User's Guide SBAU161 – February 2010 DAC8728EVM DAC8728EVM This user's guide describes the characteristics, operation, and use of the DAC8728EVM, an evaluation board for the DAC8728. The DAC8728 is a low-power, octal, ±15V output, parallel input, 16-bit digital-to-analog converter (DAC). This evaluation module (EVM) allows evaluation of all aspects of the DAC8728 and gives control over every pin on the device.
www.ti.com 1 2 3 4 5 6 7 8 Contents EVM Overview ............................................................................................................... 3 Analog Interface ............................................................................................................. 3 Digital Interface .............................................................................................................. 4 Parallel Control ......................................................................
EVM Overview www.ti.com 1 EVM Overview 1.1 Features DAC8728EVM: • Full-featured evaluation board for the DAC8728, a 16-bit, parallel input, octal output digital-to-analog converter • Onboard or external reference selection • Onboard 5V or 2.
Digital Interface www.ti.com The analog interface is populated on the top and the bottom of the evaluation board. All of the output pins are routed directly from the DAC8728 to the J5 connector. Additionally, they can be routed through an OPA277 buffer circuit using JP1 and JP2. The output of the buffer circuit is routed to TP3 and TP4. The output of the DAC8728 internal offset DAC is routed to test points TP10 and TP17. The DAC8728EVM has two external reference voltage options. J2.
Parallel Control www.ti.com 4 Parallel Control Samtec part numbers SSW-110-22-S-D-VS and TSM-110-01-T-DV provide a convenient, 10-pin, dual-row header/socket combination at J1. This header/socket provides access to the digital control pins of the EVM. Consult Samtec at http://www.samtec.com or call 1-800-SAMTEC-9 for a variety of mating connector options. Table 2 describes the parallel interface pins. Table 2. J2: Parallel Interface Pins Pin Number Signal Description J2.
Parallel Control www.ti.com Figure 1 shows the parallel control header and the connections to the SN74LVC139.
Parallel Control www.ti.com Also, in order to appropriately control the CLK input to the SN74LVC374 (U11), the LATCH_CTRL output of the SN74LVC139 (U7) had to be logic ORed with the WE signal. This configuration ensures that the data are latched into the SN74LVC374 while it is still valid from the DSP. This circuit and related truth table (Figure 3 and Table 4, respectively) can be seen below. Latch_CTRL Latch WE SN74LVC1G32 Figure 3. LATCH External Logic Table 4.
Parallel Control 4.2 www.ti.com DC_CS Signals The DC_CS signal is used as a board select for the EVM. It is an active low signal that controls the output enable bit on the SN74LVC16245 and, in conjunction with the external logic, is used to create the CS signal for the DAC8728. The user selects one of the three possible addresses using JP10. By default, the DC_CS signal is set to the 2Y1 output of the SN74LVC139.
Parallel Control www.ti.com 4.9 SN74LVC139 Outputs Table 6 through Table 8 show the truth tables for the outputs of the SN74LVC139. Note that A3 to A0 correspond to the signals from the J1 header. Table 6. A0 and A1 Address Combinations A1 A0 RST CLR R/W LATCH_CTRL 0 0 1 1 1 0 0 1 1 1 0 1 1 0 1 0 1 1 1 1 0 1 1 1 Table 7. A2 and A3 Address Combinations A3 A2 LDAC DC_CS2 DC_CS1 DC_CS0 0 0 1 1 1 0 0 1 1 1 0 1 1 0 1 0 1 1 1 1 0 1 1 1 Table 8.
Parallel Control www.ti.com 4.11 Parallel Data The DAC8728EVM uses Samtec part numbers SSW-116-22-S-D-VS and TSM-116-01-T-DV to provide a convenient, 16-pin, dual row header/socket combination at J6. This header/socket combination provides access to the parallel data pins of the DAC8728 and the inputs to the SN74LVC374. Data lines D0 to D15 are located on the odd numbered pins 1 through 31 on the J6 header. Even pin numbers 2 to 32 are connected to digital ground.
