100 MHz Differential Buffer for PCI Express and SAT
A
CY28400
Rev 1.0, November 21, 2006 Page 1 of 12
2200 Laurelwood Road, Santa Clara, CA 95054 Tel:(408) 855-0555 Fax:(408) 855-0550 www.SpectraLinear.com
Features
• CK409 or CK410 companion buffer
• Four differential 0.7V clock pairs
• Individual OE controls
• Low CTC jitter (< 50 ps)
• Programmable bandwidth
• SRC_STOP# power management control
• SMBus Block/Byte/Word Read and Write support
• 3.3V operation
• PLL Bypass-configurable
• Divide by 2 programmable outputs
• 28-pin SSOP package
Functional Description
The CY28400 is a differential buffer and serves as a
companion device to the CK409 or CK410 clock generator.
The device is capable of distributing the Serial Reference
Clock (SRC) in PCI Express and SATA implementations.
Block Diagram Pin Configuration
PLL/BYPASS#
DIFT2
DIFC2
DIFT1
DIFC1
DIFT5
DIFC5
DIFT6
DIFC6
Output
Buffer
Output
Control
PLL
DIV
SMBus
Controller
SRC_STOP#
PWRDWN#
SCLK
SDATA
SRCT_IN
SRCC_IN
HIGH_BW#
OE_(1,6)
28 SSOP
VDD
SRCT_IN
VSS
VDD
DIFT1
DIFC1
OE_1
DIFT2
DIFC2
VDD
PLL/BYPASS#
SCLK
SDATA
VDD_A
VSS_A
SRC_STOP#
PWRDWN#
HIGH_BW#
DIFC5
VDD
DIFT5
DIFC6
0E_6
DIFT6
VSS
VDD
IREF
28
27
26
25
24
23
22
21
20
19
18
17
16
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
CY28400
SRCC_IN
CY28400
Rev 1.0, November 21, 2006 Page 2 of 12
Pin Descriptions
Serial Data Interface
To enhance the flexibility and function of the clock synthesizer,
a two-signal serial interface is provided. Through the Serial
Data Interface, various device functions, such as individual
clock output buffers, can be individually enabled or disabled.
The registers associated with the Serial Data Interface
initialize to their default setting upon power-up, and therefore
use of this interface is optional. Clock device register changes
are normally made upon system initialization, if any are
required. The interface cannot be used during system
operation for power management functions.
Data Protocol
The clock driver serial protocol accepts byte write, byte read,
block write, and block read operations from the controller. For
block write/read operation, the bytes must be accessed in
sequential order from lowest to highest byte (most significant
bit first) with the ability to stop after any complete byte has
been transferred. For byte write and byte read operations, the
system controller can access individually indexed bytes. The
offset of the indexed byte is encoded in the command code,
as described in Table 1.
The block write and block read protocol is outlined in Table 2
while Table 3 outlines the corresponding byte write and byte
read protocol. The slave receiver address is 11011100 (DCh).
Pin Name Type Description
2,3 SRCT_IN, SRCC_IN I,DIF 0.7V differential SRC inputs from the clock synthesizer
6,7,9,10,19,20,22,23 DIFT/C(2:1) & (6:5) O,DIF 0.7V differential clock outputs
8,21 OE_1, OE_6 I,SE 3.3V LVTTL active LOW input for three-stating differential
outputs (DIFT2 and DIFT5 are unaffected by the assertion of OE
inputs)
17 HIGH_BW# I,SE 3.3V LVTTL input for selecting PLL bandwidth
16 SRC_STOP# I,SE 3.3V LVTTL input for SRC_STOP#, active LOW
15 PWRDWN# I,SE 3.3V LVTTL input for Power Down, active LOW
13 SCLK I,SE SMBus slave clock input
14 SDATA I/O,OC Open collector SMBus data
26 IREF I A precision resistor is attached to this pin to set the differential
output current
12 PLL/BYPASS# I 3.3V LVTTL input for selecting fan-out or PLL operation
28 VDD_A 3.3V 3.3V power supply for PLL
27 VSS_A GND Ground for PLL
4,25 VSS 3.3V Ground for outputs
1,5,11,18,24 VDD GND 3.3V power supply for outputs
Table 1. Command Code Definition
Bit Description
7 0 = Block read or block write operation
1 = Byte read or byte write operation
(6:0) Byte offset for byte read or byte write operation. For block read or block write operations, these bits should be
'0000000'
Table 2. Block Read and Block Write Protocol
Block Write Protocol Block Read Protocol
Bit Description Bit Description
