Linear Technology LTC2668 Quick setup guide

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DEMO MANUAL DC2025A
DESCRIPTION
16-Channel 16-Bit/12-Bit
±10V VOUT SoftSpan DACs with
10ppm/°C Max Reference
Demonstration circuit 2025A features the LT C
®
2668,
16-channel16-Bit/12-Bit±10VVOUT SoftSpan™DACswith
10ppm/°C max reference in a 6mm × 6mm QFN package.
This device features per-channel SoftSpan configuration
with five output ranges: 0V to 5V, 0V to 10V, ±2.5V, ±5V,
and ±10V. A toggle feature allows any or all DACs to switch
betweentwoprogrammedcodesviaasingleSPIcommand
or by the TGP input pin. The versatile SPI interface can
operate on any logic level between 1.71V and 5.5V, for
easy interface to lower voltage microcontrollers or FPGAs.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
SoftSpan and QuikEval are trademarks of Analog Devices, Inc. All other trademarks are the
property of their respective owners.
DC2025A-A is populated with the 16-bit version of the
LTC2668. DC2025A-B is populated with the 12-bit version
for lower resolution applications.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2025A
Figure 1. Connection Diagram
SIGNAL
GROUND
MEASURE REF VOLTAGE,
MUX OUTPUT
SIGNAL
GROUND
DAC
OUTPUTS
+
–
+
–
DAC
OUTPUTS
OVERTEMPERATURE
OUTPUT
SEE TEXT. LDAC, TGP, CLR
PULLED TO OVP W/5kΩ
DAC
OUTPUTS
ANALOG SUPPLIES
(±15V ALLOWS ALL
SOFTSPAN RANGES)

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DEMO MANUAL DC2025A
QUICK START PROCEDURE
Download and install QuikEval™ from:
http://www.linear.com/designtools/software/#Data
Connect a DC590 controller or DC2026 Linduino with
DC590emulatorfirmwaretotheDC2025Awith thesupplied
ribbon cable. Connect low-noise analog power supplies
as shown in Figure 1. A±15V supply will allow all of the
SoftSpan ranges to be used, refer to the LTC2668 data
sheet for other supply options if not all SoftSpan ranges
are used.
Connect the controller to the host PC’s USB port and run
QuikEval. The DC2025A software will be downloaded and
installed, after which a jumper setting window will appear
as shown in Figure 2. The default settings are internal
reference, SoftSpan operation with 0V to 5V range, 0V
output on power-up. If the jumpers on the board have been
changed to a different configuration, select the appropri-
ate options in the pull-down menus to match the board.
Click OK and the main dialog will appear. The control panel
gives access to all of the LTC2668’s functionality includ-
ing per-channel SoftSpan ranges, toggling, Power-Down,
etc. Detailed instructions are provided in the Help menu.
Figure 2. Jumper Settings Dialog

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DEMO MANUAL DC2025A
Figure 3. Main Control Panel
QUICK START PROCEDURE

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DEMO MANUAL DC2025A
QUICK START PROCEDURE
External Connections
J1: Interface connector to DC590 controller or Linduino.
Provides OVP power, SPI interface, and board identifica-
tion.
V–, GND, V+:Analog supplies, connected to the LTC2668
V+and V–pins. Nominally ±15V for operation in all Soft-
Span ranges. Refer to the data sheet for other supply
configurations.
GND: Four additional ground posts and exposed ground
plane around board edge allow solid connection to pro-
totype circuitry and measurement equipment.
AVP:Analog supply voltage. Normally supplied by an on-
board LT1761-5 fixed 5V regulator that is powered from
the V+supply. For single 5V supply applications, AVP
may be tied directly to V+and supplied with 4.5V to 5.5V.
OVP: Digital interface power. No connection to this pin is
required when used with a DC590 or Linduino controller.
If another controller is used, connect to digital supply that
powers the SPI bus controller (1.71 to 5.5V).
REF: Connection to the REF pin. In internal reference
mode, the reference voltage may be monitored at this
point. Placing REF_SEL jumper in the EXT position allows
an external reference to be connected to this point.
MUX: Monitor Mux output. Allows surveying the DAC
outputs under software control. Must be measured with
a high impedance meter (output impedance is nominally
2.1kΩ).
VOUT0 to VOUT15: DAC outputs.
CLR:Asynchronous clear input (pulled high to OVP with
a4.99k resistor). Pull to ground to reset the DAC to the
power-on reset value (determined by MSPx pins.)
TGP: Toggle input (pulled high to OVP with a 4.99k resis-
tor). A high level on this pin enables software toggling. See
data sheet for a complete description of toggle operation.
LDAC:Asynchronous DAC update. If CS/LD is high at the
falling edge of LDAC, DAC outputs will be updated with
the contents of the input registers. If CS/LD is low when
LDAC goes low, the DAC registers are updated after CS/
LD returns high.
OVRTMP:Overtemperature pin (pulled high to OVP with a
4.99k resistor). The LTC2668 pulls this pin low if the die
temperature exceeds approximately 160°C. It is released
on the next rising edge of CS/LD.

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DEMO MANUAL DC2025A
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
QUICK START PROCEDURE
Table 1
MSP2 MSP1 MSP0 OUTPUT RANGE RESET CODE MANUAL SPAN SoftSpan
0 0 0 ±10V Mid-Scale X
0 0 1 ±5V Mid-Scale X
0 1 0 ±2.5V Mid-Scale X
0 1 1 0V to 10V Zero-Scale X
1 0 0 0V to 10V Mid-Scale X
1 0 1 0V to 5V Zero-Scale X
1 1 0 0V to 5V Mid-Scale X
1 1 1 0V to 5V Zero-Scale X
Jumpers
REF_SEL (JP1): Selects internal or external reference
mode. (See data sheet description of REFCOMP pin.)
MSP0, MSP1, MSP2 (JP2, JP3, JP4): Manual Span
control. Setting all jumpers to the 1 position (Default)
selects SoftSpan operation, with a power-up default span
of 0V to 5V, and reset to Zero-Scale. Other options are
listed in Table 1.
LEDs
OVRTMP: Lights when OVRTMP pin asserts, indicating an
overtemperature state. (Note that LED will light if positive
analog supply is present and OVP is not. OVP is normally
supplied by the controller.)
Test Points
The SPI bus is available on a row of through-hole test
points next to J1 that may be used to monitor the bus or
to drive the bus with an external controller.
EEGND, WP: For factory use only.

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DEMO MANUAL DC2025A
 LINEAR TECHNOLOGY CORPORATION 2014
LT 0617 REV A • PRINTED IN USA
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