Datasheet

DAC8562
REV. A
–12–
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
= –1mV × Digital Code ×
R2
R1






+ REFOUT
×
R4
R3 + R4






× 1+
R2
R1






and, for the values shown, becomes:
V
O
=−2.44 mV × Digital Code + 5V
DAC-8562
REFOUT
V
OUT
R1
R4
R3
R2
V
O
V
O
RANGE
±5V
R2
23.7k + 715
R4
13.7k + 169
R1 = R3 = 10k
Ω
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 3 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.
910
6
11 12
14 15
7
3254
R2
5.1k
R1
510k
C1
0.02µF
C2
47µF
D1
1N4001
C3
47µF
1N5231
5.1V
ZENER
D2
1N4001
R3
470
–5V
INVERTERS = CD4049
Ω
Ω
Ω
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.
15
16
DGND
AGND
DATA
DAC-8562
13
+15V
10
CE
CLR
20
12
0.1µF
4
REF-02
6
2
0.1µF
18k
10pF
470k
P1
100kΩ
10M
OFFSET
TRIM
47pF
SYMMETRY
TRIM
P2
500kΩ
V
OUT
+15V
–15V
30k
+15V
–15V
0.1µF
0.1µF
+15V
18k
V
IN
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
SSM-2018
+5V
C
CON
1µF
R6
825
R7
1kΩ
*
0V ≤ V
C
≤ +2.24V
* – PRECISION RESISTOR PT146
1kΩ COMPENSATOR
Ω
Ω
Ω
Ω
Ω
Ω
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