TEXAS INSTRUMENTS CDC857-2 Technical data

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CDC857-2, CDC857-3

2.5-/3.3-V PHASE-LOCK LOOP CLOCK DRIVERS

SCAS627A – SEPTEMBER 1999 – DECEMBER 1999

D

Phase-Lock Loop Clock Distribution for
Double Data Rate Synchronous DRAM

DGG PACKAGE

(TOP VIEW)

Applications

D

Distributes One Differential Clock Input to
Ten Differential Outputs

D

External Feedback Pins (FBIN, FBIN) Are
Used to Synchronize the Outputs to the
Clock Input

D

Operates at VCC = 2.5 V and AVCC = 3.3 V

D

Packaged in Plastic 48-Pin (DGG) Thin
Shrink Small-Outline Package (TSSOP)

D

Spread Spectrum Clocking Tracking
Capability to Reduce EMI

description

The CDC857-2 and CDC857-3 are high-perfor­mance, low-skew, low-jitter, phase-lock loop
(PLL) clock driver. They use a PLL to precisely
align, in both frequency and phase, the feedback
(FBOUT) output to the clock (CLK) input signal.
The CDC857-3 operates at 3.3 V (PLL) and 2.5 V
(output buffer). The CDC857-2 operates at

2.5 V (PLL and output buffer).
One bank of ten inverting and noninverting

outputs provide ten low-skew, low-jitter copies of

GND

Y0
Y0

V

CC

Y1

Y1
GND
GND

Y2

Y2

V

CC

V

CC

CLK
CLK
V

CC

AV

CC

AGND

GND

Y3

Y3

V

CC

Y4

Y4
GND

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25

GND
Y5
Y5
V
Y6
Y6
GND
GND
Y7
Y7
V
G
FBIN
FBIN
V
FBOUT
FBOUT
GND
Y8
Y8
V
Y9
Y9
GND

CLK. Output signal duty cycles are adjusted to
50%, independent of the duty cycle at CLK.
All outputs can be enabled or disabled via a single output enable input. When the G input is high, the outputs
switch in phase and frequency with CLK; when the G input is low, the outputs are disabled to high impedance
state (3-state).

CC

CC

CC

CC

Unlike many products containing PLLs, the CDC857 does not require external RC networks. The loop filter for
the PLL is included on-chip, minimizing component count, board space, and cost.

Because it is based on PLL circuity, the CDC857 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 CLK, as well as following any changes to the PLL reference or
feedback signals. The PLL can be bypassed for test purposes by strapping A V

to ground. If A VCC is at GND

CC

and VCC = ON, 2 falling edges on G cause the PLL to run with FBOUT being enabled and all other outputs being
disabled, after A VCC ramps up to its specified VCC value, with G being kept low. The CDC857 is characterized
for operation from 0°C to 85°C.

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.

PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

Copyright  1999, Texas Instruments Incorporated

1

CDC857-2, CDC857-3

PLL

2.5-/3.3-V PHASE-LOCK LOOP CLOCK DRIVERS

SCAS627A – SEPTEMBER 1999 – DECEMBER 1999

FUNCTION TABLE

INPUTS

G CLK CLK Y Y FBOUT FBOUT

L X X Z Z Z Z OFF
H LHLH L H RUN
H HLHL H L RUN
H < 20 MHz < 20 MHz Z Z Z Z OFF

logic symbol

OUTPUTS

Clk
Clk

FBIN
FBIN

G

AV

CC

Test
Mode
Logic

PLL

Y0
Y0

Y1
Y1

Y2
Y2

Y3
Y3

Y4
Y4

Y5
Y5

Y6
Y6

Y7
Y7

Y8
Y8

Y9
Y9

AVCC = 3.3 V

NOTE A: All outputs are connected to VCC = 2.5 V.

2

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FBOUT
FBOUT

COMMENTS

I/O

DESCRIPTION

CDC857-2, CDC857-3

2.5-/3.3-V PHASE-LOCK LOOP CLOCK DRIVERS

SCAS627A – SEPTEMBER 1999 – DECEMBER 1999

SPECIAL TEST MODES

INPUTS

V

CC

ON 0 V L L Z Z Z Z Clock Mode
ON 0 V L H Z Z Z Z Clock Mode
ON 0 V H L L H L H Clock Mode
ON 0 V H H H L H L Clock Mode
ON UP
ON UP

†

Only one signal shown for this differential input.

‡

AVCC ramped up after two (2) high-to-low transitions on G input & G being low.

§

At least two (2) high-to-low transitions during AVCC = 0.

AV

CC

G CLK

‡
‡

§

↓

§

↓

†

LZZ L H PLL Mode

H Z Z H L PLL Mode

Y Y FBOUT FBOUT

Terminal Functions

TERMINAL

NAME NO.

