The ADF4110 family has a simple SPI® compatible serial inter-
face for writing to the device. SCLK, SDATA, and LE control the
data transfer. When latch enable (LE) goes high, the 24 bits that
have been clocked into the input register on each rising edge of
SCLK get transferred to the appropriate latch. See Figure 2 for
the timing diagram and Table 5 for the latch truth table.
The maximum allowable serial clock rate is 20 MHz. This
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 have typical lock times in the
hundreds of microseconds.
Figure 38 shows the interface between the ADF4110 family 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 ADF4110 family
needs a 24-bit word. This is accomplished by writing three 8-bit
bytes from the MicroConverter to the device. When the third
byte has been written, the LE input should be brought high to
complete the transfer.
When power is first applied to the ADF4110 family, three writes
are needed (one each to the R counter latch, N counter latch,
and initialization latch) for the output to become active.
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 the ADuC812 is operating in the mode described above,
the maximum SCLOCK rate of the ADuC812 is 4 MHz. This
means that the maximum rate at which the output frequency
can be changed is 166 kHz.
Figure 38. ADuC812 to ADF4110 Family Interface
Figure 39 shows the interface between the ADF4110 family and
the ADSP-21xx digital signal processor. The ADF4110 family
needs a 24-bit serial word for each latch write. The easiest way
to accomplish this using the ADSP-21xx family is to use the
auto buffered transmit mode of operation with alternate
framing. This provides a means for transmitting an entire block
of serial data before an interrupt is generated.
Figure 39. ADSP-21xx to ADF4110 Family Interface
Set up the word length for 8 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 auto buffered mode, and
then write to the transmit register of the DSP. This last opera-
tion initiates the autobuffer transfer.
PCB DESIGN GUIDELINES FOR CHIP SCALE
The lands on the chip scale package (CP-20) 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 ensures 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 ensures 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 thermal pad
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