MCP3461RT-ESLASHST datasheet(54/118 Pages) MICROCHIP

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MCP3461/2/4R

DS20006404C-page 54

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5.10

Low-Power Shutdown Modes

The device incorporates two low-power modes that can

be activated in order to limit power consumption of the

device when ADC is not used. These two modes are

called Partial Shutdown and Full Shutdown modes.

5.10.1

FULL SHUTDOWN MODE

The Full Shutdown mode can only be enabled by

sending a Fast Command Full Shutdown (Fast com-

mand code: ‘1101’). Note that the execution of this

Fast command forces the CONFIG0 to be set to 0x00

(no active block is enabled).

Full Shutdown mode is the lowest power mode of the

device. None of the circuits consuming static power are

active in this mode.

As stated in Section 5.8 “Power-on Reset”, the

AVDD/DVDD POR monitoring circuits are not active

while in Full Shutdown mode.

The part can still be accessed through the SPI interface

during this mode and will accept incoming SPI

commands. The ADCDATA register is not cleared

during Full Shutdown mode and still holds previous

conversion results. The other register settings are not

modified or reset due to entering Full Shutdown mode.

The Full Shutdown mode stops all internal timers and

resets them. Sending a Fast CMD to change the

operating mode exits the Full Shutdown mode.

The user should place all digital inputs to a static value

(logic low or high) in order to optimize power consumption

during Full Shutdown mode. The current consumption

specifications during Full Shutdown mode are intended

without any digital pin toggling during the measurement.

In this case, only leakage current is consumed throughout

the device and this current varies exponentially with

respect to absolute temperature.

5.10.2

PARTIAL SHUTDOWN MODE

Partial Shutdown mode is achieved when CONFIG0 is

set to ‘0000000x’. In this mode, most of the internal

circuits are shut down, with the exception of the POR

monitoring and internal biasing circuits. During the

Partial Shutdown mode, the power supply is continu-

ously monitored, whereas in Full Shutdown mode, the

POR monitoring circuits are powered down. The power

consumption is also much higher in Partial Shutdown

mode due to the POR monitoring circuits being active.

Partial Shutdown mode allows the device to be

restarted and put back in Conversion mode faster than

Full Shutdown mode. Table 5-11 describes the differ-

ences between Partial and Full Shutdown modes. If the

current consumption of Partial Shutdown mode is

acceptable for the application, it is recommended that

it is used as an alternative to Full Shutdown mode,

where the POR monitoring circuits are shut down and

no longer monitoring the AVDD and DVDD power

supplies.

Note:

If the digital power supply resides for a long

period of time below the POR threshold

and to a sufficiently low voltage (typically

below 0.6V), some bits previously set to ‘1’

can toggle to ‘0’ and not be set properly.

In order to ensure a safe operation after

the Full Shutdown mode, follow the

sequence of commands:

- Write LOCK register to 0xA5

- Write IRQ register to 0x03

- Send a Fast CMD Full Reset (1110)

- Reconfigure the chip as desired

This sequence ensures a recovery with

the desired settings in any loss-of-power

scenario.

TABLE 5-11:

LOW-POWER MODES(1)

Device

Low-Power Mode

VREF_SEL CONFIG0[6] CLK_SEL[1:0] CS_SEL[1:0] ADC_MODE[1:0]

Description

Partial Shutdown

All peripherals, except the POR

monitoring circuits and clock bias-

ing circuits, are shut down and

consume no static current.The SPI

interface remains active in this

mode and consumes no current

while the bus is Idle.

Full Shutdown

All analog and digital circuits are

shut down and consume no static

current. The SPI interface remains

active in this mode and consumes

no current while the bus is Idle.

Note 1:

x = Don’t Care

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