Application Information
......
(5)
Timing Components
(6)
Protection Diodes
In the ‘SPM Packet’ mode R
5
and C
4
set the minimum
'Tone' period (t
M
), R
6
and C
5
set the minimum 'Space'
period (t
S
), and are calculated as follows:
t
M
= 0.7(R
5
x C
4
).
t
S
= 0.7(R
6
x C
5
).
As most telephone systems operate at voltages in excess
of the Absolute Maximum Limits for damage, diodes D
1
–
D
4
are essential for device protection.
When calculating Tone and Space time settings the following
points should be taken into consideration:
(7)
(1)
(2)
(3)
Response and De-response times t
R
and t
D
.
Component tolerances can alter the calculation.
The MINIMUM expected pulse/space length must
be catered for.
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
t
R
OUTPUT
t
D
NOTE
t
R
NOTE
t
D
SPM PACKET MODE
TONE INPUT
t
R
t
M
OUTPUT
t
D
t
S
t
R
OUTPUT RESET
t
RESET
Fig.3 Output Timing
Example Values
–
for the FX621 to operate with the West German (16kHz) 'FTZ' Specification.
(a) Min. 'Will Decode' Level
(b) Max. 'Will Decode' Level
(c) Max. 'Will-Not Decode' Level
(d) Device Sensitivity @ 3.5V V
DD
Min. Gain Required
Max. Gain Allowed
Chosen Gain Figure
=
=
=
≈
≈
≈
=
71.3 mV rms
10.0 V rms
34.6 mVrms
248.0 mVrms
3.47
7.17
4.7
For a chosen gain figure of 4.7, a minimum Tone length
of 80ms, a minimum Space length of 135ms and a V
DD
of 3.5V, the required component values are :
R
1
R
2
R
3
R
4
R
5
R
6
X
1
Tolerances:
68kΩ
68kΩ
390kΩ
390kΩ
100kΩ
120kΩ
4.433619MHz
C
1
C
2
C
3
C
4
C
5
C
6
C
7
C
8
330pF
330pF
1.0µF
820nF
1.0µF
1.0µF
12pF
12pF
(d
÷
a)
(d
÷
c)
Resistors =
±1%.
Capacitors =
±10%
.
4
CMLMICRO [ CML MICROCIRCUITS ]
