Cypress AN94024 User manual

www.cypress.com Document No. 001-94024 Rev.*A 1
AN94024
Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
Author: Hiromu Takehara, Jeetendra Ashok, Amitava Banerjee
Associated Project: No
Associated Part Family: CY27410
Software Version: N/A
Related Application Notes: AN93892, AN94074
To get the latest version of this application note, please visit http://www.cypress.com/AN94024.
Cypress’s latest-generation high-performance clock generator device –CY27410 - is a 4-PLL, 12-output PCIe 3.0-
compliant device that provides a host of value-added features. This application note describes how to configure the
device in both clock generator and buffer modes with details on input/output standards, external design considerations,
reference selection including crystal, and the internal memory structure.
Contents
Getting Started with CY27410/30: 4-PLL Spread-Spectrum
Clock Generator................................................................1
Contents............................................................................1
Overview...........................................................................2
Key Specifications.............................................................2
Modes of Operation...........................................................2
CLKGEN Mode.............................................................2
ZDB Mode....................................................................3
NZDB Mode..................................................................3
Input Subsystem ...............................................................3
Choosing the Crystal....................................................4
Input Reference Block.......................................................4
Input Frequency Tolerance...........................................4
Input Circuitry...............................................................4
Input Reference System...............................................5
Differential Input Signals...............................................5
LVCMOS Input Signal ..................................................5
Clipped Sine Wave Signal............................................5
Output Subsystem.............................................................6
Output Termination............................................................6
HCSL Output Standard ................................................6
LVPECL Output Standard ............................................6
LVDS Output Standard.................................................7
CML Output Standard ..................................................7
Using Differential Output as LVCMOS .........................7
Additional Features ...........................................................7
Phase Delay of Outputs................................................7
Voltage-Controlled Frequency Shift (VCFS).................8
Cascading PLLs...........................................................9
SSCG (Spread-Spectrum Clock Generator).................9
Power-Up Sequence..................................................10
Power Supply Ramp...................................................10
Frequency Select (FS) ...............................................10
Power Ramp Considerations......................................10
Internal Memory Structure..........................................11
Programming CY27410..............................................11
Conclusion ......................................................................11
Document History............................................................12
Worldwide Sales and Design Support.............................13
Products..........................................................................13
PSoC® Solutions ............................................................13
Cypress Developer Community.......................................13
Technical Support...........................................................13

