CDC2536
www.ti.com
SCAS377E – APRIL 1994 – REVISED JULY 2004
3.3-V PHASE-LOCK LOOP CLOCK DRIVER WITH 3-STATE OUTPUTS
FEATURES
•
•
•
•
•
•
•
•
•
•
•
•
•
Low Output Skew for Clock-Distribution and
Clock-Generation Applications
Operates at 3.3-V VCC
Distributes One Clock Input to Six Outputs
One Select Input Configures Three Outputs to
Operate at One-Half or Double the Input
Frequency
No External RC Network Required
On-Chip Series Damping Resistors
External Feedback Pin (FBIN) Is Used to
Synchronize the Outputs to the Clock Input
Application for Synchronous DRAM,
High-Speed Microprocessor
TTL-Compatible Inputs and Outputs
Outputs Drive 50-Ω Parallel-Terminated
Transmission Lines
State-of-the-Art EPIC-IIB™ BiCMOS Design
Significantly Reduces Power Dissipation
Distributed VCC and Ground Pins Reduce
Switching Noise
Packaged in Plastic 28-Pin Shrink
Small-Outline Package
DB PACKAGE
(TOP VIEW)
AVCC
AGND
CLKIN
SEL
OE
GND
1Y1
VCC
GND
1Y2
VCC
GND
1Y3
VCC
1
28
2
27
3
26
4
25
5
24
6
23
7
22
8
21
9
20
10
19
11
18
12
17
13
16
14
15
AVCC
AGND
FBIN
TEST
CLR
VCC
2Y1
GND
VCC
2Y2
GND
VCC
2Y3
GND
DESCRIPTION
The CDC2536 is a high-performance, low-skew, low-jitter clock driver. It uses a phase-lock loop (PLL) to
precisely align, in both frequency and phase, the clock output signals to the clock input (CLKIN) signal. It is
specifically designed for use with synchronous DRAMs and popular microprocessors operating at speeds from
50 MHz to 100 MHz or down to 25 MHz on outputs configured as half-frequency outputs. The CDC2536
operates at 3.3-V VCC and is designed to drive a 50-W transmission line. The CDC2536 also provides on-chip
series-damping resistors, eliminating the need for external termination components.
The feedback (FBIN) input is used to synchronize the output clocks in frequency and phase to the input clock
(CLKIN). One of the six output clocks must be fed back to FBIN for the PLL to maintain synchronization between
CLKIN and the outputs. The output used as the feedback pin is synchronized to the same frequency as CLKIN.
The Y outputs can be configured to switch in phase and at the same frequency as CLKIN. The select (SEL) input
configures three Y outputs to operate at one-half or double the CLKIN frequency, depending on which pin is fed
back to FBIN (see Tables 1 and 2). All output signal duty cycles are adjusted to 50% independent of the duty
cycle at the input clock.
Output-enable (OE) is provided for output control. When OE is high, the outputs are in the high-impedance state.
When OE is low, the outputs are active. TEST is used for factory testing of the device and can be use to bypass
the PLL. TEST should be strapped to GND for normal operation.
Unlike many products containing PLLs, the CDC2536 does not require external RC networks. The loop filter for
the PLL is included on-chip, minimizing component count, board space, and cost.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
EPIC-IIB is a trademark of Texas Instruments.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 1994–2004, Texas Instruments Incorporated
CDC2536
www.ti.com
SCAS377E – APRIL 1994 – REVISED JULY 2004
Because it is based on PLL circuitry, the CDC2536 requires a stabilization time to achieve phase lock of the
feedback signal to the reference signal. This stabilization time is required following power up and application of a
fixed-frequency, fixed-phase signal at CLKIN, as well as following any changes to the PLL reference or feedback
signals. Such changes occur upon change of SEL, enabling the PLL via TEST, and upon enable of all outputs
via OE.
The CDC2536 is characterized for operation from 0°C to 70°C.
DETAILED DESCRIPTION OF OUTPUT CONFIGURATIONS
The voltage-controlled oscillator (VCO) used in the CDC2536 has a frequency range of 100 MHz to 200 MHz,
twice the operating frequency of the CDC2536 outputs. The output of the VCO is divided by two and by four to
provide reference frequencies with a 50% duty cycle of one-half and one-fourth the VCO frequency. SEL
determines which of the two signals is buffered to each bank of device outputs.
