TDA9109SN STMICROELECTRONICS [STMicroelectronics], TDA9109SN Datasheet - Page 21

• Manufacturer Part Number: TDA9109SN
• Description: LOW-COST DEFLECTION PROCESSOR FOR MULTISYNC MONITORS
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

OPERATING DESCRIPTION (continued)
III - VERTICAL PART
III.1 - Function
When the synchronization pulse is not present, an
internal current source sets the free running fre-
quency. For an external capacitor, C
the typical free running frequency is 100Hz.
The typical free running frequency can be calcu-
lated by :
A negative or positive TTL level pulse applied on
Pin 2 (VSYNC)as well as a TTLcomposite sync on
Pin 1 can synchronize the ramp in the range
[fmin , fmax]. This frequencyrange depends on the
ext e rn al capa c it or con nect ed on Pin 2 2.
A 150nF ( 5%) capacitor is recommended for
50Hz to 185Hz applications.
The typical maximum and minimum frequency, at
25
C correction), can be calculated by :
Figure 15 : AGC Loop Block Diagram
VSYNCIN
o
C and without any correction (S correction or
f
(Max.)
2
f
0
= 3.5 x f
Hz
SYNCHRO
POLARITY
1.5 10
0
and f
(Min.)
5
C
= 0.33 x f
OSC
1
OSC
OSCILLATOR
= 150nF,
0
DISCH.
If S or C corrections are applied, these values are
slighty affected.
If a synchronization pulse is applied, the internal
oscillator is synchonized immediately but its
amplitude chan ges. An internal correction then
adjusts it in less than half a second. The top
value of the ramp (Pin 22) is sampled on the
AGC capacitor (Pin 20) at each clock pulse and
a transconduct ance amplifier modifies the
charge current of the capacitor in such a way to
make the amplitude again constant.
The read status register provides the vertical Lock-
Unlock and the vertical sync polarity information.
We recommend the use of an AGC capacitor with
low leakage current. A value lower than 100nA is
mandatory.
A good stability of the internal closed loop is
reached by a 470nF
Pin 20 (VAGC).
22
Vlow
OSC
CAP
SUB0C/5bits
SUB06/7bits
CHARGE CURRENT
VPOSITION
VMOIRE
Sawth.
Disch.
VERT_AMP
SUB05/7bits
SAMPLING
5% capacitor value on
TRANSCONDUCTANCE
REF
20
SAMPLING
CAPACITANCE
AMPLIFIER
C CORRECTION
S CORRECTION
VS_AMP
SUB07/6bits
COR_C
SUB08/6bits
TDA9109/SN
18 BREATH
23 VOUT
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