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 2
Overview
CY27410 is a 4-PLL spread-spectrum clock generator
targeted at consumer, industrial, and networking
applications. CY27410 has two inputs and twelve outputs,
frequencies up to 700 MHz with a low RMS phase jitter of
1 ps max. CY27410 supports value-added features such
as voltage-controlled crystal oscillator (VCXO), frequency
select, and zero/nonzero delay buffer (ZDB/NZDB) modes.
The part is designed to support reference clocks for key
interface standards such as PCI Express
(PCIe) 1.0/2.0/3.0, USB 2.0/3.0 and 10-Gigabit Ethernet
(GbE).
This application note describes how to configure the
device for different applications and device mode
configurations. In addition, the I2C interface of the device,
its signaling levels, and external design considerations are
explained in the application note.
CY27410 has three major modes of operation: clock
generator (CLKGEN) mode, zero-delay buffer (ZDB) mode,
and nonzero-delay (NZDB) buffer. In the Clock Generator
mode, the device generates multiple clock frequencies
using an internal PLL from an external reference clock or
crystal. In the ZDB mode, the device generates the same
clock frequency as input clock, or integer-multiple or
integer-divide frequencies with little delay with respect to
the input. In the NZDB mode, the device bypasses the
PLL and buffers the input signal to outputs with support of
additional dividers.
CY27410 also provides value-added features such as
phase delay of outputs, voltage controller frequency
synthesis (VCFS), spread spectrum, frequency select, and
glitch-free outputs.
Key Specifications
•Input frequencies
•Crystal input : 8 MHz to 48 MHz
•Reference clock : 8 MHz to 250 MHz LVCMOS
•Reference clock : 8 MHz to 700 MHz differential
•Output frequencies
•LVDS, LVPECL, host-clock signal level (HCSL),
current mode logic ((CML) 25 –375 MHz, 400 –
500 MHz, 600 –700 MHz))
•LVCMOS (3 MHz to 250 MHz)
•1 kHz to 8 MHz for one LVCMOS output
•RMS phase jitter < 1 ps max at 12-kHz to 20-MHz
Offset
•PCIe 1.0/2.0/3.0, SATA 2.0, USB 2.0/3.0, 1/10GbE
•Maximum 12 outputs split in two banks of 6 outputs
each.
•Up to 8 differential output pairs (HCSL, LVPECL,
CML, or LVDS)
•Up to 12 LVCMOS outputs
•Up to 75-ps skew for differential outputs within a bank
•Four fractional N-type PLL with
•VCXO (+/-120 ppm)
•Spread-spectrum capability (Logic SS and
Lexmark profile 0.1 to 5% in 0.1% steps, down or
center-spread)
•Supply voltage: 1.8 V, 2.5 V and 3.3 V
•ZDB/NZDB configurations
•I2C-configurable with On-board programming
•Industrial and Automotive grade devices
•48-pin QFN package.
Modes of Operation
CY27410 has CLKGEN, ZDB, and NZDB modes. It can
also be configured in a combination of CLKGEN and ZDB,
CLKGEN and NZDB, and ZDB and NZDB modes.
CLKGEN Mode
Figure 1 shows the PLL block diagram in CLKGEN mode.
In this mode, CY27410 generates multiple clock
frequencies from one reference crystal or clock input. Up
to four unrelated clock frequencies can be generated in
this mode from the four PLLs of the device. Each PLL has
again four independent dividers, so you may generate up
to four different related frequencies from a PLL. Two
frequencies are said to be unrelated if there is no common
multiple for the two clock frequencies within the PLL VCO
range of 2.4 GHz to 3.0 GHz.
Figure 1: Clock Generator Configuration

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 3
ZDB Mode
In ZDB mode, the device acts as a zero-propagation-delay
device from input to output as shown in Figure 2. In order
to achieve this functionality, CY27410 requires a feedback
clock from one of the outputs for tracking its phase.
Figure 2. ZDB Configuration
Input frequency range (Single Ended): 8 MHz to 250 MHz
Input frequency range (Differential): 8 MHz to 300 MHz
Typical ZDB input/output delay is less than 250 ps.
CY27410 can also provide the Frequency Multiplying/
Dividing ZDB configuration by modifying R1 or R2 divider
appropriately.
When R1 = R2, the output frequency is the same as IN1,
when R1 value is half of R2, the output will be twice of IN1.
CY27410 provides R1 and R2 value of 1, 2, 4, or 8, so you
can configure CY27410 as ZDB with the frequency
multiplying/dividing function.
NZDB Mode
In NZDB mode, the device acts as simple buffering of the
input signal to outputs, also known as fan-out buffer. In the
NZDB mode as shown in Figure 3, the PLL is bypassed
making the device act as a fanout buffer.
Input frequency range (Single-Ended): 8 MHz to 250 MHz
Input frequency range (Differential): 8 MHz to 700 MHz
Figure 3. NZDB Configuration
CY27410 can also be configured in combination of
CLKGEN and ZDB, CLKGEN and NZDB, and ZDB and
NZDB modes. This offers unprecedented flexibility to the
customer. Figure 4 shows how the CLKGEN and NZDB
mode can be used in CY27410.
Figure 4: CLKGEN AND NZDB Configuration
Input Subsystem
The device can accept both crystal and reference input.
The crystal input pins are XIN and XOUT, which are
connected to a crystal oscillator block to generate the
required clock to be fed into the VCO. The differential
tuning-capacitor range supported is 8 pF to 12 pF.
The device also support four reference input pins (IN1P,
IN1N, IN2P, and IN2N). These pins are designed to
receive a reference input which can either be single-ended
or differential clock.
IN1 is multiplexed with IN1 (clock signal: single-ended or
differential) or crystal oscillator.
IN2 can be configured as differential or single-ended.
See Table 1 for input frequency specifications.
Table 1. Input Frequency Specifications
Input Frequency
Min.
Max.
Crystal
8 MHz
48 MHz
IN1,2-SE
8 MHz
250 MHz
IN1,2-DE
8 MHz
700 MHz
Note CY27410 incorporates a narrow-bandwidth PLL
(VCO). Therefore, you cannot use the reference clock that
has large distortion/drift; for example, spread-spectrum
clock (typically 0.5 to 1.0% modulation). Switching from
one frequency to another (different) frequency cannot be
used as the reference clock either.

