ICST ICS2595 User-programmable dual high-performance clock generator Datasheet

Integrated
Circuit
Systems, Inc.
ICS2595
Not recommended for new designs
User-Programmable Dual High-Performance Clock Generator
Description
Features
The ICS2595 is a dual-PLL (phase-locked loop) clock
generator specifically designed for high-resolution, highrefresh rate, video applications. The video PLL generates
any of 16 pre-programmed frequencies through selection
of the address lines FS0-FS3. Similarly, the auxiliary PLL
can generate any one of four pre-programmed frequencies
via the MS0 & MS1 lines.
•
Advanced ICS monolithic phase-locked loop
technology for extremely low jitter
•
Supports high-resolution graphics - VCLK
output to 145 MHz
•
Completely integrated - requires only external
crystal (or reference frequency and decoupling)
•
Power-down modes support portable computing
•
Sixteen selectable VCLK frequencies
(all user re-programmable)
•
Four selectable MCLK frequencies
(all user re-programmable)
A unique feature of the ICS2595 is the ability to redefine
frequency selections in both the VCLK and MCLK synthesizers after power-up. This permits complete set-up of the
frequency table upon system initialization.
Applications
Block Diagram
•
PC Graphics
•
VGA/Supper VGA/XGA Applications
Pin Configuration
20-Pin DIP or SOIC
ICS2595 RevB 3/2/00
ICS2595
Pin Descriptions
PIN NUMBER
PIN NAME
TYPE
DESCRIPTION
1
X1
IN
2
X2
OUT
Quartz crystal connection2
3
EXTFREQ
IN
External Frequency Input
4
FS0
IN
VCLK PLL Frequency Select LSB
Quartz crystal connection 1/Reference Frequency Input
5
FS1
IN
VCLK PLL Frequency Select Bit
6
STROBE
IN
Control for Latch of VCLK Select its (FS0-FS3)
7
FS2
IN
VCLK PLL Frequency Select Bit
8
FS3
IN
VCLK PLL Frequency Select MSB
9
MS0
IN
MCLK PLL Frequency Select LSB
10,14,16
GND
PWR
11
MS1
IN
12
MCLK
OUT
MCLK Frequency Output
13,20
VDD
PWR
Output Stage VDD. All pins must be connected
15
VAA
PWR
Synthesizer VDD
17
RESERVED
N/C
Must be connected to GND
18
REFCLK
OUT
Buffered Referenced Clock Output
19
VCLK
OUT
VCLK Frequency Output
Device Ground. All pins must be connected
MCLK PLL Frequency Select MSB
2
ICS2595
Digital Inputs
The FS0-FS3 pins and the STROBE pin are used to select
the desired operating frequency of the VCLK output from
the 16 pre-programmed/user-programmed selections in
the ICS2595. These pins are also used to load new frequency
data into the registers.
Because the same pins are used for both VCLK frequency
selection and re-programming the device frequency table,
a specific procedure must be observed for selection between
these modes. Device programming is accomplished by
Table 1: Programming Sequence
The standard interface for the ICS2595 matches the interface
of the industry standard ICS2494. That is, the FS0-FS3
inputs access the device internals transparently when the
STROBE pin is high.
FS0
X
X
X
X
FS1
X
X
X
X
5
X
X
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Nibble
1
2
3
4
The digital interface for the ICS2595 (i.e. the FS0-FS3
inputs) may be optionally configured for edge-triggered
or level-activated operation of the STROBE pin. Example
timing requirements for each of the four options are
shown in Figure 1.
The programming sequence has been designed in such a
way that STROBE pin need not be used (as in situations
where the device is connected to the frequency select port
of some VGA chips).
VCLK Output Frequency Selection
To change the VCLK output frequency, simply write the
appropriate data to the ICS2595 FS inputs. The synthesizer
will output the new frequency programmed into that location
after a brief delay (see time-out specifications).
Upon device power-up, the selected frequency will be the
frequency pre-programmed into address 0 until a device
write is performed.
MCLK Output Frequency Selection
The MS0-MS1 pins are used to directly select the desired
operating frequency of the MCLK output from the four
pre-programmed/user-programmed selections in the
ICS2595. These inputs are not latched, nor are they involved
with memory programming operations.
