MCP3421 datasheet(15/42 Pages) MICROCHIP

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DS22003E-page 15

MCP3421

5.0

USING THE MCP3421 DEVICE

5.1

Operating Modes

The user operates the device by setting up the device

configuration register using a write command (see

Figure 5-2) and reads the conversion data using a read

command (see Figure 5-3 and Figure 5-4). The device

operates in two modes: (a) Continuous Conversion

Mode or (b) One-Shot Conversion Mode (single

conversion). This mode selection is made by setting

the O/C bit in the Configuration Register. Refer to

Section 5.2 “Configuration Register” for more

information.

5.1.1

CONTINUOUS CONVERSION

MODE (O/C BIT = 1)

The device performs a Continuous Conversion if the

O/C bit is set to logic “high”. Once the conversion is

completed, RDY bit is toggled to ‘0’ and the result is

placed at the output data register. The device

immediately begins another conversion and overwrites

the output data register with the most recent result. The

device clears the data ready flag (RDY bit = 0) when

the conversion is completed. The device sets the ready

flag bit (RDY bit = 1), if the latest conversion result has

been read by the Master.

• When writing configuration register:

- Setting RDY bit in continuous mode does not

affect anything

• When reading conversion data:

- RDY bit = 0 means the latest conversion

result is ready

- RDY bit = 1 means the conversion result is

not updated since the last reading. A new

conversion is under processing and the RDY

bit will be cleared when the new conversion

result is ready

5.1.2

ONE-SHOT CONVERSION MODE

(O/C BIT = 0)

Once the One-Shot Conversion (single conversion)

Mode is selected, the device performs only one

conversion, updates the output data register, clears the

data ready flag (RDY = 0), and then enters a low power

standby mode. A new One-Shot Conversion is started

again when the device receives a new write command

with RDY = 1.

• When writing configuration register:

- The RDY bit needs to be set to begin a new

conversion in one-shot mode

• When reading conversion data:

- RDY bit = 0 means the latest conversion

result is ready

- RDY bit = 1 means the conversion result is

not updated since the last reading. A new

conversion is under processing and the RDY

bit will be cleared when the new conversion is

done

This

One-Shot

Conversion

Mode

highly

recommended for low power operating applications

where the conversion result is needed by request on

demand. During the low current standby mode, the

device consumes less than 1 µA maximum (or 300 nA

typical). For example, if the user collects 18 bit

conversion

data

once

second

One-Shot

Conversion mode, the device draws only about one

fourth of its total operating current. In this example, the

device consumes approximately 39 µA (145 µA / 3.75

SPS = 39 µA), if the device performs only one

conversion per second (1 SPS) in 18-bit conversion

mode with 3V power supply.

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