MCP6S92 datasheet(30/40 Pages) MICROCHIP

30 / 40 page

 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

VOUT

MCP6S92

# 0

Sensors

MCP6S28

# 1-8

VIN

SPI™

MCP6S93

PICmicro®

Microcontroller

OUT

MCP3201

12-bit

ADC

MCP6S92

VIN

Low-pass

Filter

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