Motorola MC12439FN Datasheet

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SEMICONDUCTOR TECHNICAL DATA

REV 3

 Motorola, Inc. 1997

1/97

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The MC12439 is a general purpose synthesized clock source targeting applications that require both serial and parallel interfaces. Its internal VCO will operate over a range of frequencies from 400 to 800MHz. The differential PECL output can be configured to be the VCO frequency divided by 1, 2, 4, or 8. With the output configured to divide the VCO frequency by 1, and with a 16.66MHz external quartz crystal used to provide the reference frequency, the output frequency can be specified in

16.66MHz steps.

• 50 to 800MHz Differential PECL Outputs

• ±25ps Typical Peak–to–Peak Output Jitter

• Minimal Frequency Over–Shoot

• Synthesized Architecture

• Serial 3–Wire Interface

• Parallel Interface for Power–Up

• Quartz Crystal Interface

• 28–Lead PLCC Package

• Operates from 3.3V or 5.0V Power Supply

Functional Description

The internal oscillator uses the external quartz crystal as the basis of its frequency reference. The output of the reference oscillator is sent directly to the phase detector. With a 16.66MHz crystal, this provides a reference frequency of 16.66MHz. Although this data sheet illustrates functionality only for a 16MHz and 16.66MHz crystal, any crystal in the 10–20MHz range can be used. In addition to the crystal, an LVCMOS input can also be used as the PLL reference. The reference is selected via the XTAL_SEL input pin.

The VCO within the PLL operates over a range of 400 to 800MHz. Its output is scaled by a divider that is configured by either the serial or parallel interfaces. The output of this loop divider is also applied to the phase detector.

The phase detector and loop filter attempt to force the VCO output frequency to be M times the reference frequency by adjusting the VCO control voltage. Note that for some values of M (either too high or too low) the PLL will not achieve loop lock.

The output of the VCO is also passed through an output divider before being sent to the PECL output driver. This output divider is configured through either the serial or the parallel interfaces, and can provide one of four division ratios (1, 2, 4, or 8). This divider extends performance of the part while providing a 50% duty cycle.

The output driver is driven differentially from the output divider, and is capable of driving a pair of transmission lines terminated in 50Ω to VCC – 2.0.

The configuration logic has two sections: serial and parallel. The parallel interface uses the values at the M[6:0] and N[1:0] inputs to configure the internal counters. Normally, on system reset, the P_LOAD

input is held LOW until sometime after power

becomes valid. On the LOW–to–HIGH transition of P_LOAD

, the parallel inputs are captured. The parallel interface has priority over the serial interface. Internal pullup resistors are provided on the M[6:0] and N[1:0] inputs to reduce component count in the application of the chip.

The serial interface centers on a twelve bit shift register. The shift register shifts once per rising edge of the S_CLOCK input. The serial input S_DATA must meet setup and hold timing as specified in the AC Characteristics section of this document. The configuration latches will capture the value of the shift register on the HIGH–to–LOW edge of the S_LOAD input. See the programming section for more information.

The TEST output reflects various internal node values, and is controlled by the T[2:0] bits in the serial data stream. See the programming section for more information.

The PWR_DOWN pin, when asserted, will synchronously divide the FOUT by 16. The power down sequence is clocked by the PLL reference clock, thereby causing the frequency reduction to happen relatively slowly. Upon de–assertion of the PWR_DOWN pin, the FOUT input will step back up to its programmed frequency in four discrete increments.

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HIGH FREQUENCY PLL

CLOCK GENERATOR

FN SUFFIX

28–LEAD PLCC PACKAGE

CASE 776–02

MC12439

MOTOROLA TIMING SOLUTIONS

BR1333 — Rev 6

N[1]

N[0]

XTAL_SEL

M[6]

M[5]

M[4]XTAL1

FREF_EXT

PWR_DOWN

PLL–V

S_LOAD

S_DATA

S_CLOCK

11109

Figure 1. 28–Lead Pinout (Top View)

P_LOAD

VCCFOUT FOUT GND V

TEST GND

M[3]M[2]M[1]M[0]

XTAL2

N[1:0]

