MCP3461RT-ESLASHST datasheet(53/118 Pages) MICROCHIP

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DS20006404C-page 53

MCP3461/2/4R

5.9

ADC Operating Modes

The ADC can be placed into three different operating

modes: ADC Shutdown, Standby and Conversion. The

ADC operating mode is controlled by the user through

the ADC_MODE[1:0] bits in the CONFIG0 register. The

user can directly launch conversions or place the ADC

into ADC Shutdown or Standby mode by writing these

bits. Additional Fast commands are available for each

of the three possible states of these bits to allow faster

programming in case of time-sensitive applications

(see Section 6.2.4 “Command-Type Bits (CMD[1:0])”).

Table 5-10 describes the available ADC_MODE[1:0]

bits setting.

The ADC_MODE[1:0] bits do not give an instantaneous

representation

the ADC

state.

Writing

the

ADC_MODE[1:0] bits sets the desired state of the ADC,

but this state is only attained after a start-up time depend-

ing on the current state of the ADC (see Section 5.11

“ADC Start-up Timer” for details about the start-up

timer). Typically, the device starts in ADC Shutdown

mode after a POR (ADC_MODE[1:0] = 00 by default). To

launch conversions in the desired configuration, the user

should program the part in the desired configuration and

then set the ADC_MODE[1:0] bits to ‘11’. In this case, the

first conversion will start after TADC_SETUP = 256 DMCLK

periods. This time is necessary for the part to adjust to the

new programmed settings and settle in to its operating

point to accurately convert the input signals.

Internally, the device tracks the current state of the

ADC, as well as the start-up timer counter, to be able to

optimize the start-up time depending on the desired

transitions and internal configurations required, and set

by the user.

In MUX mode, overwriting the ADC_MODE[1:0] bits to

‘11’ when the ADC is already in conversion resets and

restarts the current conversion immediately. The

conversion start pulse will also be regenerated if the

EN_STP bit is enabled.

In Scan mode (see Section 5.15 “Scan Mode”),

writing the ADC_MODE[1:0] bits to ‘11’ starts the

conversion Scan cycle. During the complete cycle,

even when the scan timer is enabled, reading the

ADC_MODE[1:0] bits gives a ‘11’ code output, mean-

ing that the Scan cycle is ongoing. Rewriting

ADC_MODE[1:0] = 11 during Scan mode will immedi-

ately reset and restart the entire Scan sequence from

the beginning of the sequence. The conversion start

pulse will also be regenerated if the EN_STP bit is

enabled. The restart of the Scan sequence may induce

a TADC_SETUP additional delay if the ADC is in ADC

Shutdown mode when the ADC_MODE bits are over-

written (this can happen if the ADC_MODE bits are

overwritten during the timer delay period, where the

ADC is placed into ADC Shutdown mode in between

two Scan cycles).

The ADCDATA register is always updated with the last

conversion results. The ADCDATA register cannot

provide incomplete conversion results. The A/D con-

version must be completed to be able to provide a

result in the ADCDATA register. Each end of conver-

sion generates a data ready interrupt on all three IRQ

mechanisms (see Section 6.8.1 “Conversion Data

Ready Interrupt”). The ADCDATA register is never

cleared when the device transitions from one mode to

another. The only way to clear the ADCDATA register is

a POR event or a Full Reset Fast command (see

Section 6.2.5 “Fast Commands Description”).

TABLE 5-10:

ADC OPERATING MODES DESCRIPTION

ADC_MODE[1:0]

ADC Mode

Description

Conversion

The ADC is placed into Conversion mode and consumes the specified

current. A/D conversions can be reset and restarted immediately once this

mode is effectively reached. This mode may be reached after a maximum of

TADC_SETUP time, depending of the current state of the ADC.

Standby

Conversions are stopped. ADC is placed into Reset but consumes almost

as much current as in Conversion mode. A/D conversions can start immedi-

ately once this mode is effectively reached. This mode may be reached after

a maximum of TADC_SETUP time, depending of the current state of the ADC.

ADC Shutdown

Conversions are stopped. ADC is placed into ADC Shutdown mode and

does not consume any current. A/D conversions can only start after

TADC_SETUP start-up time. This mode is effective immediately after being

programmed.

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