DAC7553 datasheet(17/20 Pages) TI

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INTEGRAL AND DIFFERENTIAL LINEARITY

GLITCH ENERGY

CHANNEL-TO-CHANNEL CROSSTALK

APPLICATION INFORMATION

Waveform Generation

Generating ±5-V, ±10-V, and ± 12-V Outputs For

DAC7553

VREFH

DAC7553

Vdac

REF3140

VREF

Vtail

VOUT

OPA130

Vout + VREF

R1 )

Din

4096 *

tail

(1)

DAC7553

SLAS477 – AUGUST 2005

change the loop can generate. A DNL error less than

–1 LSB (non-monotonicity) can create loop instability.

The DAC7553 uses precision thin-film resistors pro-

A DNL error greater than +1 LSB implies unnecess-

viding exceptional linearity and monotonicity. Integral

arily large voltage steps and missed voltage targets.

linearity error is typically within (+/-) 0.35 LSBs, and

With high DNL errors, the loop loses its stability,

differential linearity error is typically within (+/-) 0.08

resolution, and accuracy. Offering 12-bit ensured

LSBs.

monotonicity and ± 0.08 LSB typical DNL error, 755X

DACs are great choices for precision control loops.

Loop Speed:

The DAC7553 uses a proprietary architecture that

Many factors determine control loop speed. Typically,

minimizes glitch energy. The code-to-code glitches

the conversion time of the ADC and the computation

are so low, they are usually buried within the

time of the MCU are the two major factors that

wide-band noise and cannot be easily detected. The

dominate the time constant of the loop. DAC settling

DAC7553 glitch is typically well under 0.1 nV-s. Such

time is rarely a dominant factor because ADC conver-

low glitch energy provides more than 10X improve-

sion times usually exceed DAC conversion times.

ment over industry alternatives.

DAC offset, gain, and linearity errors can slow the

loop down only during the start-up. Once the loop

reaches its steady-state operation, these errors do

The DAC7553 architecture is designed to minimize

not affect loop speed any further. Depending on the

channel-to-channel crosstalk. The voltage change in

ringing characteristics of the loop's transfer function,

one channel does not affect the voltage output in

DAC glitches can also slow the loop down. With its 1

another channel. The DC crosstalk is in the order of a

MSPS (small-signal) maximum data update rate,

few microvolts. AC crosstalk is also less than –100

DAC7553 can support high-speed control loops.

dBs. This provides orders of magnitude improvement

Ultralow glitch energy of the DAC7553 significantly

over certain competing architectures.

improves loop stability and loop settling time.

Generating Industrial Voltage Ranges:

For control loop applications, DAC gain and offset

errors are not important parameters. This could be

exploited to lower trim and calibration costs in a

Due to its exceptional linearity, low glitch, and low

high-voltage control circuit design. Using an oper-

crosstalk, the DAC7553 is well suited for waveform

ational amplifier (OPA130), and a voltage reference

generation (from DC to 10 kHz). The DAC7553

(REF3140), the DAC7553 can generate the wide

large-signal settling time is 5 µs, supporting an

voltage swings required by the control loop.

update rate of 200 KSPS. However, the update rates

can exceed 1 MSPS if the waveform to be generated

consists of small voltage steps between consecutive

DAC updates. To obtain a high dynamic range,

REF3140 (4.096 V) or REF02 (5 V) are rec-

ommended for reference voltage generation.

Precision Industrial Control

Industrial control applications can require multiple

feedback loops consisting of sensors, ADCs, MCUs,

DACs, and actuators. Loop accuracy and loop speed

Figure 31. Low-cost, Wide-swing Voltage Gener-

are the two important parameters of such control

ator for Control Loop Applications

loops.

Loop Accuracy:

The output voltage of the configuration is given by:

In a control loop, the ADC has to be accurate. Offset,

gain, and the integral linearity errors of the DAC are

not factors in determining the accuracy of the loop.

Fixed R1 and R2 resistors can be used to coarsely

As long as a voltage exists in the transfer curve of a

set the gain required in the first term of the equation.

monotonic DAC, the loop can find it and settle to it.

Once R2 and R1 set the gain to include some

On the other hand, DAC resolution and differential

minimal over-range, a DAC7553 channel could be

linearity do determine the loop accuracy, because

used to set the required offset voltage. Residual

each DAC step determines the minimum incremental

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