CDC2586
3.3-V PHASE-LOCK LOOP CLOCK DRIVER
WITH 3-STATE OUTPUTS
SCAS337C – FEBRUARY 1993 – REVISED OCTOBER 1998
description (continued)
The Y outputs can be configured to switch in phase and at the same frequency as CLKIN. Select inputs
(SEL1, SEL0) configure up to nine Y outputs, in banks of three, to operate at one-half or double the CLKIN
frequency depending on which output 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 CLKIN.
Output-enable (OE) provides 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 used to bypass
the PLL. TEST should be strapped to GND for normal operation.
Unlike many products containing PLLs, the CDC2586 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 CDC2586 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 the select inputs, enabling of the PLL via TEST, and upon
enable of all outputs via OE.
The CDC2586 is characterized for operation from 0°C to 70°C.
detailed description of output configurations
The voltage-controlled oscillator (VCO) used in the CDC2586 PLL has a frequency range of 100 MHz to
200 MHz, twice the operating frequency range of the CDC2586 outputs. The output of the VCO is divided by
two and four to provide reference frequencies with a 50% duty cycle of one-half and one-fourth the VCO
frequency. The SEL0 and SEL1 inputs select 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 and phase of this output matches that of the CLKIN signal. 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
twice or the same as the CLKIN frequency.
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