IMISG508
May 1996
REDUCED EMI CLOCK CHIP
CMOS LSI
SPECTRUM SPREAD CLOCK GENERATOR
PRODUCT FEATURES
S
S
S
S
S
S
S
S
S
S
S
S
PRODUCT DESCRIPTION
The IMISG508 is a spectrum spread clock generator
specially designed for personal computers, laser
printers and other digital systems. IMISG508 uses a
patented concept to generate popular clock frequencies
that are intentionally boradbanded to reduce
electromagnetic interference. IMISG508 attenuates the
radiated emission amplitudes from products associated
with either the clock harmonics or any signals derived
from the clock signals nominally 10 dB and could
significantly reduce the cost of complying with the
regulatory requirements.
PRCLK is the broadbanded output and can be
programmed by the PRCLK Frequency Selection Table
on page 2. A single, low cost external crystal is required
as reference frequency for the synthesizer. Output
modulation function can be turned off with the SSON
pin. Several power down modes add the flexibility to
operate the device in a completely static mode to
reduce standby currents and simplify system board
tests.
Generates CPU Clock Signals for Microprocessor
Systems
Reduces Measured EMI by 10 dB nominal
4V to 6V Operating Supply Range
Supports CPUs from all major manufacturers
Wide Range of Selectable Output Frequencies
including 40, 30, 25, and 16.7 MHz.
Single, Low Cost Crystal used as Reference
Frequency
Glitch-Free Switching
50% Duty Cycle
Power Down Mode for Low Power consumption
TTL or CMOS Compatible Outputs with 6 mA Drive
Capability
Low, Short- and Long-Term Jitter
16 Pin PDIP and 16 Pin SOIC (300 mil Body)
Package Options
CONNECTION DIAGRAM
VDD
OSCin
OSCout
VSS
MPSEL
AVDD
S0
S1
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
TS
VDD
MPCLK
VSS
PRCLK
AVSS
LF1
SSON
BLOCK DIAGRAM
3
44.2
MHz
2
REF
/4 or /12
14
MPCLK
APPLICATIONS
MPSEL 5
LF 10
S0 7 SPECTRUM
SPREAD
S1 8
CLOCK GEN
TS 16
SSON
9
The IMISG508 eliminates the need for multiple
oscillators and generates the CPU clock signals for
personal computers, laser printers and other digital
systems. Supports CPUs from all major manufacturers.
IMISG508 can be used with laptop or notebook
computers to save power by running the system slower
than normal CPU speeds or completely disabling the
clocks in standby mode.
12
/2
PRCLK
INTERNATIONAL MICROCIRCUITS, INC. 525 LOS COCHES ST.
MILPITAS, CA 95035 TEL: 408-263-6300 FAX 408-263-6571
Rev. 1.0
Page 1 of 7
IMISG508
May 1996
REDUCED EMI CLOCK CHIP
CMOS LSI
SPECTRUM SPREAD CLOCK GENERATOR
PIN DESCRIPTION
OSCin, OSCout
- These pins form an on-chip
reference oscillator when connected to terminals of an
external 44.2 MHz third overtone parallel resonant
crystal. OSCin may also serve as an input for an
externally generated CMOS level or AC coupled
reference signal.
S0, and S1
- Frequency select inputs. These inputs
control the PRCLK frequency selection. S0-S1 inputs
control the CPU clock frequencies. All these inputs have
internal pull-downs.
PRCLK
- Output from the spectrum spread clock
generator. Frequency selection is shown in Table 1.
Table 1 shows the output frequency selection
conditions.
TS
- Controls power down and Tri-State Mode
selection. When high, S1 input controls the mode
selection as shown in Table 1 and Table 2. When low,
the device operates in normal mode. This pin has an
internal pull-down.
LF1
- This is the control output for the clock generator,
It is a single-ended, tri-state output. Component
connections are shown in Figure 1.
SSON
- This pin controls the spectrum spread function.
When low, PRCLK is modulated. When high, spreading
is turned off. This pin has an internal pull-up.
MPSEL
- Controls MPCLK output frequency selections.
Table 2 shows the selected frequencies for MPCLK.
This input has an internal pull-up.
MPCLK
- This is a nonmodulated output. This output
can be programmed to be 3.7 MHz or 11.06 MHz. The
selection of these frequencies are controlled by the
MPSEL pin shown in Table 1.
VSS
- Circuit ground.
VDD
- Positive power supply.
AVSS
- Analog circuit ground.
AVDD
- Analog positive power supply.
LF
2k
R2
C2
330 pf
C1
2200 pf
PRCLK FREQUENCY TABLE
INPUTS
OUTPUT
TS
S1
S0
PRCLK
0
0
0
16.7 MHz
0
0
1
40 MHz
0
1
0
25
0
1
1
30 MHz
1
0
0
0; Power Down
1
0
1
1; Power Down
1
1
0
TEST
1
1
1
Hi-Z
TABLE 1:
When Power Down address is selected, the
VCO is turned off and the device goes to standby mode.
Phase detector is in tri-state mode. The Table is based
on using 44.2 MHz crystal. Output can be scaled own
using lower frequency crystals, see page 6.
MPCLK FREQUENCY SELECTION
INPUTS
OUTPUT
TS
MPSEL
S1
S0
MPCLK
0
0
X
X
3.7 MHz
0
1
X
X
11.06 MHz
1
X
0
0
0; Power Down
1
X
0
1
1; Power Down
1
X
1
0
TEST
1
X
1
1
Hi-Z
TABLE 2:
When Power down address is selected, the
VCO is turned off and the device goes to standby mode.
Phase detector is in tri-state mode.
