Linear Technology LTC1592 User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 572
16-BIT SOFTSPAN DAC
1
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
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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
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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
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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
16
= 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
16
/ 10 = 0.85LSB.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 572
16-BIT SOFTSPAN DAC
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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
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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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