TDA9105A View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
TDA9105A Datasheet PDF : 31 Pages
| |||
TDA9105A
OPERATING DESCRIPTION (continued)
The PLL1 ensures the coincidence between the
leading edge of the synchro signal and a phase
reference obtained by comparison between the
sawtooth of the VCO and an internal DC voltage
adjustable between 2.4V and 4V (by Pin 15). So a
±45° phase adjustment is possible (see Figure 11).
Figure 14 : PLL1 Timing Diagram
H Osc
Sawtooth 0.75T
0.25T
Phase REF1
6.4V
2.4V<Vb<4V
Vb
1.6V
H Synchro
Phase REF1 is obtained by comparison between the sawtooth and
a DC voltage adjustable between 2.4V and 4V. The PLL1 ensures
the exact coincidence between the signals phase REF and
HSYNS. A ± T/8 phase adjustment is possible.
The two VCO threshold can be filtered by connect-
ing capacitor on Pins 8-9.
The TDA9103 also includes a LOCK/UNLOCK
identification block which senses in real-time
Figure 15 : LOCK/UNLOCK Block Diagram
whether the PLL is locked on theincoming horizon-
tal sync signal or not. The resulting information is
available on HLOCKOUT output (Pin 2). The block
diagram of the LOCK/UNLOCK function is de-
scribed in Figure 12.
The NOR1 gate is receiving the phase comparator
output pulses (which also drive the charge pump).
When the PLL is locked, on point A there is a very
small negative pulse (100ns) at each horizontal
cycle, so after R-C filter, there is a high level on
Pin 13 which force HLOCKOUT to high level (pro-
vided that HLOCKOUT is pulled up to VCC).
When the PLL is unlocked, the 100ns negative
pulse on A becomesmuch larger and consequently
the average level on Pin 13 will decrease. When it
reaches 6.5V, point B goes to low level forcing
HLOCKOUT output to “0”.
The status of Pin 13 is approximately the following :
- Near 0V when there is no H-SYNC,
- Between 0 and 4V with H-SYNC frequency differ-
ent from VCO,
- Between 4 and 8V when H-SYNC frequency
= VCO frequency but not in phase,
- Near to 8V when PLL is locked.
It is important to notice that Pin 13 is not an output
pin and must only be used for filtering purpose (see
Figure 12).
From
Phase
A
NOR1
20kΩ H-Lock CAP
13
B
Comparator
6.5V
220nF
2
HLOCKOUT
16/31
Share Link: 