AD9558 Datasheet, PDF (27/104 Pages) Analog Devices – Quad Input Multiservice Line Card Adaptive

Data Sheet
Program the System Clock and Free Run Tuning Word
The system clock multiplier (SYSCLK) parameters are at
Register 0x0100 to Register 0x0108, and the free run tuning
word is at Register 0x0300 to Register 0x0303. Use the following
steps for optimal performance:
1. Set the system clock PLL input type and divider values.
2. Set the system clock period.
It is essential to program the system clock period because
many of the AD9558 subsystems rely on this value.
3. Set the system clock stability timer.
It is highly recommended that the system clock stability
timer be programmed. This is especially important when
using the system clock multiplier and also applies when
using an external system clock source, especially if the
external source is not expected to be completely stable
when power is applied to the AD9558. The system clock
stability timer specifies the amount of time that the system
clock PLL must be locked before the part declares that the
system clock is stable. The default value is 50 ms.
4. Program the free run tuning word.
The free run frequency of the digital PLL (DPLL) determines
the frequency appearing at the APLL input when free run
mode is selected. The free run tuning word is at Register
0x0300 to Register 0x0303. The correct free run frequency
is required for the APLL to calibrate and lock correctly.
5. Set user free run mode (Register 0x0A01[5] = 1b).
Initialize and Calibrate the Output PLL (APLL)
The registers controlling the APLL are at Register 0x0400
to Register 0x0408. This low noise, integer-N PLL multiplies
the DPLL output (which is usually 175 MHz to 200 MHz) to a
frequency in the 3.35 GHz to 4.05 GHz range. After the system
clock is configured and the free run tuning word is set in
Register 0x0300 to Register 0x0303, the user can set the manual
APLL VCO calibration bit (Register 0x0405[0]) and issue an I/O
update (Register 0x0005[0]). This process performs the APLL
VCO calibration. VCO calibration ensures that, at the time of
calibration, the dc control voltage of the APLL VCO is centered in
the middle of its operating range. It is important to remember the
following points when calibrating the APLL VCO:
• The system clock must be stable.
• The APLL VCO must have the correct frequency from the
30-bit DCO (digitally controlled oscillator) during
calibration.
• The APLL VCO must be recalibrated any time the APLL
frequency changes.
• APLL VCO calibration occurs on the low-to-high transition
of the manual APLL VCO calibration bit, and this bit is not
autoclearing. Therefore, this bit must be cleared (and an I/O
update issued) before another APLL calibration is started.
• The best way to monitor successful APLL calibration is to
monitor Bit 2 in Register 0x0D01 (APLL lock).
AD9558
Program the Clock Distribution Outputs
The APLL output goes to the clock distribution block. The
clock distribution parameters reside in Register 0x0500 to
Register 0x0509. They include the following:
• Output power-down control
• Output enable (disabled by default)
• Output synchronization
• Output mode control
• Output divider functionality
See the Clock Distribution section for more information.
Generate the Output Clock
If Register 0x0500[1:0] is programmed for automatic clock
distribution synchronization via the DPLL phase or frequency
lock, the synthesized output signal appears at the clock distribution
outputs. Otherwise, set and then clear the soft sync clock
distribution bit (Register 0x0A02, Bit 1), or use a multifunction
pin input (if programmed for use) to generate a clock
distribution sync pulse, which causes the synthesized output
signal to appear at the clock distribution outputs.
Program the Multifunction Pins (Optional)
This step is required only if the user intends to use any of the
multifunction pins for status or control. The multifunction pin
parameters are at Register 0x0200 to Register 0x0208.
Program the IRQ Functionality (Optional)
This step is required only if the user intends to use the IRQ feature.
The IRQ monitor registers are at Register 0x0D02 to Register
0x0D09. If the desired bits in the IRQ mask registers at Register
0x020A to Register 0x020F are set high, the appropriate IRQ
monitor bit at Register 0x0D02 to Register 0x0D07 is set high
when the indicated event occurs.
Individual IRQ events are cleared by using the IRQ clearing
registers at Register 0x0A04 to Register 0x0A09, or by setting
the clear all IRQs bit (Register 0x0A03[1]) to 1b.
The default values of the IRQ mask registers are such that
interrupts are not generated. The IRQ pin mode default is open-
drain NMOS.
Program the Watchdog Timer (Optional)
This step is required only if the user intends to use the watchdog
timer. The watchdog timer control is in Register 0x0210 and
Register 0x0211 and is disabled by default.
The watchdog timer is useful for generating an IRQ after a fixed
amount of time. The timer is reset by setting the clear watchdog
timer bit (Register 0x0A03[0]) to 1b.
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