STV9425 STMicroelectronics, STV9425 Datasheet - Page 13

• Manufacturer Part Number: STV9425
• Description: Video ICs On-Screen Disp Montr
• Manufacturer: STMicroelectronics
• Type: Multisync On-Screen Display For Monitorr

Specifications of STV9425

• Maximum Operating Temperature: + 70 C
• Package / Case: DIP-24
• Minimum Operating Temperature: 0 C
• Mounting Style: Through Hole
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FUNCTIONAL DESCRIPTION (continued)
VIII.2 - How to choose the value of the time
constant ?
The time response of the PLL is given by its char-
acteristic equation which is :
Where :
(LD[5:0] = value of the LINE DURATION register,
A = value of the 1st time constant, AF or AS and
B = value of the 2
As you can see, the solution depend only on the
LINE DURATION and the TIME CONSTANTS
given by the I
If
ble and its response is like this presented on
Figure 11.
Figure 11 : Time Response of the PLL/Charac-
If
this presented on Figure 12.
Table 2 : Valid Time Constants Examples
Note : 1. Case of A[2:0] = 1 (001) and B[2:0] = 4 (100) :
LD
Valid Time Constants
3 LD[5:0] 2
B \ A
0
1
2
3
4
5
6
7
PLL
Frequency
Input
Frequency
2
2
x
4
4
1
teristic Equation Solutions (with
Real Solutions)
2
C registers.
2
f
f
f
f
1
0
1
0
NNNY
NNNN
NNNN
NNNN
NNNN
0 and 2
0, the response of the PLL is like
YYYY
YYYY
NYYY
A
d
0
time constant, BF or BS).
11
and
16
N
x
NYYY
NNNN
NNNN
NNNY
YYYY
YYYY
YYYY
YYYY
3 LD[5:0] 2
1
1
4, the PLL is sta-
32
Y
(1)
48
0
Y
.
t
t
NNNY
YYYY
YYYY
YYYY
YYYY
YYYY
YYYY
NYYY
B
2
63
Y
19
.
In this case the PLL is stable if
coefficient).
The Table 2 gives some good values for A and B
constants for different values of the LINE DURA-
TION.
Summary
For a good working of the PLL :
- A and B time constants must be chosen among
- B must be equal or greater than A and the differ-
- The greater (A, B) are, the faster the capture is.
An optimalchoice for the most of applicationsmight
be :
- For locking condition : AS = 0 and BS = 1,
- For capture process : AS = 2 and BS = 4.
But for each application the time constants can be
calculated by solving the characteristic equation
and choosing the best response.
Value of LINE DURATION Register (@ 3FF0) :
LD = 16 : LD[5:0] = 010000
LD = 32 : LD[5:0] = 100000
LD = 48 : LD[5:0] = 110000
LD = 63 : LD[5:0] = 111111
Table meaning :
N = No possible capture
Y = PLL can lock
Figure 12 : Time Response of the PLL/Charac-
YYYN
YYYN
YYYN
YYYN
YYYN
YYYN
YYYN
YYYN
values for which the PLL is stable,
ence between them must be less than 3,
3
PLL
Frequency
Input
Frequency
STV9425 - STV9425B - STV9426
f
f
f
f
1
0
1
0
teristic Equation Solutions (with
Complex Solutions)
YNNN
YNNN
YNNN
YNNN
YNNN
YNNN
YNNN
YNNN
4
NNNN
NNNN
NNNN
NNNN
NNNN
NNNN
NNNN
NNNN
5
> 0.7 damping
NNNN
NNNN
NNNN
NNNN
NNNN
NNNN
NNNN
NNNN
6
t
t
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