MCP3461 datasheet(32/108 Pages) MICROCHIP

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MCP3461/2/4

DS20006180D-page 32

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The possible selections are described in Table 5-1 and

can be set with the MUX[7:0] register 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 on which channel

has been selected by the user. The SCAN sequence

channels’ configuration corresponds to a certain code in

the MUX[7:0] register, as defined in Table 5-14.

In order to monitor the digital power supply (DVDD), it is

necessary to externally connect DVDD 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 MCP3461 and MCP3462, 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

Temperature Sensor” for more details).

The

“VCM”

selection

measures

the

internal

Common-mode voltage source that biases the

Sigma-Delta 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 the

REFIN+/- inputs, AVDD and AGND, as well as tempera-

ture sensor outputs and 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 appli-

cations (for example, the analog power supply or the

temperature can be constantly monitored in SCAN

mode; see Section 5.14.3 “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 TABLE

MUX[7:4] (VIN+) or

MUX[3:0] (VIN-) Code

Selected

Channel

Comment

0000

CH0

0001

CH1

0010

CH2

Not Connected (NC) for MCP3461

0011

CH3

Not Connected (NC) for MCP3461

0100

CH4

Not Connected (NC) for MCP3461, MCP3462

0101

CH5

Not Connected (NC) for MCP3461, MCP3462

0110

CH6

Not Connected (NC) for MCP3461, MCP3462

0111

CH7

Not Connected (NC) for MCP3461, MCP3462

1000

AGND

1001

AVDD

1010

Reserved

Do not use

1011

REFIN+

1100

REFIN-

1101

TEMP Diode P

1110

TEMP Diode M

1111

Internal VCM

Internal Common-mode voltage for modulator biasing

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