Datasheet

 2004 Microchip Technology Inc. DS21908A-page 29
MCP6S91/2/3
6.4 Typical Applications
6.4.1 GAIN RANGING
Figure 6-5 shows a circuit that measures the current I
X
.
The circuit’s performance 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 6-5: Wide Dynamic Range
Current Measurement Circuit.
6.4.2 SHIFTED GAIN RANGE PGA
Figure 6-6 shows a circuit using a MCP6291 at a gain
of +10 in front of a MCP6S91. This shifts the overall
gain range to +10 V/V to +320 V/V (from +1 V/V to
+32 V/V).
FIGURE 6-6: PGA with Higher Gain
Range.
It is also easy to shift the gain range to lower gains (see
Figure 6-7). The MCP6291 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 6-7: PGA with Lower Gain
Range.
6.4.3 EXTENDED GAIN RANGE PGA
Figure 6-8 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
multiplexing capability, while the second PGA only
needs one input. These devices can be daisy-chained
(Section 5.3 “Daisy-Chain Configuration”).
FIGURE 6-8: PGA with Extended Gain
Range.
6.4.4 MULTIPLE SENSOR AMPLIFIER
The multiple-channel PGAs (MCP6S92 and MCP6S93)
allow the user to select which sensor appears on the
output (see Figure 6-9). These devices can also change
the gain to optimize performance for each sensor.
FIGURE 6-9: PGA with Multiple Sensor
Inputs.
I
X
V
OUT
MCP6S9X
R
S
V
IN
V
OUT
MCP6291
MCP6S91
1.11 kΩ
10.0 kΩ
V
IN
MCP6291
1.11 kΩ
10.0 kΩ
V
OUT
MCP6S91
V
IN
V
OUT
MCP6S92
MCP6S91
Sensor # 0
V
OUT
MCP6S93
Sensor # 1