Manualsbrain.com
  1. Manuales
  2. Marcas
  3. Microchip Technology
  4. MCP4728EV
  5. Hoja De Datos

Microchip Technology MCP4728EV Hoja De Datos

Descargar
Página de 68
MCP4728
DS22187E-page 26
© 2010 Microchip Technology Inc.
4.5
Voltage Reference
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
DD
 as the
voltage reference source of each channel using the
V
REF
 configuration bit. The internal voltage reference
circuit is turned off when all channels select V
DD
 as
their references. However, it stays turned on if any one
of the channels selects the internal reference.
4.6
LSB Size
The LSB is defined as the ideal voltage difference
between two successive codes. LSB sizes of the
MCP4728 device are shown in 
4.7
DAC Output Voltage
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
REF
 = internal), it supplies the internal V
REF
 voltage
to the resistor string DAC of the channel. When the
external reference (V
REF
=V
DD
) is selected, V
DD
 is used
for the channel’s resistor string DAC.
The V
DD
 needs to be as clean as possible for accurate
DAC performance. When the V
DD
 is selected as the
voltage reference, any variation or noises on the V
DD
line can directly affect on the DAC output.
The analog output of each channel has a
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
DD
 is selected for the voltage
reference. The formula for the analog output voltage is
given in 
 
and
4.7.1
OUTPUT VOLTAGE RANGE
The DAC output voltage range varies depending on the
voltage reference selection.
• When the internal reference (V
REF
=2.048V) is 
selected:
- V
OUT
 = 0.000V to 2.048V * 4095/4096 for 
Gain of 1
- V
OUT
 = 0.000V to 4.096V * 4095/4096 for 
Gain of 2
• When the external reference (V
REF
=V
DD
) is 
selected:
- V
OUT
 = 0.000V to V
DD
EQUATION 4-1:
V
OUT
 
FOR
 V
REF
 = 
INTERNAL REFERENCE
EQUATION 4-2:
V
OUT
 
FOR 
V
REF
 = 
V
DD
4.8
Output Voltage Update
The following events update the output registers
(V
OUT
):
a.
LDAC pin to “Low”: Updates all DAC channels.
b.
UDAC bit to “Low”: Updates a selected channel
only.
c.
General Call Software Update Command:
Updates all DAC channels.
d.
Power-on Reset or General Call Reset
command: Both input and output registers are
updated with EEPROM data. All channels are
affected.
4.8.1
LDAC PIN AND UDAC BIT
The user can use the LDAC pin or UDAC bit to upload
the input DAC register to output DAC register (V
OUT
).
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.
 shows the output update vs. LDAC pin and
UDAC bit conditions.
TABLE 4-4:
LSB SIZES (EXAMPLE)
V
REF
Gain (G
X
) 
Selection
LSB Size
Condition
 Internal 
V
REF
(2.048V)
x1
0.5 mV
2.048V/4096
x2
1 mV
4.096V/4096
V
DD
x1
V
DD
/4096
)
Note 1:
LSB size varies with the V
DD
 range. 
When V
REF
 = V
DD
, the device uses 
G
X
= 1 by default. G
X
 = 2 option is 
ignored.
Note:
The gain selection bit is not applicable
for V
REF
 = V
DD
. In this case, Gain of 1
is used regardless of the gain selection
bit setting.
Where: 
V
REF
=
2.048V for internal reference selection
D
n
=
 DAC input code
G
x
=
 Gain Setting
 
 (V
REF
 
x
 D
n 
)
x
  G
x
4096
≤  
V
DD
V
OUT =
V
OUT
V
DD
D
n
×
(
)
4096
-----------------------------
=
Where: 
D
n
=
 DAC input code