FD7745T Pletronics, Inc., FD7745T Datasheet - Page 4

• Manufacturer Part Number: FD7745T
• Description: Fd7t Series Multi-output Cmos Clock Oscillator
• Manufacturer: Pletronics, Inc.

Description:
The FD7T series Multi-Output CMOS Clock Oscillator is a modular PLL-based low cost, high-performance,
programmable oscillator. The FD7T generates up to seven output frequencies, OUT1 through OUT7.
Frequencies are mutually independent and may be programmed to any frequency from 100KHz to 230-
MHZ and one output can be as low as 12KHz. There are versions including 1 to 4 PLLs, the number of
PLLs impacts the cost.
The FD7T base frequency, as noted in the device part number, is established during manufacture and is
permanently fixed. For convenience, the divider for output OUT1 and the remaining seven output
frequencies, and their characteristics may be pre-programmed at the factory, or field programmed.
The FD7T has a separate output supply pin, V
device supply, V
The FD7xxxTL version has increased output drive for then 1.8V output levels. This version can be used at
1.8V V
The deep M/N PLL divider ratio allows the generation of zero-ppm clocks for applications such as WLAN,
BlueTooth, Ethernet, GPS, USB, IEEE1394, etc. from the base frequency.
Each of the independent PLLs supports Spread Spectrum Clocking (SSC). SSC may be programmed to
be either center-spread or down-spread. This is an important technique to reduce electro-magnetic
interference (EMI).
The device supports non-volatile eePROM programming for easy customization of the device. As
shipped, the device is pre-programmed. Standard combinations are denoted by three characters in the
device part number. However, the FD7T may be reprogrammed to a different configuration.
Reprogramming may be either prior to assembly, or in-circuit via a 2-wire SDA/SCL I
Three programmable control inputs, S0, S1 and S2, may be used to control various aspects of FD7T
operation including selection of alternative frequency set(s), selection of SSC functionality, output tri-state
and power-down.
Reference Oscillator
Reference Oscillator - VCXO
The Reference Oscillator is an AT cut quartz crystal based oscillator. This oscillator is very similar to the
Pletronics SM77xxH product oscillator. This signal is the lowest jitter and can be an output on Out1,
Out2 or Out3 and can be divided down by the Divider #1. The user may specify any frequency between
12MHz and 32MHz for this reference. All output frequencies are derived from (referenced to) this
Reference Oscillator.
The reference oscillator frequency can be modulated by the Vcontrol input, if the VCXO option is
selected. As this Reference Signal is the reference for all other parts of this circuit, all PLLs will be
modulated also.
The VCXO input has a limited voltage range, the VCXO is associated with the internal 1.8V core. A
resistor in series with the Vcontrol input will permit interfacing to 3.3V analog circuits, the voltage range
that changes the frequency will still be limited but the larger voltages swings will not cause problems.
DDOUT
www.pletronics.com
only.
DD
which provides power to all the internal circuits, is nominally 1.8V.
425-776-1880
DDOUT
, for either 1.8, 2.5 or 3.3V output logic levels. The
FD7T Series Multi-Output
CMOS Clock Oscillator
2
May 2008
C bus.
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