Datasheet

 2003-2012 Microchip Technology Inc. DS21117B-page 27
MCP6S21/2/6/8
6.4.5 EXPANDED INPUT PGA
Figure 6-8 shows cascaded MCP6S28s that provide
up to 15 input channels. Obviously, Sensors #7-14
have a high total gain range available, as explained in
Section 6.4.3, “Extended Gain Range”. These devices
can be daisy chained (Section 5.3, “Daisy Chain
Configuration”).
FIGURE 6-8: PGA with Expanded Inputs.
6.4.6 PIC MCU WITH EXPANDED INPUT
CAPABILITY
Figure 6-9 shows an MCP6S28 driving an analog input
to a PIC microcontroller. This greatly expands the input
capacity of the microcontroller, while adding the ability
to select the appropriate gain for each source.
FIGURE 6-9: Expanded Input for a PIC
®
Microcontroller.
6.4.7 ADC DRIVER
The family of PGA’s is well suited for driving Analog-to-
Digital Converters (ADC). The binary gains (1, 2, 4, 8,
16 and 32) effectively add five more bits to the input
range (see Figure 6-10). This works well for applica-
tions needing relative accuracy more than absolute
accuracy (e.g., power monitoring).
FIGURE 6-10: PGA as an ADC Driver.
At low gains, the ADC’s Signal-to-Noise Ratio (SNR)
will dominate since the PGAs input noise voltage den-
sity is so low (10 nV/Hz @ 10 kHz, typ.). At high gains,
the PGA’s noise will dominate the SNR, but its low
noise supports most applications. Again, 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 MCP6S28’s output and serves
as an anti-aliasing filter. This filter may be designed
using Microchip’s FilterLab
®
software, available at
www.microchip.com.
Sensors
Sensors
MCP6S28
MCP6S28
V
OUT
# 0-6
# 7-14
V
IN
MCP6S28
PIC
®
Microcontroller
SPI™
V
IN
OUT
MCP6S28
Lowpass
Filter
12
MCP3201