Texas Instruments ADS1178EVM, User Manual, Page: 12 / 52

8.3 ADS1278EVM-PDK Power Supply
EVM Operation
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The SCLK input of the converter is driven by the serial port signal CLKX, pin J5.3.
•
The signal from the selected source for the clock (see Section 7 , Clock Source ) is connected to the
CLKR pin (J5.5) allowing the serial port of a processor to be synchronized to the converters master
clock.
•
The signal from the selected clock source is routed to the CLK input of the converter.
•
Port P10 of the I2C port expander U18 is connected to a logic high level, so that the position of switch
S12 can be read back by software.
The right position of S12, marked FS , selects the frame-sync format. In this format, the signals are
connected in this configuration:
•
The SCLK input of the converter is driven by the serial port signal CLKR, pin J5.5.
•
The signal from the selected clock source is connected to the CLKX pin (J5.3), allowing the serial port
of a processor to be synchronized to the converter's master clock.
•
The CLK input of the converter is driven by the CLKR signal (J5.5). This ensures that the CLK and
SCLK signals have the same phase and the correct ratio as outlined in the data sheet of the device.
•
Port P10 of the I
2
C port expander U18 is connected to a logic low level, so that the position of switch
S12 can be read back by software.
For use in the ADS1278EVM-PDK, S12 must be in the right (FS) position, which is the factory default
setting.
Switching to SPI format will allow users to connect the EVM to any SPI-compatible processor not
supporting the frame-sync mode. If this format is selected, please keep in mind that the high-speed mode
will not work at full speed (32.768MHz) because of the limitations outlined in the device product data
sheet.
The ADS1278EVM can either be powered by an AC adapter or by applying the 5V, +10V, and –10V to the
connectors on the MMB0 board. The MMB0 board will provide the 5V and 3.3V to the ADS1278EVM
along with the +10V and –10V signals. Because the circuitry is provided on the ADS1278EVM to generate
+10V and –10V, the complete system can be powered from the supplied AC adapter that su6V
and 3A.
ADS1178EVM, ADS1278EVM, ADS1178EVM-PDK, and ADS1278EVM-PDK 12 SBAU129C – November 2007 – Revised July 2008
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