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AD7801 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer AD7801
Beschreibung +2.7 V to +5.5 V/ Parallel Input/ Voltage Output 8-Bit DAC
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 16 Seiten
AD7801 Datasheet, Funktion
a
FEATURES
Single 8-Bit DAC
20-Pin SOIC/TSSOP Package
+2.7 V to +5.5 V Operation
Internal and External Reference Capability
DAC Power-Down Function
Parallel Interface
On-Chip Output Buffer Rail-to-Rail Operation
Low Power Operation 1.75 mA max @ 3.3 V
Power-Down to 1 A max @ 25؇C
APPLICATIONS
Portable Battery Powered Instruments
Digital Gain and Offset Adjustment
Programmable Voltage and Current Sources
Programmable Attenuators
+2.7 V to +5.5 V, Parallel Input,
Voltage Output 8-Bit DAC
AD7801
FUNCTIONAL BLOCK DIAGRAM
D7
D0
INPUT
REGISTER
DAC
REGISTER
I DAC
I/V
VOUT
POWER-ON
WR CONTROL
MUX
RESET
CS LOGIC
AD7801
÷2
AGND
PD CLR LDAC
REFIN VDD
DGND
GENERAL DESCRIPTION
The AD7801 is a single, 8-bit, voltage out DAC that operates
from a single +2.7 V to +5.5 V supply. Its on-chip precision output
buffer allows the DAC output to swing rail to rail. The AD7801
has a parallel microprocessor and DSP compatible interface with
high speed registers and double buffered interface logic. Data is
loaded to the input register on the rising edge of CS or WR.
Reference selection for the AD7801 can be either an internal
reference derived from the VDD or an external reference applied
at the REFIN pin. The output of the DAC can be cleared by
using the asynchronous CLR input.
The low power consumption of this part makes it ideally suited
to portable battery operated equipment. The power consump-
tion is less than 5 mW at 3.3 V, reducing to less than 3 µW in
power-down mode.
The AD7801 is available in a 20-lead SOIC and a 20-lead
TSSOP package.
PRODUCT HIGHLIGHTS
1. Low Power, Single Supply operation. This part operates
from a single +2.7 V to +5.5 V supply and consumes typically
5 mW at 3 V, making it ideal for battery powered applications.
2. The on-chip output buffer amplifier allows the output of the
DAC to swing rail to rail with a settling time of typically 1.2 µs.
3. Internal or external reference capability.
4. High speed parallel interface.
5. Power-down capability. When powered down the DAC
consumes less than 1 µA at 25°C.
6. Packaged in 20-lead SOIC and TSSOP packages.
REV. 0
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 World Wide Web Site: http://www.analog.com
Fax: 617/326-8703
© Analog Devices, Inc., 1997






AD7801 Datasheet, Funktion
AD7801–Typical Performance Characteristics
T
VDD
1
T
2
VOUT
CH1 5.00V CH2 5.00V M20.0ms CH1
Figure 11. Power-On—Reset
10
9
8
7
VDD = 2.7 TO 5.5V
6 DAC LOADED WITH ALL ZEROES
INTERNAL REFERENCE
5
4
3
2
1
0
–50 –25
0 25 50 75 100 125
TEMPERATURE – C
Figure 12. Zero Code Error vs.
Temperature
WR
1
VOUT
VDD = 5V
INTERNAL VOLTAGE
REFERENCE
10 LSB STEP CHANGE
TA = +25؇C
2
CH1 5.00V, CH2 50.0mV, M 250ns
Figure 13. Small-Scale Settling Time
0.5
0.4 VDD = 5V
INTERNAL REFERENCE
0.3
5k100pF LOAD
LIMITED CODE RANGE (15–245)
0.2 TA = +25°C
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
0
32 64 96 128 160 192 224 256
INPUT CODE (15 to 245)
Figure 14. Integral Linearity Plot
0.5
0.4
0.3
0.2 VDD = 5V
INTERNAL REFERENCE
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
–60 –40 –20 0 20 40 60 80 100 120 140
TEMPERATURE – C
Figure 15. Typical INL vs. Temperature
0.5
0.4
0.3
0.2
0.1 VDD = 5V
INTERNAL REFERENCE
0
–0.1
–0.2
–0.3
–0.4
–0.5
–60 –40 –20 0 20 40 60 80 100 120 140
TEMPERATURE – C
Figure 16. Typical DNL vs. Temperature
1.0
VDD = 5V
0.8
0.6
0.4
0.2
0
–60 –40 –20 0 20 40 60 80 100 120 140
TEMPERATURE – C
Figure 17. Typical Internal Reference
Error vs. Temperature
1000
900
800
700
600
500
400
300
200
100
0
–50
VDD = 5V
LOGIC INPUTS = VDD OR GND
–25 0 25 50 75 100 150
TEMPERATURE – C
Figure 18. Power-Down Current vs.
Temperature
–6– REV. 0

