SP8855 Ver la hoja de datos (PDF) - Mitel Networks
Número de pieza
componentes Descripción
Fabricante
SP8855 Datasheet PDF : 14 Pages
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SP8855E
VCC
+5V
* VALUES DEPEND
ON APPLICATION
RF COUNTER
PROGRAMMING
1k
1n
VCO
APPLICATION USING
CRYSTAL REFERENCE
SP8855
27
28
33p
10MHz
100p
CRYSTAL
1n
7
8
9
10
11
12
13
14
15
16
17
2k2
10n
*100n
Fpd Fref
1µ
10n
REFERENCE COUNTER
PROGRAMMING
VCC
39
38
37
36
35
34
33
32
31
30
29
LOOP
FILTER
*
*
*
+30V
-
+ OP27
ETC
1n
100n
Fig. 5 Typical application diagram
Ref in
DESCRIPTION
Prescaler and AM counter
The programmable divider chain is of AM counter
construction and therefore contains a dual modulus front end
prescaler, an A counter which controls the dual modulus ratio
and an M counter which performs the bulk multi-modulus
division. A programmable divider of this construction has a
division ratio of MN+A and a minimum integer steppable
division ratio of N(N-1), where N is the prescaler ratio.
Phase Comparator and Charge pump
The SP8855E has a digital phase/frequency comparator
driving a charge pump with programmable current output.
The charge pump current level at the minimum gain setting
is approximately equal to the current fed into the Rset input
pin 19 and can be increased by programming pins 40 and
41 according to Table 1 by up to 4 times.
Programming
The device is programmed by connecting the
programming pins to either VCC or ground. The programming
inputs will go high if left open circuit but for best noise immunity
a wired connection to VCC is preferable. The programming
inputs can be driven from TTL or CMOS logic levels if required.
Reference input
The reference source can be either driven from an external
sine or square wave source of up to 100MHz or a crystal can
be connected as shown in Fig. 5.
Pin 40
0
0
1
1
Pin 41
Current Multiplication
Factor
0
1.0
1
1.5
0
2.5
1
4.0
Table 1
6
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