PGA203AG BURR-BROWN [Burr-Brown Corporation], PGA203AG Datasheet - Page 8

• Manufacturer Part Number: PGA203AG
• Description: Digitally Controlled Programmable-Gain INSTRUMENTATION AMPLIFIER
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

GAIN SELECTION
Gain selection is accomplished by the application of a 2-bit
digital word to the gain select inputs. Table I shows the gains
for the different possible values of the digital input word.
The logic inputs are referred to their own separate digital
common pin, which can be connected to any voltage be-
tween the minus supply and 8V below the positive supply.
The gains are all internally trimmed to an initial accuracy of
better than 0.1%, so no external gain adjustment is required.
However, if necessary the gains can be increased by the use
of an external attenuator around the output stage as shown in
Figure 3. Recommended resistor values for certain selected
output gains are given in Table II.
TABLE II. Output Stage Gain Control.
FIGURE 3. Gain Increase with Buffered Attenuator.
COMMON-MODE INPUT RANGE
Unlike the classical three op amp type of circuit, the input
common-mode range of the PGA202/203 does not depend
on the differential input and the gain. In the standard three
op amp circuit, the input common-mode signal must be kept
below the maximum output voltage of the input amplifier
minus 1/2 the final output voltage. If, for example, these
amplifiers can swing 12V, then to get 12V at the output you
must restrict the input common-mode voltage to only 6V.
The circuitry of the PGA202/203 is such that the common-
mode input range applies to either input pin regardless of the
output voltage.
TABLE I. Software Gain Selection.
A
0
0
1
1
1
A
0
1
0
1
0
OUTPUT GAIN
V
IN
®
10
2
5
GAIN
1000
100
PGA202/203
10
1
8
7
PGA202
+
–
PGA202
4
ERROR
0.05%
0.05%
0.05%
0.10%
OPA602
11 12
+
–
5k
2k
1k
R
1
GAIN
R
R
1
2
4
8
1
2
PGA203
V
OUT
ERROR
0.05%
0.05%
0.05%
0.05%
5k
8k
9k
R
2
8
OUTPUT SENSE
An output sense has been provided to allow greater accuracy
in connecting the load. By attaching this feedback point to
the load at the load site, IR drops due to the load currents are
eliminated since they are inside the feedback loop. Proper
connection is shown in Figure 1. When more current is
required, a power booster can be placed in the feedback loop
as shown in Figure 4. Buffer errors are minimized by the
loop gain of the output amplifier.
FIGURE 4. Current Boosting the Output.
OUTPUT FILTERING
The summing nodes of the output amplifier have also been
made available to allow for output filtering. By placing
matched capacitors in parallel with the existing internal
capacitors as shown in Figure 5, you can lower the fre-
quency response of the output amplifier. This will reduce the
noise of the amplifier, at the cost of a slower response. The
nominal frequency responses for some selected values of
capacitor are shown in Table III.
FIGURE 5. Output Filtering.
TABLE III. Output Frequency vs Filter Capacitors.
V
CUTOFF FREQUENCY
IN
V
IN
100kHz
10kHz
1MHz
8
7
8
7
+
–
A
PGA202
0
1
+
–
14
PGA202
A
1
2
10
5
C
C
11 12
EXT
EXT
4
11
4
OPA633
12
C
1
525pF
None
R
47pF
AND C
L
V
OUT
V
OUT
2