Power Supplies www.ti.com 5 Power Supplies J4 is the power-supply input connector. Table 9 lists the configuration details for J4. The voltage inputs to the DAC can be applied directly to the device. The DAC8728 requires multiple power supplies to operate. AVDD, AVSS, DVDD, and IOVDD are required to properly power the DAC. The power should be applied in this order: IOVDD, DVDD, then AVDD and AVSS, followed by the reference voltage.
Reference Voltage 6 www.ti.com Reference Voltage The DAC8728EVM is configured with two different onboard precision references. The evaluation module has both a +2.5V and +5V reference using the REF5025 and the REF02, respectively. By using the screw terminal J2, the user can also apply external reference voltages to the board. Any external voltage applied to J2 must be within the +1.0 to +5.5V reference voltage range specification for the DAC8728.
EVM Operation www.ti.com 7.3 Default Jumper Settings and Switch Positions The default configuration of the DAC8728EVM is summarized in Table 10. Table 10.
EVM Operation 7.4 www.ti.com Unipolar/Single-Supply Setup (Default) Follow the configuration given in Table 11 and illustrated in Figure 5 to set up the board for single-supply operation. NOTE: The OFFSET_A and OFFSET_B pins must be shorted directly to GND for unipolar/single-supply operation. Table 11. Unipolar/Single-Supply Configuration Jumper Position JP3, JP4, JP5, JP6, JP7, JP9, JP15, JP17, JP19, JP20 1-2 JP14 2-3 JP1, JP2, JP18 Open JP8, JP16, JP11, JP13 Closed JP10 3-4 Figure 5.
EVM Operation www.ti.com 7.5 Bipolar/Dual-Supply Setup Follow the configuration shown in Table 12 and Figure 6 to set up the board for bipolar/dual-supply operation. Table 12. Bipolar/Dual-Supply Configuration Jumper Position JP3, JP4, JP5, JP6, JP7, JP9, JP14, JP15, JP17, JP19, JP20, 1-2 JP1, JP2, JP8, JP13, JP16, JP18 Open JP11 Closed JP10 3-4 Figure 6.
Schematics and Layout 8 www.ti.com Schematics and Layout Schematics for the DAC8728EVM are appended to this user's guide. The bill of materials is provided in Table 13. 8.1 Bill of Materials NOTE: All components should be compliant with the European Union Restriction on Use of Hazardous Substances (RoHS) Directive. Some part numbers may be either leaded or RoHS. Verify that purchased components are RoHS-compliant. (For more information about TI's position on RoHS compliance, see the TI web site.
Schematics and Layout www.ti.com Table 13. DAC8728EVM Bill of Materials (1) (continued) Ref Des (2) Item No. Qty Description Manufacturer 30 15 TP1-TP4, TP6 TP12, TP15-TP18 Test Point: sSingle .025 Pin, Red Keystone 5000 Mfr Part Number 31 3 TP5, TP13, TP14 Test Point: single .025 Pin, Black Keystone 5001 32 1 U1 5V Reference 8-SOP TI REF02BU 33 1 U2 2.
1 2 3 4 5 6 IOVDD IOVDD R2 49.9 5 0.01uF AVDD C8 8 0.1uF R5 V- V+ 2 3 R3 6 REF5V TP2 C9 47uF 1 8 7 C11 DNI C13 REF2.5V JP7 REF_B JP5 REF2.5V C18 1uF TP6 AVDD AVDD L1 IOVDD C27 10uF 10uF C31 1uF C32 1uF 4 12 TP10 OFFSET_A VOUT_0 13 VOUT_1 10 VOUT_2 7 VOUT_3 5 VOUT_4 44 VOUT_5 42 VOUT_6 39 VOUT_7 36 37 OFFSET_B 14 22 23 31 JP16 OFFSET_B C24 10uF B +3.
Evaluation Board/Kit Important Notice Texas Instruments (TI) provides the enclosed product(s) under the following conditions: This evaluation board/kit is intended for use for ENGINEERING DEVELOPMENT, DEMONSTRATION, OR EVALUATION PURPOSES ONLY and is not considered by TI to be a finished end-product fit for general consumer use. Persons handling the product(s) must have electronics training and observe good engineering practice standards.
IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete.