MCP4728 Datasheet, PDF (28/66 Pages) Microchip Technology – 12-Bit, Quad Digital-to-Analog Converter with EEPROM Memory

MCP4728
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 (V_REF = V_DD).
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 (V_OUT) 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 V_DD 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.
DS22187C-page 28
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 (V_OUT). This time delay is not
included in the output settling time specification. See
Section 2.0 “Typical Performance Curves” for more
details.
TABLE 4-7: POWER-DOWN BITS
PD1 PD0
Function
0
0
1
1
Note 1:
0 Normal Mode
1 1 kΩ resistor to ground (Note 1)
0 100 kΩ resistor to ground
(Note 1)
1 500 kΩ resistor to ground
(Note 1)
In Power-Down mode: V_OUT is off and
most of internal circuits in the selected
channel are disabled.
OP
Amp
V_OUT
Power-Down
Control Circuit
1 kΩ
Resistor String DAC
Resistive
Load
100 kΩ 500 kΩ
FIGURE 4-1:
Output Stage for
Power-Down Mode.
© 2009 Microchip Technology Inc.