FX489 Просмотр технического описания (PDF) - CML Microsystems Plc
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FX489 Datasheet PDF : 12 Pages
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Application Information
VDD
C3
C2
V SS
XTAL
1
X1
R2
2
XTAL/CLOCK
XTAL
XTAL/CLOCK
ClkDivA
ClkDivB
Rx HOLD
RxDCacq
PLLacq
Rx PS
V BIAS
R4
Rx FEEDBACK
R3
Rx SIGNAL IN
C6
VSS
C5
1
24
2
23
3
22
4
21
5
20
6 FX489P 19
7
18
8
17
9
16
10
15
11
14
12
13
VDD
Rx S/N
Tx CLOCK
Rx CLOCK
Rx DATA
Tx DATA
Tx PS
Tx ENABLE
Tx OUT
R1
BT
Doc2
Doc1
C4
V SS
C7
C8
C1
External Components
Component
Value
R1
Note 1
R2
1.0MΩ
R3
Note 2
R4
100kΩ
C1
Note 1
C
33.0pF
2
C
33.0pF
3
Fig.2 External Components
Tolerance
±5%
±10%
±10%
±10%
±10%
±20%
±20%
V SS
C4
C5
C6
C7
C8
X
1
100nF
1.0µF
22.0pF
15.0nF
15.0nF
Note 3
±20%
±20%
±20%
±20%
±20%
Notes
1. The RC network formed by R1 and C1 is required
between the Tx Out pin and the input to the modulator.
This network, which can form part of any d.c. level
shifting and gain adjustment circuitry, forms an
important part of the transmit signal filtering. The ground
connection to the capacitor C1 should be positioned to
give maximum attenuation of high-frequency noise into
the modulator.
The component values should be chosen so that the
product of the resistance (Ohms) and the capacitance
(Farads) is:
BT of 0.3 = 0.34/bit rate (bits/second)
BT of 0.5 = 0.22/bit rate (bits/second)
- with suitable values for common bit rates being:
R1
C1
8000 bits/sec BT = 0.3 91.0kΩ 470pF
4800 bits/sec BT = 0.5 100kΩ 470pF
9600 bits/sec BT = 0.5 47.0kΩ 470pF
NOTE that in all cases, the value of R1 should be not
less than 47.0kΩ and the calculated value of C1 includes
calculated parasitic (circuit) capacitances.
2. R3, R4 and C6 form the gain components for the Rx Input
signal.
R3 should be chosen as required by the signal input
level.
3. The FX489 can operate correctly with Xtal/Clock
frequencies as detailed in Table 1.
Operation of this device without a Xtal or Clock input
may cause device damage.
4
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