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ADDAC85 Datasheet(PDF) 12 Page - Analog Devices

Part No. ADDAC85
Description  Complete Low Cost 12-Bit D/A Converters
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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ADDAC85 Datasheet(HTML) 12 Page - Analog Devices

 
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REV. B
ADDAC80/ADDAC85/ADDAC87
–12–
DRIVING A RESISTOR LOAD BIPOLAR
The equivalent output circuit for a bipolar output voltage range
is shown in Figure 13, RL = RLI + RLS. VOUT is determined by:
VmA
Rk
Rk
OUT
L
L
×
+


1
322
322
.
.
(2)
where RL max = 11.18 k
Ω and VOUT max = ±2.5 V
To achieve specified drift, connect the internal scaling resistors
(RLI) as shown in Table IV for the COB or CTC codes and add
an external metal film resistor (RLS) in series to obtain a full scale
output range of
±1 V. In this configuration, with RLS equal to
zero, the full scale range will be
±0.874 V.
1mA
CURRENT CONTROLLED
BY DIGITAL INPUT
3.22k
RLI
1.2k
COMMON
VOUT
RLS
+
15
20
21
Figure 13. ADDAC80-CBI-I Connected for Bipolar
Output Voltage with Resistive Load
DRIVING AN EXTERNAL OP AMP
The current model ADDAC80 will drive the summing junction
of an op amp used as a current to voltage converter to produce
an output voltage. As seen in Figure 14,
VI
R
OUT
OUT
F
(3)
where IOUT is the ADDAC80 output current and RF is the feed-
back resistor. Using the internal feedback resistors of the current
model ADDAC80 provides output voltage ranges the same as
the voltage model ADDAC80. To obtain the desired output
voltage range when connecting an external op amp, refer to
Table V and Figure 14.
20V RANGE
5k
I
0 TO 2mA
6.6k
5k
CBI
10V RANGE
AD509KH*
VOUT
*FOR FAST SETTLING TIME
19
18
15
21
A
Figure 14. External Op Amp Using Internal
Feedback Resistors
OUTPUT LARGER THAN 20 V RANGE
For output voltage ranges larger than
±10 V, a high voltage op
amp may be employed with an external feedback resistor. Use
IOUT values of
±l mA for bipolar voltage ranges and –2 mA for
unipolar voltage ranges (see Figure 15). Use protection diodes
when a high voltage op amp is used.
The feedback resistor, RF, should have a temperature coefficient
as low as possible. Using an external feedback resistor, overall
drift of the circuit increases due to the lack of temperature track-
ing between RF and the internal scaling resistor network. This will
typically add 50 ppm/
°C + RF drift to total drift.
17
16
15
24
21
V
+
I
0 TO 2mA
VREF
6.3V
6.6k
6.3k
*FOR OUTPUT VOLTAGE SWINGS UP TO 140V p-p
VOUT
RF
171K*
Figure 15. External Op Amp Using External
Feedback Resistors
Table IV. Current Model/Resistive Load Connections
1%
Metal Film
RLI Connections
Reference
Bipolar Offset
Internal
External
Digital
Output
Resistance
Resistance
Connect
Connect
Connect
Connect
Connect
Input Codes
Range
RLI (k )RLS
Pin 15 to
Pin 18 to
Pin 20 to Pin 16 to
Pin 17 to
RLS
CSB
0 to –2 V
0.968
210
20
19 and RLS
15
24
Com (21)
Between
Pin 18 and
Com (21)
COB or CTC
±1 V
1.2
249
18
19
RLS
24
15
Between
Pin 20 and
Com (21)
CCD
0 to
±2 V 3
N/A
NC
21
NC
24
NC
N/A


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