MCP33131 datasheet(31/54 Pages) MICROCHIP

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 2018 Microchip Technology Inc.

DS20006122A-page 31

MCP33131/MCP33121/MCP33111-XX

6.1.1

INPUT VOLTAGE RANGE

The device has two analog input pins: AIN+ and AIN-

pins. The analog input signal is applied to the AIN+ pin,

and the ground reference of the input signal is tied to

the AIN- pin.

The voltage difference between AIN+ and AIN- is the

ADC input (VIN) and needs to be between 0V and

+VREF to produce unsaturated output codes.

Equation 6-4 shows the input full-scale range (FSR)

and input range.

The device will output unipolar straight binary codes for

the analog input. If the input (VIN) is greater than the

reference voltage (VREF), the output code will be

saturated. If the input (VIN) is less than or equals to 0V,

the output will be all 0’s.

EQUATION 6-1:

FSR AND INPUT RANGE

6.2

Analog Input Conditioning Circuit

The MCP33131/MCP33121/MCP33111-XX can be

driven directly when the source impedance of the input

driver is low.

Large source impedance of the input signal may affect

the ADC’s performance. In general, the source imped-

ance is less sensitive to the ADC’s DC performances

such as INL and DNL. However, it affects significantly

to the dynamic performances such as THD, SFDR and

SNR.

Therefore, it is a good design practice to isolate the

ADC input from the high impedance source using a low

noise input driver amplifier. Figure 6-1 shows an input

configuration example using a low-noise OP amplifier

such as MCP6286 and Figure 6-2 shows the transfer

function of the MCP33131/MCP33121/MCP33111-XX.

FIGURE 6-1:

Unipolar-Input Application Example

FIGURE 6-2:

Transfer Function for Figure 6-1.

0VVIN

VREF 1LSB

–





VREF

Input Full-Scale Range (FSR)

Input Range:

where VIN = AIN+ - AIN-

Note 1: Contact Microchip Technology Inc. for more selections of the low-noise input driver amplifiers.

(Note 1)

2: Contact Microchip Technology Inc. for the MCP1501 application circuit.

AIN+

F

Reference

Voltage

AIN-

VREF AVDD DVIO

SDI

SCLK

SDO

CNVST

1.8V

1.7V to 5.5V

GND

VREF

(PIC32MZ)

Host Device

(Note 2)

VDC

Analog Input

(22

±0.1%)

(1.7nF, NPO)

VREF

MCP331x1-XX

2.5V to 5.1V

0.1

F

0.1

F

R1C1

C =

MCP6286

VIN

MCP1501

Ground Reference of

Analog Input

(Tantalum)

Analog Input Voltage

+VREF

Digital Output Code

VIN (V)

+VREF/2

2n/2

VIN range

2n - 1

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