AD558 查看數據表（PDF） - Analog Devices
零件编号
产品描述 (功能)
生产厂家
AD558 Datasheet PDF : 8 Pages
| |||
AD558
DATA
INPUTS
0.8V
tD H
tDS
2.0V
16 VOUT
AD558
15 VOUT SENSE
RL
CS OR CE
0.8V
tW
2.0V
DAC
V OUTPUT
1/2 LSB
tSETTLING
tW = STORAGE PULSE WIDTH = 200ns MIN
tDH = DATA HOLD TIME = 10ns MIN
tDS = DATA SETUP TIME = 200ns MIN
tSETTLING = DAC OUTPUT SETTLING TIME TO ±1/2 LSB
Figure 7. AD558 Timing
USE OF VOUT SENSE
Separate access to the feedback resistor of the output amplifier
allows additional application versatility. Figure 8a shows how
I × R drops in long lines to remote loads may be cancelled by
putting the drops “inside the loop.” Figure 8b shows how the
separate sense may be used to provide a higher output current
by feeding back around a simple current booster.
NEGATIVE
SUPPLY
RP-D = 2x VEE
VEE (in kΩ)
Figure 9. Improved Settling Time
available, bipolar output ranges may be achieved by suitable
output offsetting and scaling. Figure 10 shows how a ± 1.28 volt
output range may be achieved when a –5 volt power supply is
available. The offset is provided by the AD589 precision 1.2 volt
reference which will operate from a +5 volt supply. The AD544
output amplifier can provide the necessary ± 1.28 volt output
swing from ± 5 volt supplies. Coding is complementary offset
binary.
VOUT = 0V TO +2.56V
AD558
12
13
16
15
14
5kΩ
4.53kΩ
AD589
500Ω
BIPOLAR
VIN OFFSET
ADJUST
5kΩ
+5V
0.01µF
AD544
0.01µF
1.5kΩ
VO
+1.28 TO
–1.27
–5V
AD558
16 VOUT
15 VOUT SENSE
12 13
14
GND GAIN
SELECT
VOUT
0V TO +10V
RL
a. Compensation for I × R Drops in Output Lines
VCC
AD558
VOUT
16
VOUT SENSE
15
12 13
14
GAIN
GND SELECT
2N2222
VOUT
0V TO +2.56V
RL
b. Output Current Booster
Figure 8. Use of VOUT Sense
OPTIMIZING SETTLING TIME
In order to provide single-supply operation and zero-based
output voltage ranges, the AD558 output stage has a passive
“pull-down” to ground. As a result, settling time for negative
going output steps may be longer than for positive-going output
steps. The relative difference depends on load resistance and
capacitance. If a negative power supply is available, the
negative-going settling time may be improved by adding a pull-
down resistor from the output to the negative supply as shown
in Figure 9. The value of the resistor should be such that, at
zero voltage out, current through that resistor is 0.5 mA max.
–1.2V
0.01µF 4.7kΩ
INPUT CODE
00000000
10000000
11111111
VOUT
+128V
0V
–1.27V
–5V
Figure 10. Bipolar Operation of AD558 from ±5 V Supplies
MEASURING OFFSET ERROR
One of the most commonly specified endpoint errors associated
with real-world nonideal DACs is offset error.
In most DAC testing, the offset error is measured by applying
the zero-scale code and measuring the output deviation from 0
volts. There are some DACs, like the AD558 where offset errors
may be present but not observable at the zero scale, because of
other circuit limitations (such as zero coinciding with single-
supply ground) so that a nonzero output at zero code cannot be
read as the offset error. Factors like this make testing the
AD558 a little more complicated.
By adding a pulldown resistor from the output to a negative
supply as shown in Figure 11, we can now read offset errors
at zero code that may not have been observable due to circuit
limitations. The value of the resistor should be such that, at zero
voltage out, current through the resistor is 0.5 mA max.
OUTPUT
AMP
16
15
VOUT
0.5mA
–V
VOUT SENSE
14 VOUT SELECT
BIPOLAR OUTPUT RANGES
The AD558 was designed for operation from a single power
supply and is thus capable of providing only unipolar (0 V to
+2.56 V and 0 V to 10 V) output ranges. If a negative supply is
13
AGND
a. 0 V to 2.56 V Output Range
–6–
REV. A
Share Link: 