MCP4728 Microchip Technology Inc., MCP4728 Datasheet - Page 26

• Manufacturer Part Number: MCP4728
• Description: 12-bit, Quad Digital-to-analog Converter With Eeprom Memory
• Manufacturer: Microchip Technology Inc.

MCP4728
4.5
The device has a precision internal voltage reference
which provides a nominal voltage of 2.048V. The user
can select the internal voltage reference or V
voltage reference source of each channel using the
V
circuit is turned off when all channels select V
their references. However, it stays turned on if any one
of the channels selects the internal reference.
4.6
The LSB is defined as the ideal voltage difference
between two successive codes. LSB sizes of the
MCP4728 device are shown in
TABLE 4-4:
4.7
Each channel has an independent output associated
with its own configuration bit settings and DAC input
code. When the internal voltage reference is selected
(V
to the resistor string DAC of the channel. When the
external reference (V
for the channel’s resistor string DAC.
The V
DAC performance. When the V
voltage reference, any variation or noises on the V
line can directly affect on the DAC output.
The
programmable gain block. The rail-to-rail output
amplifier has a configurable gain of 1 or 2. But the gain
of 2 is not applicable if V
reference. The formula for the analog output voltage is
given in
DS22187A-page 26
Note 1:
REF
(2.048V)
REF
Internal
V
V
V
REF
REF
DD
configuration bit. The internal voltage reference
DD
analog
= internal), it supplies the internal V
Equation 4-1
Voltage Reference
LSB Size
DAC Output Voltage
needs to be as clean as possible for accurate
LSB size varies with the V
When V
G
ignored.
X
Gain (G
Selection
= 1 by default. G
output
x1
x2
x1
LSB SIZES (EXAMPLE)
REF
REF
X
and
)
= V
=V
of
DD
Equation
V
LSB Size
DD
DD
0.5 mV
DD
is selected for the voltage
1 mV
each
, the device uses
) is selected, V
/4096
Table
X
DD
= 2 option is
is selected as the
4-2.
channel
4-4.
DD
2.048V/4096
4.096V/4096
Condition
range.
(Note 1
REF
DD
DD
has
voltage
is used
as the
DD
DD
as
a
4.7.1
The DAC output voltage range varies depending on the
voltage reference selection.
• When the internal reference (V
V
• When the external reference (V
V
EQUATION 4-1:
EQUATION 4-2:
4.8
The following events update the output registers
(V
a.
b.
c.
d.
4.8.1
The user can use the LDAC pin or UDAC bit to upload
the input DAC register to output DAC register (V
However, the UDAC affects only the selected channel
while the LDAC affects all channels. The UDAC bit is
not used in the Fast Mode Writing.
Table 4-5
UDAC bit conditions.
Note that the gain selection bit is not applicable for
V
gain selection bit setting.
Where:
Where:
OUT
OUT
V
selected:
selected:
REF
OUT
REF
D
G
D
LDAC pin to “Low”: Updates all DAC channels.
UDAC bit to “Low”: Updates a selected channel
only.
General Call Software Update Command:
Updates all DAC channels.
Power-On-Reset or General Call Reset com-
mand: Both input and output registers are
updated with EEPROM data. All channels are
affected.
= 0.000V to 4.096V * 4095/4096 for Gain of 2
n
n
x
= 0.000V to 2.048V * 4095/4096 for Gain of 1
= 0.000V to V
):
= V
V
=
=
=
Output Voltage Update
=
OUT
shows the output update vs. LDAC pin and
DD
OUTPUT VOLTAGE RANGE
LDAC PIN AND UDAC BIT
2.048V for internal reference selection
. Gain of 1 is used regardless of the
DAC input code
Gain Setting
DAC input code
=
(
------------------------------ - G
V
V
OUT
REF
DD
4096
V
INTERNAL REFERENCE
V
×
=
© 2009 Microchip Technology Inc.
OUT
OUT
D
(
---------------------------- -
n
V
)
DD
FOR
FOR
4096
×
x
REF
REF
D
V
V
n
REF
REF
)
=2.048V) is
=V
DD
≤
=
=
V
) is
V
DD
DD
OUT
).