Programming Mode Selection
FS2
0
1
START bit (must be "0")
"
R/W* control bit (must be
"0")
"
LO (location LSB)
"
L1
"
L2
"
L3
"
L4 (location MSB)
"
N 0 (feedback LSB
"
N1
"
N2
"
N3
"
N4
"
N5
"
N6
"
N 7(feedback MSB)
"
EXTFREQ (select if "1")
"
D0 (post- divder MSB)
"
D1 (post- divder MSB)
"
STO P1 bit (must be "1")
"
STO P2 bit (must be '1")
"
FS3
0
0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
executing a "programming sequence". The latched FS2
input functions as a data input, and the latched FS3 input
functions as a data clock when this mode is activated. As
the latched FS3 data transitions from 0 to 1, the latched
FS2 data is shifted into the register. Note that it is the
In order to ensure that reliable programming under all
circumstances, we require that two "nibble" writes be
added to the beginning of the programming sequence that
was previously specified. The new sequence is shown in
Table 1. Note that the FS3 data is "0" for these first two
writes.
3
ICS2595
Data Description
LATCHED FS inputs, not the FS inputs themselves, that
are interpreted by the internal logic. Interface logic resides
between the FS input pins and the programming/frequency
select logic. The appropriate "data write" procedure must
be observed. See the section "Digital Interface" in this
supplement for more information.
Location Bits (l0-L4)
The first five bits after the start bit control the frequency
location to be re-programmed according to this table. The
rightmost bit (the LSB) of the five shown in each
selection of the table is the first one sent.
These rules must be followed:
•
L(4.0)
00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
01101
01110
01111
10000
10001
10010
10011
Calculate Tmax and Tmin in seconds (where R is the
modulus of the reference divider and Fref is the
reference frequency in Hz) by the following formulas:
Tmin =
Tmax =
6* R
Fref
4096* R
Fref
•
A programming sequence consists of 42 successive
data writes to the device as shown in table 1: no delay
greater than Tmax or less than Tmin may occur between
any two successive writes.
•
A readback sequence consists of 64 successive data
writes to the device as shown in table 2: no delay
greater than Tmax or less than Tmin may occur between
any two successive writes.
•
Programming or readback sequences must be preceded
by a "quiet" period of at least 2* Tmax with no data
writes to the device unless it was immediately preceded
by another legal programming (or readback) sequence
(nothing else in between)
•
Table 3 - Location Bit Programming
LOCATION
VCLK Address 0
VCLK Address 1
VCLK Address 2
VCLK Address 3
VCLK Address 4
VCLK Address 5
VCLK Address 6
VCLK Address 7
VCLK Address 8
VCLK Address 9
VCLK Address 10
VCLK Address 11
VCLK Address 12
VCLK Address 13
VCLK Address 14
VCLK Address 15
MCLK Address 0
MCLK Address 1
MCLK Address 2
MCLK Address 4
Feedback Set Bits (N0-N7)
These bits control the feedback divider setting for the
location specified. The modulus of the feedback divider
will be equal to the value of these bits + 257. The least
significant bit (N0) is sent first.
To change the active VCLK frequency selection, simply
write that data to the device; the last data written to the
part will always become VCLK frequency select after
a delay of approximately 2* Tmax. The internal shift
register is cleared at this time also.
Post-Divider Set Bits (D0-D1)
These bits control the post-divider setting for the location
specified according to this table. The least significant bit
(D0) is sent first.
The FS0 & FS1 inputs are not used for programming, so it
is possible to use a two-pin interface for programming and
frequency selection (any bank of four VCLK addresses).
Table 4 - Post-Divider Programming
D(1-0)
00
01
10
11
The reference frequency source must be operational for
proper execution of the programming sequence. If the onchip crystal oscillator is, allow at least 4* Tmax after the
device has valid power before attempting to program it.
4
POST-DIVIDER
8
4
2
1
ICS2595
Read/Write* Control Bit
Frequency Synthesizer Description
When set to a “0,” the ICS2595 shift register will transfer its
contents to the selected memory register at the completion
of the programming sequence.
Refer to the block diagram of the ICS2595. The ICS2595
generates its output frequencies using phase-locked loop
techniques. The phase-locked loop (or PLL) is a closed-loop
feedback system that drives the output frequency to be
ratiometrically related to the reference frequency pro-vided
to the PLL. The phase-frequency detector shown in the
block diagram drives the VCO to a frequency that will cause
the two inputs to the phase-frequency detector to be matched
in frequency and phase. This occurs when:
When this bit is a “1,” the selected memory location will be
transferred to the shift register to permit a subsequent readback
of data. No modification of device memory will be performed.
"Readback" of a location in the frequency table may be
performed by execution the 64 step readback sequence. The
readback sequence is shown in Table 2. Note that the readback
sequence is essentially the programming sequence (with the
R/W* bit set high) followed by the actual data readback.
FVCO = FXTAL1*
N
R
where N is the effective modulus of the feedback divider
chain and R is the modulus of the reference divider chain.