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 4
Choosing the Crystal
CY27410 supports a crystal input between 8 MHz and
48 MHz. The equivalent crystal circuit with components is
shown in Figure 5.
Figure 5. Equivalent Crystal Circuit with L-R-C
Components
C0
R1 C1 L1
C0 = Crystal Shunt Capacitance
C1 = Crystal Motional Capacitance
R1 = Equivalent series Resistance
For CY27410, we recommend a crystal with parameters
as shown in the Table 2.
Table 2. Equivalent Resistance and Shunt Capacitance for
Values for Crystal
Nominal Frequency (in MHz)
R1 (MAX)
CL (pF)
8 to 12
150 ohms
8 to12
12 to 20
70 ohms
8 to12
20 to 48
50 ohms
8 to12
CL for All ranges
Associated Max C0 (pF)
8
2
9
2
10
2
12
3
CY27410 Crystal oscillator circuit implements a low-power
(up to 100 micro watt drive level) and high-precision buffer
so that the crystal selection is important. Layout designers
are advised to keep the trace length between CY27410
and crystal as short as possible, and not to route any
active signal around the trace and crystal.
Input Reference Block
This section describes how to interface the input reference
signals to CY27410 and design considerations for input
signals.
Input Frequency Tolerance
The CY27410 design incorporates a narrow-bandwidth,
high-performance, low-noise PLL. The device cannot track
input clock tolerance more than 300 ppm. As a result, the
ceramic resonator that would vary in order of 1000s of
ppm cannot be used as a reference crystal. Also, spread-
spectrum clocks cannot be used as inputs to CY27410.
Input Circuitry
Figure 6 shows the input structure for the CY27410 device.
Figure 6. Input Structure for CY27410
IN_P
CMOS
Bias
ON: SE
OFF: DE
IN_N
VT
VLD-VT LDO
VLD VDD 2.5-3.3
TO: Internal Reference
VDD 1.8
When the single-ended (LVCMOS) configuration is
selected, both IN_P and IN_N pins are pulled down to
GND, and the AC coupled input signal is fed to P-N-
transistors shown above. Both P- and N- transistors are
then biased as fixed level (VLD-VT and VT). This voltage
difference provides enough margins for noisy inputs and
act with small input amplitude defined in the datasheet,
such as 0.8 Vp-p for clipped sine wave.
Input P-N- transistors are high-voltage (5 V) tolerant. You
may apply the input voltage more than the VDD, even
though VDD core supply is 1.8 V.
When DE (differential) input is selected, both IN_P and
IN_N are biased to certain level (1.2 V typical).

