MCP3464T-ESLASHST datasheet(45/108 Pages) MICROCHIP

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DS20006180D-page 45

MCP3461/2/4

5.8

ADC Operating Modes

The ADC can be placed into three different operating

modes: ADC Shutdown, Standby and Conversion. The

ADC operating mode is controlled directly by the user

using 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

directly to 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])”). The different ADC_MODE[1:0] bits

settings available are described in Table 5-9.

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

representation of the state of the ADC. 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

depending on the current state of the ADC. See

Section 5.10 “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 in this

case if the EN_STP bit was enabled.

In SCAN mode (see Section 5.14 “SCAN Mode”), writ-

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

SCAN cycle. During the whole cycle, even when the scan

timer is enabled, reading the ADC_MODE[1:0] bits will

give a ‘11’ code output, meaning that the SCAN cycle

is ongoing. Rewriting ADC_MODE[1:0] = 11 during

SCAN mode will immediately reset and restart the

whole SCAN sequence, from the beginning of the

sequence. The conversion start pulse will also be

regenerated in this case if the EN_STP bit was

enabled. The restart of the SCAN sequence may

induce a TADC_SETUP additional delay if the ADC was

effectively in ADC Shutdown mode when the

ADC_MODE bits are overwritten (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 only. The ADCDATA register cannot

provide incomplete conversion results. The A/D

conversion needs to 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 ADC Output register

is a POR event or a full Reset Fast command. See

Section 6.2.5 “Fast Commands Description”.

TABLE 5-9:

ADC OPERATING MODES DESCRIPTION

ADC_MODE[1:0]

ADC Mode

Description

Conversion

The ADC is placed into Conversion mode and consumes the specified current

(see the Electrical Characteristics table). 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 on 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 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.

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

no current. A/D conversions can start only after TADC_SETUP start-up time. This

mode is effective immediately after being programmed.

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