EVAL-ADF4252EBZ2 Analog Devices Inc, EVAL-ADF4252EBZ2 Datasheet - Page 25

• Manufacturer Part Number: EVAL-ADF4252EBZ2
• Description: BOARD EVAL ADF4252 NO VCO/FILTER
• Manufacturer: Analog Devices Inc

Specifications of EVAL-ADF4252EBZ2

• Main Purpose: Timing, Frequency Synthesizer
• Embedded: No
• Utilized Ic / Part: ADF4252
• Primary Attributes: Dual Fractional-N PLL
• Secondary Attributes: Board excludes Loop Filter & VCO
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

± 100 kHz from the RF carrier. Harmonics of all spurs mentioned
will also appear. With the lowest spur setting enabled, the spurs
will be attenuated into the noise floor.
Prescaler
The prescaler limits the INT value. With P = 4/5, Nmin = 31.
With P = 8/9, Nmin = 91.
The prescaler can also influence the phase noise performance.
If INT < 91, a prescaler of 4/5 should be used. For applications
where INT > 91, P = 8/9 should be used for optimum noise
performance.
Filter Design—ADIsimPLL
A filter design and analysis program is available to help users
implement their PLL design. Visit
free download of the ADIsimPLL software. The software
designs, simulates, and analyzes the entire PLL frequency
domain and time domain response. Various passive and active
filter architectures are allowed.
INTERFACING
The ADF4252 has a simple SPI compatible serial interface for
writing to the device. SCLK, SDATA, and LE control the data
transfer. When LE (latch enable) goes high, the 24 bits that have
been clocked into the input register on each rising edge of SCLK
will be transferred to the appropriate latch. See Figure 1 for the
Timing Diagram and Table I for the Control Bit Truth Table.
The maximum allowable serial clock rate is 20 MHz, which
means that the maximum update rate possible for the device is
833 kHz or one update every 1.2 µs. This is certainly more than
adequate for systems that will have typical lock times in hun-
dreds of microseconds.
ADuC812 Interface
Figure 8 shows the interface between the ADF4252 and the
ADuC812 microconverter. Since the ADuC812 is based on
an 8051 core, this interface can be used with any 8051 based
microcontroller. The microconverter is set up for SPI master
mode with CPHA = 0. To initiate the operation, the I/O port
driving LE is brought low. Each latch of the ADF4252 needs
(at most) a 24-bit word. This is accomplished by writing three
8-bit bytes from the microconverter to the device. When the third
REV. B
ADuC812
I/O PORTS
Figure 8. ADuC812 to ADF4252 Interface
SCLOCK
MOSI
www.analog.com/pll
SCLK
SDATA
CE
MUXOUT
(LOCK DETECT)
LE
ADF4252
for a
–25–
byte has been written, the LE input should be brought high to
complete the transfer.
I/O port lines on the ADuC812 are also used to control power-
down (CE input) and to detect lock (MUXOUT configured as
lock detect and polled by the port input).
When operating in the mode described, the maximum SCLOCK
rate of the ADuC812 is 4 MHz. This means that the maximum
rate at which the output frequency can be changed will be 166 kHz.
ADSP-2181 Interface
Figure 9 shows the interface between the ADF4252 and the
ADSP-21xx digital signal processor. Each latch of the ADF4252
needs (at most) a 24-bit word. The easiest way to accomplish this
using the ADSP-21xx family is to use the autobuffered transmit
mode of operation with alternate framing. This provides a means
for transmitting an entire block of serial data before an interrupt is
generated. Set up the word length for eight bits and use three memory
locations for each 24-bit word. To program each 24-bit latch, store
the three 8-bit bytes, enable the autobuffered mode, and then write
to the transmit register of the DSP. This last operation initiates the
autobuffer transfer.
PCB DESIGN GUIDELINES FOR CHIP SCALE PACKAGE
The leads on the chip scale package (CP-24) are rectangular. The
printed circuit board pad for these should be 0.1 mm longer than
the package land length and 0.05 mm wider than the package land
width. The land should be centered on the pad. This will ensure
that the solder joint size is maximized.
The bottom of the chip scale package has a central thermal pad.
The thermal pad on the printed circuit board should be at least
as large as this exposed pad. On the printed circuit board, there
should be a clearance of at least 0.25 mm between the thermal
pad and the inner edges of the pad pattern. This will ensure that
shorting is avoided.
Thermal vias may be used on the printed circuit board thermal pad
to improve thermal performance of the package. If vias are used,
they should be incorporated in the thermal pad at 1.2 mm pitch
grid. The via diameter should be between 0.3 mm and 0.33 mm,
and the via barrel should be plated with 1 oz copper to plug the via.
The user should connect the printed circuit board to A
ADSP-21xx
Figure 9. ADSP-21xx to ADF4252 Interface
I/O FLAGS
SCLK
TFS
DT
SCLK
SDATA
CE
MUXOUT
(LOCK DETECT)
LE
ADF4252
ADF4252
GND
.