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 5
Input Reference System
Figure 7 shows the input reference system of CY27410.
IN1 and XO signal will be multiplexed and fed to internal
reference as IN1B. IN2 can be used for feedback input in
ZDB mode or can be used as another input reference
clock for NZDB mode.
The output from DIV-C of PLL3 is the special-purpose
input that will be used, if you need more than four copies
of the same clocks.
Figure 7. Input Reference System of CY27410
INC
(fromPLL3) IN1B INI
IN2B
DIV R1
DIV R2
IN1P
IN2P
IN1S
IN2S
XO
IN1N
IN2N
XIN
XOUT
Differential Input Signals
The CY27410 supports various differential I/O standards
like LVPECL, CML, LVDS and HCSL. These I/O standards
have different common mode voltages. The common-
mode voltage (VCM) for various interface standards are
VDD - 1.2 V (LVPECL), VDD - 0.2 V (CML), 1.2 V (LVDS),
and 0.4 V (HCSL).
To maintain multiple differential signals, inputs must be
AC-coupled (100-pF capacitors in series), and termination
resistors should be added outside if needed. Figure 8
illustrates this design recommendation.
Figure 8. Sample Design Recommendation for Differential
I/O Standards
Termination
IN_P
IN_N
ATLAS
PECL,CML,
LVDS,HCSL
Bias
Bias
As described in the previous section, CY27410 accepts
multiple differential signals using AC-coupled inputs. The
input swing amplitude should be more than 300 mV pp for
the signal to meet the VIH/VIL specifications.
LVCMOS Input Signal
Figure 9 shows a simplified LVCMOS input buffer
structure of CY27410. The CMOS input signal is AC-
coupled inside the device. Cypress recommends the
minimum peak-to-peak amplitude to be 300 mV. Both the
inputs are pulled down internally in LVCMOS configuration,
so unused pins can be left floating for CMOS input.
The input circuit of CY27410 uses overvoltage-tolerant
cells. In case an input voltage is applied higher than VDD,
it will not cause any reliability issues. Multiple input voltage
levels can be interfaced to CY27410. Any combination of
different voltages may be used (VDD core=1.8 V, 2.5 V, or
3.3 V, and input voltage level=1.8 V, 2.5 V, or 3.3 V)
Figure 9. Simplified LVCMOS Input Buffer Structure
ATLAS
LVCMOS
Clipped Sine Wave Signal
A typical TCXO output signal is a clipped sine-wave signal.
CY27410 treats this input signal in the same manner as
LVCMOS. The device guarantees only functional
operation when using clipped sine-wave inputs. The
datasheet parameters are not guaranteed for clipped sine-
wave inputs.
Do not use a series capacitor between TCXO and IN1_P if
the CY27410 input mode is configured as LVCMOS
(typically recommended by TCXO vendors). Use a series
capacitor if the input setting is configured as differential.
Figure 10. Connection to the TCXO module
The typical TCXO output signal is shown in figure 11. The
typical peak-to-peak voltage (VP-P) is 0.8 V-1.0 V.
Figure 11. Typical TCXO Output Signal
0.8-1.0V
Typ.

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 6
Output Subsystem
CY27410 consists of two banks of outputs. Each bank
consists of six outputs with OUT11–OUT14 and OUT21–
OUT24 supporting both differential and single-ended
outputs and OUT15–OUT16 and OUT25–OUT26
supporting only single-ended outputs. Each output is fed
from a PLL through a divider and then to a MUX, which
helps in selecting the source for the output, as shown in
Figure 12 and Figure 13.
Figure 12. Output Bank 1
Figure 13. Output Bank 2
Output Termination
CY27410 supports LVCMOS, LVPECL, CML, LVDS, and
HCSL standards for output. This section describes the
recommended termination circuits for the outputs.
HCSL Output Standard
HCSL interface standard is a differential I/O standard and
is defined in PCIe SIG standard. Figure 14 shows the
typical interface termination, while Table 3 summarizes the
recommended trace length parameters and termination
resistors.
Figure 14. Typical HSCL Interface Termination
Z=50W
Z=50W
RTRT
RS
RS
L1 L2 L3
Table 3. HSCL Interface Parameters
Parameter
Value
Unit
L1 length
0.5 (max)
Inch
L2 length
0.2 (max)
Inch
L3 length
10
Inch
RS
33 (3.3 V or 2.5 V supply)
Ohm
RS
20 (1.8 V supply)
Ohm
RT
49.9
Ohm
LVPECL Output Standard
LVPECL standard signaling level is a differential I/O
standard and is defined in JEDEC JESD8-2 (Emitter
Coupled Logic). Figure 15 shows the typical termination
scheme for this standard.
Figure 15. LVPECL Output Termination Scheme
Z=50W
Z=50W
RTRT
VTT=VDD -2 V
In the above scheme, RT= 50 W
Since VDD –2 V (1.3 V for 3.3-V operation) may be
difficult to generate, you may use the Y-Termination
instead (see Figure 16).
Figure 16. Y-Termination Scheme
Z=50W
Z=50W
RTRT
RTT

