DC2459A - Demo Manual

DEMO MANUAL DC2459A
LTC1668
16-Bit, 50Msps DAC
DESCRIPTION
Demonstration circuit 2459A features the LTC®1668, 16-bit,
50Msps current output DAC in a 28-lead SSOP package.
Pin-compatible 14-bit and 12-bit versions are available for
lower resolution requirements, but all DC2459A assembly
types are populated with the LTC1668.
DC2459A can be connected directly to a digital pattern generator or customer circuit. The DC2459A is also compatible
with several popular low cost FPGA development boards for
Altera and Xilinx devices. These include the Arrow SoCkit
(Altera Cyclone 5 SoC), C5G (Altera Cyclone 5), DE0 Nano
(Altera Cyclone 4), Embedded Micro Mojo (Xilinx Spartan
6), and Numato Labs Mimas (Xilinx Spartan 6) boards1.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2459A
L, LT, LTC, LTM, Linear Technology, Linduino and the Linear logo are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
1. Refer to Design Files for Parts List/Bill of Materials.
DC2459a F01
Figure 1. Basic Connections
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DEMO MANUAL DC2459A
ASSEMBLY OPTIONS
Table 1. Demonstration Circuit Output Options
ASSEMBLY TYPE
OP AMP
OUTPUT
DC2459A-A
LT1812
Single-Ended: ±1V (2VP-P)
DC2459A-B
LT6600
Differential: ±0.25V (1VP-P)
DC2459A-C
LT1468
Single-Ended: ±10V (20VP-P)
QUICK START PROCEDURE
The LTC1668 is a general purpose DAC with a wide range
of applications. Depending on the end application, the
best data source for evaluating the LTC1668 may be a
digital pattern generator or the actual customer application
circuit. However, a basic test of distortion and signal-tonoise ratio using a sinewave output can be a valuable first
step in evaluating the performance of the LTC1668. As
such, several example FPGA programs are provided that
produce a sinewave output.
1.There are several options for providing digital data to
the DC2459A, shown in Figures 2 to 6. Connect the
DC2459A to a digital pattern generator (which can be
the customer application circuit) or supported low cost
FPGA board. Do not enable the data source until power
is applied to the DC2459A.
When using the Mojo board, install a 0Ω resistor on
R28, which is located on the bottom of the board. This
routes the clock signal to the correct input for the Mojo
board.
DC2459a F02
Figure 2. Basic Connection to Digital Pattern Generator
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DEMO MANUAL DC2459A
QUICK START PROCEDURE
DC2459a F03
Figure 3. DC2459A Connected to the SoCkit
DC2459a F04
Figure 4. DC2459A Connected to the DE0 Nano
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DEMO MANUAL DC2459A
QUICK START PROCEDURE
Table 2. Jumper Configurations
ASSEMBLY TYPE
JP1
JP2
DC2459A-A
5V
–5V
DC2459A-B
5V
–5V
DC2459A-C
V+
V–
2.Ensure JP1 and JP2 are set to the correct position as
shown by Table 2.
3.Connect ±12V to the V+ and V– turret posts. Apply a
3.3V, 50MHz clock to J5.
4. Enable the digital data source. If an FPGA board is being
used, apply power, and load the bitstream into the FPGA.
Bitstreams are included in the design files, available at
http://www.linear.com/demo/2459. Refer to the FPGA
user manual for uploading bitstream files.
5. The FPGA bitstreams default to a 10kHz sinusoidal output. Refer to Table 1 for demo board assembly output
configuration and voltages.
DC2459a F05
Figure 5. DC2459A Connected to the Mimas Board
DC2459a F06
Figure 6. DC2459A Connected to the Mojo Board
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DEMO MANUAL DC2459A
QUICK START PROCEDURE
Analog Circuit Descriptions
This demo board option is the simplest configuration and
allows the most flexibility for modifications.
Assembly type A implements a differential resistor loaded
output to a differential to single-ended output shown in
Figure 7. The circuit delivers good AC distortion performance at signal frequencies of a few MHz down to DC.
The capacitor adds a single real pole of filtering and helps
reduce distortion by limiting the high frequency signal
amplitude at the op amp inputs. The circuit swings ±1V
around ground.
Assembly version B implements a differential amplifier
using the LT6600-2.5, a 4th order, 2.5MHz lowpass filter
as shown in Figure 8. The outputs each swing ±0.25V
around ground for a total differential output of 1VP-P.
Assembly version C implements a dual op amp current to
voltage converter shown in Figure 9. The circuit delivers
good distortion and AC performance to a few kHz. The
output swings ±10V around ground.
