REV. B
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a
LC
2
MOS
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 65 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
2
MOS), an advanced, mixed technology process that com-
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.
