AD558 Analog Devices, AD558 Datasheet - Page 4

• Manufacturer Part Number: AD558
• Description: Voltage-output 8-bit digital-to-analog converter, including output amplifier, full microprocessor interface and precision
• Manufacturer: Analog Devices

Specifications of AD558

• Resolution (bits): 8bit
• Dac Update Rate: 1.25MSPS
• Dac Settling Time: 800ns
• Max Pos Supply (v): +16.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: Par

AD558
CIRCUIT DESCRIPTION
The AD558 consists of four major functional blocks, fabricated
on a single monolithic chip (see Figure 2). The main D-to-A
converter section uses eight equally-weighted laser-trimmed
current sources switched into a silicon-chromium thin-film
R/2R resistor ladder network to give a direct but unbuffered 0
mV to 400 mV output range. The transistors that form the
DAC switches are PNPs; this allows direct positive-voltage logic
interface and a zero-based output range.
The high speed output buffer amplifier is operated in the non-
inverting mode with gain determined by the user-connections
at the output range select pin. The gain-setting application
resistors are thin-film laser-trimmed to match and track the
DAC resistors and to assure precise initial calibration of the two
output ranges, 0 V to 2.56 V and 0 V to 10 V. The amplifier
output stage is an NPN transistor with passive pull-down for
zero-based output capability with a single power supply. The
internal precision voltage reference is of the patented bandgap
type. This design produces a reference voltage of 1.2 volts and
thus, unlike 6.3 volt temperature compensated Zeners, may be
operated from a single, low voltage logic power supply. The
microprocessor interface logic consists of an 8-bit data latch and
control circuitry. Low power, small geometry and high speed
are advantages of the I
bipolar process compatible so that the performance of the ana-
log sections need not be compromised to provide on-chip logic
capabilities. The control logic allows the latches to be operated
from a decoded microprocessor address and write signal. If the
application does not involve a P or data bus, wiring CS and
CE to ground renders the latches “transparent” for direct DAC
access.
MIL-STD-883
The rigors of the military/aerospace environment, temperature
extremes, humidity, mechanical stress, etc., demand the utmost
in electronic circuits. The AD558, with the inherent reliability
of integrated circuit construction, was designed with these ap-
plications in mind. The hermetically-sealed, low profile DIP
package takes up a fraction of the space required by equivalent
modular designs and protects the chip from hazardous environ-
ments. To further ensure reliability, military temperature range
AD558 grades S and T are available screened to MIL-STD-883.
For more complete data sheet information consult the Analog
Devices’ Military Databook.
REFERENCE
BAND-
GAP
Figure 2. AD558 Functional Block Diagram
CONTROL
CONTROL
CS
INPUTS
LOGIC
I
2
L
CE
CONTROL
AMP
LSB
8-BIT VOLTAGE-SWITCHING
2
L design as applied to this section. I
DIGITAL INPUT DATA
D-TO-A CONVERTER
I
2
L LATCHES
MSB
+V
CC
OUTPUT
AMP
GND
V
V
GND
OUT
OUT
V
OUT
SELECT
SENSE
2
L is
–4–
CHIP AVAILABILITY
The AD558 is available in laser-trimmed, passivated chip form.
AD558J and AD558T chips are available. Consult the factory
for details.
Binary
0000 0000
0000 0001
0000 0010
0000 1111
0001 0000
0111 1111
1000 0000
1100 0000
1111 1111
CONNECTING THE AD558
The AD558 has been configured for ease of application. All ref-
erence, output amplifier and logic connections are made inter-
nally. In addition, all calibration trims are performed at the
factory assuring specified accuracy without user trims. The only
connection decision that must be made by the user is a single
jumper to select output voltage range. Clean circuit board lay-
out is facilitated by isolating all digital bit inputs on one side of
the package; analog outputs are on the opposite side.
Figure 3 shows the two alternative output range connections.
The 0 V to 2.56 V range may be selected for use with any power
supply between +4.5 V and +16.5 V. The 0 V to 10 V range
requires a power supply of +11.4 V to +16.5 V.
a. 0 V to 2.56 V Output Range b. 0 V to 10 V Output Range
Because of its precise factory calibration, the AD558 is intended
to be operated without user trims for gain and offset; therefore
no provisions have been made for such user trims. If a small in-
crease in scale is required, however, it may be accomplished
by slightly altering the effective gain of the output buffer. A
resistor in series with V
range.
For example if a 0 V to 10.24 V output range is desired (40 mV
= 1 LSB), a nominal resistance of 850
remembered that, although the internal resistors all ratio-
match and track, the absolute tolerance of these resistors is
typically 20% and the absolute TC is typically –50 ppm/ C
(0 to –100 ppm/ C). That must be considered when rescaling is
performed. Figure 4 shows the recommended circuitry for a
full-scale output range of 10.24 volts. Internal resistance values
shown are nominal.
Digital Input Code
OUTPUT
AMP
Hexadecimal Decimal
00
01
02
0F
10
7F
80
C0
FF
Figure 3. Connection Diagrams
16
15
14
13
V
V
OUT
OUT
GND
Input Logic Coding
V
OUT
SENSE
SELECT
OUT
0
1
2
15
16
127
128
192
255
SENSE will increase the output
2.56 V Range 10.000 V Range
0
0.010 V
0.020 V
0.150 V
0.160 V
1.270 V
1.280 V
1.920 V
2.55 V
Output Voltage
is required. It must be
OUTPUT
AMP
16
15
14
13
0
0.039 V
0.078 V
0.586 V
0.625 V
4.961 V
5.000 V
7.500 V
9.961 V
V
V
OUT
OUT
GND
REV. A
V
SENSE
SELECT
OUT