DN96 - 12-Bit Rail-to-Rail Micropower DACs in an SO-8

12-Bit Rail-to-Rail Micropower DACs in an SO-8
Design Note 96
Hassan Malik and Jim Brubaker
The LTC ®1451, LTC1452 and LTC1453 are complete,
single supply, rail-to-rail voltage output 12-bit digitalto-analog (DAC) converters. They include an output
buffer amplifier and a space saving SPI compatible
three-wire serial interface. There is also a data output pin
that allows daisy-chaining multiple DACs. These DACs
use a proprietary architecture which guarantees a DNL
(Differential Nonlinearity) error of less than 0.5LSB. The
typical DNL error is about 0.2LSB as shown in Figure 1.
There is a built-in power-on reset that resets the output
to zero scale. The output amplifier can swing to within
5mV of VCC when unloaded and can source or sink 5mA
even at a 4.5V supply. These DACs come in an 8-pin
PDIP and SO-8 package.
5V and 3V Operation
The LTC1451 has an on-board reference of 2.048V and
a nominal output swing of 4.095V. It operates from a
single 4.5V to 5.5V supply dissipating 2mW (ICC(TYP)
= 400μA).
The LTC1452 is a multiplying DAC with no on-board
reference and a full-scale output of twice the reference
input. It operates from a single supply that can range
from 2.7V to 5.5V. It dissipates 1.125mW (ICC(TYP) =
225μA) at a 5V supply and a mere 0.5mW (ICC(TYP) =
160μA) at a 3V supply.
The LTC1453 has a 1.22V on-board reference and a
convenient full scale of 2.5V. It can operate on a single
supply with a wide range of 2.7V to 5.5V as shown in
Figure 2. It dissipates 0.75mW (ICC(TYP) = 220μA) at a
3V supply. The digital inputs can swing above VCC for
easy interfacing with 5V logic.
True Rail-to-Rail Output
The output rail-to-rail amplifier can source or sink 5mA
over the entire operating temperature range while pulling to within 300mV of the positive supply voltage or
ground. The output swings to within a few millivolts of
either supply rail when unloaded and has an equivalent
output resistance of 50Ω when driving to either rail.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
2.7V TO 5.5V
0.1μF
VCC
DIN
CLK
MICROPROCESSOR
LTC1453
CS/LD
DOUT
TO NEXT DAC
FOR DAISY-CHAINING
VREF
VOUT
OUTPUT
0V TO 2.5V
GND
1.22V
DN96 • F02
Figure 2. The 3V LTC1453 is SPI Compatible and Talks to
Both 5V and 3V Processors
8 VCC
CLK 1
0.5
12-BIT
SHIFT
REGISTER
DAC
REGISTER
12-BIT DAC
+
7 VOUT
–
CS/LD 3
POWER-ON
RESET
DOUT 4
REFERENCE
LTC1451: 2.048V
LTC1453: 1.22V
DNL ERROR (LSB)
LD
DIN 2
0.0
6 REF
–0.5
0
5 GND
512 1024 1536 2048 2560 3072 3584 4095
CODE
DN96 • F02B
DN96 • F01A
Figure 1. Proprietary Architecture Guarantees Excellent DNL
02/95/96_conv
The output can drive a capacitive load of up to 1000pF
without oscillating.
Flexibility, True Rail-to-Rail Performance and
Micropower; All In a Tiny SO-8
The LTC1451, LTC1452 and LTC1453 are the most
flexible micropower, stand alone DACs that offer true
rail-to-rail performance. This flexibility along with the
tiny SO-8 package allows these parts to be used in a
wide range of applications where size, power, DNL and
single supply operation are important.
Wide Range of Applications
Some of the applications for this family include digital
calibration, industrial process control, automatic test
equipment, cellular telephones and portable batterypowered applications where low supply current is
essential. Figure 3 shows how to use an LTC1453 to
make an opto-isolated digitally controlled 4mA to 20mA
process controller. The controller circuitry, including
the opto-isolator, is powered by the loop voltage that
can have a wide range of 3.3V to 30V. The 1.22V reference output of the LTC1453 is used for the 4mA offset
current and VOUT is used for the digitally controlled
0mA to 16mA current. RS is a sense resistor and the
LT®1077 op amp modulates the transistor Q1 to provide
the 4mA to 20mA current through this resistor. The
potentiometers allow for offset and full-scale adjustment. The control circuitry consumes well under the
4mA budget at zero scale.
Table 1. LTC Serial Voltage Output DACs
VCC Range
LTC1451
4.5V to 5.5V 2.048V-Internal 4.095V 400μA at 5V
LTC1452
2.7V to 5.5V
LTC1453
2.7V to 5.5V 1.22V-Internal
LTC1257
4.75V to
15.75V
Reference
Full
Scale
Part
External
ICC
2 × REF 225μA at 5V
2.5V
250μA at 3V
2.048V-Internal 2.048V 350μA at 5V
(2.5V to
(2.5V to
12V-External) 12V)
VLOOP
3.3V TO 30V
LT1121-3.3
IN
90k
5k
45k
5k
OUT
1μF
FROM
OPTO-ISOLATED
INPUTS
CLK
VCC
DIN
LTC1453
CS/LD
VREF
+
OUT
1k
LT1077
3k
–
RS
10Ω
3.3V
OPTO-ISOLATERS
CLK
DIN
CS/LD
10k
500Ω
4N28
Q1
2N3440
IOUT
CLK
DIN
CS/LD
DN96 • F03
Figure 3. 4mA to 20mA Process Controller Has 3.3V Minimum Loop Voltage
Data Sheet Download
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