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 7
In the above scheme, RT=50Wderives the RTT value:
Figure 17 shows a simple termination scheme that is
sometimes employed when there is a very short trace
length, but is not always recommended.
Figure 17. Simple LVPECL Termination Scheme
Z=50W
Z=50W
RTRT
In the above scheme, RT=150W
Note VDD=1.8 V is not applicable for LVPECL standard.
LVDS Output Standard
LVDS signaling standard is also a differential I/O standard
and is defined by TIA/EIA-644-A (JEDEC standard) and its
typical termination is shown in Figure 18.
Figure 18. LVDS Signaling Termination (2.5 V, 3.3 V)
Z=50W
Z=50WRT
VDD=2.5, 3.3V
Outputs (OUTxP and OUTxN) should be connected
together through a 100-Ωresistor (RT=100 W.
For VDD=1.8 V operation, you require AC coupling
(100-nF series capacitor) and bias at the destination using
termination resistors. Figure 19 shows such a termination
scheme.
Figure 19. LVDS Signaling Termination (1.8 V)
Z=50W
Z=50W
RT
VDD=1.8V RP
RD
In the above scheme, RT=100 W
RP and RD must be chosen to meet VCM (common-mode
voltage) of 1.2 V (Typical).
CML Output Standard
CML interface is a differential I/O standard and is defined
in IEEE 802.3 spec. Figure 20 shows the termination
scheme of this standard.
Figure 20. CML Signaling Termination
Z=50W
Z=50W
RT RT
In the above figure, RT=50Wand should be terminated to
VDD.
Using Differential Output as LVCMOS
The CY27410 device is highly flexible, enabling the use of
differential outputs in single-ended mode. Figure 21
illustrates the same: OUTxP and OUTxN should be tied
together for LVCMOS output.
Figure 21. Using Differential Output as LVCMOS standard
RS
CLOAD
RS should be chosen for impedance matching
appropriately.
CLOAD represents the capacitive load of entire circuits.
Additional Features
CY27410 supports additional features like early/late output
phase synchronization circuit, voltage controller frequency
shift (VCFS), spread spectrum clock generator (SSCG)
and cascading PLLs.
Phase Delay of Outputs
Outputs of CY27410 can be configured to introduce a
certain delay in the outputs. This feature can be used in
both CLOCKGEN and ZDB mode. This feature is provided
as some ASIC and SoCs require fixed delay between 2
clocks.
The following equation derives one period unit for delay
circuit:
Wherein tDL=1 delay unit
Example: If fVCO=3.0 GHz, tDL = 0.666 ns
Figure 22 shows an example of a conceptual delay circuit.

