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DAC-08EDR2G View Datasheet(PDF) - ON Semiconductor

Part Name
Description
Manufacturer
DAC-08EDR2G
ON-Semiconductor
ON Semiconductor ON-Semiconductor
DAC-08EDR2G Datasheet PDF : 14 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
DAC−08 SERIES
+VREF
OPTIONAL RESISTOR
FOR OFFSET
INPUTS
0V
NOTES:
RIN RREF
REQ 14
4
RP =200W 15 16 2
REQ = RIN || RP
Typical Values
NO CAP
RIN = 5kW
+VIN = 10V
Pulsed Referenced Operation
Figure 23. Typical Application
FUNCTIONAL DESCRIPTION
Reference Amplifier Drive and Compensation
The reference amplifier input current must always flow
into Pin 14 regardless of the setup method or reference
supply voltage polarity.
Connections for a positive reference voltage are shown
in Figure 2. The reference voltage source supplies the full
reference current. For bipolar reference signals, as in the
multiplying mode, R15 can be tied to a negative voltage
corresponding to the minimum input level. R15 may be
eliminated with only a small sacrifice in accuracy and
temperature drift.
The compensation capacitor value must be increased as
R14 value is increased. This is in order to maintain proper
phase margin. For R14 values of 1.0, 2.5, and 5.0 kW,
minimum capacitor values are 15, 37, and 75 pF,
respectively. The capacitor may be tied to either VEE or
ground, but using VEE increases negative supply rejection.
(Fluctuations in the negative supply have more effect on
accuracy than do any changes in the positive supply.)
A negative reference voltage may be used if R14 is
grounded and the reference voltage is applied to R15 as
shown. A high input impedance is the main advantage of
this method. The negative reference voltage must be at
least 3.0 V above the VEE supply. Bipolar input signals may
be handled by connecting R14 to a positive reference
voltage equal to the peak positive input level at Pin 15.
When using a DC reference voltage, capacitive bypass to
ground is recommended. The 5.0 V logic supply is not
recommended as a reference voltage, but if a well regulated
5.0 V supply which drives logic is to be used as the
reference, R14 should be formed of two series resistors with
the junction of the two resistors bypassed with 0.1 mF to
ground. For reference voltages greater than 5.0 V, a clamp
diode is recommended between Pin 14 and ground.
If Pin 14 is driven by a high impedance such as a
transistor current source, none of the above compensation
methods applies and the amplifier must be heavily
compensated, decreasing the overall bandwidth.
Output Voltage Range
The voltage at Pin 4 must always be at least 4.5 V more
positive than the voltage of the negative supply (Pin 3)
when the reference current is 2.0 mA or less, and at least
8.0 V more positive than the negative supply when the
reference current is between 2.0 mA and 4.0 mA. This is
necessary to avoid saturation of the output transistors,
which would cause serious accuracy degradation.
Output Current Range
Any time the full-scale current exceeds 2.0 mA, the
negative supply must be at least 8.0 V more negative than
the output voltage. This is due to the increased internal
voltage drops between the negative supply and the outputs
with higher reference currents.
Accuracy
Absolute accuracy is the measure of each output current
level with respect to its intended value, and is dependent
upon relative accuracy, full-scale accuracy and full-scale
current drift. Relative accuracy is the measure of each
output current level as a fraction of the full-scale current
after zero-scale current has been nulled out. The relative
accuracy of the DAC-08 series is essentially constant over
the operating temperature range due to the excellent
temperature tracking of the monolithic resistor ladder. The
reference current may drift with temperature, causing a
change in the absolute accuracy of output current.
However, the DAC-08 series has a very low full-scale
current drift over the operating temperature range.
The DAC-08 series is guaranteed accurate to within
"LSB at +25°C at a full-scale output current of 1.992 mA.
The relative accuracy test circuit is shown in Figure 2. The
12-bit converter is calibrated to a full-scale output current
of 1.99219 mA, then the DAC-08 full-scale current is
trimmed to the same value with R14 so that a zero value
appears at the error amplifier output. The counter is
activated and the error band may be displayed on the
oscilloscope, detected by comparators, or stored in a peak
detector.
Two 8-bit D-to-A converters may not be used to construct
a 16-bit accurate D-to-A converter. 16-bit accuracy implies
a total of " part in 65,536, or "0.00076%, which is much
more accurate than the "0.19% specification of the
DAC-08 series.
Monotonicity
A monotonic converter is one which always provides
analog output greater than or equal to the preceding value
for a corresponding increment in the digital input code. The
DAC-08 series is monotonic for all values of reference
current above 0.5 mA. The recommended range for
operation is a DC reference current between 0.5 mA and
4.0 mA.
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