Philips Semiconductors
Product specification
Economy Autosync Deflection Controller
(EASDC)
TDA4858
This operation ensures a smooth tuning and avoids fast
changes of horizontal frequency during catching.
Table 1 Calculation of total spread
spread of:
IC
for fmax
3%
for fmin
In this concept it is not allowed to load HPLL1.
3%
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.
CHCAP
RHREF
2%
2%
1%
−
RHREF, RHBUF
−
1% × (2.3 × nS − 1)
8.69%
Total
6%
PLL1 phase detector
Thus the typical frequency range of the oscillator in this
example is:
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).
fmax = fS (max) × 1.06 = 67.84 kHz
fS (min)
fmin
=
= 28.93 kHz
-----------------
1.087
Horizontal oscillator
The resistors RHREF and RHBUF can be calculated with the
following formulae:
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.
74 × kHz × kΩ
RHREF
=
=
= 1.091 kΩ
--------------------------------------
f
max [kHz]
The maximum oscillator frequency is determined by a
resistor from HREF to ground. A resistor from HREF to
HBUF defines the frequency range.
R
HREF × 1.18 × n
RHBUF
= 2.241 kΩ
---------------------------------------------
n – 1
f
The reference current at HREF also defines the integration
time constant of the vertical sync integration.
--m-----a--x-
fmin
Where: n =
= 2.35
The spread of fmin increases with the frequency ratio
fS (max)
Calculation of line frequency range
First the oscillator frequencies fmin and fmax have to be
calculated. This is achieved by adding the spread of the
relevant components to the highest and lowest sync
frequencies fS(min) and fS(max). The oscillator is driven by
the difference of the currents in RHREF and RHBUF. At the
highest oscillator frequency RHBUF does not contribute to
the spread. The spread will increase towards lower
frequencies due to the contribution of RHBUF. It is also
------------------
fS (min)
For higher ratios this spread can be reduced by using
resistors with less tolerances.
fS (max)
dependent on the ratio nS
=
------------------
fS (min)
The following example is a 31.45 to 64 kHz application:
f S (max)
64 kHz
n S
=
=
= 2.04
------------------
fS (min)
---------------------------
31.45 kHz
1997 Oct 27
7
NXP [ NXP ]
