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AD7245A Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer AD7245A
Beschreibung LC2MOS 12-Bit DACPORTs
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 16 Seiten
AD7245A Datasheet, Funktion
a
FEATURES
12-Bit CMOS DAC with Output Amplifier and
Reference
Improved AD7245/AD7248:
12 V to 15 V Operation
؎1/2 LSB Linearity Grade
Faster Interface–30 ns typ Data Setup Time
Extended Plastic Temperature Range (–40؇C to +85؇C)
Single or Dual Supply Operation
Low Power–65 mW typ in Single Supply
Parallel Loading Structure: AD7245A
(8+4) Loading Structure: AD7248A
LC2MOS
12-Bit DACPORTs
AD7245A/AD7248A
AD7245A FUNCTIONAL BLOCK DIAGRAM
GENERAL DESCRIPTION
The AD7245A/AD7248A is an enhanced version of the industry
standard AD7245/AD7248. Improvements include operation
from 12 V to 15 V supplies, a ± 1/2 LSB linearity grade, faster
interface times and better full scale and reference variations with
VDD. Additional features include extended temperature range
operation for commercial and industrial grades.
The AD7245A/AD7248A is a complete, 12-bit, voltage output,
digital-to-analog converter with output amplifier and Zener volt-
age reference on a monolithic CMOS chip. No external user
trims are required to achieve full specified performance.
Both parts are microprocessor compatible, with high speed data
latches and double-buffered interface logic. The AD7245A ac-
cepts 12-bit parallel data which is loaded into the input latch on
the rising edge of CS or WR. The AD7248A has an 8-bit wide
data bus with data loaded to the input latch in two write opera-
tions. For both parts, an asynchronous LDAC signal transfers
data from the input latch to the DAC latch and updates the ana-
log output. The AD7245A also has a CLR signal on the DAC latch
which allows features such as power-on reset to be implemented.
The on-chip 5 V buried Zener diode provides a low noise, tem-
perature compensated reference for the DAC. For single supply
operation, two output ranges of 0 V to +5 V and 0 V to +10 V
are available, while these two ranges plus an additional ± 5 V
range are available with dual supplies. The output amplifiers are
capable of developing +10 V across a 2 kload to GND.
The AD7245A/AD7248A is fabricated in linear compatible
CMOS (LC2MOS), an advanced, mixed technology process that
combines precision bipolar circuits with low power CMOS logic.
The AD7245A is available in a small, 0.3" wide, 24-pin DIP and
DACPORT is a registered trademark of Analog Devices, Inc.
AD7248A FUNCTIONAL BLOCK DIAGRAM
SOIC and in 28-terminal surface mount packages. The
AD7248A is packaged in a small, 0.3" wide, 20-pin DIP and
SOIC and in 20-terminal surface mount packages.
PRODUCT HIGHLIGHTS
1. The AD7245A/AD7248A is a 12-bit DACPORT® on a single
chip. This single chip design and small package size offer
considerable space saving and increased reliability over
multichip designs.
2. The improved interface times on the part allows easy, direct
interfacing to most modern microprocessors.
3. The AD7245A/AD7248A features a wide power supply range
allowing operation from 12 V supplies.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703






AD7245A Datasheet, Funktion
AD7245A/AD7248A
AD7248A PIN FUNCTION DESCRIPTION
(ANY PACKAGE)
Pin Mnemonic Description
l VSS
Negative Supply Voltage (0 V for single
supply operation).
2 ROFS
Bipolar Offset Resistor. This provides
access to the on-chip application resistors
and allows different output voltage ranges.
3 REF OUT Reference Output. The on-chip reference
is provided at this pin and is used when
configuring the part for bipolar outputs.
4 AGND
Analog Ground.
5 DB7
Data Bit 7.
6 DB6
Data Bit 6.
7 DB5
Data Bit 5.
8 DB4
Data Bit 4.
9 DB3
Data Bit 3.
10 DGND
Digital Ground.
11 DB2
Data Bit 2/Data Bit 10.
12 DB1
Data Bit 1/Data Bit 9.
13 DB0
Data Bit 0 (LSB)/Data Bit 8.
Pin Mnemonic Description
14 CSMSB
Chip Select Input for MS Nibble. (Active
LOW). This selects the upper 4 bits of the
input latch. Input data is right justified.
15 CSLSB
Chip Select Input for LS byte. (Active
LOW). This selects the lower 8 bits of the
input latch.
16 WR
Write Input. This is used in conjunction
with CSMSB and CSLSB to load data
into the input latch of the AD7248A.
17 LDAC
Load DAC Input (Active LOW). This is
an asynchronous input which when active
transfers data from the input latch to the
DAC latch.
18 VDD
19 RFB
Positive Supply Voltage.
Feedback Resistor. This allows access to
the amplifier’s feedback loop.
20 VOUT
Output Voltage. Three different output
voltage ranges can be chosen: 0 V to +5 V,
0 V to +10 V or –5 V to +5 V.
DIP and SOIC
AD7248A PIN CONFIGURATIONS
LCCC
PLCC
–6– REV. A

