ADDAC80/ADDAC85/ADDAC87
TO REF CONTROL CIRCUIT
VOLTAGE OUTPUT MODELS
Internal scaling resistors provided in the ADDAC80 may be
connected to produce bipolar output voltage ranges of 10 V,
5 V or 2.5 V or unipolar output voltage ranges of 0 V to +5 V
or 0 V to +10 V (see Figure 9).
6.3kꢀ
17
19
20
16
18
15
REF IN
3kꢀ
2kꢀ
5kꢀ
REF
INPUT
16
TO REF
6.3kꢀ
BIPOLAR
OFFSET
CONTROL
CIRCUIT
17
Figure 10. Internal Scaling Resistors
21 COM
6.3kꢀ
17
16
BIPOLAR OFFSET
SUMMING
JUNCTION
TO REF
REFERENCE
INPUT
CONTROL
CIRCUIT
20
18
FROM
WEIGHTED
RESISTOR
NETWORK
5kꢀ
5kꢀ
15
21
I
OUT
19
15
I
OUTPUT
–
6.6kꢀ
0TO 2mA
+
COMMON
–
V
6.3V
Figure 9. Output Amplifier Voltage Range Scaling Circuit
+
24
REFERENCE OUT
Gain and offset drift are minimized in the ADDAC80 because
of the thermal tracking of the scaling resistors with other device
components. Connections for various output voltage ranges are
shown in Table III. Settling time is specified for a full-scale
range change: 4 s for a 10 kΩ feedback resistor; 3 s for a 5 kΩ
feedback resistor when using the compensation capacitor shown
in Figure 3a.
Figure 11. ADDAC80 Current Model Equivalent Output Circuit
Internal resistors are provided to scale an external op amp or to
configure a resistive load to offer two output voltage ranges of 1 V
or 0 V to –2 V. These resistors (RLI TCR = 20 ppm/°C) are an
integral part of the ADDAC80 and maintain gain and bipolar
offset drift specifications. If the internal resistors are not used, exter-
nal RL (or RF) resistors should have a TCR of 25 ppm/°C or
less to minimize drift. This will typically add 50 ppm/°C + the
TCR of RL (or RF) to the total drift.
The equivalent resistive scaling network and output circuit of
the current model are shown in Figures 10 and 11. External RLS
resistors are required to produce exactly 0 V to –2 V or 1 V
output. TCR of these resistors should be 100 ppm/°C or less
to maintain the ADDAC80 output specifications. If exact output
ranges are not required, the external resistors are not needed.
Table III. Output Voltage Range Connections, Voltage Model ADDAC80
Output
Range
Digital
Input Codes
Connect
Pin 15 to
Connect
Pin 17 to
Connect
Pin 19 to
Connect
Pin 16 to
10 V
5 V
2.5 V
0 V to 10 V
0 V to 5 V
0 V to 10 V
COB or CTC 19
COB or CTC 18
COB or CTC 18
20
20
20
21
21
NC
15
NC
20
NC
20
15
24
24
24
24
24
24
CSB
CSB
CCD
18
18
19
NC = No Connect
DRIVING A RESISTIVE LOAD UNIPOLAR
A load resistance, RL = RLI, + RLS, connected as shown in
Figure 12 will generate a voltage range, VOUT, determined by:
15
+
R
LI
968ꢀ
R
0TO
2mA
LS
18
21
V
OUT
6.6kꢀ
6.6 kΩ ×RL
COMMON
VOUT = –2 mA
(1)
–
6.6 kΩ +R
L
CURRENT CONTROLLED
BY DIGITAL INPUT
where RL max = 1.54 kΩ and VOUT max = –2.5 V
Figure 12. Equivalent Circuit ADDAC80-CBI-I Connected
for Unipolar Voltage Output with Resistive Load
To achieve specified drift, connect the internal scaling resistor
(RLI) as shown in Table IV to an external metal film trim resistor
(RLS) to provide full scale output voltage range of 0 V to –2 V.
With RLS = 0 V, VOUT = –1.69 V.
REV. B
–11–
ADI [ ADI ]
