DAC8562
Alternatively, the output voltage can be coded in complementary
offset binary using the circuit in Figure 35. This configuration
eliminates the need for a pull-down resistor or an op amp for
REFOUT The transfer equation of the circuit is given by:
audio mixing consoles, music synthesizers, and other audio proces-
sors, VCAs, such as the SSM2018, adjust audio channel gain and
attenuation from front panel potentiometers. The VCA provides a
clean gain transition control of the audio level when the slew rate of
the analog input control voltage, VC, is properly chosen. The cir-
cuit in Figure 37 illustrates a volume control application using the
DAC8562 to control the attenuation of the SSM2018.
R2
VO = –1mV × Digital Code ×
+ REFOUT
R1
+15V
R4
R3 + R4
R2
R1
×
× 1+
10M
Ω
P1
100kΩ
SYMMETRY
TRIM
OFFSET
TRIM
Ω
470k
P2
500kΩ
and, for the values shown, becomes:
10pF
–15V
VO = −2.44 mV × Digital Code + 5V
Ω
18k
V
OUT
R2
1
2
3
4
16
R1
15
14
13
12
11
+15V
V
OUT
0.1µF
DAC-8562
V
O
Ω
30k
SSM-2018
5
6
+15V
–15V
R3
18kΩ
V
REFOUT
IN
Ω
7
8
10
9
R1 = R3 = 10k
R4
+15V
0.1µF
0.1µF
47pF
V
O
RANGE
2
R4
R2
+5V
0.1µF
±5V
13.7k + 169
Ω
23.7k + 715
REF-02
6
Figure 35 Bipolar Output Operation Without
Trim Version 2
4
20
CE
16
15
R6
825
Generating a Negative Supply Voltage
DAC-8562
Ω
CLR
0V
≤ V ≤ +2.24V
C
13
Some applications may require bipolar output configuration, but
only have a single power supply rail available. This is very com-
mon in data acquisition systems using microprocessor-based sys-
tems. In these systems, only +12 V, +15 V, and/or +5 V are
available. Shown in Figure 36 is a method of generating a nega-
tive supply voltage using one CD4049, a CMOS hex inverter,
operating on +12 V or +15 V. The circuit is essentially a charge
pump where two of the six are used as an oscillator. For the val-
ues shown, the frequency of oscillation is approximately 3.5 kHz
and is fairly insensitive to supply voltage because R1 > 2 ϫ R2.
The remaining four inverters are wired in parallel for higher out-
put current. The square-wave output is level translated by C2 to
a negative-going signal, rectified using a pair of 1N4001s, and
then filtered by C3. With the values shown, the charge pump
will provide an output voltage of –5 V for current loading in the
range 0.5 mA ≤ IOUT ≤ 10 mA with a +15 V supply and
0.5 mA ≤ IOUT ≤ 7 mA with a +12 V supply.
C
R7
1kΩ
DATA
CON
1µF
AGND
12
DGND
10
*
* – PRECISION RESISTOR PT146
1kΩ COMPENSATOR
Figure 37. Audio Volume Control
Since the supply voltage available in these systems is typically
±15 V or ±18 V, a REF02 is used to supply the +5 V required
to power the DAC. No trimming of the reference is required be-
cause of the reference’s tight initial tolerance and low supply
current consumption of the DAC8562. The SSM2018 is config-
ured as a unity-gain buffer when its control voltage equals
0 volt. This corresponds to a 000H code from the DAC8562.
Since the SSM2018 exhibits a gain constant of –28 mV/dB
(typical), the DAC’s full-scale output voltage has to be scaled
down by R6 and R7 to provide 80 dB of attenuation when the
digital code equals FFFH. Therefore, every DAC LSB corre-
sponds to 0.02 dB of attenuation. Table V illustrates the attenu-
ation versus digital code of the volume control circuit.
7
6
INVERTERS = CD4049
C2
47µF
9
11
14
10
12
15
R3
D2
470
Ω
1N4001
3
2
5
4
Table V. SSM2018 VCA Attenuation vs.
DAC8562 Input Code
–5V
R2
5.1k
R1
510k
Ω
Ω
1N5231
C3
47µF
D1
Hexadecimal Number
in DAC Register
Control Voltage VCA Attenuation
5.1V
1N4001
ZENER
(V)
(dB)
C1
0.02µF
000
400
800
C00
FFF
0
0
Figure 36. Generating a –5 V Supply When
Only +12 V or +15 V Are Available
+0.56
+1.12
+1.68
+2.24
20
40
60
80
Audio Volume Control
The DAC8562 is well suited to control digitally the gain or
attenuation of a voltage controlled amplifiers. In professional
–12–
REV. A
ADI [ ADI ]