6 Page









AD7245A pdf, datenblatt
AD7245A/AD7248A
The circuit of Figure 10 can be modified to provide a program-
mable current source to AGND or –VSINK (for –VSINK, dual sup-
plies are required on the AD7245A/AD7248A). The AD7245A/
AD7248A is configured as before. The current through R1 is
mirrored with a current mirror circuit to provide the program-
mable source current (see CMOS DAC Application Guide,
Publication No. G872-30-10/84, for suitable current mirror cir-
cuit). As before the absolute value of the source current will be
affected by the ± 0.2% tolerance on VREF. In this case the per-
formance of the current mirror will also affect the value of the
source current.
FUNCTION GENERATOR WITH PROGRAMMABLE
FREQUENCY
Figure 11 shows how the AD7245A/AD7248A with the AD537,
voltage-to-frequency converter and the AD639, trigonometric
function generator to provide a complete function generator
with programmable frequency. The circuit provides square
wave, triwave and sine wave outputs, each output of ± 10 V
amplitude.
The AD7245A/AD7248A provides a programmable voltage to
the AD537 input. Since both the AD7245A/AD7248A and
AD537 are guaranteed monotonic, the output frequency will al-
ways increase with increasing digital code. The AD537 provides
a square wave output which is conditioned for ± 10 V by ampli-
fier A1. The AD537 also provides a differential triwave output.
This is conditioned by amplifiers A2 and A3 to provide the
± 1.8 V triwave required at the input of the AD639. The triwave
is further scaled by amplifier A4 to provide a ± 10 V output.
Adjusting the triwave applied to the AD639 adjust the distortion
performance of the sine wave output, (+10 V in configuration
shown). Amplitude, offset and symmetry of the triwave can af-
fect the distortion. By adjusting these, via VR1 and VR2, an
output sine wave with harmonic distortion of better than –50 dB
can be achieved at low and intermediate frequencies.
Using the capacitor value shown in Figure 11 for CF (i.e.,
680 pF) the output frequency range is 0 to 100 kHz over the
digital input code range. The step size for frequency increments
is 25 Hz. The accuracy of the output frequency is limited to 8 or
9 bits by the AD537, but is guaranteed monotonic to 12 bits.
MICROPROCESSOR INTERFACING—AD7245
AD7245A—8086A INTERFACE
Figure 12 shows the 8086 16-bit processor interfacing to the
AD7245A. In the setup shown the double buffering feature of
the DAC is not used and the LDAC input is tied LOW. AD0–
AD11 of the 16-bit data bus are connected to the AD7245A
data bus (DB0-DB11). The 12-bit word is written to the
AD7245A in one MOV instruction and the analog output re-
sponds immediately. In this example the DAC address is D000.
A software routine for Figure 12 is given in Table V.
Figure 12. AD7245A to 8086 Interface
Table V. Sample Program for Loading AD7245A from 8086
ASSUME DS: DACLOAD, CS: DACLOAD
DACLOAD SEGMENT AT 000
00 8CC9
MOV CS, : DEFINE DATA SEGMENT
CS REGISTER
02 8ED9
MOV DS, : EQUAL TO CODE
CX SEGMENT REGISTER
04 BF00D0 0MOV DI, : LOAD DI WITH D000
#D000
07 C705 MOV MEM, : DAC LOADED WITH WXYZ
“YZWX” #YZWX
0B EA00 00
0E 00 FF
: CONTROL IS RETURNED TO
THE MONITOR PROGRAM
Figure 11. Programmable Function Generator
–12–
REV. A

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