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 8
Figure 22. Phase Delay Circuit Example
O1d4
Low
DIVO1
1/2*fVCO
Shift Register
O1d2
O1d3
O1d1
O1
O1d4
Low
DIVO2
O1d2
O1d3
O1d1
O1x O2
O1x
0
1
2
3
4
5
6
0
1
2
3
4
5
6
Figure 23. Phase Delay Timing Diagram
CY27410 supports a maximum of four units (tDL) of
delay(s)
Even when you choose the same DIVO (Ox above) value
for O1 and O2 (O3, O4), it does not guarantee phase-
aligned clocks between outputs. To get phase-aligned
outputs, use O1x for other output(s).
Most of the ZDB outputs should use O1x for all outputs.
However, if you intentionally choose delayed output to
provide feedback, you can get the Early (or Late) phase
clocks described below.
Figure 24. Alignment of Delayed Outputs of CY27410
In the example shown in figure 24, one delayed output
(O1d1) is fed back to IN2, while early clock selected is
O1x, and delayed output selected is O1d3.
In CLKGEN mode, you may use this delay circuit to
generate N (x tDL) delayed phase clock(s). For applications
that need to adjust some skew or need fixed delay phase,
you may use this function. For example, if trace
characteristics are such that the propagation delay is
175 ps/inch, then a four inch-delay will be 700 ps.
Voltage-Controlled Frequency Shift (VCFS)
CY27410 mimics the VCXO feature found in crystal
oscillators with VCFS. The device modulates the PLL
(VCO) frequency up to 120 ppm. The modulation is
completely programmable. Please see Figure 26 for the
VCFS shift profile.
Figure 25. VCFS Shift Profile
-200
-150
-100
-50
0
50
100
150
200
250
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2
Atlas VCFS Char
Gain=000 Gain=001 Gain=010 Gain=011
Gain=100 Gain=101 Gain=110 Gain=111
VCFS in Applications
For some applications, the output clock frequency should
track incoming data stream by using analog feedback. The
CY27410 device acts as a part of the large phase lock
loop shown in Figure 26. The ASIC or SoC tracks the
incoming stream, calculates the error, and generates the
PWM signal (typically), following which the error
information is fed back to the local clock generator
(CY27410) for frequency tuning.
Figure 26. VCFS Example
The VCFS function modifies the PLL frequency, so the
frequency pulling is not dependent on the crystal
characteristic, temperature, voltage, or device process.
The VCFS modulation profile is linear and accurate and
you may use clock reference as well.
CY27410
VCFS plot

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 9
Cascading PLLs
With CY27410, you can make the output of one PLL and
provide it as an input to another PLL. This feature is called
PLL cascading. This feature can be used to generate very
precise frequencies using multiple dividers from two PLLs.
It can also take the VCFS modulated output from one PLL
and feed it to other PLLs, thus generating multiple
frequencies that track the change in the frequency. Figure
27 shows PLL1 configured in VCFS mode, its output
cascaded to PLL2 and PLL3, but PLL4 will run as the fixed
(un-modulated) frequency generation.
Figure 27. Cascading PLLs
SSCG (Spread-Spectrum Clock Generator)
CY27410’S spread-spectrum feature helps overcome
EMI/EMC concerns. The device supports both linear and
nonlinear spread profiles, and by using the patented
Lexmark profile as the nonlinear profile, offers the best
peak EMI reduction in the industry.
Figure 28 shows the scope sot for the Modulation Domain
Analyzer (time is plotted on the X-axis, while frequency is
shown on the Y-axis).
Figure 28. Spread Spectrum Clock Generator Profile
The spectrum is flat for nonlinear profiles, and raised at
the edges for linear profiles. In Figure 29, the nonspread-
spectrum profile is shown in red, while the modulated
nonlinear (Lexmark) and linear modulation spectrums,
~10 dB peak reduction at 633 MHz are shown in blue.
Figure 29. Spread-Spectrum Profiles Supported by
CY27410
-80.00
-75.00
-70.00
-65.00
-60.00
-55.00
-50.00
-45.00
-40.00
-35.00
-30.00
623.80 624.75 625.70 626.65 627.60 628.55 629.50 630.45 631.40 632.35 633.30 634.25 635.20 636.15 637.10 638.05 639.00 639.95 640.90 641.85 642.80 643.75
SS 1% Non-SS
Linear Profile

