MCP4728 datasheet(28/66 Pages) MICROCHIP

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MCP4728

DS22187C-page 28

4.10

Normal and Power-Down Modes

Each channel has two modes of operation: (a) Normal

mode where analog voltage is available and (b)

Power-Down mode which turns off most of the internal

circuits for power savings.

The user can select the operating mode of each

channel individually by setting the Power-Down

selection bits (PD1 and PD0). For example, the user

can select normal mode for channel A while selecting

power-down mode for all other channels.

See

Section 5.6 “Write Commands for DAC

Registers and EEPROM” for more details on the

writing the power-down bits.

Most of the internal circuit in the powered down chan-

nel are turned off. However, the internal voltage refer-

ence circuit is not affected by the Power-Down mode.

The internal voltage reference circuit is turned off only

if all channels select external reference (VREF = VDD).

Device actions during Power-Down mode:

• The powered down channel stays in a power sav-

ing condition by turning off most of its circuits.

• No analog voltage output at the powered down

channel.

• The output (VOUT) pin of the powered down

channel is switched to a known resistive load. The

value of the resistive load is determined by the

state of the Power-Down bits (PD1 and PD0).

Table 4-7 shows the outcome of the Power-Down

bit settings.

• The contents of both the DAC registers and

EEPROM are not changed.

• Draws less than 40 nA (typical) when all four

channels are powered down and VDD is selected

as the voltage reference.

Circuits that are not affected during Power-Down

Mode:

•The I2C serial interface circuits remain active in

order to receive any command from the Master.

• The internal voltage reference circuit stays

turned-on if it is selected as reference by at least

one channel.

Exiting Power-Down Mode:

The device exits Power-Down mode immediately by

the following commands:

• Any write command for normal mode. Only

selected channel is affected.

• I2C General Call Wake-Up Command. All

channels are affected.

•I2C General Call Reset Command. This is a

conditional case. The device exits Power-Down

mode depending on the Power-Down bit settings

in EEPROM as the configuration bits and DAC

input codes are uploaded from EEPROM. All

channels are affected.

When the DAC operation mode is changed from the

Power-Down to normal mode, there will be a time delay

until the analog output is available. Typical time delay

for the output voltage is approximately 4.5 µs. This time

delay is measured from the acknowledge pulse of the

I2C serial communication command to the beginning of

the analog output (VOUT). This time delay is not

included in the output settling time specification. See

Section 2.0 “Typical Performance Curves” for more

details.

FIGURE 4-1:

Output Stage for

Power-Down Mode.

TABLE 4-7:

POWER-DOWN BITS

PD1

PD0

Function

Normal Mode

Ω resistor to ground (Note 1)

100 k

Ω resistor to ground

(Note 1)

500 k

Ω resistor to ground

(Note 1)

Note 1: In Power-Down mode: V

OUT is off and

most of internal circuits in the selected

channel are disabled.

100 k

Ω 500 kΩ

Power-Down

Control Circuit

Resistive

Load

VOUT

Amp

Resistor String DAC

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