1Start 1Start
2:8 Slave address – 7 bits 2:8 Slave address – 7 bits
9 Write = 0 9 Write = 0
10 Acknowledge from slave 10 Acknowledge from slave
11:18 Command Code – 8 bits
'00000000' stands for block operation
11:18 Command Code – 8 bits
'00000000' stands for block operation
19 Acknowledge from slave 19 Acknowledge from slave
CY28400
Rev 1.0, November 21, 2006 Page 3 of 12
20:27 Byte Count from master – 8 bits 20 Repeat start
28 Acknowledge from slave 21:27 Slave address – 7 bits
29:36 Data byte 0 from master – 8 bits 28 Read = 1
37 Acknowledge from slave 29 Acknowledge from slave
38:45 Data byte 1 from master – 8 bits 30:37 Byte count from slave – 8 bits
46 Acknowledge from slave 38 Acknowledge from host
.... Data bytes from master/Acknowledge 39:46 Data byte 0 from slave – 8 bits
.... Data Byte N – 8 bits 47 Acknowledge from host
.... Acknowledge from slave 48:55 Data byte 1 from slave – 8 bits
.... Stop 56 Acknowledge from host
.... Data bytes from slave/Acknowledge
.... Data byte N from slave – 8 bits
.... Acknowledge from host
.... Stop
Table 3. Byte Read and Byte Write Protocol
Byte Write Protocol Byte Read Protocol
Bit Description Bit Description
1 Start 1 Start
2:8 Slave address – 7 bits 2:8 Slave address – 7 bits
9 Write = 0 9 Write = 0
10 Acknowledge from slave 10 Acknowledge from slave
11:18 Command Code – 8 bits
'100xxxxx' stands for byte operation, bits[6:0] of the
command code represents the offset of the byte to be
accessed
11:18 Command Code – 8 bits
'100xxxxx' stands for byte operation, bits[6:0]
of the command code represents the offset of
the byte to be accessed
19 Acknowledge from slave 19 Acknowledge from slave
20:27 Data byte from master – 8 bits 20 Repeat start
28 Acknowledge from slave 21:27 Slave address – 7 bits
29 Stop 28 Read = 1
29 Acknowledge from slave
30:37 Data byte from slave – 8 bits
38 Acknowledge from master
39 Stop
Byte 0: Control Register 0
Bit @Pup Name Description
7 0 PWRDWN# drive mode
0 = Driven when stopped, 1 = Three-state
6 0 SRC_STOP# drive mode
0 = Driven when stopped, 1 = Three-state
50 Reserved
40 Reserved
30 Reserved
2 1 HIGH_BW# HIGH_BW#
0 = High Bandwidth, 1 = Low bandwidth
Table 2. Block Read and Block Write Protocol (continued)
Block Write Protocol Block Read Protocol
Bit Description Bit Description
CY28400
Rev 1.0, November 21, 2006 Page 4 of 12
1 1 PLL/Bypass# PLL/Bypass#
0 = Fanout buffer, 1 = PLL mode
0 1 SRC_DIV/2
0 = Divided by 2 mode,1 = Normal (output = input)
Byte 1: Control Register 1
Bit @Pup Name Description
71 Reserved
6 1 DIFT/C6 DIFT/C6 Output Enable
0 = Disabled (three-state), 1 = Enabled
5 1 DIFT/C5 DIFT/C5 Output Enable
0 = Disabled (three-state), 1 = Enabled
41 Reserved
31 Reserved
2 1 DIFT/C2 DIFT/C2 Output Enable
0 = Disabled (three-state), 1 = Enabled
1 1 DIFT/C1 DIFT/C1 Output Enable
0 = Disabled (three-state), 1 = Enabled
01 Reserved
Byte 2: Control Register 2
Bit @Pup Name Description
70 Reserved
6 0 Allow Control DIFT/C6 with assertion of SRC_STOP#
0 = Free-running, 1 = Stopped with SRC_STOP#
5 0 Allow Control DIFT/C5 with assertion of SRC_STOP#
0 = Free-running, 1 = Stopped with SRC_STOP#
40 Reserved
30 Reserved
2 0 Allow Control DIFT/C2 with assertion of SRC_STOP#
0 = Free-running, 1 = Stopped with SRC_STOP#
1 0 Allow Control DIFT/C1 with assertion of SRC_STOP#
0 = Free-running, 1 = Stopped with SRC_STOP#
00 Reserved
Byte 3: Control Register 3
Bit @Pup Name Description
70 Reserved
60 Reserved
50 Reserved
40 Reserved
30 Reserved
20 Reserved
10 Reserved
00 Reserved
Byte 0: Control Register 0 (continued)
Bit @Pup Name Description
CY28400
Rev 1.0, November 21, 2006 Page 5 of 12
PWRDWN# Clarification[1]
The PWRDWN# pin is used to shut off all clocks cleanly and
instruct the device to evoke power savings mode. Additionally,
PWRDWN# should be asserted prior to shutting off the input
clock or power to ensure all clocks shut down in a glitch-free
manner. PWRDWN# is an asynchronous active LOW input.