0 0 0 1 1 0 1 1

Output Division

2 4 8 1

Input

PWR_DOWN

XTAL_SEL

FOUT

FREF_EXT

Disabled

FOUT/16

XTAL

Enabled

PIN DESCRIPTIONS

Pin Name Type Function

Inputs

XTAL1, XTAL2 — These pins form an oscillator when connected to an external series–resonant crystal. S_LOAD Int. Pulldown This pin loads the configuration latches with the contents of the shift registers. The latches will be

transparent when this signal is HIGH, thus the data must be stable on the HIGH–to–LOW transition of

S_LOAD for proper operation. S_DATA Int. Pulldown This pin acts as the data input to the serial configuration shift registers. S_CLOCK Int. Pulldown This pin serves to clock the serial configuration shift registers. Data from S_DAT A is sampled on the rising

edge. P_LOAD Int. Pullup This pin loads the configuration latches with the contents of the parallel inputs .The latches will be

transparent when this signal is LOW, thus the parallel data must be stable on the LOW–to–HIGH transition

of P_LOAD

for proper operation.

M[6:0] Int. Pullup These pins are used to configure the PLL loop divider. They are sampled on the LOW–to–HIGH transition

of P_LOAD

. M[6] is the MSB, M[0] is the LSB.

N[1:0] Int. Pullup These pins are used to configure the output divider modulus. They are sampled on the LOW–to–HIGH

transition of P_LOAD

OE Int. Pullup Active HIGH Output Enable.

Outputs

OUT

, F

OUT

— These differential positive–referenced ECL signals (PECL) are the output of the synthesizer.

TEST — The function of this output is determined by the serial configuration bits T[2:0].

Power

— This is the positive supply for the chip, and is connected to +3.3V or 5.0V (VCC = PLL_VCC).

PLL_V

— This is the positive supply for the PLL, and should be as noise–free as possible for low–jitter operation. This

supply is connected to +3.3V or 5.0V (VCC = PLL_VCC). GND — These pins are the negative supply for the chip and are normally all connected to ground.

Other

PWR_DOWN Int. Pulldown LVCMOS input that forces the FOUT output to synchronously reduce its frequency by a factor of 16. FREF_EXT Int. Pulldown LVCMOS input which can be used as the PLL reference frequency. XTAL_SEL Int. Pullup LVCMOS input that selects between the XTAL and FREF_EXT PLL reference inputs. A HIGH selects the

XTAL input.

MC12439

TIMING SOLUTIONS BR1333 — Rev 6

3 MOTOROLA

Figure 2. MC12439 Block Diagram

16.66MHz

S_LOAD P_LOAD

S_DATA

S_CLOCK

XTAL1

XTAL2

OSC

PHASE

DETECTOR

7–BIT DIV M

COUNTER

LATCH

VCO

DIV N

(1, 2, 4, 8)

LATCH

400–800

MHz

FOUT FOUT

+3.3 or 5.0V

25 24

CC0

LATCH

TEST

+3.3 or 5.0V

PLL_V

7–BIT SR

2–BIT SR 3–BIT SR

CC1

+3.3 or 5.0V

M[6:0]

→

N[1:0]

17, 1821 22, 19

FREF_EXT

0 1

XTAL_SEL

PWR_DOWN

POWER DOWN

PROGRAMMING INTERF ACE

Programming the device amounts to properly configuring the internal dividers to produce the desired frequency at the outputs. The output frequency can by represented by this formula:

FOUT = F

XTAL

x M ÷ N (1)

Where F

XTAL

is the crystal frequency, M is the loop divider modulus, and N is the output divider modulus. Note that it is possible to select values of M such that the PLL is unable to achieve loop lock. To avoid this, always make sure that M is selected to be 25 ≤ M ≤ 50 for a 16MHz input reference.

For input references other than 16MHz, the valid M values

can be calculated from the valid VCO range of 400–800MHz.

Assuming that a 16MHz reference frequency is used the

above equation reduces to:

FOUT = 16 x M ÷ N

Substituting the four values for N (1, 2, 4, 8) yields:

FOUT = 16M, FOUT = 8M, FOUT = 4M and FOUT = 2M for 25 < M < 50

The user can identify the proper M and N values for the desired frequency from the above equations. The four output frequency ranges established by N are 400–800MHz, 200–400MHz, 100–200MHz and 50–100MHz respectively. From these ranges the user will establish the value of N required, then the value of M can be calculated based on the appropriate equation above. For example if an output frequency of 384MHz was desired the following steps would be taken to identify the appropriate M and N values. 384MHz falls within the frequency range set by an N value of 2 so N [1:0] = 00. For N = 2 FOUT = 8M and M = FOUT ÷ 8. Therefore M = 384 ÷ 8 = 48, so M[8:0] = 0110000.

