Philips Semiconductors
Product specification
Economy Autosync Deflection Controller
(EASDC)
This operation ensures a smooth tuning and avoids fast
changes of horizontal frequency during catching.
In this concept it is not allowed to load HPLL1.
The frequency dependent voltage at this pin is fed
internally to HBUF (pin 27) via a sample-and-hold and
buffer stage. The sample-and-hold stage removes all
disturbances caused by horizontal sync or composite
vertical sync from the buffered voltage. An external
resistor from HBUF to HREF defines the frequency range.
PLL1 phase detector
The phase detector is a standard type using switched
current sources. It compares the middle of horizontal sync
with a fixed point on the oscillator sawtooth voltage.
The PLL1 loop filter is connected to HPLL1 (pin 26).
Horizontal oscillator
The horizontal oscillator is of the relaxation type and
requires a capacitor of 10 nF at HCAP (pin 29).
For optimum jitter performance the value of 10 nF must not
be changed.
The maximum oscillator frequency is determined by a
resistor from HREF to ground. A resistor from HREF to
HBUF defines the frequency range.
The reference current at HREF also defines the integration
time constant of the vertical sync integration.
Calculation of line frequency range
First the oscillator frequencies f
min
and f
max
have to be
calculated. This is achieved by adding the spread of the
relevant components to the highest and lowest sync
frequencies f
S(min)
and f
S(max)
. The oscillator is driven by
the difference of the currents in R
HREF
and R
HBUF
. At the
highest oscillator frequency R
HBUF
does not contribute to
the spread. The spread will increase towards lower
frequencies due to the contribution of R
HBUF
. It is also
f
S
(
max
)
dependent on the ratio n
S
=
------------------
-
f
S
(
min
)
The following example is a 31.45 to 64 kHz application:
f
S
(
max
)
64 kHz
n
S
=
------------------
=
---------------------------
=
2.04
-
f
S
(
min
)
31.45 kHz
Table 1
Calculation of total spread
for f
max
3%
2%
1%
−
6%
TDA4858
spread of:
IC
C
HCAP
R
HREF
R
HREF
, R
HBUF
Total
for f
min
3%
2%
−
1%
×
(2.3
×
n
S
−
1)
8.69%
Thus the typical frequency range of the oscillator in this
example is:
f
max
=
f
S
(
max
)
×
1.06
=
67.84 kHz
f
S
(
min
)
f
min
=
-----------------
=
28.93 kHz
-
1.087
The resistors R
HREF
and R
HBUF
can be calculated with the
following formulae:
74
×
kHz
×
k
Ω
R
HREF
=
-------------------------------------
=
1.091 kΩ
-
f
max
[
kHz
]
R
HREF
×
1.18
×
n
R
HBUF
=
--------------------------------------------
=
2.241 kΩ
-
n
–
1
f
max
Where:
n
=
----------
=
2.35
-
f
min
The spread of f
min
increases with the frequency ratio
f
S
(
max
)
------------------
-
f
S
(
min
)
For higher ratios this spread can be reduced by using
resistors with less tolerances.
1997 Oct 27
7
PHILIPS [ NXP SEMICONDUCTORS ]