This signal is synchronized internal to the device prior to
powering down the clock buffer. PWRDWN# is an
asynchronous input for powering up the system. When
PWRDWN# is asserted LOW, all clocks will be held HIGH or
three-stated (depending on the state of the control register
drive mode and OE bits) prior to turning off the VCO. All clocks
will start and stop without any abnormal behavior and must
meet all AC and DC parameters. This means no glitches,
frequency shifting or amplitude abnormalities among others.
PWRDWN# Assertion
When PWRDWN# is sampled LOW by two consecutive rising edges of DIFC, all DIFT outputs will be held HIGH or three-stated
(depending on the state of the control register drive mode and OE bits) on the next DIFC HIGH-to-LOW transition. When the
SMBus power-down drive mode bit is programmed to ‘0’, all clock outputs will be held with the DIFT pin driven HIGH at 2 x Iref
and DIFC three-state. However, if the control register PWRDWN# drive mode bit is programmed to ‘1’, then both DIFT and the
DIFC are three-stated.
Note:
1. Disabling of the SRCT_IN input clock prior to assertion of PWRDWN# is an undefined mode and not recommended. Operation in this mode may result in glitches
excessive frequency shifting.
Byte 4: Vendor ID Register
Bit @Pup Name Description
7 0 Revision Code Bit 3
6 0 Revision Code Bit 2
5 0 Revision Code Bit 1
4 0 Revision Code Bit 0
3 1 Vendor ID Bit 3
2 0 Vendor ID Bit 2
1 0 Vendor ID Bit 1
0 0 Vendor ID Bit 0
Byte 5: Control Register 5
Bit @Pup Name Description
70 Reserved
60 Reserved
50 Reserved
40 Reserved
30 Reserved
20 Reserved
10 Reserved
00 Reserved
PWRDWN#
DIFC
DIFT
Figure 1. PWRDWN# Assertion Diagram
CY28400
Rev 1.0, November 21, 2006 Page 6 of 12
PWRDWN#—Deassertion
The power-up latency is less than 1 ms. This is the time from
the deassertion of the PWRDWN# pin or the ramping of the
power supply or the time from valid SRC_IN input clocks until
the time that stable clocks are output from the buffer chip (PLL
locked). If the control register PWRDWN# three-state bit is
programmed to ‘1’, all differential outputs will be driven HIGH
in less than 300 Ps of PWRDWN# deassertion to a voltage
greater than 200 mV.
Notes:
2. The total power-up latency from power on to all outputs active is less than 1 ms (assuming a valid clock is present on SRC_IN input).
3. If power is valid and PWRDWN# is deasserted but no input clocks are present on the SRC_IN input, DIF clocks will remain disabled. Only after valid input clocks
are detected, valid power, PWRDWN# deasserted with the PLL locked and stable are the DIF outputs enabled.
