MC1408-8 Datasheet, PDF (6/10 Pages) NXP Semiconductors – 8-bit multiplying D/A converter

Philips Semiconductors
8-bit multiplying D/A converter
Product data
MC1408-8
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 MC1408-8 is essentially constant over
the operating temperature range because of 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 MC1408-8 has a very low
full-scale current drift over the operating temperature range.
The MC1408-8 series is guaranteed accurate to within ±1/2 LSB at
+25 °C at a full-scale output current of 1.99 mA. The relative
accuracy test circuit is shown in Figure 6. The 12-bit converter is
calibrated to a full-scale output current of 1.99219 mA; then the
MC1408-8’s 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
±1/2 part in 65,536, or ±0.00076%, which is much more accurate
than the ±0.19% specification of the MC1408-8.
Monotonicity
A monotonic converter is one which always provides an analog
output greater than or equal to the preceding value for a
corresponding increment in the digital input code. The MC1408-8 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 1/2LSB for
8-bit accuracy. This time applies when R_L < 500 Ω and C_O < 25 pF.
The slowest single switch is the least significant bit, which typically
turns on and settles in 65 ns. In applications where the D-to-A
converter 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, good ground planes, and avoidance of
ground loops are all mandatory.
8-BIT
COUNTER
MSB
A1
A2
A3
12-BIT
D-TO-A
A4 CONVERTER
A5
(±0.02%
A6 ^{ERROR MAX)}
A7
A8A9 _{A10 A11 A12}
LSB
0 TO +10V OUTPUT
5k
50k
V_REF = 2V 0.1µF
100
950
R₁₄
V_CC
–
+
NE530
ERROR (1V = 1%)
MSB ¹⁴
13
5
6
7
8
4
9
MC1408
10
11
12
LSB _{15 16 3 2 1}
1k
C
V_EE
Figure 6. Relative Accuracy
SL00053
2001 Aug 03
6