Datasheet

DAC7552
SLAS442D –JANUARY 2005– REVISED JUNE 2011 www.ti.com
Generating ±5-V, ±10-V, and ± 12-V Outputs For
INTEGRAL AND DIFFERENTIAL LINEARITY
Precision Industrial Control
The DAC7552 uses precision thin-film resistors
Industrial control applications can require multiple
providing exceptional linearity and monotonicity.
feedback loops consisting of sensors, ADCs, MCUs,
Integral linearity error is typically within (+/-) 0.35
DACs, and actuators. Loop accuracy and loop speed
LSBs, and differential linearity error is typically within
are the two important parameters of such control
(+/-) 0.08 LSBs.
loops.
GLITCH ENERGY
Loop Accuracy:
The DAC7552 uses a proprietary architecture that
In a control loop, the ADC has to be accurate. Offset,
minimizes glitch energy. The code-to-code glitches
gain, and the integral linearity errors of the DAC are
are so low, they are usually buried within the
not factors in determining the accuracy of the loop.
wide-band noise and cannot be easily detected. The
As long as a voltage exists in the transfer curve of a
DAC7552 glitch is typically well under 0.1 nV-s. Such
monotonic DAC, the loop can find it and settle to it.
low glitch energy provides more than 10X
On the other hand, DAC resolution and differential
improvement over industry alternatives.
linearity do determine the loop accuracy, because
each DAC step determines the minimum incremental
CHANNEL-TO-CHANNEL CROSSTALK
change the loop can generate. A DNL error less
than –1 LSB (non-monotonicity) can create loop
The DAC7552 architecture is designed to minimize
instability. A DNL error greater than +1 LSB implies
channel-to-channel crosstalk. The voltage change in
unnecessarily large voltage steps and missed voltage
one channel does not affect the voltage output in
targets. With high DNL errors, the loop loses its
another channel. The DC crosstalk is in the order of a
stability, resolution, and accuracy. Offering 12-bit
few microvolts. AC crosstalk is also less than –100
ensured monotonicity and ± 0.08 LSB typical DNL
dBs. This provides orders of magnitude improvement
error, 755X DACs are great choices for precision
over certain competing architectures.
control loops.
APPLICATION INFORMATION
Loop Speed:
Many factors determine control loop speed. Typically,
DAC SPI Interfacing
the ADC's conversion time and the MCU's
Care must be taken with the digital control signals
computation time are the two major factors that
that are applied directly to the DAC, especially with
dominate the time constant of the loop. DAC settling
the SYNC pin. The SYNC pin must not be toggled
time is rarely a dominant factor because ADC
without having a full SCLK pulse in between. If this
conversion times usually exceed DAC conversion
condition is violated, the SPI interface locks up in an
times. DAC offset, gain, and linearity errors can slow
erroneous state, causing the DAC to behave
the loop down only during the start-up. Once the loop
incorrectly and possibly have errors. The DAC can be
reaches its steady-state operation, these errors do
recovered from this faulty state by writing a valid SPI
not affect loop speed any further. Depending on the
command or using the SYNC pin correctly;
ringing characteristics of the loop's transfer function,
communication is then restored. Avoid glitches and
DAC glitches can also slow the loop down. With its 1
transients on the SYNC line to ensure proper
MSPS (small-signal) maximum data update rate,
operation.
DAC7552 can support high-speed control loops.
Ultralow glitch energy of the DAC7552 significantly
Waveform Generation
improves loop stability and loop settling time.
Due to its exceptional linearity, low glitch, and low
Generating Industrial Voltage Ranges:
crosstalk, the DAC7552 is well suited for waveform
For control loop applications, DAC gain and offset
generation (from DC to 10 kHz). The DAC7552
errors are not important parameters. This could be
large-signal settling time is 5 µs, supporting an
exploited to lower trim and calibration costs in a
update rate of 200 KSPS. However, the update rates
high-voltage control circuit design. Using an
can exceed 1 MSPS if the waveform to be generated
operational amplifier (OPA130), and a voltage
consists of small voltage steps between consecutive
reference (REF3140), the DAC7552 can generate the
DAC updates. To obtain a high dynamic range,
wide voltage swings required by the control loop.
REF3140 (4.096 V) or REF02 (5 V) are
recommended for reference voltage generation.
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