AGND 17 Ground Analog ground. AGND provides the ground reference for the analog circuitry .
AV

CC

CLK
CLK

FBIN
FBIN

FBOUT
FBOUT

G 37 I Output bank enable. G is the output enable for outputs Y and Y . When G is low outputs Y are disabled

GND 1, 7, 8, 18,

V

CC

Y0, Y1, Y2,
Y3, Y4, Y5,
Y6, Y7, Y8,
Y9

Y0, Y1, Y2,
Y3

, Y4, Y5,
, Y7, Y8,

Y6
Y9

16 Power Analog power supply . AVCC provides the power reference for the analog circuitry. In addition, AV

13
14

36
35

32
33

24, 25, 31,

41, 42, 48

4, 11, 12,

15, 21, 28,

34, 38, 45

3, 5, 10,
20, 22, 46,
44, 39, 29,

27

2, 6, 9,
19, 23, 47,
43, 40, 30,

26

O Feedback output. FBOUT is dedicated for external feedback. It switches at the same frequency as

Ground Ground

Power Power supply

O Clock outputs. These outputs provide low-skew copies of CLK.

O Clock outputs. These outputs provide low-skew copies of CLK.

can be used to bypass the PLL for test purposes. When AVCC is strapped to ground, PLL is bypassed
and CLK is buffered directly to the device outputs. During disable (G = 0), the PLL is powered down.

I Clock input, CLK provides the clock signal to be distributed by the CDC857 clock driver. CLK is used

to provide the reference signal to the integrated PLL that generates the clock output signals. CLK
must have a fixed frequency and fixed phase for the PLL to obtain phase lock. Once the circuit is
powered up and a valid CLK signal is applied, a stabilization time is required for the PLL to phase
lock the feedback signal to its reference signal.

I Feedback input. FBIN provides the feedback signal to the internal PLL. FBIN must be hard-wired

to FBOUT to complete the PLL. The integrated PLL synchronizes CLK and FBIN so that there is
nominally zero phase error between CLK and FBIN.

CLK. When externally wired to FBIN, FBOUT completes the feedback loop of the PLL.

to a high-impedance state. When G is high, all outputs Y are enabled and switch at the same
frequency as CLK.

OUTPUTS

CC

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3

CDC857-2, CDC857-3

Analog suppl

oltage, AV

gg,

ID

2.5-/3.3-V PHASE-LOCK LOOP CLOCK DRIVERS

SCAS627A – SEPTEMBER 1999 – DECEMBER 1999

absolute maximum ratings over operating free-air temperature (unless otherwise noted)

†

Supply voltage range, VCC or AVCC –0.5 V to 4.6 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Input voltage range VI (see Notes 1 and 2) –0.5 V to VCC +0.5 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Output voltage range, VO, (see Notes 1 and 2) –0.5 V to VCC +0.5 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Input clamp current, I

(VI < 0 or VI > VCC) ±50 mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

IK

Output clamp current, IOK (VO < 0 or VO > VCC ±50 mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Continuous total output current, IO (VO = 0 to VCC) ±50 mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Package thermal impedance, θJA (see Note 3) 89°C/W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Storage temperature range T

†

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.

NOTES: 1. The input and output negative voltage ratings may be exceeded if the input and output clamp-current ratings are observed.

2. This value is limited to 4.6 V maximum.

3. The package thermal impedance is calculated in accordance with JESD 51.

–65°C to 150°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

stg

recommended operating conditions (see Note 4)

MIN NOM MAX UNIT

Supply voltage, V

Low–level input voltage, VIL(G)
High–level input voltage, VIH(G)

DC input signal voltage (see Note 5) CLK, FBIN –0.3 VCC+0.3 V
Differential input signal voltage, V

(see Note 6)
Differential cross-point input voltage (see Note 7) VCC/2–0.2 VCC/2 VCC/2+0.2 V

High-level output current, I
Low-level output current, I
Input slew rate, SR 1 V/ns
Operating free-air temperature, T

NOTES: 4. Unused inputs must be held high or low to prevent them from floating.

CC

pp

y v

5. DC input signal voltage specifies the allowable dc execution of differential input.

6. Differential input signal voltage specifies the differential voltage |VTR – VCP| required for switching, where VTR is the true input level
and VCP is the complementary input level (see figure 3).

7. Differential cross-point voltage is expected to track variations of VCC and is the voltage at which the differential signals must be
crossing.

CC

OH

OL

A

CDC857–2 2.3 2.7 V
CDC857–3 3 3.6 V

G input 0.3 × V
G input 0.7 × V

dc CLK, FBIN 0.35 VCC+0.6 V
ac CLK, FBIN 0.7 VCC+0.6 V

2.3 2.7 V

CC

CC

–12 mA

12 mA

0 85 °C

V
V

4

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