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 10
Power-Up Sequence
CY27410 has a CPU inside. While the supply (VDD) is
ramping, the CPU initializes its internal settings, input
configuration, output standard, output driver setting, etc.
Before CPU startup, all inputs and outputs are in an
unknown state. Figure 30 shows the start-up sequence.
Figure 30: Start-Up Sequence
Power Ramp
unknown Initialize Normal
Operation
VDD
XRES
Internal
Operation
POR(internal)
Crystal Oscillation
Input / Output Initialize
Output
State unknown Hi-Z Active
unknown Hi-Z Active
I2C
BUS
Power Supply Ramp
CY27410 requires a timing sequence for power ramp
(please see CY27410 datasheet). If your system cannot
meet this specification, provide the XRES (active LOW)
signal to ensure startup.
While XRES is asserted, CY27410 enters low-power
mode; outputs and the I2C bus signals are in a high
impedance (HI-Z) state until initialization is complete after
XRES is de-asserted. Figure 31 shows the considerations
for bus signals during power supply ramp.
Figure 31: I2C Bus Signal Consideration
In this section, the I2C behavior during power ramp is
discussed. Further details about the I2C interface are
discussed in the section “Programming CY27410”.
If you have a power supply switching while VDD is
approximately 0.7 V to 0.9 V, CY27410 may pull the SCK
signal LOW; therefore the I2C bus transaction may get
affected by this behavior. You should pay close attention
to this when you turn the CY27410 power supply ON or
OFF.
Frequency Select (FS)
CY27410 supports up to eight user profiles that contain
individual configurations. For FS pin transitions, CY27410
has two timing specifications –fast switching and slow
switching.
Fast switching is applicable for the output ON/OFF,
output-divider value change, and output MUX setting
change. Slow switching is applicable for changes to the
PLL parameter (including PLL ON/OFF). As the name
implies, the output will change fast in fast switching and
slow for slow switching. For each case, the output will be
turned off and on without any glitch. See Figure 32 that
shows the timing relationship between FS and the output
clock. You can refer to the device datasheet for further
details.
Figure 32: Frequency Select Operation
Power Ramp Considerations
CY27410 contains an internal CPU and requires reliable
POR (Power-on-Reset) for proper operation. The device
requires XRES signal when the power ramp is greater
than the specification.
Multiple Power Supply Domains
CY27410 has six different types of power supply pins -
VDD, VDDIO1D, VDDIO1S, VDDIO2D, VDDIO2S, and
VCCD. VDD is the core power supply, while the VDDIOx
supplies are for I/Os. The VCCD is the analog power
supply. There is no sequencing requirement for power
supplies, but VDD and VCCD must be monotonic.
Power Supply Filtering
Power supply filtering is especially important for clock
signal integrity. Each VDD and VDDIO pin must have a
100-nF capacitor close to the pin, and a 2.2-µF (or higher)
capacitor
VCCD is an additional power supply pin for this device,
since the device (CY27410) internal power supply is 1.8 V,
this pin will be the LDO (Low Drop Out) output when using
2.5 V or 3.3 V range of core power supplies (VDD and
VDDA), so you should connect the 100-nF capacitor to
this pin closely and not connect any power from external
sources. However, if you use the device with a 1.8-V
power supply, the internal LDO will be bypassed, so this
pin requires 1.8 V externally generated power supply for
the core, 100-nF capacitor must be connected close to this
pin.

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 11
Internal Memory Structure
Figure 33 shows the internal memory structure of the
CY27410 device. It has a nonvolatile (NV) and a volatile
(RAM) inside. The RAM directly controls the CY27410
hardware. An internal hardware communication buffer
handles I2C communications.
Figure 33: Internal Memory Structure
Programming CY27410
CY27410 programming is done using the I2C bus interface.
On-Board Programming
On-board programming can be done by the on-board Host
that communicates with CY27410 through commands and
data that contains COM, FS, and miscellaneous
information like I2C address, read/write protection etc.
Using an External I2C Master
You can use an external I2C master device such as
Cypress MiniProg™, Cypress TT-Bridge™or another I2C-
qualified device to program user configuration into an un-
programmed (virgin) CY27410 device on the system.
Figure 34. Using an External I2C Master to Program
CY27410
.
Conclusion
CY27410 is a 4-PLL spread-spectrum clock generator
targeted at consumer, industrial, and networking
applications. Its superior specifications and value-added
features such as voltage-controlled crystal oscillator
(VCXO), frequency select, and zero/nonzero delay buffer
(ZDB/NZDB) modes make it an ideal choice for a wide
variety of applications.

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 12
Document History
Document Title: Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator –AN94024
Document Number: 001-94024
Revision
ECN
Orig. of
Change
Submission
Date
Description of Change
**
4664885
XHT
02/18/2015
New Application Note
*A
5847700
GNKK
08/08/2017
Updated the Cypress logo and copyright information.

Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com Document No. 001-94024 Rev.*A 13
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