CDC2582
3.3-V PHASE-LOCK LOOP CLOCK DRIVER
WITH DIFFERENTIAL LVPECL CLOCK INPUTS
SCAS379B – FEBRUARY 1993 – REVISED FEBRUARY 1996
description (continued)
The Y outputs can be configured to switch in phase and at the same frequency as differential clock inputs (CLKIN
and CLKIN). Select (SEL1, SEL0) inputs configure up to nine Y outputs, in banks of three, to operate at one-half
or double the differential clock input frequency, depending upon the feedback configuration (see Tables 1
and 2). All output signal duty cycles are adjusted to 50% independent of the duty cycle at the input clocks.
Output-enable (OE) is provided for output control. When OE is high, the outputs are in the low state. When OE
is low, the outputs are active. CLR is negative-edge triggered and can be used to reset the outputs operating
at half frequency. TEST is used for factory testing of the device and can be used to bypass the PLL. TEST should
be strapped to GND for normal operation.
Unlike many products containing a PLL, the CDC2582 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 circuitry, the CDC2582 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 and CLKIN, as well as following any changes to the PLL
reference or feedback signal. Such changes occur upon change of SEL1 and SEL0, enabling the PLL via TEST,
and upon enable of all outputs via OE.
The CDC2582 is characterized for operation from 0°C to 70°C.
detailed description of output configurations
The voltage-controlled oscillator (VCO) used in the CDC2582 has a frequency range of 100 MHz to 200 MHz,
twice the operating frequency range of the CDC2582 outputs. The output of the VCO is divided by 2 and by 4
to provide reference frequencies with a 50% duty cycle of one-half and one-fourth the VCO frequency. SEL0
and SEL1 determine which of the two signals are 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 this output matches that of the CLKIN/CLKIN signals. In the case that a VCO/2 output is wired to
FBIN, the VCO must operate at twice the CLKIN/CLKIN frequency, resulting in device outputs that operate at
the same or one-half the CLKIN/CLKIN frequency. If a VCO/4 output is wired to FBIN, the device outputs operate
at the same or twice the CLKIN/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 frequency range for the differential clock input is 50 MHz to 100 MHz when using output configuration
A. Outputs configured as 1/2× outputs operate at half the input clock frequency, while outputs configured as 1×
outputs operate at the same frequency as the differential clock input.
Table 1. Output Configuration A
INPUTS
SEL1
L
L
H
H
SEL0
L
H
L
H
OUTPUTS
1/2×
FREQUENCY
None
1Yn
1Yn, 2Yn
1Yn, 2Yn, 3Yn
1×
FREQUENCY
All
2Yn, 3Yn, 4Yn
3Yn, 4Yn
4Yn
NOTE: n = 1, 2, 3
2
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