6 Page









AD7801 pdf, datenblatt
AD7801
AD7801 as a Digitally Programmable Indicator
A digitally programmable upper limit detector using the DAC is
shown in Figure 34. The upper limit for the test is loaded to the
DAC, which in turn sets the limit for the CMP04. If a signal at
the VIN input is not below the programmed value, an LED will
indicate the Fail condition.
+5V
0.1 F
10 F
VIN
VDD REFIN
AD7801
VOUT
D7
D0
1k
FAIL
1k
PASS
PASS/
DVDD
DGND AGND
1/4 1/6
CMP-04 74HC05
Figure 34. Digitally Programmable Indicator
Programmable Current Source
Figure 35 shows the AD7801 used as the control element of a
programmable current source. In this circuit the full-scale
current is set to 1 mA. The output voltage from the DAC is
applied across the current setting resistor of 4.7 kin series with
the full-scale setting resistor of 470 . Suitable transistors to
place in the feedback loop of the amplifier include the BC107
and the 2N3904, which enable the current source to operate
from a minimum VSOURCE of 6 V. The operating range is
determined by the operating characteristics of the transistor.
Suitable amplifiers include the AD820 and the OP295, both of
which have rail-to-rail operation on their outputs. The current
for any digital input code can be calculated as follows:
( )I = 2 V REF D
( )256 (5 k)
VDD = 5V
0.1µF 10µF
VIN
EXT REF VOUT
GND
VDD
REF IN
0.1µF
VOUT
AD7801
AD780/ REF192
WITH VDD = 5V
AGND DGND
VSOURCE
LOAD
+5V
AD820/
OP295
2N3904/
BC107
4.7k
470
Figure 35. Programmable Current Source
Coarse and Fine Adjustment using two AD7801s
The two DACs can be paired together to form a coarse and fine
adjustment function for a setpoint as shown in Figure 36. In this
circuit, the first DAC is used to provide the coarse adjustment
and the second DAC is used to provide the fine adjustment.
Varying the ratio of R1 and R2 will vary the relative effect of the
coarse and fine tune elements in the circuit. For the resistor
values shown, the second DAC has a resolution of 148 µV
giving a fine tune range of 38 mV (approximately 2 LSB) for
operation with a VDD of 5 V and a reference of 2.5 V. The
amplifier shown allows a rail-to-rail output voltage to be
achieved on the output. A typical application for the circuit
would be in a setpoint controller.
0.1µF 10µF
VDD = 5V
R3
51.2k
VIN
EXT REF VOUT
GND
VDD
REF IN
0.1µF
VOUT
AD7801
R1
390
R4
390
+5V
AD820/
OP295
VO
AD780/ REF192
WITH VDD = 5V
OR
AD589 WITH VDD = 3V
0.1µF
AGND DGND
VDD
REF IN
VOUT
AD7801
R2
51.2k
AGND DGND
Figure 36. Coarse and Fine Adjustment
–12–
REV. 0

12 Page





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