One device output must be externally wired to FBIN to complete the PLL. The VCO operates such that the
frequency of the output matches that of CLKIN. In the case that a VCO/2 output is wired to FBIN, the VCO must
operate at twice the CLKIN frequency resulting in device outputs that operate at either the same or one-half the
CLKIN frequency. If a VCO/4 output is wired to FBIN, the device outputs operate at the same or twice the CLKIN
frequency.
Output Configuration A
Output configuration A is valid when any output configured as a 1× frequency output in Table 1 is fed back to
FBIN. The input frequency range for CLKIN is 50 MHz to 100 MHz when using output configuration A. Outputs
configured as 1/2× outputs operate at half the CLKIN frequency, while outputs configured as 1× outputs operate
at the same frequency as CLKIN.
Table 1. Output Configuration A
INPUT
OUTPUTS
SEL
1/2×
FREQUENCY
1×
FREQUENCY
L
None
All
H
1Yn
2Yn
Output Configuration B
Output configuration B is valid when any output configured as a 1× frequency output in Table 2 is fed back to
FBIN. The input frequency range for CLKIN is 25 MHz to 50 MHz when using output configuration B. Outputs
configured as 1× outputs operate at the CLKIN frequency, while outputs configured as 2× outputs operate at
double the frequency of CLKIN.
Table 2. Output Configuration B
INPUT
2
OUTPUTS
SEL
1×
FREQUENCY
2×
FREQUENCY
H
1Yn
2Yn
L
All
None
CDC2536
www.ti.com
SCAS377E – APRIL 1994 – REVISED JULY 2004
FUNCTIONAL BLOCK DIAGRAM
OE
5
24
CLR
FBIN
26
Phase-Lock Loop
3
CLKIN
TEST
SEL
2
2
25
4
7
10
13
22
19
16
1Y1
1Y2
1Y3
2Y1
2Y2
2Y3
3
CDC2536
www.ti.com
SCAS377E – APRIL 1994 – REVISED JULY 2004
FUNCTIONAL BLOCK DIAGRAM (continued)
Terminal Functions
TERMINAL
NAME
NO.
I/O
DESCRIPTION
CLKIN
3
I
Clock input. CLKIN provides the clock signal to be distributed by the CDC2536 clock-driver circuit. CLKIN
provides the reference signal to the integrated PLL that generates the clock output signals. CLKIN must
have a fixed frequency and fixed phase for the phase-lock loop to obtain phase lock. Once the circuit is
powered up and a valid CLKIN signal is applied, a stabilization time is required for the PLL to phase lock
the feedback signal to its reference signal.
CLR
24
I
CLR is used for testing purposes only. Connect CLR to GND for normal operation.
FBIN
26
I
Feedback input. FBIN provides the feedback signal to the internal PLL. FBIN must be hardwired to one of
the six clock outputs to provide frequency and phase lock. The internal PLL adjusts the output clocks to
obtain zero phase delay between the FBIN and differential CLKIN inputs.
OE
5
I
Output enable. OE is the output enable for all outputs. When OE is low, all outputs are enabled. When OE
is high, all outputs are in the high-impedance state. Since the feedback signal for the PLL is taken directly
from an output, placing the outputs in the high-impedance state interrupts the feedback loop; therefore,
when a high-to-low transition occurs at OE, enabling the output buffers, a stabilization time is required
before the PLL obtains phase lock.
SEL
4
I
Output configuration select. SEL selects the output configuration for each output bank (e.g. 1×, 1/2×, or
2×).(see Tables 1 and 2).
TEST
25
I
TEST is used to bypass the PLL circuitry for factory testing of the device. When TEST is low, all outputs
operate using the PLL circuitry. When TEST is high, the outputs are placed in a test mode that bypasses
the PLL circuitry. TEST should be grounded for normal operation.
O
These outputs are configured by SEL to transmit one-half or one-fourth the frequency of the VCO. The
relationship between the CLKIN frequency and the output frequency is dependent on SEL. The duty cycle
of the Y output signals is nominally 50%, independent of the duty cycle of the CLKIN signal. Each output
has an internal series resistor to dampen transmission-line effects and improve the signal integrity at the
load.
