DAC1220
www.ti.com...................................................................................................................................... SBAS082G –FEBRUARY 1998–REVISED SEPTEMBER 2009
Isolation
Full-Scale Range (FSR)—This is the magnitude of
the typical analog output voltage range, which is 2 ×
VREF. For example, when the converter is configured
with a 2.5V reference, the Full-Scale range is 5.0V.
The DAC1220 serial interface allows for connection
using as few as two wires. This is an advantage
when galvanic isolation is required. An example
isolated connection is shown in Figure 13. Here,
chip-select is unused and therefore grounded, and
the DAC1220 is being operated unidirectionally.
Gain Error—This error represents the difference in
the slope between the actual and ideal transfer
functions.
Linearity Error—The deviation of the actual transfer
function from an ideal straight line between the data
end points.
DAC1220 Revisions
As of this writing, there have been two released
revisions of the DAC1220. The only difference
between the two versions is bit 13 of the Command
Register. In the first revision, this bit was writable,
and defaulted to '0'. In the current revision, which was
released in 1999, this bit is fixed at '1', and is not
writable.
Least Significant Bit (LSB) Weight—This is the
ideal change in voltage that the analog output
changes with a change in the digital input code of
1LSB.
Monotonicity—Monotonicity assures that the analog
output will increase or stay the same for increasing
digital input codes.
For first revision chips, always write a '1' to this bit.
Although the bit is not critical, performance is not
optimal unless this bit is set.
Offset Error—The difference between the expected
and actual output, when the output is zero. The value
This does no harm in current revision chips, and
ensures that first revision chips perform optimally.
is calculated from measurements made when VOUT
20mV.
=
Settling Time—The time it takes the output to settle
to a new value after the digital code has been
changed.
Definition of Terms
Differential Nonlinearity Error—The difference
between an actual step width and the ideal value of
1LSB. If the step width is exactly 1LSB, the
differential nonlinearity error is zero. A differential
nonlinearity specification of less than 1LSB ensures
monotonicity.
fXIN —The frequency of the crystal oscillator or
CMOS-compatible input signal at the XIN input of the
DAC1220.
Drift—The change in a parameter over temperature.
Isolated
Power
DVDD
Opto
Coupler
8051
P1.1
P1.0
DAC1220
C1
12pF
1
2
3
4
5
6
7
8
DVDD
XOUT
XIN
SCLK 16
SDIO 15
CS 14
Opto
Coupler
XTAL
C2
12pF
DGND
AVDD
DNC
DNC
DNC
AGND 13
VREF 12
VOUT 11
C2 10
AVDD
VREF
= Isolated
= DGND
= AGND
VOUT
C2
C1
C1
9
Figure 13. Isolation for Two-Wire Interface
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