參數(shù)資料
型號(hào)： DAC8512GBC
廠商： ANALOG DEVICES INC
元件分類： DAC
英文描述： % V, Serial Input Complete 12-Bit DAC
中文描述： SERIAL INPUT LOADING, 16 us SETTLING TIME, 12-BIT DAC, UUC8
封裝： DIE-8
文件頁(yè)數(shù)： 16/20頁(yè)
文件大?。?/td> 757K
代理商： DAC8512GBC
DAC8512
–16–
REV. A
A Serial DAC, Audio Volume Control
The DAC8512 is well suited to control digitally the gain or at-
tenuation of a voltage controlled amplifier. In professional audio
mixing consoles, music synthesizers, and other audio processors,
VCAs, such as the SSM2018, adjust audio channel gain and at-
tenuation 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 circuit in Figure 40 illustrates a volume control application
using the DAC8512 to control the attenuation of the SSM2018.
6
2
DAC8512
8
+15V
7
CS
CLR
1
0.1
μ
F
4
REF02
6
2
18k
10pF
470k
P1
100k
OFFSET
TRIM
10M
47pF
SYMMETRY
TRIM
P2
500k
V
OUT
+15V
–15V
30k
+15V
–15V
0.1
μ
F
0.1
μ
F
+15V
18k
V
IN
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
SSM2018
+5V
0.1
μ
F
C
CON
1
μ
R6
825
R7
1k
*
0V
≤
V
C
≤
+2.24V
* – PRECISION RESISTOR
PT146
1k
COMPENSATOR
5
LD
3
SCLK
4
SDI
Figure 40. A Serial DAC, 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 DAC8512. 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 DAC8512.
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
Table IV. SSM-2018 VCA Attenuation vs.
DAC8512 Input Code
Hexadecimal Number
in DAC Register
Control
Voltage (V)
VCA
Attenuation (dB)
000
400
800
C00
FFF
0
+0.56
+1.12
+1.68
+2.24
0
20
40
60
80
digital code equals FFF
H
. Therefore, every DAC LSB corre-
sponds to 0.02 dB of attenuation. Table IV illustrates the at-
tenuation vs. digital code of the volume control circuit.
To compensate for the SSM2018’s gain constant temperature
coefficient of –3300 ppm/
°
C, a 1 k
, temperature-sensitive re-
sistor (R7) manufactured by the Precision Resistor Company
with a temperature coefficient of +3500 ppm/
°
C is used. A
C
CON
of 1
μ
F provides a control transition time of 1 ms which
yields a click-free change in the audio channel attenuation. Sym-
metry and offset trimming details of the VCA can be found in
the SSM2018 data sheet.
Information regarding the PT146 1 k
“Compensator” can be
obtained by contacting:
Precision Resistor Company, Incorporated
10601 75th Street North
Largo, Fl 34647
(813) 541-5771
An Isolated, Programmable, 4-20 mA Process Controller
In many process control system, applications, two-wire current
transmitters are used to transmit analog signals through noisy
environments. These current transmitters use a “zero-scale” sig-
nal current of 4 mA that can be used to power the transmitter’s
signal conditioning circuitry. The “full-scale” output signal in
these transmitters is 20 mA. The converse approach to process
control can also be used; a low-power, programmable current
source can be used to control remotely located sensors or de-
vices in the loop.
A circuit that performs this function is illustrated in Figure 41.
Using the DAC8512 as the controller, the circuit provides a
programmable output current of 4 mA to 20 mA, proportional
to the DAC’s digital code. Biasing for the controller is provided
by the REF02 and requires no external trim for two reasons:
(1) the REF02’s tight initial output voltage tolerance and (2) the
low supply current consumption of both the OP90 and the
DAC8512. The entire circuit, including opto-couplers, con-
sumes less than 3 mA from the total budget of 4 mA. The OP90
regulates the output current to satisfy the current summation at
the noninverting node of the OP-90. The KCL equation at
Pin 3 is given by:
I
OUT
=
1
R
7
×
1
mV
×
Digital Code
×
R
3
R
1
+
V
REF
×
R
3
R
2
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