O
These outputs transmit one-half the frequency of the VCO. The relationship between the CLKIN frequency
and the output frequency is dependent on the frequency of the output being fed back to FBIN. The duty
cycle of the Y output signals is nominally 50%, independent of the duty cycle of the CLKIN signal. Each
output has an internal series resistor to dampen transmission-line effects and improve the signal integrity at
the load.
1Y1-1Y3
2Y1-2Y3
7, 10, 13
22, 19, 16
ABSOLUTE MAXIMUM RATINGS
over operating free-air temperature range (unless otherwise noted) (1)
UNIT
Supply voltage range, VCC
Input voltage range, VI (see
-0.5 V to 4.6 V
(2))
-0.5 V to 7 V
Voltage range applied to any output in the high state or power-off state, VO (see
(2))
-0.5 V to 5.5 V
Current into any output in the low state, IO
24 mA
Input clamp current, IIK(VI< 0)
-20 mA
Output clamp current, IOK(VO< 0)
Maximum power dissipation at TA = 55°C (in still air) (see
Storage temperature range, Tstg
(1)
(2)
(3)
4
-50 mA
(3))
0.68 W
-65°C to 150°C
Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating
conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
The input and output negative-voltage ratings may be exceeded if the input and output clamp-current ratings are observed.
The maximum package power dissipation is calculated using a junction temperature of 150°C and a board trace length of 75 mils. For
more information, refer to the Package Thermal Considerations application note in the 1994 ABT Advanced BiCMOS Technology Data
Book, literature number SCBD002B.
CDC2536
www.ti.com
SCAS377E – APRIL 1994 – REVISED JULY 2004
RECOMMENDED OPERATING CONDITIONS (SEE
(1)
)
MIN
MAX
VCC
Supply voltage
3
3.6
VIH
High-level input voltage
2
VIL
Low-level input voltage
VI
Input voltage
IOH
High-level output current
IOL
Low-level output current
TA
Operating free-air temperature
(1)
0
V
V
0.8
0
UNIT
V
5.5
V
12
mA
12
mA
70
°C
Unused inputs must be held high or low to prevent them from floating.
ELECTRICAL CHARACTERISTICS
over recommended operating free-air temperature range, TA = 25°C (unless otherwise noted)
PARAMETER
VIK
VOH
VCC = 3 V,
VCC = MIN to
MIN
MAX
II = -18 mA
MAX (1),
1.2
VCC0.2
IOH = -100 µA
UNIT
V
V
VCC = 3 V,
IOH = -12 mA
VCC = 3 V,
IOL = 100 µA
0.2
VCC = 3 V,
IOL = 12 mA
0.8
VCC = 0 or MAX (1),
VI = 3.6 V
±10
VCC = 3.6 V,
VI = VCC or GND
±1
IOZH
VCC = 3.6 V,
VO = 3 V
10
µA
IOZL
VCC = 3.6 V,
VO = 0
10
µA
ICC
VCC = 3.6 V, IO = 0, VI = VCC or GND
VOL
II
(1)
TEST CONDITIONS
2
Outputs high
2
Outputs low
2
Outputs disabled
2
V
µA
mA
Ci
VI = VCC or GND
6
pF
Co
VO = VCC or GND
9
pF
For conditions shown as MIN or MAX, use the appropriate value specified under recommended operating conditions.
TIMING REQUIREMENTS
over recommended ranges of supply voltage and operating free-air temperature
MIN
fclock
Clock frequency
When VCO is operating at four times the CLKIN frequency
25
50
When VCO is operating at double the CLKIN frequency
50
100
40%
60%
Duty cycle, CLKIN
Stabilization time (1)
(1)
MAX
After SEL
50
After OE↓
50
After power up
50
After CLKIN
50
UNIT
MHz
µs
Time required for the integrated PLL circuit to obtain phase lock of its feedback signal to its reference signal. For phase lock to be
obtained, a fixed-frequency, fixed-phase reference signal must be present at CLKIN. Until phase lock is obtained, the specifications for
propagation delay and skew parameters given in the switching characteristics table are not applicable.
