Applications–AD558
OUTPUT
AMP
16
500Ω
15
40kΩ
14
2kΩ
14kΩ
13
GND
V
OUT
604Ω
The only consideration in selecting a supply voltage is that, in
order to be able to use the 0 V to 10 V output range, the power
supply voltage must be between +11.4 V and +16.5 V. If, how-
ever, the 0 V to 2.56 V range is to be used, power consumption
will be minimized by utilizing the lowest available supply voltage
(above +4.5 V).
TIMING AND CONTROL
Figure 4. 10.24 V Full-Scale Connection
NOTE: Decreasing the scale by putting a resistor in series with GND
will not work properly due to the code-dependent currents in GND.
Adjusting offset by injecting dc at GND is not recommended for the
same reason.
GROUNDING AND BYPASSING*
All precision converter products require careful application of
good grounding practices to maintain full rated performance.
Because the AD558 is intended for application in microcom-
puter systems where digital noise is prevalent, special care must
be taken to assure that its inherent precision is realized.
The AD558 has two ground (common) pins; this minimizes
ground drops and noise in the analog signal path. Figure 5
shows how the ground connections should be made.
OUTPUT
AMP
16
15
14
13
12
GND
11
+V
CC
V
OUT
V
OUT
SENSE
V
OUT
SELECT
GND
TO SYSTEM GND
TO SYSTEM GND
0.1µF (SEE TEXT)
TO SYSTEM V
CC
(SEE NEXT
PAGE)
The AD558 has data input latches that simplify interface to 8-
and 16-bit data buses. These latches are controlled by Chip
Enable (CE) and Chip Select (CS) inputs.
CE
and
CS
are inter-
nally “NORed” so that the latches transmit input data to the
DAC section when both
CE
and
CS
are at Logic “0”. If the ap-
plication does not involve a data bus, a “00” condition allows
for direct operation of the DAC. When either
CE
or
CS
go to
Logic “1”, the input data is latched into the registers and held
until both
CE
and
CS
return to “0”. (Unused
CE
or
CS
inputs
should be tied to ground.) The truth table is given in Table I.
The logic function is also shown in Figure 6.
Table I. AD558 Control Logic Truth Table
Input Data
0
1
0
1
0
1
X
X
CE
0
0
g
g
0
0
1
X
CS
0
0
0
0
g
g
X
1
DAC Data
0
1
0
1
0
1
Previous Data
Previous Data
Latch
Condition
“Transparent”
“Transparent”
Latching
Latching
Latching
Latching
Latched
Latched
R
L
NOTES
X = Does not matter.
g
= Logic Threshold at Positive-Going Transition.
Figure 5. Recommended Grounding and Bypassing
It is often advisable to maintain separate analog and digital
grounds throughout a complete system, tying them common in
one place only. If the common tie-point is remote and acciden-
tal disconnection of that one common tie-point occurs due to
card removal with power on, a large differential voltage between
the two commons could develop. To protect devices that inter-
face to both digital and analog parts of the system, such as the
AD558, it is recommended that common ground tie-points
should be provided at
each
such device. If only one system
ground can be connected directly to the AD558, it is recom-
mended that analog common be selected.
POWER SUPPLY CONSIDERATIONS
Figure 6. AD558 Control Logic Function
The AD558 is designed to operate from a single positive power
supply voltage. Specified performance is achieved for any supply
voltage between +4.5 V and +16.5 V. This makes the AD558
ideal for battery-operated, portable, automotive or digital main-
frame applications.
*For additional insight, “An IC Amplifier Users’ Guide to Decoupling,
Grounding and Making Things Go Right For A change,” is available
at no charge from any Analog Devices Sales Office.
In a level-triggered latch such as that in the AD558 there is an
interaction between data setup and hold times and the width of
the enable pulse. In an effort to reduce the time required to test
all possible combinations in production, the AD558 is tested
with t
DS
= t
W
= 200 ns at 25°C and 270 ns at T
MIN
and T
MAX
,
with t
DH
= 10 ns at all temperatures. Failure to comply with
these specifications may result in data not being latched properly.
Figure 7 shows the timing for the data and control signals;
CE
and
CS
are identical in timing as well as in function.
REV. A
–5–
AD [ ANALOG DEVICES ]