MAXIMUM RATINGS
Page 2 of 7
INTERNATIONAL MICROCIRCUITS, INC. 525 LOS COCHES ST.
MILPITAS, CA 95035 TEL: 408-263-6300 FAX 408-263-6571
Rev. 1.0
IMISG508
May 1996
REDUCED EMI CLOCK CHIP
CMOS LSI
SPECTRUM SPREAD CLOCK GENERATOR
Voltage Relative to VSS:
-03V to 6V
Voltage Relative to VDD:
0.3V
Storage Temperature:
-65°C to 150°C
Ambient Temperature:
0°C to 70°C
Recommended Operating Range:
4.5 - 5.5V
This device contains circuitry to protect the inputs
against damage due to high static voltages or electric
field; however, precautions should be taken to avoid
application of any voltage higher than the maximum
rated voltages to this circuit. For proper operation, Vin
and Vout should be constrained to the range:
V
SS
< (Vin or Vout) < V
DD
Unused inputs must always be tied to an appropriate
logic voltage level (either VSS or VDD).
ELECTRICAL CHARACTERISTICS
Characteristic
Input Low Voltage
Input High Voltage
Input Low Current with Pull-up/Pull-down
Output Low Voltage IOL = 6mA
Output High Voltage IOH = 6mA
Tri-State leakage Current
Static Supply Current
Dynamic Supply Current
Short Circuit Current
Symbol
Min
Typ
Max
Units
V
IL
V
IH
I
IH
/I
IL
V
OL
V
OH
I
OZ
I
DD
I
CC
I
SC
-
2.0
-
-
2.5
-
-
-
25
-
-
-
-
-
-
-
25
-
0.8
-
10/100
0.4
-
10
250
30
-
Vdc
Vdc
uA
Vdc
Vdc
uA
uA
mA
mA
°
°
VDD = 5V + 10%, TA = 0°C to 70°C
INTERNATIONAL MICROCIRCUITS, INC. 525 LOS COCHES ST.
MILPITAS, CA 95035 TEL: 408-263-6300 FAX 408-263-6571
Rev. 1.0
Page 3 of 7
IMISG508
May 1996
REDUCED EMI CLOCK CHIP
CMOS LSI
SPECTRUM SPREAD CLOCK GENERATOR
SWITCHING CHARACTERISTICS
Characteristic
Output Rise and Fall Time Measured at 10% - 90% of
VDD
Output Rise and Fall Time Measured at 0.8V - 2.0V
Output Duty Cycles
Jitter One Sigma
Symbol
t
TLH
,t
THL
Min
-
Typ
-
Max
5
Units
ns
t
TLH
,t
THL
T
sym
F1
tj1s
-
-
-
-
-
-
3
45/55
2
ns
%
% of Fout
°
VDD = 5V + 10%, TA = 0°C, CL = 15 pF
OSCILLATOR CHARACTERISTICS
Characteristic
Transconductance
Output Impedance
Input Capacitance
Output Capacitance
DC Bias Voltage
Start-up Time
Duty Cycle
Input Rise Time OSCin
Input Fall Time OSCout
Symbol
gm
Zo
Ci
Co
V
B
ts
TsymF1
ICLKr
ICLKf
Min
20
-
8
3
1.5
-
-
-
-
Typ
80
200
13
6
VDD/2
-
-
-
-
Max
180
800
18
9
3.5
2
45/55
20
20
Units
millimhos
ohms
pf
pf
Volt
ms
%
ns
ns
Conditions
@44.2 MHz
@ 44.2 MHz
-
-
-
@ VDD = 4.5V
-
-
-
VCO CHARACTERISTICS
Characteristic
VCO Gain
Phase Detector Gain
Symbol
K
0
K
d
Min
35
100
Typ
55
145
Max
65
200
Units
MHz/volt
Conditions
∆F/∆V
Measured with VCO Control at 2V - 3V
uA
-
Page 4 of 7
INTERNATIONAL MICROCIRCUITS, INC. 525 LOS COCHES ST.
MILPITAS, CA 95035 TEL: 408-263-6300 FAX 408-263-6571
Rev. 1.0
IMISG508
May 1996
REDUCED EMI CLOCK CHIP
CMOS LSI
SPECTRUM SPREAD CLOCK GENERATOR
EXTERNAL CONNECTIONS
VCC
DIGITAL GND PLANE
DIGITAL POWER PLANE
DVDD
C11
10uF
ANALOG GND PLANE
ANALOG POWER PLANE
AVDD
R1
C10 10 Ohms
22uF
L1
1.5 uH
DVDD
C3
10pF
XTAL
44.2 MHz
C5
C4
10pF
.033uF
L2 1.2uH
C6
.1uF
SG508
1
2
3
4
5
6
7
8
VDD
XIN
XOUT
VSS
MPSEL
AVDD
S1
S0
TEST
VDD
MPCLK
VSS
PRCLK
AVSS
LF1
SSON
16
15
14
13
12
11
10
9
C9
.1uF
DVDD
JP5
1
2
HEADER
R2
2K
MPSEL
JP1
C2
2200pF
C8
.1uF
AVDD
C1
330 pf
C7 10pF
S0 JP2
S1 JP3
TEST
JP4
DVDD
NOTE1: KEEP C3, C4, C5, C6 CLOSE TO THEIR PINS (4, 11, 13, 10, 9 RESPECTIVELY).
IMISG508
INTERNATIONAL MICROCIRCUITS, INC. 525 LOS COCHES ST.
MILPITAS, CA 95035 TEL: 408-263-6300 FAX 408-263-6571
Page 5 of 7
Rev. 1.0
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