Table 4. Buffer Power-up State Machine
State Description
0 3.3V Buffer power off
1 After 3.3V supply is detected to rise above 1.8V–2.0V, the buffer enters state 1 and initiates a 0.2-ms–0.3-ms delay
2[3] Buffer waits for a valid clock on the SRC_IN input and PWRDWN# deassertion
3[2] Once the PLL is locked to the SRC_IN input clock, the buffer enters state 3 and enables outputs for normal operation
DIFC
DIFT
Tstable
<1mS
PWRDWN#
Tdrive_Pwrdwn#
<300uS, >200mV
Figure 2. PWRDWN# Deassertion Diagram
S2
Wait for Input
Clock &
PWRDWN# De-
assertion
PWRDWN# Asserted
S1
Delay
>0.25ms
S0
Power Off
S3
Normal
Operation
No Input Clock
Figure 3. Buffer Power-up State Diagram
CY28400
Rev 1.0, November 21, 2006 Page 7 of 12
SRC_STOP# Clarification
The SRC_STOP# signal is an active LOW input used for clean
stopping and starting the DIF outputs (valid clock must be
present on SRCT_IN). The SRC_STOP# signal is a
de-bounced signal in that it’s state must remain unchanged
during two consecutive rising edges of DIFC to be recognized
as a valid assertion or deassertion. (The assertion and
deassertion of this signal is absolutely asynchronous.)
SRC_STOP# Assertion
The impact of asserting the SRC_STOP# pin is all DIF outputs
that are set in the control registers to stoppable via assertion
of SRC_STOP# are stopped after their next transition. When
the control register SRC_STOP# three-state bit is
programmed to ‘0’, the final state of all stopped DIFT/C signals
is DIFT clock = HIGH and DIFC = LOW. There is to be no
change to the output drive current values, DIFT will be driven
HIGH with a current value equal 6 x Iref, and DIFC will not be
driven. When the control register SRC_STOP# three-state bit
is programmed to ‘1’, the final state of all stopped DIF signals
is LOW, both DIFT clock and DIFC clock outputs will not be
driven.
SRC_STOP# Deassertion
All differential outputs that were stopped will resume normal
operation in a glitch-free manner. The maximum latency from
the deassertion to active outputs is between 2–6 DIFT/C clock
periods (two clocks are shown) with all DIFT/C outputs
resuming simultaneously. If the control register three-state bit
is programmed to ‘1’ (three-state), then all stopped DIFT
outputs will be driven high within 10 ns of SRC_STOP#
deassertion to a voltage greater than 200 mV.
Note:
4. In the case where OE is asserted HIGH, the output will always be three-stated regardless of SRC_STOP# drive mode register bit state.
Table 5. SRC_STOP# Functionality[4]
SRC_STOP# DIFT DIFC
1 Normal Normal
0 Iref * 6 or Float Low
DIFC (Stoppable)
DIFT (Stoppable)
DIFC(Free Running
DIFT(Free Running
PWRDWN#
1mS
SRC_STOP#
Figure 4. SRC_STOP# = Driven, PWRDWN# = Driven
DIFC (Stoppable)
DIFC(Free Running
PWRDWN#
1mS
SRC_STOP#
DIFT (Stoppable)
DIFT(Free Running
Figure 5. SRC_STOP# =Driven, PWRDWN# = Three-state
CY28400
Rev 1.0, November 21, 2006 Page 8 of 12
Output Enable Clarification
The outputs may be disabled in two ways, via writing a ‘0’ to
the SMBus register bit corresponding to output of interest or
by asserting an OE input pin LOW. In both methods, if SMBus
registered bit has been written LOW or the OE pin is LOW or
both, the output of interest will be three-stated. The assertion
and deassertion of this signal is asynchronous.
OE Assertion (Transition from ‘0’ to ‘1’)
All differential outputs that were three-stated will resume
normal operation in a glitch-free manner. The maximum
latency from the assertion to active outputs is between 2–6 DIF
clock periods. In addition, DIFT clocks will be driven HIGH
within 10 ns of OE assertion to a voltage greater than 200 mV.
OE Deassertion (Transition from ‘1’ to ‘0’)
The impact of deasserting OE is that each corresponding output
will transition from normal operation to three-state in a
glitch-free manner. The maximum latency from the deassertion
to three-stated outputs is between 2–6 DIF clock periods.
SRC_DIV2# Clarification
The SRC_DIV2# feature is used to configure the DIF output
mode to be equal to the SRCT_IN input frequency or half the
input frequency in a glitch-free manner. The SRC_DIV2# function
may be implemented by writing a ‘0’ to SMBus register bit.
