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groups, and the PLL aligns the rising edges of REF and FB, you

can create wider output skews by proper selection of the xFn

inputs. For example, a +10 tU between REF and 3Qx is achieved

by connecting 1Q0 to FB and setting 1F0 = 1F1 = GND, 3F0 =

MID, and 3F1 = High. (Since FB aligns at –4 tU and 3Qx skews

to +6 tU, a total of +10 tU skew is realized). Many other configu-

rations are realized by skewing both the outputs used as the FB

input and skewing the other outputs.

Figure 4. Inverted Output Connections

REF

4Q0

4F0

4Q1

4F1

3Q0

3F0

3Q1

3F1

2Q0

2F0

2Q1

2F1

1Q0

1F0

1Q1

1F1

TEST

Figure 4

shows an example of the invert function of the LVPSCB.

In this example, the 4Q0 output used as the FB input is

programmed for invert (4F0 = 4F1 = HIGH) while the other three

pairs of outputs are programmed for zero skew. When 4F0 and

4F1 are tied HIGH, 4Q0 and 4Q1 become inverted zero phase

outputs. The PLL aligns the rising edge of the FB input with the

rising edge of the REF. This causes the 1Q, 2Q, and 3Q outputs

to become the "inverted" outputs with respect to the REF input.

By selecting the output connected to FB, you can have two

inverted and six non-inverted outputs or six inverted and two

non-inverted outputs. The correct configuration is determined by

the need for more (or fewer) inverted outputs. 1Q, 2Q, and 3Q

outputs are also skewed to compensate for varying trace delays

independent of inversion on 4Q.

Figure 5. Frequency Multiplier with Skew Connections

20 MHz

REF

4Q0

4F0

4Q1

4F1

3Q0

3F0

3Q1

3F1

2Q0

2F0

2Q1

2F1

1F0

1Q0

1Q1

1F1

TEST

Document Number: 38-07408 Rev. *D

REF

40 MHz

20 MHz

80 MHz

Figure 5

shows the LVPSCB configured as a clock multiplier. The

3Q0 output is programmed to divide by four and is sent back to

FB. This causes the PLL to increase its frequency until the 3Q0

and 3Q1 outputs are locked at 20 MHz, while the 1Qx and 2Qx

outputs run at 80 MHz. The 4Q0 and 4Q1 outputs are

programmed to divide by two, that results in a 40 MHz waveform

at these outputs. Note that the 20 and 40 MHz clocks fall simul-

taneously and are out of phase on their rising edge. This enables

the designer to use the rising edges of the

frequency outputs without concern for rising edge skew. The

2Q0, 2Q1, 1Q0, and 1Q1 outputs run at 80 MHz and are skewed

by programming their select inputs accordingly. Note that the FS

pin is wired for 80 MHz operation because that is the frequency

of the fastest output.

Figure 6. Frequency Divider Connections

REF

20 MHz

REF

4Q0

4F0

4Q1

4F1

3Q0

3F0

3Q1

3F1

2F0

2Q0

2Q1

2F1

1F0

1Q0

1F1

1Q1

TEST

Figure 6

shows the LVPSCB in a clock divider application. 2Q0

is sent back to the FB input and programmed for zero skew. 3Qx

is programmed to divide by four. 4Qx is programmed to divide by

two. Note that the falling edges of the 4Qx and 3Qx outputs are

aligned. This enables use of the rising edges of the

⁄

and

frequency without concern for skew mismatch. The 1Qx

outputs are programmed to zero skew and are aligned with the

2Qx outputs. In this example, the FS input is grounded to

configure the device in the 15 to 30 MHz range, since the highest

frequency output is running at 20 MHz.

Figure 7

shows some of the functions that are selectable on the

3Qx and 4Qx outputs. These include inverted outputs and

outputs that offer divide-by-2 and divide-by-4 timing. An inverted

output enables the system designer to clock different

subsystems on opposite edges, without suffering from the pulse

asymmetry typical of non-ideal loading. This function enables

each of the two subsystems to clock 180 degrees out of phase,

but still is aligned within the skew specification.

The divided outputs offer a zero delay divider for portions of the

system that divide the clock by either two or four, and still remain

within a narrow skew of the "1X" clock. Without this feature, an

external divider is added, and the propagation delay of the

divider adds to the skew between the different clock signals.

These divided outputs, coupled with the Phase Locked Loop,

allow the LVPSCB to multiply the clock rate at the REF input by

either two or four. This mode enables the designer to distribute

a low frequency clock between various portions of the system,

and then locally multiply the clock rate to a more suitable

CY7B9911V

3.3V RoboClock+™

⁄

frequency and

10 MHz

5 MHz

20 MHz

⁄

frequency

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