cy28508 SpectraLinear Inc, cy28508 Datasheet - Page 6

• Manufacturer Part Number: cy28508
• Description: 333 Mhz Low-voltage Differential Sscg
• Manufacturer: SpectraLinear Inc

Rev 1.0, November 24, 2006
Byte 7: Dial-a-Frequency Control Register N3 - Only bit 7 is used by the CY28508
Byte 8: Dial-a-Frequency Control Register M3, Only bit 7 is used by the CY28508
Dial-a-Frequency Feature
Dial-a-frequency gives the designer direct access to the
reference divider (M) and the feedback divider (N) of the
internal PLL.
VCO = (XTAL x 26.823) x (N/ M).
Output Frequency = VCO/Output Divider.
The VCO operating range is between 333 MHz and 675 MHz.
The user must not program N and M values that would result
in a VCO frequency outside of this specified range.
Bit
Bit
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
@Pup
@Pup
1
0
1
1
0
0
0
0
1
1
0
0
0
0
0
0
Ns Setting. Ns is the total step time index during Smooth-Track for each increment or decrement during
Smooth-Track. The default is 1 = 2048 and if you program a 0 = 1024, the step time will be half of this value.
Reserved, set = 0.
Reserved, set = 1.
Reserved, set = 1.
Reserved, set = 0.
Reserved, set = 0.
Reserved, set = 0.
Reserved, set = 0.
ICP Tracking. In the default mode (= 1) the ICP current increases and the VCO frequency increase to
maintain constant bandwidth. If you program a “0,” then the ICP current will stay constant.
Reserved, set = 0.
Reserved, set = 1.
Reserved, set = 1.
Reserved, set = 0.
Reserved, set = 0.
Reserved, set = 0.
Reserved, set = 0.
Hardware Switching of Dial-a-Frequency
Registers
The architectural design of the HW Smooth-Track feature
allows the system designer to configure two DAF registers that
are selected via an FSEL input pin to select the desired final
frequency. This slew rate control is defined as Smooth-Track
and is used for all frequency change values programmed into
the two DAF registers. There exists a LOCK output signal,
which will activate when the final frequency is achieved by the
VCO. For Ns = 2048 and M = 48, each step takes 492 μs such
that to increment 40 steps would take 19.7 ms.
Spread Spectrum Modulation Rate
Fmodulation (KHz) = 1500.25/M.
The profile of the modulation is tuned for M = 48, such that
deviations from this value could affect the Lexmark profile.
Description
Description
CY28508
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