ADF4154BCP datasheet(19/20 Pages) AD

19 / 20 page

ADF4154

Rev. 0 | Page 19 of 20

ADuC812 Interface

ADSP-21xx

ADF4154

SCLOCK

SCLK

SDATA

MUXOUT

(LOCK DETECT)

TFS

I/O FLAGS

Figure 24 shows the interface between the ADF4154 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, bring the I/O

port driving LE low. Each latch of the ADF4154 needs a 24-bit

word, which is accomplished by writing three 8-bit bytes from

the MicroConverter to the device. After the third byte is written,

the LE input should be brought high to complete the transfer.

Figure 25. ADSP-21xx to ADF4154 Interface

PCB DESIGN GUIDELINES FOR CHIP SCALE

PACKAGE

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 is

180 kHz.

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.

ADuC812

ADF4154

SCLOCK

SCLK

SDATA

MUXOUT

(LOCK DETECT)

MOSI

I/O PORTS

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 to avoid shorting.

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 into 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. of

copper to plug the via.

Figure 24. ADuC812 to ADF4154 Interface

ADSP-2181 Interface

Figure 25 shows the interface between the ADF4154 and the

ADSP-21xx digital signal processor. As discussed previously, the

ADF4154 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 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 each of the

three 8-bit bytes, enable the autobuffered mode, and write to the

transmit register of the DSP. This last operation initiates the

autobuffer transfer.

The user should connect the printed circuit board thermal pad

to AGND.

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