SRC_DIV2# Assertion
The impact of writing a ‘0’ to the SRC_DIV/2 register bit is that
all DIF outputs will transition cleanly in a glitch-free manner
from normal operation (output frequency equal to input) to half
the input frequency within 2–6 DIF clock periods.
SRC_DIV2# Deassertion
The impact of writing a ‘0’ to the SRC_DIV/2 register bit is that
all DIF outputs will transition cleanly in a glitch-free manner
from divide by 2 mode to normal (output frequency is equal to
the input frequency) operation within 2–6 DIF clock periods.
PLL/BYPASS# Clarification
The PLL/Bypass# input is used to select between bypass
mode (no PLL) and PLL mode. In bypass mode, the input clock
is passed directly to the output stage resulting in 50 ps additive
jitter (50 ps + input jitter) on DIF outputs. In the case of PLL
mode, the input clock is pass through a PLL to reduce
high-frequency jitter. The BYPASS# mode may be selected in
two ways, via writing a ‘0’ to SMBus register bit or by asserting
the PLL/BYPASS# pin LOW. In both methods, if the SMBus
register bit has been written low or PLL/BYPASS# pin is LOW
or both, the device will be configure for BYPASS operation.
HIGH_BW# Clarification
The HIGH_BW# input is used to set the PLL bandwidth. This
mode is intended to minimize PLL peaking when two or more
buffers are cascaded by staggering device bandwidths. The
PLL low-bandwidth mode may be selected in two ways, via
writing a ‘0’ to SMBus register bit or by asserting the
HIGH_BW# pin is LOW or both, the device will be configured
for low-bandwidth operation.
DIFC (Stoppable)
DIFC(Free Running
DIFT(Free Running
PWRDWN#
1mS
SRC_STOP#
DIFT (Stoppable)
Figure 6. SRC_STOP# = Three-state, PWRDWN# = Driven
DIFC(Free Running
DIFT(Free Running
DIFT (Stoppable)
DIFC (Stoppable)
PWRDWN#
1mS
SRC_STOP#
Figure 7. SRC_STOP# = Three-state, PWRDWN# = Three-state
Table 6. OE Functionality
OE (Pin) OE (SMBus Bit) DIFT DIFC
1 1 Normal Normal
1 0 Three-state Three-state
0 1 Three-state Three-state
0 0 Three-state Three-state
CY28400
Rev 1.0, November 21, 2006 Page 9 of 12
Absolute Maximum Conditions
Parameter Description Condition Min. Max. Unit
VDD Core Supply Voltage –0.5 4.6 V
VDD_A Analog Supply Voltage –0.5 4.6 V
VIN Input Voltage Relative to VSS –0.5 VDD + 0.5 VDC
TSTemperature, Storage Non-functional –65 150 °C
TATemperature, Operating Ambient Functional 0 70 °C
TJTemperature, Junction Functional – 150 °C
ØJC Dissipation, Junction to Case Mil-Spec 883E Method 1012.1 – TBD °C/W
ØJA Dissipation, Junction to Ambient JEDEC (JESD 51) – TBD °C/W
ESDHBM ESD Protection (Human Body Model) MIL-STD-883, Method 3015 2000 – V
UL-94 Flammability Rating At 1/8 in. V–0
MSL Moisture Sensitivity Level 1
Multiple Supplies: The Voltage on any input or I/O pin cannot exceed the power pin during power-up. Power supply sequencing is NOT required.
