datasheetbank_Logo
Integrated circuits, Transistor, Semiconductors Search and Datasheet PDF Download Site

DAC-08F View Datasheet(PDF) - Philips Electronics

Part Name
Description
View to exact match
DAC-08F
Philips
Philips Electronics Philips
DAC-08F Datasheet PDF : 16 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
Philips Semiconductors
8-bit high-speed multiplying D/A converter
Product data
DAC-08 Series
TYPICAL APPLICATION
+VREF
OPTIONAL RESISTOR
FOR OFFSET
INPUTS
RIN RREF
0V
REQ 14
4
RP =20015 16 2
NO CAP
NOTES:
REQ = RIN || RP
Typical Values
RIN = 5k
+VIN = 10V
Pulsed Referenced Operation
Figure 9. Typical Application
SL00009
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 3.
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 k, 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 5.0V 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 µF 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 mA or less, and at least 8 V more positive than the
negative supply when the reference current is between 2 mA and
4 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 mA, the negative supply
must be at least 8 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 3. 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.
Settling Time
The worst-case switching condition occurs when all bits are
switched on, which corresponds to a low-to-high transition for all
input bits. This time is typically 70 ns for settling to within LSB for
8-bit accuracy. This time applies when RL<500 and CO<25 pF.
The slowest single switch is the least significant bit, which typically
turns on and settles in 65 ns. In applications where the DAC
functions in a positive-going ramp mode, the worst-case condition
does not occur and settling times less than 70 ns may be realized.
Extra care must be taken in board layout since this usually is the
dominant factor in satisfactory test results when measuring settling
time. Short leads, 100 µF supply bypassing for low frequencies,
minimum scope lead length, and avoidance of ground loops are all
mandatory.
2001 Aug 03
10
 

Share Link: 

datasheetbank.com [ Privacy Policy ] [ Request Datasheet ] [ Contact Us ]