DAC8562 Datasheet, PDF (12/16 Pages) Analog Devices – +5 Volt, Parallel Input Complete 12-Bit DAC

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:
V_O
= –1 mV
× Digital
Code
×


R2
R1


+ REFOUT
×


R4 
R3 + R4 
×
_{1 +}
R2
R1 
and, for the values shown, becomes:
V_O = −2.44 mV × Digital Code + 5 V
R2
R1
V_OUT
DAC-8562
V_O
R3
REFOUT
R4
R1 = R3 = 10kΩ
V_O
RANGE
±5V
R2
23.7k + 715
R4
13.7k + 169 Ω
Figure 35 Bipolar Output Operation Without
Trim Version 2
Generating a Negative Supply Voltage
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 Ï« 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 ≤ I_OUT ≤ 10 mA with a +15 V supply and
0.5 mA ≤ I_OUT ≤ 7 mA with a +12 V supply.
7
6
INVERTERS = CD4049
9
3
25
4
11
R1
510kΩ
R2
5.1k Ω
14
C1
0.02µF
10
C2
47µF
D2
1N4001
R3
470 Ω
–5V
12
15
D1
C3
1N5231
1N4001 47µF 5.1V
ZENER
Figure 36. Generating a –5 V Supply When
Only +12 V or +15 V Are Available
Audio Volume Control
The DAC8562 is well suited to control digitally the gain or
attenuation of a voltage controlled amplifiers. In professional
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, V_C, is properly chosen. The cir-
cuit in Figure 37 illustrates a volume control application using the
DAC8562 to control the attenuation of the SSM2018.
+15V
P1
100kΩ
OFFSET
TRIM
–15V
10M Ω
P2
500kΩ
SYMMETRY
TRIM
470k Ω
10pF
18kΩ
V_OUT
+15V
0.1µF
V_IN
+15V
18kΩ
0.1µF
2
REF-02 6
1
16
2
15
3
14
4
13
SSM-2018
5
12
6
11
7
10
8
9
47pF
+5V 0.1µF
30kΩ
+15V
–15V
0.1µF
4
CE
16
CLR 15
DATA
20
DAC-8562
13
DGND ^AGND
10
12
R6
825Ω _{0V ≤ VC ≤ +2.24V}
R7
1kΩ*
C_CON
1µF
* – 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 000_H 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 FFF_H. 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.
Table V. SSM2018 VCA Attenuation vs.
DAC8562 Input Code
Hexadecimal Number Control Voltage VCA Attenuation
in DAC Register
(V)
(dB)
000
0
0
400
+0.56
20
800
+1.12
40
C00
+1.68
60
FFF
+2.24
80
–12–
REV. A