Linear Technology LTC1592 Manuel utilisateur

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 572

16-BIT SOFTSPAN DAC

LTC1592

DESCRIPTION

Demonstration circuit 572 features the LTC1592, a

16-bit current output DAC with five software-

selectable output ranges.

DC572 is a member of Linear Technology‘s

QuickEval™ family of demonstration boards. It is de-

signed to allow easy evaluation of the LTC1592 and

may be connected directly to the target application’s

analog signals while using the DC590 USB Serial

Controller board and supplied software to measure

performance. The exposed ground planes allow

proper grounding to prototype circuitry. After evaluat-

ing with Linear Technology’s software, the digital sig-

nals can be connected to the end application’s proc-

essor / controller for development of the serial inter-

face.

Design files for this circuit board are available. Call

the LTC factory.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 572

16-BIT SOFTSPAN DAC

QUICK START PROCEDURE

Connect a regulated, +/-15VDC power supply to the

power connections on DC572. This must be done

first because the +5V supply to the LTC1592 is de-

rived from the +15V supply. Connect DC572 to a

DC590 USB Serial Controller using the supplied 14

conductor ribbon cable. Connect DC590 to host PC

with a standard USB A/B cable. Run the evaluation

software supplied with DC590 or downloaded from

www.linear.com. The correct program will be

loaded automatically.

By default, the control program will load a DC value

into the LTC1592. The value may be changed by

typing a voltage into the appropriate box, either in

voltage, hexadecimal counts (0000 - FFFF), or

decimal counts (0 – 65535) depending on the units

selected.

The other option is a square wave output. The fre-

quency of the square wave is not tightly controlled;

it is intended to allow measurement of settling time

and glitch impulse.

Features may be periodically added to the software,

see the software’s help menu for the latest informa-

tion.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 572

16-BIT SOFTSPAN DAC

HARDWARE SET-UP

POWER CONNECTIONS

A low-noise, +/-15V power supply must be con-

nected to E1, E2, and E3 (+15V, Ground, and –15V,

respectively.) This provides power to the LT1469 op

amp and LT1236 reference. The LTC1592 power is

taken from the reference output to minimize cou-

pling of supply noise to the output.

JUMPERS

JP1 – Select the source for REF+, either external or

5.00 volts from the onboard LT1236 reference (de-

fault.)

JP2 – Select normal or triggered mode. In normal

mode, the LTC1592 is updated as fast as the con-

troller can, which is dependant on the speed of the

PC. In triggered mode, the update rate can be re-

duced by applying a 5V pulse to the TRIGGER tur-

ret.

CONNECTION TO DC590 SERIAL CONTROLLER

J1 is the power and digital interface connector.

Connect to DC590 serial controller with supplied 14

conductor ribbon cable.

OUTPUT CONNECTIONS

The output voltage is connected to E4 (VOUT) and

the center conductor of BNC connector J3. The BNC

connector is intended for measuring settling time

and glitch impulse by connecting directly to an os-

cilloscope input with a barrel connector. Do not use

a long cable, as the output amplifier may not be

stable.

REFERENCE CONNECTIONS

The onboard LT1236 reference should be adequate

for most applications. However, for multiplying

mode applications an external reference signal may

be applied to J2 (no connector is installed.)

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 572

16-BIT SOFTSPAN DAC

EXPERIMENTS

OUTPUT VOLTAGE

The offset and gain errors of the LT1592 are rela-

tively easy to measure. These errors are on the or-

der of several LSBs, so a voltmeter with an accu-

racy of 5V/2

= 76µV, or 5 digits, is required. Note

that errors are dependent on several factors, includ-

ing reference error, amplifier offset, DAC errors, and

errors in measurement equipment.

OFFSET ERROR

Offset error is the output voltage when the digital

code for zero output is loaded into the DAC. For the

unipolar ranges (0-5V, 0-10V) the code for zero

output is 0x0000. For the symmetric bipolar ranges

(+/-2.5V, +/-5V, +/-10V) it is 0x8000. For the –2.5 to

+7.5V range, it is 0x4000.

GAIN ERROR

Gain error is the error in slope of the DAC output,

and is calculated by subtracting the zero code error

from the maximum code error. For instance, in the

–2.5 to 7.5V range a certain LTC1592 produces –

2.50004V at zero code and +7.50009 at maximum

code, the gain error is 0.00009V – (-0.00004V) =

130µV.

The error in LSBs is 130µV * 2

/ 10 = 0.85LSB.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 572

16-BIT SOFTSPAN DAC

SETTLING TIME

To measure settling of the LTC1592, connect the

output BNC to an oscilloscope input with a barrel

connector (not a cable.) Be sure that the oscillo-

scope can tolerate the voltage that is being applied

directly to the input. Select the Square wave output

on the control panel, and enter the desired high and

low voltages.

For large voltage swings, the oscilloscope can trig-

ger directly on the analog output. For smaller

swings it may be useful to trigger on the

CS/LD tur-

ret. The rising edge of this signal initiates a transi-

tion on the DAC output.

Figures 1 through 4 show the full-scale step re-

sponse of DC572 for various output ranges.

Scope Channel 4 is the analog output from the

LT1469 amplifier and Channel 3 is the

CS/LD signal.

Figure 1.

5V Step, 0-5V Range

Figure 2.

–5V Step, 0-5V Range

Figure 3.

20V Step, +/-10V Range

Figure 4.

-20V Step, +/-10V Range

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 572

16-BIT SOFTSPAN DAC

GLITCH IMPULSE

Glitch impulse is the area in volt-seconds of the

glitch produced when the DAC switches between

two adjacent codes. Typically the glitch is largest

when the DAC switches from 0x7FFF to 0x8000, as

all of the DAC switches are changing state while the

output is changing by 1 LSB. The LTC1592 has an

internal deglitcher that reduces the midscale glitch

impulse to less than 0.5 nV-s (typical.) Figure 5

shows the midscale glitch impulse of the LTC1592,

configured as shown in the DC572 schematic (with

LT1469 output amplifier and a 30pF compensation

capacitor.) The amplitude is approximately 2mV and

the width is approximately 250nS, giving an area of

0.5nV-S.

This test is best performed by connecting the out-

put BNC connector directly to the oscilloscope input

with a barrel connector. Using a 10x probe may

produce unpredictable results due to ground clip

inductance.

Figure 5.

Glitch Impulse, +/10V Range

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 572

16-BIT SOFTSPAN DAC

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