For input reference frequencies other than 16MHz the set of appropriate equations can be deduced from equation 1. For computer applications another useful frequency base would be 16.666MHz. From this reference one can generate a family of output frequencies at multiples of the 33.333MHz PCI clock. As an example to generate a 533.333MHz clock

MC12439

MOTOROLA TIMING SOLUTIONS

BR1333 — Rev 6

from a 16.666MHz reference the following M and N values would be used:

FOUT = 16.666 x M ÷ N

Let N = 1, M = 533.333 ÷ 16.666 = 32

The value for M falls within the constraints set for PLL stability (400÷16.666 ≤ M ≤ 800÷16.666; 24 ≤ M ≤ 48), therefore N[1:0] = 11 and M[6:0} = 0100000. If the value for M fell outside of the valid range a different N value would be selected to try to move M in the appropriate direction.

The M and N counters can be loaded either through a parallel or serial interface. The parallel interface is controlled via the P_LOAD

signal such that a LOW to HIGH transition will latch the information present on the M[6:0] and N[1:0] inputs into the M and N counters. When the P_LOAD

signal is LOW the input latches will be transparent and any changes on the M[6:0] and N[1:0] inputs will affect the FOUT output pair. To use the serial port the S_CLOCK signal samples the information on the S_DA TA line and loads it into a 12 bit shift register. Note that the P_LOAD

signal must be HIGH for the serial load operation to function. The Test register is loaded with the first three bits, the N register with the next two and the M register with the final eight bits of the data streeam on the S_DATA input. For each register the most significant bit is loaded first (T2, N1 and M6). A pulse on the S_LOAD pin after the shift register is fully loaded will transfer the divide values into the counters. The HIGH to LOW transition on the S_LOAD input will latch the new divide values into the counters. NO TAG illustrates the timing diagram for both a parallel and a serial load of the MC12439 synthesizer.

M[6:0] and N[1:0] are normally specified once at power–up through the parallel interface, and then possibly again through the serial interface. This approach allows the application to come up at one frequency and then change or fine–tune the clock as the ability to control the serial interface becomes available.

The TEST output provides visibility for one of the several internal nodes as determined by the T[2:0] bits in the serial

configuration stream. It is not configurable through the parallel interface. Although it is possible to select the node that represents FOUT, the CMOS output may not be able to toggle fast enough for some of the higher output frequencies. The T2, T1 and T0 control bits are preset to ‘000’ when P_LOAD

is LOW so that the PECL FOUT outputs are as jitter–free as possible. Any active signal on the TEST output pin will have detrimental affects on the jitter of the PECL output pair. In normal operations, jitter specifications are only guaranteed if the TEST output is static. The serial configuration port can be used to select one of the alternate functions for this pin.

Most of the signals available on the TEST output pin are useful only for performance verification of the MC12439 itself. However the PLL bypass mode may be of interest at the board level for functional debug. When T[2:0] is set to 110 the MC12439 is placed in PLL bypass mode. In this mode the S_CLOCK input is fed directly into the M and N dividers. The N divider drives the FOUT differential pair and the M counter drives the TEST output pin. In this mode the S_CLOCK input could be used for low speed board level functional test or debug. Bypassing the PLL and driving FOUT directly gives the user more control on the test clocks sent through the clock tree. NO TAG shows the functional setup of the PLL bypass mode. Because the S_CLOCK is a CMOS level the input frequency is limited to 250MHz or less. This means the fastest the FOUT pin can be toggled via the S_CLOCK is 250MHz as the minimum divide ratio of the N counter is 1. Note that the M counter output on the TEST output will not be a 50% duty cycle due to the way the divider is implemented.

T2 T1 T0 TEST (Pin 20)

0 0 0 0 1 1 1 1

0 0 1 1 0 0 1 1

0 1 0 1 0 1 0 1

SHIFT REGISTER OUT HIGH FREF M COUNTER OUT FOUT LOW PLL BYPASS FOUT/4

Figure 3. Timing Diagram

S_CLOCK

S_DATA

S_LOAD

M[6:0]

N[1:0]

P_LOAD

T2 T1 T0 N1 N0 M6 M5 M4 M3 M2 M1

M, N

First

Bit

Last

Bit

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