REV. B

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a

Complete 14-Bit DAC

AD7840

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 617/329-4700

Fax: 617/326-8703

FUNCTIONAL BLOCK DIAGRAM

FEATURES

Complete 14-Bit Voltage Output DAC

Parallel and Serial Interface Capability

80 dB Signal-to-Noise Ratio

Interfaces to High Speed DSP Processors

e.g., ADSP-2100, TMS32010, TMS32020

45 ns min WR Pulse Width

Low Power – 70 mW typ.

Operates from

5 V Supplies

GENERAL DESCRIPTION

The AD7840 is a fast, complete 14-bit voltage output D/A con-

verter. It consists of a 14-bit DAC, 3 V buried Zener reference,

DAC output amplifier and high speed control logic.

The part features double-buffered interface logic with a 14-bit

input latch and 14-bit DAC latch. Data is loaded to the input

latch in either of two modes, parallel or serial. This data is then

transferred to the DAC latch under control of an asynchronous

LDAC

signal. A fast data setup time of 21 ns allows direct

parallel interfacing to digital signal processors and high speed

16-bit microprocessors. In the serial mode, the maximum serial

data clock rate can be as high as 6 MHz.

The analog output from the AD7840 provides a bipolar output

range of

±3 V. The AD7840 is fully specified for dynamic per-

formance parameters such as signal-to-noise ratio and harmonic

distortion as well as for traditional dc specifications. Full power

output signals up to 20 kHz can be created.

The AD7840 is fabricated in linear compatible CMOS

(LC

bines precision bipolar circuits with low power CMOS logic.

The part is available in a 24-pin plastic and hermetic

dual-in-line package (DIP) and is also packaged in a 28-termi-

nal plastic leaded chip carrier (PLCC).

PRODUCT HIGHLIGHTS

1. Complete 14-Bit D/A Function

The AD7840 provides the complete function for creating ac

signals and dc voltages to 14-bit accuracy. The part features

an on-chip reference, an output buffer amplifier and 14-bit

D/A converter.

2. Dynamic Specifications for DSP Users

In addition to traditional dc specifications, the AD7840 is

specified for ac parameters including signal-to-noise ratio and

harmonic distortion. These parameters along with important

timing parameters are tested on every device.

3. Fast, Versatile Microprocessor Interface

The AD7840 is capable of 14-bit parallel and serial interfac-

ing. In the parallel mode, data setup times of 21 ns and write

pulse widths of 45 ns make the AD7840 compatible with

modern 16-bit microprocessors and digital signal processors.

In the serial mode, the part features a high data transfer rate

of 6 MHz.