MCP3461RT-ESLASHST datasheet(30/118 Pages) MICROCHIP

30 / 118 page

MCP3461/2/4R

DS20006404C-page 30

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3.1

Differential Reference Voltage

Inputs: REFIN+/OUT, REFIN-

The REFIN+/OUT pin is the noninverting differential

reference input (VREF+) when VREF_SEL = 0. When

VREF_SEL = 1, it is the internal voltage reference out-

put voltage as well as the ADC voltage noninverting

reference pin.

The REFIN- pin is the inverting differential reference

input (VREF-).

For single-ended reference applications, the REFIN-

pin should be directly connected to AGND.

The differential reference voltage pins must respect

this condition at all times: 0.6V ≤ VREF ≤ AVDD. The

differential reference voltage input is given by the

following equation:

EQUATION 3-1:

For optimal ADC accuracy, appropriate bypass

capacitors should be placed between REFIN+/OUT

and AGND at all times. Using a 0.1 µF and a 10 µF

ceramic capacitor can help to decouple the reference

voltage around the sampling frequency (which would

lead to aliasing noise in the baseband). These bypass

capacitors are not mandatory for correct ADC opera-

tion, but removing these capacitors may degrade the

accuracy of the ADC.

3.2

Analog Inputs (CHn): Differential

or Single-Ended

The CHn pins are the analog input signal pins for the

ADC. Two analog multiplexers are used to connect the

CHn pins to the VIN+/VIN- analog inputs of the ADC.

Each multiplexer independently selects one input to be

connected to an ADC input (VIN+ or VIN-). Each CHn

pin can either be connected to the VIN+ or VIN- inputs

of the ADC. This multiplexer selection is controlled by

either the MUX register in MUX mode or the SCAN

on the multiplexer structure.

When the input is selected by the multiplexer, the

differential (VIN) and Common-Mode Voltage (VINCOM)

at the ADC inputs are defined by:

EQUATION 3-2:

The input signal level is multiplied by the internal

programmable analog gain at the front end of the

Delta-Sigma

modulator.

For

single-ended

input

measurements, the user can select VIN- to be internally

connected to AGND.

The differential input voltage should not exceed an

absolute of ±VREF/Gain for accurate measurement. If

the input is out of range, the converter output code will

be saturated or overloaded depending on how the out-

put data format (DATA_FORMAT[1:0]) is selected. See

Section 5.6 “ADC Output Data Format” for further

information on the ADC output coding.

The absolute voltage on each of the analog signal

input pins can range from AGND – 0.1V to VDD + 0.1V.

Any voltage above or below this range will cause leak-

age currents through the Electrostatic Discharge

(ESD) diodes at the input pins. This ESD current can

cause unexpected performance of the device. The

Common-mode of the analog inputs should be chosen

such that both the differential analog input range and

the absolute voltage range on each pin are within the

specified operating range defined in the Electrical

Characteristics table.

3.3

SPI Serial Interface

Communication Pins

The SPI interface is compatible with both SPI Mode 0,0

and 1,1.

3.3.1

CHIP SELECT (CS)

This is the SPI Chip Select pin that enables/disables

the SPI serial communication. The CS falling edge

initiates the serial communication and the rising edge

terminates the communication. No communication can

take place when this pin is in a Logic High state. This

input is Schmitt Triggered.

3.3.2

SERIAL DATA CLOCK (SCK)

This is the serial clock input pin for SPI communication.

This input has a Schmitt Trigger structure. The maxi-

mum SPI clock speed is 20 MHz. Data are clocked into

the device on the rising edge of SCK. Data are clocked

out of the device on the falling edge of SCK. The device

interface is compatible with both SPI Mode 0,0 and 1,1.

SPI modes can be changed when CS is in Logic High

status.

SCK and MCLK are two different and asynchronous

clocks. SCK is only required during a communication,

while MCLK is continuously required when the part

converts analog inputs.

VREF

VREF+ VREF-

–

VIN

VIN+ VIN-

–

VINCOM

VIN+ VIN-

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