MCP6S21 datasheet(27/43 Pages) MICROCHIP

27 / 43 page

 2003 Microchip Technology Inc.

DS21117A-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

PICmicro® MCU WITH EXPANDED

INPUT CAPABILITY

Figure 6-9 shows an MCP6S28 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 6-9:

Expanded Input for a

PICmicro 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

MCP6S28

VOUT

# 0-6

# 7-14

VIN

MCP6S28

PICmicro®

Microcontroller

SPI™

VIN

OUT

MCP6S28

Lowpass

Filter

MCP3201

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