MCP3465R datasheet(50/110 Pages) MICROCHIP

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MCP3465R

DS20006414C-page 50

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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 of 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

depending 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 neces-

sary 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.

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,

meaning 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 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 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. The ADCDATA register cannot

provide incomplete conversion results. The A/D

conversion 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 both IRQ

mechanisms (see Section 6.8.1 “Conversion Data

Ready (DR) Interrupt”). The ADCDATA register is

never cleared when the device transitions from one

mode to another. The only way to clear the ADCDATA

(see Section 6.2.5 “Fast Commands Description”).

Note:

Since there is no IRQ pin, the IRQ

mechanisms are the STATUS byte and

IRQ register bits.

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 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 immedi-

ately 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.

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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