MCP3461RT-ESLASHST datasheet(38/118 Pages) MICROCHIP

38 / 118 page

MCP3461/2/4R

DS20006404C-page 38

 2020-2021 Microchip Technology Inc.

The possible selections are described in Table 5-1 and

can be set with the MUX[7:0] register bits during the

MUX mode. The MUX[7:4] bits define the selection for

the VIN+ (noninverting analog input of the ADC). The

MUX[3:0] bits define the selection for the VIN- (inverting

analog input of the ADC).

During Scan mode, the two single-ended input

multiplexers are automatically set to a certain position,

depending on the Scan sequence and which channel

has been selected by the user. The Scan sequence

channels’ configuration corresponds to a certain code

in the MUX[7:0] register bits, as defined in Table 5-15.

In order to monitor the Digital Power Supply (DVDD), it

is necessary to connect DVDD externally to one of the

CHn analog inputs, since DVDD is not one of the pos-

sible selections of the analog multiplexer. A similar

setup can be implemented to monitor DGND if DGND is

not connected externally to AGND.

For MCP3461R and MCP3462R, some codes are not

available in the selection since the pins are not bonded

out on these devices. These codes should then be

avoided in the application, as the input they connect to

is effectively a high-impedance node.

The TEMP Diodes P and M are two internal diodes that

are biased by a current source, and that can be used to

perform a temperature measurement. If TEMP Diode P

is connected to VIN+ and TEMP Diode M to VIN-, then

the ADC output code is a function of the temperature

using Equation 5-1 (see Section 5.1.2, Internal Tem-

perature Sensor for more details). The VCM selection

measures the internal Common-mode voltage source

that biases the Delta-Sigma modulator (this voltage is

not provided at any output of the part).

The possible inputs of the analog multiplexer include

not only the analog input channels, but also REFIN+/-

inputs, AVDD and AGND, as well as temperature sensor

outputs and the VCM internal Common-mode. This

large selection offers many possibilities for measuring

internal or external data resources of the system and

can serve as diagnostic purposes to increase the

security of the applications. Some monitor channels

are already predefined in Scan mode to further help

users to integrate diagnostics to their applications (for

example, the analog power supply or the temperature

can be constantly monitored in Scan mode; see

Section 5.15.3 “Scan Mode Internal Resource

Channels” for more details of the different resources

that can be monitored in Scan mode).

TABLE 5-1:

ANALOG INPUT MUX DECODING

MUX[7:4] (VIN+) or

MUX[3:0] (VIN-) Code

Selected

Channel

Comment

0000

CH0

0001

CH1

0010

CH2

Not Connected (NC) for MCP3461R

0011

CH3

Not Connected (NC) for MCP3461R

0100

CH4

Not Connected (NC) for MCP3461R/MCP3462R

0101

CH5

Not Connected (NC) for MCP3461R/MCP3462R

0110

CH6

Not Connected (NC) for MCP3461R/MCP3462R

0111

CH7

Not Connected (NC) for MCP3461R/MCP3462R

1000

AGND

1001

AVDD

1010

Reserved

Do not use

1011

REFIN+/OUT

1100

REFIN-

1101

TEMP Diode P

1110

TEMP Diode M

1111

Internal VCM

Internal Common-mode voltage for modulator biasing

Note:

When VREF_SEL = 0 (external VREF) and

REFIN+/OUT and REFIN- are selected as

analog inputs for the ADC, the same

REFIN+/OUT and REF- pin voltages are

used as the reference for the ADC. This

diagnostic mode is useful for determining

the full-scale Gain error of the ADC when

a Gain setting of 1/3x or 1x is used.

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