DC Electrical Specifications
Parameter Description Condition Min. Max. Unit
VDD_A, VDD 3.3V Operating Voltage 3.3 ± 5% 3.135 3.465 V
VILI2C Input Low Voltage SDATA, SCLK – 1.0 V
VIHI2C Input High Voltage SDATA, SCLK 2.2 – V
VIL 3.3V Input Low Voltage VSS – 0.5 0.8 V
VIH 3.3V Input High Voltage 2.0 VDD + 0.5 V
IIL Input Low Leakage Current Except internal pull-up resistors, 0 < VIN < VDD –5 PA
IIH Input High Leakage Current Except internal pull-down resistors, 0 < VIN < VDD 5PA
IOZ High-impedance Output Current –10 10 PA
CIN Input Pin Capacitance 2 5 pF
COUT Output Pin Capacitance 3 6 pF
LIN Pin Inductance – 7 nH
IDD3.3V Dynamic Supply Current At max. load and 100 MHz per Figure 8 – 215 mA
IPD3.3V Power-down Supply Current PD asserted, Outputs driven – 40 mA
IPD3.3V Power-down Supply Current PD asserted, Outputs Three-stated – 5 mA
AC Electrical Specification
Parameter Description Condition Min. Max. Unit
DIF at 0.7V
TDC DIFT and DIFC Duty Cycle Measured at crossing point VOX 45 55 %
TSKEW Any DIFT/C to DIFT/C Clock Skew, SSC Measured at crossing point VOX –150ps
TPERIOD Average Period Measured at crossing point VOX at 100 MHz 9.9970 10.0533 ns
TCCJ DIFT/C Cycle to Cycle Jitter Measured at crossing point VOX –50ps
TR / TFDIFT and DIFC Rise and Fall Times Measured from VOL = 0.175 to VOH = 0.525V 175 700 ps
TRFM Rise/Fall Matching Determined as a fraction of 2*(TR – TF)/(TR+ TF)– 20 %
'TRRise Time Variation – 125 ps
'TFFall Time Variation – 125 ps
VHIGH Voltage High Measured SE 660 850 mv
VLOW Voltage Low Measured SE –150 – mv
VOX Crossing Point Voltage at 0.7V Swing 250 550 mv
CY28400
Rev 1.0, November 21, 2006 Page 10 of 12
Switching Waveforms
'VOX Vcross Variation over all edges – 140 mV
VOVS Maximum Overshoot Voltage – VHIGH +
0.3
V
VUDS Minimum Undershoot Voltage – –0.3 V
VRB Ring Back Voltage Measured SE 0.2 N/A V
tPD(PLL) Input to output skew in PLL mode Measured at crossing point VOX –±250ps
tPD(NONPLL) Input to output skew in Non - PLL mode Measured at crossing point VOX 2.5 6.5 ns
AC Electrical Specification (continued)
Parameter Description Condition Min. Max. Unit
DIFT
TPCB
TPCB
DIFC
:
:
:
:
Measurem ent
Point
2pF
:
IR E F
Measurem ent
Point
2pF
Trace Im pedance Measured Differentially
Figure 8. Differential Clock Termination
Figure 9. Single-Ended Measurement Points for TRise and TFall
VOH = 0.525V
TRise (CLOCK)
TFall (CLOCK)
CLOCK#
VOL = 0.175V
VCROSS
CLOCK
CY28400
Rev 1.0, November 21, 2006 Page 11 of 12
VOVS
VRB
VLOW
VUDS
VRB
Figure 10. Single-ended Measurement Points for VOVS,VUDS and VRB
0.000V
TPERIOD
High Duty Cycle % Low Duty Cycle %
Skew Management Point
Figure 11. Differential (Clock-CLock#) Measurement Points (Tperiod, Duty Cycle and Jitter)
Ordering Information
Ordering Code Package Type Operating Range
CY28400OC 28-pin SSOP Commercial, 0°C to 70 °C
CY28400OCT 28-pin SSOP (Tape & Reel) Commercial, 0°C to 70 °C
Lead-free
CY28400OXC 28-pin SSOP Commercial, 0°C to 70 °C
CY28400OXCT 28-pin SSOP (Tape & Reel) Commercial, 0°C to 70 °C
Rev 1.0, November 21, 2006 Page 12 of 12
CY28400
While SLI has reviewed all information herein for accuracy and reliability, Spectra Linear Inc. assumes no responsibility for the use of any cir-
cuitry or for the infringement of any patents or other rights of third parties which would result from each use. This product is intended for use in
normal commercial applications and is not warranted nor is it intended for use in life support, critical medical instruments, or any other applica-
tion requiring extended temperature range, high reliability, or any other extraordinary environmental requirements unless pursuant to additional
processing by Spectra Linear Inc., and expressed written agreement by Spectra Linear Inc. Spectra Linear Inc. reserves the right to change any
circuitry or specification without notice.
Package Drawing and Dimensions
28-Lead (5.3 mm) Shrunk Small Outline Package O28
