FX621 查看數據表（PDF） - CML Microsystems Plc
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FX621 Datasheet PDF : 6 Pages
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Application Information ......
(5)
Timing Components
In the ‘SPM Packet’ mode R and C set the minimum
5
4
'Tone' period (tM), R6 and C5 set the minimum 'Space'
period (t ), and are calculated as follows:
S
t = 0.7(R x C ).
M
5
4
t = 0.7(R x C ).
S
6
5
When calculating Tone and Space time settings the following
points should be taken into consideration:
(1) Response and De-response times tR and tD.
(2) Component tolerances can alter the calculation.
(3) The MINIMUM expected pulse/space length must
be catered for.
(6)
Protection Diodes
As most telephone systems operate at voltages in excess
of the Absolute Maximum Limits for damage, diodes D1 –
D are essential for device protection.
4
(7)
Component Tolerances
The tolerances of external components used with this
device are dependent upon the required accuracy of the
gain and pulse period timings.
Timing
Figure 3 shows the FX621 output timing – Timing value limits are given on the “Specification” page.
Note – There is no reaction to pulses or drop-outs of less than the valid Response or De-response time.
TONE FOLLOWER MODE
TONE INPUT
tR
tD
NOTE
tR
NOTE
tD
OUTPUT
TONE INPUT
OUTPUT
tR
tM
SPM PACKET MODE
tD
tR
tS
OUTPUT RESET
Fig.3 Output Timing
t RESET
Example Values – for the FX621 to operate with the West German (16kHz) 'FTZ' Specification.
(a) Min. 'Will Decode' Level
(b) Max. 'Will Decode' Level
= 71.3 mV rms
= 10.0 V rms
For a chosen gain figure of 4.7, a minimum Tone length
of 80ms, a minimum Space length of 135ms and a VDD
of 3.5V, the required component values are :
(c) Max. 'Will-Not Decode' Level
R
= 34.6 mVrms
1
R
2
68kΩ
68kΩ
C
330pF
1
C
330pF
2
(d) Device Sensitivity @ 3.5V V
DD
≈
248.0 mVrms
R3
R
4
390kΩ
390kΩ
C3
1.0µF
C
820nF
4
Min. Gain Required
(d÷a) ≈ 3.47
R5
100kΩ
R
6
120kΩ
C5
1.0µF
C
6
1.0µF
Max. Gain Allowed
(d÷c) ≈ 7.17
C7
12pF
X
4.433619MHz
C
12pF
1
8
Chosen Gain Figure
= 4.7
Tolerances: Resistors = ±1%. Capacitors = ±10%.
4
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