Datasheet

MCP6S21/2/6/8
DS21117B-page 26  2003-2012 Microchip Technology Inc.
6.4 Typical Applications
6.4.1 GAIN RANGING
Figure 6-3 shows a circuit that measures the current I
X
.
It benefits from changing the gain on the PGA. Just as
a hand-held multimeter uses different measurement
ranges to obtain the best results, this circuit makes it
easy to set a high gain for small signals and a low gain
for large signals. As a result, the required dynamic
range at the PGA’s output is less than at its input (by up
to 30 dB).
FIGURE 6-3: Wide Dynamic Range
Current Measurement Circuit.
6.4.2 SHIFTED GAIN RANGE PGA
Figure 6-4 shows a circuit using an MCP6021 at a gain
of +10 in front of an MCP6S21. This changes the over-
all gain range to +10 V/V to +320 V/V (from +1 V/V to
+32 V/V).
FIGURE 6-4: PGA with Modified Gain
Range.
It is also easy to shift the gain range to lower gains (see
Figure 6-6). The MCP6021 acts as a unity gain buffer,
and the resistive voltage divider shifts the gain range
down to +0.1 V/V to +3.2 V/V (from +1 V/V to +32 V/V).
FIGURE 6-5: PGA with lower gain range.
6.4.3 EXTENDED GAIN RANGE PGA
Figure 6-6 gives a +1 V/V to +1024 V/V gain range,
which is much greater than the range for a single PGA
(+1 V/V to +32 V/V). The first PGA provides input mul-
tiplexing capability, while the second PGA only needs
one input. These devices can be daisy chained
(Section 5.3, “Daisy Chain Configuration”).
FIGURE 6-6: PGA with Extended Gain
Range.
6.4.4 MULTIPLE SENSOR AMPLIFIER
The multiple channel PGAs (except the MCP6S21)
allow the user to select which sensor appears on the
output (see Figure 6-7). These devices can also
change the gain to optimize performance for each
sensor.
FIGURE 6-7: PGA with Multiple Sensor
Inputs.
MCP6S2X
V
OUT
I
X
R
S
V
IN
MCP6021
MCP6S21
V
OUT
10.0 k
1.11 k


V
IN
MCP6021
MCP6S21
V
OUT
10.0 k
1.11 k


V
IN
V
OUT
MCP6S28
MCP6S21
Sensor # 0
Sensor # 1
Sensor # 5
MCP6S26
V
OUT