5
CDC2536
www.ti.com
SCAS377E – APRIL 1994 – REVISED JULY 2004
SWITCHING CHARACTERISTICS
over recommended ranges of supply voltage and operating free-air temperature, CL = 15 pF (see
and Figure 3)
FROM
(INPUT)
PARAMETER
(1)
and Figure 1, Figure 2
TO
(OUTPUT)
MIN
Y
45%
55%
CLKIN↑
Y↑
500
+500
ps
CLKIN↑
Y↑
200
ps
0.5
ns
fmax
MAX
100
Duty cycle
tphase
error
(2)
tjitter (RMS)
MHz
tsk(o) (2)
tsk(pr)
UNIT
(2)
1
ns
tr
1.4
ns
tf
1.4
ns
(1)
(2)
The specifications for parameters in this table are applicable only after any appropriate stabilization time has elapsed.
The propagation delay, tphase error, is dependent on the feedback path from any output to FBIN. The tphase error, tsk(o), and tsk(pr)
specfications are only valid for equal loading of all outputs.
PARAMETER MEASUREMENT INFORMATION
3V
Input
1.5 V
1.5 V
0V
tphase error
From Output
Under Test
CL = 15pF
(see Note A)
500
2V
0.8 V
Output
tr
LOAD CIRCUIT FOR OUTPUTS
0.8 V
VOL
tf
VOLTAGE WAVEFORMS
PROPAGATION DELAY TIMES
A.
NOTES: . CL includes probe and jig capacitance.
B.
All input pulses are supplied by generators having the following characteristics: PRR≤ 100 MHz, ZO = 50 Ω, tr≤ 2.5 ns,
tf≤ 2.5 ns.
C.
The outputs are measured one at a time with one transition per measurement.
Figure 1. Load Circuit and Voltage Waveforms
6
VOH
2V
1.5 V
CDC2536
www.ti.com
SCAS377E – APRIL 1994 – REVISED JULY 2004
PARAMETER MEASUREMENT INFORMATION (continued)
CLKIN
tphase error 1
Outputs
Operating
at 1/2 CLKIN
Frequency
tphase error 2
tphase error 3
Outputs
Operating
at CLKIN
Frequency
A.
B.
tphase error 4
tphase error 7
tphase error 5
tphase error 8
tphase error 6
tphase error 9
NOTES: . Output skew, tsk(o), is calculated as the greater of:
•
The difference between the fastest and slowest of tphase error n (n = 1, 2, . . . 6)
•
The difference between the fastest and slowest of tphase error n (n = 7, 8, 9)
Process skew, tsk(pr), is calculated as the greater of:
•
The difference between the maximum and minimum tphase
identical operating conditions
•
The difference between the maximum and minimum tphase
identical operating conditions
error n
(n = 1, 2, . . . 6) across multiple devices under
error n
(n = 7, 8, 9) across multiple devices under
Figure 2. Waveforms for Calculations of tsk(o) and tsk(pr)
7
CDC2536
www.ti.com
SCAS377E – APRIL 1994 – REVISED JULY 2004
PARAMETER MEASUREMENT INFORMATION (continued)
CLKIN
tphase error 10
Outputs
Operating
at CLKIN
Frequency
tphase error 11
tphase error 12
tphase error 13
Outputs
Operating
at 2X CLKIN
Frequency
tphase error 14
tphase error 15
A.
NOTES: . Output skew, tsk(o), is calculated as the greater of:
B.
Process skew, tsk(pr), is calculated as the greater of:
•
•
The difference between the fastest and slowest of tphase error n (n = 10, 11, . . . 15)
The difference between the maximum and minimum tphase
under identical operating conditions.
error n
(n = 10, 11, . . . 15) across multiple devices
Figure 3. Waveforms for Calculation of tsk(o) and tsk(pr)
8
PACKAGE OPTION ADDENDUM
www.ti.com
14-Oct-2022
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
CDC2536DB
ACTIVE
SSOP
DB
28
50
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
CDC2536
Samples
CDC2536DBR
ACTIVE
SSOP
DB
28
2000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
CDC2536
Samples
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of