Document Number: 001-88434 Rev. *B Page 4 of 13
Operation
The CY22392 is an upgrade to the existing CY2292. The new
device has a wider frequency range, greater flexibility, improved
performance, and incorporates many features that reduce PLL
sensitivity to external system issues.
The device has three PLLs which, when combined with the
reference, enable up to four independent frequencies to be
output on up to six pins. These three PLLs are completely
programmable.
Configurable PLLs
PLL1 generates a frequency that is equal to the reference
divided by an 8-bit divider (Q) and multiplied by an 11-bit divider
in the PLL feedback loop (P). The output of PLL1 is sent to the
crosspoint switch. The output of PLL1 is also sent to a /2, /3, or
/4 synchronous post-divider that is output through CLKE. The
frequency of PLL1 can be changed by external CMOS inputs,
S0, S1, S2. See the following section on General Purpose Inputs
for more details.
PLL2 generates a frequency that is equal to the reference
divided by an 8-bit divider (Q) and multiplied by an 11-bit divider
in the PLL feedback loop (P). The output of PLL2 is sent to the
crosspoint switch.
PLL3 generates a frequency that is equal to the reference
divided by an 8-bit divider (Q) and multiplied by an 11-bit divider
in the PLL feedback loop (P). The output of PLL3 is sent to the
cross-point switch.
General Purpose Inputs
S0, S1, and S2 are general purpose inputs that can be
programmed to enable eight different frequency settings.
Options that may be switched with these general purpose inputs
are as follows: the frequency of PLL1, the output divider of CLKB,
and the output divider of CLKA.
CLKA and CLKB both have 7-bit dividers that point to one of two
programmable settings (register 0 and register 1). Both clocks
share a single register control, so both must be set to register 0,
or both must be set to register 1.
For example, the part may be programmed to use S0, S1, and
S2 (0, 0, 0 to 1, 1, 1) to control eight different values of P and Q
on PLL1. For each PLL1 P and Q setting, one of the two CLKA
and CLKB divider registers can be chosen. Any divider change
as a result of switching S0, S1, or S2 is guaranteed to be glitch
free.
Crystal Input
The input crystal oscillator is an important feature of this device
because of its flexibility and performance features.
The oscillator inverter has programmable drive strength. This
enables maximum compatibility with crystals from various
manufacturers, processes, performances, and qualities.
The input load capacitors are placed on-die to reduce external
component cost. These capacitors are true parallel-plate
capacitors for ultra-linear performance. These were chosen to
reduce the frequency shift that occurs when non-linear load
capacitance interacts with load, bias, supply, and temperature
changes. Non-linear (FET gate) crystal load capacitors must not
be used for MPEG, POTS dial tone, communications, or other
applications that are sensitive to absolute frequency
requirements.
The value of the load capacitors is determined by six bits in a
programmable register. The load capacitance can be set with a
resolution of 0.375 pF for a total crystal load range of 6 pF to
30 pF.
For driven clock inputs the input load capacitors may be
completely bypassed. This enables the clock chip to accept
driven frequency inputs up to 166 MHz. If the application requires
a driven input, then XTALOUT must be left floating.
Output Configuration
Under normal operation there are four internal frequency
sources that may be routed through a programmable crosspoint
switch to any of the four programmable 7-bit output dividers. The
four sources are: reference, PLL1, PLL2, and PLL3. In addition,
many outputs have a unique capability for even greater flexibility.
The following is a description of each output.
CLKA’s output originates from the crosspoint switch and goes
through a programmable 7-bit post divider. The 7-bit post divider
derives its value from one of two programmable registers. Each
of the eight possible combinations of S0, S1, S2 controls which
of the two programmable registers is loaded into CLKA’s 7-bit
post divider. See the section General Purpose Inputs for more
information.
CLKB’s output originates from the crosspoint switch and goes
through a programmable 7-bit post divider. The 7-bit post divider
derives its value from one of two programmable registers. Each
of the eight possible combinations of S0, S1, and S2 controls
which of the two programmable registers is loaded into CLKA’s
7-bit post divider. See the section General Purpose Inputs for
more information.
CLKC’s output originates from the crosspoint switch and goes
through a programmable 7-bit post divider. The 7-bit post divider
derives its value from one programmable register.
CLKD’s output originates from the crosspoint switch and goes
through a programmable 7-bit post divider. The 7-bit post divider
derives its value from one programmable register.
CLKE’s output originates from PLL1 and goes through a post
divider that may be programmed to /2, /3, or /4.
XBUF is simply the buffered reference.
The clock outputs have been designed to drive a single point
load with a total lumped load capacitance of 15 pF. While driving
multiple loads is possible with proper termination, it is generally
not recommended.
Power Saving Features
The SHUTDOWN/OE input tristates the outputs when pulled low.
If system shutdown is enabled, a Low on this pin also shuts off
the PLLs, counters, the reference oscillator, and all other active
components. The resulting current on the V
DD
pins is less than
5 A (typical). After leaving shutdown mode, the PLLs must
relock.
The S2/SUSPEND
input can be configured to shut down a
customizable set of outputs and/or PLLs, when LOW. All PLLs
and any of the outputs can be shut off in nearly any combination.
The only limitation is that if a PLL is shut off, all outputs derived
from it must also be shut off. Suspending a PLL shuts off all
