Datasheet

AD9859

Rev. A | Page 12 of 24

DAC Output

The AD9859 incorporates an integrated 10-bit current output

DAC. Unlike most DACs, this output is referenced to AVDD,

not AGND.

Two complementary outputs provide a combined full-scale

output current (I

OUT

). Differential outputs reduce the amount of

common-mode noise that might be present at the DAC output,

offering the advantage of an increased signal-to-noise ratio. The

full-scale current is controlled by an external resistor (R

SET

)

connected between the DAC_R

SET

pin and the DAC ground

(AGND_DAC). The full-scale current is proportional to the

resistor value as follows:

OUTSET

IR /19.39=

The maximum full-scale output current of the combined DAC

outputs is 15 mA, but limiting the output to 10 mA provides the

best spurious-free dynamic range (SFDR) performance. The DAC

output compliance range is AVDD + 0.5 V to AVDD – 0.5 V.

Voltages developed beyond this range cause excessive DAC

distortion and could potentially damage the DAC output

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Serial I/O Port

The AD9859 serial port is a flexible, synchronous serial

communications port that allows easy interface to many industry-

standard microcontrollers and microprocessors. The serial I/O port

is compatible with most synchronous transfer formats, including

both the Motorola 6905/11 SPI® and Intel® 8051 SSR protocols.

The interface allows read/write access to all registers that configure

the AD9859. MSB first or LSB first transfer formats are supported.

The AD9859’s serial interface port can be configured as a single pin

I/O (SDIO), which allows a 2-wire interface or two unidirectional

pins for in/out (SDIO/SDO), which in turn enables a 3-wire

interface. Two optional pins, IOSYNC and

, enable greater

flexibility for system design in the AD9859.

The register map is listed in Table 5.