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

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

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

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

resistor value as follows:

OUT

SET

I

R

/

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

try. Proper attention should be paid to the load

keep the output voltage within this compliance

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 CS

Register Map and Descriptions

, enable greater

flexibility for system design in the AD9859.

The register map is listed in Table 5.