MCP3462R-ESLASHST datasheet(86/118 Pages) MICROCHIP

86 / 118 page

MCP3461/2/4R

DS20006404C-page 86

 2020-2021 Microchip Technology Inc.

The ADC can be used in Differential or Single-Ended

mode due to the internal dual multiplexer (Figure 5-1).

The user can select the input connection settings from

the MUX register (Section 8.7 “Multiplexer (MUX)

the positive and negative inputs of the ADC. The

single-ended configuration is achieved by selecting

AGND for the VIN- input of the ADC (MUX[3:0] = 1000)

or by selecting any CHn input channel for VIN- and

connecting the corresponding CHn input channel to

AGND.

7.1.1

HIGH-SIDE AND LOW-SIDE

CURRENT SENSING

The ADC has the ability to perform differential

measurements with an analog input Common-mode

equal to or slightly larger than AVDD, or equal to or slightly

lower than AGND (see the Electrical Characteristics

table).

A differential input structure and a Kelvin connection

are required in order to achieve the most accurate

measurements. An anti-aliasing filter is required to

avoid aliasing of the oversampling frequency (DMCLK)

back into the baseband of the input signal and possible

corruption of the output data. Figure 7-1 provides an

example of an anti-aliasing filter.

For the measurement of voltages that can reach AVDD

or a few mV higher, a gain setting of 0.33x is useful

since it increases the input range to a 3 x VREF value,

so a 1.2V VREF will allow a theoretical input range of

3.6V. However, the maximum voltage that can be

measured is always bounded by AVDD + 0.1V in order

to limit excess leakage current at the input pins created

by the ESD structures. Therefore, in order to properly

measure 3.6V with a 1.2V voltage reference, it is

recommended to use an AVDD supply voltage as close

as possible to 3.6V.

7.1.2

THERMOCOUPLE CONNECTION

One of the most used temperature transducers in the

industry is the thermocouple. Thermocouples provide a

voltage dependent on the temperature difference

between cold junction and hot junction. This voltage is

in the order of magnitude of tens of µV/°C, which

requires amplification that can be provided by the

internal gain stage of the ADC.

FIGURE 7-2:

Thermocouple Connection

to MCP3461R.

The connection of the thermocouple to the ADC

requires minimal extra components. A differential input

structure is recommended. The cold junction can be

measured by using a digital temperature sensor, such

as MCP9804, connected to the MCU. If high accuracy

is not required, the cold junction temperature can be

estimated directly with the internal temperature sensor

of the ADC (see Figure 7-2).

7.2

Typical Application for

Ratiometric Voltage Measurement

A wide range of sensors provides an output voltage

directly related to the power supply of the sensors.

These sensors are known as ratiometric output. These

sensors often have a Wheatstone bridge structure,

such as pressure sensors or load cells (Figure 7-3).

FIGURE 7-3:

Wheatstone Bridge

Ratiometric Connection.

Others act as a single resistor with a value dependent

on temperature (pure metal resistance thermometer

RTD and negative temperature coefficient resistor

NTC). To accurately measure the signal from these

sensors, REFIN+/OUT is usually connected to the

same power supply of the sensor (Figure 7-4), as long

as this respects the specified voltage range on the

REFIN+/OUT pin (see the Electrical Characteristics

table.

FIGURE 7-4:

RTD Ratiometric Connection.

VIN+

VIN-

REFIN+/OUT

REFIN-

MCP3461R

Input

Signal

RTD

Anti-aliasing

Filter

Sensor

VIN+

VIN-

REFIN+/OUT

REFIN-

MCP3461R

AGND

DGND

MCP3462R-E/ST Datasheet(PDF) 86 Page - Microchip Technology

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