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DAC8562
REV. A
–13–
To compensate for the SSM2018’s gain constant temperature
coefficient of –3300 ppm/
°
C, a 1 k
, temperature-sensitive
resistor (R7) manufactured by the Precision Resistor Com-
pany 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
A High-Compliance, Digitally Controlled Precision Current
Source
The circuit in Figure 38 shows the DAC8562 controlling a
high-compliance, precision current source using an AMP05 in-
strumentation amplifier. The AMP05’s reference pin becomes
the input, and the “old” inputs now monitor the voltage across a
precision current sense resistor, R
CS
. Voltage gain is set to unity,
so the transfer function is given by the following equation:
I
OUT
=
V
IN
R
CS
If R
CS
equals 100
, the output current is limited to +10 mA
with a 1 V input. Therefore, each DAC LSB corresponds to
2.4
μ
A. If a bipolar output current is required, then the circuit
in Figure 33 can be modified to drive the AMP05’s reference
pin with a
±
1 V input signal.
Potentiometer P1 trims the output current to zero with the in-
put at 0 V. Fine gain adjustment can be accomplished by adjust-
ing R1 or R2.
A Digitally Programmable Window Detector
A digitally programmable, upper/lower limit detector using two
DAC8562s is shown in Figure 39. The required upper and
lower limits for the test are loaded into each DAC individually
by controlling HDAC/
LDAC
. If a signal at the test input is not
within the programmed limits, the output will indicate a logic
zero which will turn the red LED on.
9
18
1
2
17
R1
100k
7
6
R2
5k
P1
100k
5
4
11
0.1μF
–15V
AMP-05
10
R
CS
100
0mA
≤
I
≤
10mA
2.4μA/ LSB
12
0.1μF
+15V
15
DGND
10
AGND
12
DATA
DAC-8562
13
+15V
16
CE
CLR
20
0.1μF
4
REF-02
6
2
0.1μF
R3
3k
R4
1k
8
Figure 38. A High-Compliance, Digitally Controlled
Precision Current Source
15
16
DGND AGND
DAC-8562
13
10
12
0.1μF
20
+5V
2
1
1/6
74HC05
HDAC/LDAC
CLR
+5V
1k
C1
C2
0.1μF
+5V
12
3
2
1
4
6
7
5
+5V
R1
604
RED LED
T1
3
4
+5V
R2
604
GREEN LED
T1
PASS/FAIL
C1, C2 = 1/4 CMP-404
15
16
DGND AGND
DAC-8562
13
10
12
0.1μF
20
+5V
DATA
1/6
74HC05
V
IN
Figure 39. A Digitally Programmable Window Detector