[8:0] and N[1:0] inputs will
2002 Jun 03
5
5 Page 
Philips Semiconductors
25–400 MHz differential PECL clock generator
SO28: plastic small outline package; 28 leads; body width 7.5 mm
Product data
PCK12429
SOT136-1
2002 Jun 03
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet PCK12429D.PDF ] | |
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