MCP3461RT-ESLASHST datasheet(59/118 Pages) MICROCHIP

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DS20006404C-page 59

MCP3461/2/4R

5.14

Conversion Modes

The ADC includes several Conversion modes that can

be selected through the CONV_MODE[1:0] bits located

in the CONFIG3 register. The ADC behavior, with

respect to these bits, depends on whether the ADC is

in MUX or Scan mode. Table 5-14 summarizes the

possible configurations.

5.14.1

CONVERSION MODES IN MUX

MODE

In MUX mode, the user can choose between one-shot

and continuous conversions.

A one-shot conversion is a single conversion and takes

a certain Conversion Time, TCONV (or 2 x TCONV when

AZ_MUX = 1, see Section 5.1.3 “ADC Offset Cancel-

lation Algorithm”).

Once

this

conversion

performed, the part automatically returns to a Standby

or ADC

Shutdown

state,

depending

the

CONV_MODE[1:0] bits setting. The Conversion mode

determined by the CONV_MODE[1:0] bits setting will

also affect the state of the ADC_MODE[1:0] as

described in Table 5-14.

The conversion can be preceded by a start-up time that

depends on the ADC state (see Section 5.11 “ADC

Start-up Timer”). In One-Shot mode, the ADC data

have to be read completely with the SPI interface for

the interrupt to be cleared on the IRQ pin (the IRQ pin

cannot be automatically cleared like in the Continuous

Conversion mode).

This mode is recommended for low-power, low

bandwidth applications, requiring a once in a while A/D

conversion.

In Continuous Conversion mode, the ADC is never

placed in Standby or ADC Shutdown mode and con-

verts continuously without any internal Reset. In this

mode, the output data rate of the ADC is defined by

DRCLK (see Figure 5-5). The digital decimation filter

induces a pipeline or group delay of TCONV for the first

data ready and is structured to give a continuous

stream of data at the DRCLK rate after these first data

(the internal registers of the filter are never reset in this

mode, thus the decimation filter acts as a moving aver-

age). Each data ready interrupt corresponds to a valid

and complete conversion that was processed through

the digital filter (the digital filter has no latency in this

respect). This mode allows a faster data rate than the

One-Shot mode, and is therefore, recommended for

higher bandwidth applications. The pipeline delay

should be carefully determined and adapted to the user

needs, especially in closed-loop, low-latency applica-

tions. This mode is recommended for applications

requiring continuous sampling/averaging of the input

signals. If AZ_MUX = 1, the Continuous Conversion

mode is replaced by a series of subsequent One-Shot

mode conversions with a reset in between each

conversion. This makes the group delay equal to

2x TCONV and the data rate equal to 1/(2 x TCONV).

Figure 5-14 and Figure 5-15 detail One-Shot and

Continuous Conversion modes for MUX mode.

TABLE 5-14:

ADC CONVERSION MODES IN MUX OR SCAN MODES

CONV_MODE[1:0]

ADC Behavior (MUX Mode)

ADC Behavior

(Scan Mode)

ADC_MODE[1:0] Bits Setting

Performs a one-shot conversion

and automatically returns to

ADC Shutdown mode.

Performs one complete

Scan cycle and

automatically returns to

ADC Shutdown mode.

Returns to ‘0x’ after one

conversion (MUX mode) or one

Scan cycle (Scan mode).

Performs a one-shot conversion

and automatically returns to

Standby mode.

Performs one complete

Scan cycle and

automatically returns to

Standby mode.

Returns to ‘10’ after one

conversion (MUX mode) or one

Scan cycle (Scan mode).

Performs continuous

conversions.

Performs continuous Scan

cycles with TIMER[23:0]

delay between each cycle.

Stays at ‘11’.

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