STV6889 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'STV6889' PDF : 56 Pages View PDF
STV6889
Figure 5. Horizontal PLL1 block diagram
H/HVSyn
1
Sync
Polarity
INPUT
INTERFACE
Extracted
V-sync
PLL1
HLckVBk
Blank 3
PLL1InhEn
(I²C) V-sync (extracted)
HLock
(I²C)
HPLL1F RO CO HOscF
9 86 4
LOCK
DETECTOR
High
PLL
INHIBITION
COMP
REF1
CHARGE
PUMP
Low
PLL1Pump
(I²C)
HPosF
10
SHAPER
VCO
HOSC
HPOS
(I²C)
Figure 6. Horizontal oscillator (VCO) schematic diagram
(PLL1 filter)
HPLL1F 9 VHO +
-
from charge pump
I0
I0
2
4 I0
RO 8
4 HOscF
VHOThrHi
+
-
-
VHOThrLo +
RS
Flip-Flop
6 CO
VHOThrHi
VHOThrLo
VCO discharge
control
9.3.3 Voltage controlled oscillator
The VCO makes part of both PLL1 and PLL2
loops, being an “output” to PLL1 and “input” to
PLL2. It delivers a linear sawtooth. Figure 6 ex-
plains its principle of operation. The linears are ob-
tained by charging and discharging an external ca-
pacitor on pin CO, with currents proportional to the
current forced through an external resistor on pin
RO, which itself depends on the input tuning volt-
age VHO (filtered charge pump output). The rising
and falling linears are limited by VHOThrLo and VHO-
ThrHi thresholds filtered through HOscF pin.
At no signal condition, the VHO tuning voltage is
clamped to its minimum (see section 6.4 - page
10), which corresponds to the free-running VCO
frequency fHO(0). Refer to subsection 9.3.1 for formu-
la to calculate this frequency using external com-
ponents values. The ratio between the frequency
corresponding to maximum VHO and the one corre-
sponding to minimum VHO (free-running frequen-
cy) is about 4.5. This range can easily be in-
creased in the application. The PLL1 can only lock
to input frequencies falling inside these two limits.
33/56
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