The feedback divider on the ICS2595 may be set to any
integer value from 257 to 512. This is done by the setting of
the N0-N7 bits. The standard reference divider on the ICS2595
is fixed to a value of 43 (this may be set to a different value
via ROM programming; contact factory). The ICS2595 is
equipped with a post-divider and multiplexer that allows
the output frequency range to be scaled down from that of
the VCO by a factor of 2, 4, or 8,
therefore, the VCO frequency range will be from 5.976 to
11.906 (257/43 to 512/43) of the reference frequency. The
output frequency range will be from 0.747 to 11.906 times
the reference frequency. Worst case accuracy for any desired
fre-quency within that range will be 0.2%.
If a 14.31818 MHz reference is used, the output frequency
range would be from 10.697 MHz to 170.486 MHz (but the
upper end is first limited to 145 MHz by the ICS2595 output
driver).
The bi-directional FS0 pin will convert to output mode after
the 42nd nibble write and the logic level output will be that
of the first data bit (N0). Subsequent "clocking" by latching
FS3 to "0" and then to "1" will shift out the remaining data
bits. The last two writes will return the FS0 pin to input
mode.
EXTFREQ Input
The EXTFREQ input allows an externally generated frequency to be routed to the VCLK or MCLK output pins
under device programming control. If the EXTFREQ bit is
set (logic “1”) at the selected address location, the frequency
applied to the EXTFREQ input will be routed to the output
instead of the frequency generated by the VCLK (or MCLK)
PLL.
When setting the EXTFREQ bit to a “1,” be sure that the D0
and D1 bits are not both set to “1” also, unless it is intended
that the phase-locked loop be shutdown as well.
Programming Example
Suppose that we want differential CLK output to be 45.723
MHz. We will assume the reference frequency to be 14.31818
MHz.
Power Conservation
The ICS2595 supports power conservation by permitting
either or both of the phase-locked loops to be disabled. This
can be done by programming a particular address to have
EXTFREQ, D0, & D1 bits set to a logic “1.” Any frequency
applied to the EXTFREQ pin will still be passed through the
output multiplexer and appear at the respective output.The
crystal oscillator is not affected by this power-down function
and will continue to operate normally.
The VCO frequency range will be 85.565 MHz to 170.486
MHz (5.976 * 14.31818 to 11.906 * 14.31818). We will
need to set the post-divider to two to get an output of 45.723
MHz.
The VCO will then need to be programmed to two times
45.723 MHz, or 91.446 MHz. To calculate the required feed-
5
ICS2595
Power Supply
back divider modulus we divide the VCO frequency by the
reference frequency and multiply by the reference divider:
The ICS2595 has three GND pins to reduce the effects of
package inductance. All pins are connected to the same
potential on the die (the ground bus). All of these pins
should connect to the ground plane of the video board as
close to the package as is possible.
91.446
*43=274.62
14.31818
which we round off to 275. The exact output frequency will
be:
275 *14.31818* 1 =45.784 MHz
2
43
The ICS2595 has two VDD pins which supply of +5 volt
power to the output stages. These pins should be connected
to the power plane (or bus) using standard high-frequency
decoupling practice. That is, use low-capacitors should have
low series inductance and be mounted close to the ICS2595.
The value of the N programming bits may be calculated by
subtracting 257 from the desired feedback divider modulus.
Thus, the N value will be set to 18 (275-257) or 000100102.
The D bit programming is set to 10 (from Table 4).
The VAA pin is the power supply for the synthesizer
circuitry and other lower current digital functions. We
recommend that RC decoupling or zener regulation be
provided for this pin. This will allow the PLL to “track”
through power supply fluctuations without visible effects.
Reference Oscillator & Crystal
Selection
The ICS2595 has on-board circuitry to implement a Pierce
oscillator with the addition of only one external component,
a quartz crystal. Pierce oscillators operate the crystal in
parallel-resonant (also called anti-resonant mode). See the
AC Characteristics for the effective capacitive loading to
specify when ordering crystals.
Crystals characterized for their series-resonant frequency
may also be used with the ICS2595. Be aware that the
oscillation frequency in circuit will be slightly higher than
the frequency that is stamped on the can (typically 0.0250.05%).
As the entire operation of the phaselocked loop depends on
having a stable reference frequency, we recommend that the
crystal be mounted as closely as possible to the package.
Avoid routing digital signals or the ICS2595 outputs
underneath or near these traces. It is also desirable to ground
the crystal can to the ground plane, if possible.
External Reference Sources
An external frequency source may be used as the reference
for the VCLK and MCLK PLLs. To implement this, simply
connect the reference frequency source to the X1 pin of the
ICS2595. For best results, insure that the clock edges are as
clean and fast as possible and that the input voltage thresholds
are not violated.
