Datasheet

 2004 Microchip Technology Inc. DS21908A-page 30
MCP6S91/2/3
6.4.5 EXPANDED INPUT PGA
Figure 6-10 shows cascaded MCP6S28 and
MCP6S92s PGAs that provide up to 9 input channels.
Obviously, Sensors #1-8 have a high total gain range
available, as explained in Section 6.4.3 “Extended
Gain Range PGA”. These devices can be daisy-
chained (Section 5.3 “Daisy-Chain Configuration”).
FIGURE 6-10: PGA with Expanded Inputs.
6.4.6 PICmicro
®
MCU WITH EXPANDED
INPUT CAPABILITY
Figure 6-11 shows a MCP6S93 driving an analog input
to a PICmicro microcontroller. This greatly expands the
input capacity of the microcontroller, while adding the
ability to select the appropriate gain for each source.
FIGURE 6-11: Expanded Input for a
PICmicro
®
Microcontroller.
6.4.7 ADC DRIVER
This family of PGAs is well suited for driving Analog-to-
Digital Converters (ADCs). The binary gains (1, 2, 4, 8,
16 and 32) effectively add five more bits to the input
range (see Figure 6-12). This works well for applica-
tions needing relative accuracy more than absolute
accuracy (e.g., power monitoring).
FIGURE 6-12: PGA as an ADC driver.
At low gains, the ADC’s Signal-to-Noise Ratio (SNR)
will dominate since the PGA’s input noise voltage
density is so low (10 nV/√Hz @ 10 kHz, typ.). At high
gains, the PGA’s noise will dominate the SNR, but it is
low enough to support most applications. These PGAs
add the flexibility of selecting the best gain for an
application.
The low-pass filter in the block diagram reduces the
integrated noise at the MCP6S92’s output and serves
as an anti-aliasing filter. This filter may be designed
using Microchip’s FilterLab
®
software, available at
www.microchip.com.
Sensor
V
OUT
MCP6S92
# 0
Sensors
MCP6S28
# 1-8
V
IN
SPI
™
MCP6S93
PICmicro
®
Microcontroller
OUT
MCP3201
12-bit
ADC
3
MCP6S92V
IN
Low-pass
Filter