500Ω
5V
5V
200Ω
IOUTA
LTC1666/
LTC1667/
LTC1668
LT1809
60pF
200Ω
IOUTB
1580Ω
LADCOM
IOUTA
–
+
±1V
10dBm
2
IOUTB
8
1580Ω
52.3Ω
52.3Ω
500Ω
–5V
1
7
1580Ω
LTC1668
VOUT
1580Ω
–
0.1µF
3
+
4
LT6600-2.5
–
+
6
5
VOUT–
0.1µF
50MHz
–5V
DC2459a F07
Figure 7. Differential to Single-Ended Op Amp I-V Converter
VOUT+
DC2459a F08
Figure 8. Differential Op Amp I-V Converter
12V
VREF
1k
VREF
12V
+
1k
LT1468
25Ω
IOUTA
25Ω
20pF
LTC1668
IOUTB
–
+
VOUT
LT1468
1k
–
–12V
1k
–12V
1k
25Ω
25Ω
47pF
20pF
20pF
DC2459a F08
Figure 9. Dual Op Amp Differential to Single-Ended Op Amp I-V Converter
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DEMO MANUAL DC2459A
EXTERNAL CONNECTIONS
GND: Four ground turrets are provided. These are connected directly to the ground plane and are the common
connection for all supplies and signals.
V+
V–:
and
Power Supply Turrets. ±12V supply. The ±5V
supplies for the LTC1668 and op amp circuits are derived
from this supply.
3.3V: FPGA Power Rail. Do not connect this turret to a
power supply, it is for monitoring the 3.3V supply on the
connected FPGA board.
50M_CLK: Input Clock. Frequency range is DC to 50MHz.
Logic level should be 3.3V when used with an FPGA board.
The logic level can be up to 5V when used with a digital
pattern generator.
OUT+: Voltage from the noninverting DAC output amplifiers. Assembly options A and C use this connector as
the single-ended output. Assembly option B uses this
connector for the noninverting differential output.
OUT–: Voltage from the inverting DAC output amplifier.
Assembly option B uses this connector for the inverting
differential output.
P1: This connector is used to connect to Altera’s SoCkit
board. The pins are 3.3V logic level.
J1: Linduino Connector. Provides a SPI interface to the
FPGA board. The pins are 3.3V logic level.
J2: All pins are ground. These connections are intended
for logic analyzer or digital pattern generator grounds.
J3: This connector is used to connect to the DE0 Nano
FPGA board. The pins are 3.3V to 5V (TTL compatible)
logic level.
J4: This connector is used for the Mimas board and the
Mojo FPGA board. Follow the footprint on the silkscreen
to ensure proper placement. The pins are 3.3V to 5V (TTL
compatible) logic level.
Setting the Frequency of the FPGA Digital Pattern
Generator
The FPGA examples generate a digital sinusoidal output
using either a numerically controlled oscillator (NCO, for
Altera examples) or direct digital synthesizer (DDS, Xilinx
examples). The input to these generators is a 32-bit word
that sets the output frequency according to Equation 1. A
simple SPI interface allows the 32-bit word to be set using
a 4-wire interface from a SPI master such as a Linduino
microcontroller. The MISO output returns the previous
32-bit configuration word, shown in Figure 10.
Equation 1:
CONFIGURE WORD =
DESIRED FREQUENCY
• ( 232 – 1)
SYSTEM CLOCK FREQUENCY
CS
SCK
MSO
D31 D30 D29 D28 D27 D26 D25 D24 D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
D8
D7
D6
D5
D4
D3
D2
D1
D0
32-BIT INPUT WORD
MOSI
D31 D30 D29 D28 D27 D26 D25 D24 D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9
PREVIOUS 32-BIT INPUT WORD
DC2459a F10
Figure 10. SPI Interface Data Format
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DEMO MANUAL DC2459A
EXTERNAL CONNECTIONS
Using the Linduino® as a USB to SPI Interface for
LinearLabTools
The Linduino can be used to configure the FPGA via a SPI
port with a Python program included in LinearLabTools.
Linduino Interface
1.DC2459A example designs use the default Linduino
firmware (DC590 emulator.) If the Linduino has been
reprogrammed, follow the procedure in the Linduino
(DC2026) demo manual to reprogram the DC590
emulator.
2.Set JP3 to EXT (This causes the Linduino to use the
FPGA board’s 3.3V supply to set the logic levels.)
Software Installation for LinearLabTools
1.Download and install LinearLabTools from:
http://www.linear.com/solutions/linearlabtools
2.Follow the Quick Start procedure for installing
LinearLabTools.
3.Examples for the DC2459 are written in Python;
Anaconda distribution is used as an example below.
Running the LinearLabTools DC2459A Script
1. Open the Spyder IDE. In the File menu select Linear_
lab_tools folder  python  app_examples 
LTC1668  DC2459A.py
Figure 11. Spyder IDE
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DEMO MANUAL DC2459A
EXTERNAL CONNECTIONS
A new tab will appear with the script.
Figure 12. DC2459A Python Script
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DEMO MANUAL DC2459A
EXTERNAL CONNECTIONS
2.Run the script by clicking the run button:
The IPython console will show the simple program
interface.
Figure 13. Simple Text Interface
3.To use the interface, enter the commands next to
the “Enter a command:” text and hit enter.
Figure 14. Entered Data
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Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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DEMO MANUAL DC2459A
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:
This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT
OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete
in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety
measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union
directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.
If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date
of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU
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ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims
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appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or
agency certified (FCC, UL, CE, etc.).
No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,
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Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and
observe good laboratory practice standards. Common sense is encouraged.
This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application
engineer.
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Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation
10 Linear Technology Corporation
dc2459af
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