6
ICS2595
Absolute Maximum Ratings
Supply Voltage ............................................................................................... -5V to +7 V
Logic inputs ........................................................................................... 5V to VDD +.5V
Ambient operating temp ................................................................................. 0° to 70°C
Storage temperature ............................................................................. -85°C to +150°C
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. These ratings
are stress specifications only and functional operation of the device at these or any other conditions above those listed
in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for
extended periods may affect product reliability.
DC Characteristics
PARAMETER
SYMBOL
DC Characteristics
TEST CONDITIONS
MIN
TYP
MAX
UNITS
TTL-Compatible Inputs
-
-
-
-
(VS0-3, MS0-1, STROBE):
-
-
-
-
Input High Voltage
Vih
2.0
-
VDD=0.5
V
Input Low Voltage
Vil
VSS-0.5
-
0.8
V
Input High Current
Iih
-
-
10
µA
Input Low Current
Iil
-
-
200
µA
Input capacitance
Cin
-
-
8
pF
-
-
-
-
Input High Voltage
Vxh
VDD*0.75
-
VDD+0.5
V
Input Low Voltage
Vx1
VSS-0.5
-
VDD*0.25
V
-
-
-
-
2.4
-
-
V
XTAL1:
VCLK, MCLK Outputs:
Output High Voltage
Voh
@Ioh=0.4mA
Output Low Voltage
Vol
@Iol=8.0mA
7
-
-
-
-
-
-
0.4
V
-
-
-
-
ICS2595
AC Characteristics
PARAMETER
Phase-Locked Loop:
VCLK, MCLK VCO
Frequency
PLL Acquire Time
Crystal Oscillator
Crystal Frequency Range
Parallel Loading
Capacitance
XTAL1 Minimum High Time
XTAL1 Minimum Low Time
Power Supplies:
VDD Supply Current
VAA Supply Current
Digital Outpluts:
VCLK, MCLK, XTALOUT
Rise Time @Cload=20pF
VCLK, MCLK, STALOUT
Fall Time @Cload=20pF
SYMBOL
AC Characteristics
TEST CONDITIONS
MIN
-
TYP
-
MAX
-
UNITS
-
Fvco
60
-
185
MHz
Tlock
5
500
-
25
µSec
MHz
-
20
-
pF
8
8
-
-
35
10
-
ns
ns
mA
mA
-
Tr
-
-
2
ns
Tf
-
-
2
ns
Fxtal
Txhi
Txlo
idd
Iaa
8
ICS2595
Table 2: Readback Sequence
Nibble
1
2
3
4
FS0
FS1
FS2
FS3
X
X
X
X
X
X
X
X
0
0
0
1
5
X
X
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
0
1
START bit (must be "0")
"
R/W* control bit (must be
"0")
"
LO (location LSB)
"
L1
"
L2
"
L3
"
L4 (location MSB)
"
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
STOP1 bit (must be "1")
"
STOP2 bit (must be '1")
"
FS0 becomes output after
write #42
X
43
X
Nibble
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
59
60
61
62
63
64
FS0
FS1
FS2
FS3
"
N1
"
N2
"
N3
"
N4
"
N5
"
N6
"
N7
"
EXTFRE
"
D0
"
D1
"
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
X
X
0
X
X
X
X
X
1
0
1
0
1
X
X
X
X
X
X
X
FS0 returns to input mode
after write #64
"X" = don't care
0
9
ICS2595
All times shown are minimums.
Figure 1. ICS2595 Digital Interface Timing
10
ICS2595
Frequency Table
PATTERN
ICS2595-02
ICS2595-04
Reference Divider
46
43
VCLK ADDR
VCLK
VCLK
0
100.27
50.28
1
125.90
56.60
2
93.06
64.93
3
36.27
71.92
4
50.76
80.08
5
57.03
89.90
6
External Frequency
62.93
7
45.28
74.92
8
135.99
25.14
9
32.20
28.30
A
110.51
31.46
B
80.21
35.96
C
40.11
40.04
D
45.28
44.95
E
75.51
49.94
F
65.49
64.93
MCLK ADDR
MCLK
MCLK
0
40.42
40.20
1
45.59
41.54
2
N/A
44.54
3
N/A
49.61
11
ICS2595
20 PIN DIP Package
20 PIN SOIC Package
Ordering Information
ICS2595
Example:
ICS XXXX N-SXX
S=Strobe Option/XX=Default Freq2uencies
Package T ype
N=DIP (Plastic)
M=SOIC
Device Type (consists of 3 or 4 digit numbers)
Prefix
ICS, AV=Standard Device; GSP=Genlock Device
Where:
“S” denotes strobe option:
“XX”denotes default frequencies:
D - Negative edge triggered
12
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