ICS1523
Video Clock Synthesizer with I
2
C Programmable Delay
The DPA Resolution Select register (0x5:0~1) is
double-buffered. Working registers are loaded only
after a DPA software reset (0x8=xA)
For more details, See
Section 6
OSC Divider and REF
The ICS1523 accepts a single-ended clock on pin 12,
the OSC input. The period of this input signal becomes
the high time of the REF signal and the low time is
controlled by 0x7:0~6.
The resulting REF signal can be used as an input to the
PLL’s phase detector to allow the ICS1523 to
synthesize frequencies without an HSYNC input when
0x7:7=1.
This REF signal may also be output on the LOCK/REF
pin (14) when 0x0:6-7 = 11
Table 6-1 REF Functionality
While the internal loop filter works well for most
applications, ICS still recommends the implementation
of an external filter network on all designs.
Implementing the external loop filter gives the system
engineer flexibility to add external filter functionality if
without having to alter the PCB.
7.1 External Filter Recommendations
ICS recommends the following as a general purpose
external loop filter:
CS = 3300 pF
RS = 6.8 kΩ
CP = 33 pF
Special considerations must be made in selecting loop
capacitors C
S
and C
P
. These recommendations can be
found at:
Parameter
REF Frequency
REF High Time
REF Low Time
Minimum OSC Divider
Maximum OSC Divider
Value
(Input Osc Frequency) *
[(0x7: 6~0) + 2]
Input OSC Period
[(0x7: 6~0) + 1] * Input
OSC Period
3 (0x7:6~0 = 000001)
129 (0x7:6~0 = 111111)
Section 8
PLL Parameter Settings
RESERVED OSC Divider 0 (0x7:6~0 = 000000)
Settings for all standard VESA video modes are
provided by ICS as a starting point for the systems
engineer. These files are in human readable text files
(*.ics files) and come bundled within the ICS1523
Register Editor Tool.
This tool directly drives the ICS1523EB Evaluation
Board and can be downloaded from:
Section 7
Loop Filter
The ICS1523 contains an internal loop filter, but also
supports the use of an external loop filter configured as
in
Selection between these two filters is
controlled by 0x4:7. The external filter is selected when
4:7=0;
internal filter is selected with
a 1.
Figure 7-1
External Loop Filter
CS
RS
CP
Pin 8
Pin 9
MDS 1523 Y
Integrated Circuit Systems
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