ADS1278EVM Hardware Details
Table 5. Jumper and Switch Descriptions (continued)
Jumper/Switch
Functions
Descriptions
FS - Frame Sync format
(3)
S6
Serial Interface format
SPI - SPI-compatible mode
(3)
Selects Channel 2 input source - header or input buffer
S7
Channel 2 Input source selector
Left - header
Right - input buffer
Selects Channel 1 input source - header or input buffer
S8
Channel 1 Input source selector
Left - header
Right - input buffer
(3)
Refer to
for more details.
5.2
Power-Down, Mode, and Format Control
The ADS1278 has several pins to control the power-down of individual channels, and select the mode and
format for the digital interface.
For users of the ADS1278EVM as a stand-alone module, these pins may be pulled high or low through
DIP switches S1 and S2 (see
). Refer to the
for complete details on
these pins and which state sets which options.
For use in the ADS1x7xEVM-PDK, the state of these pins is controlled by software, using the I
2
C port
expander on the EVM. When using the EVM with the EVM-PDK, the DIP switches S1 and S2 must all be
switched down (toward the center of the board). The ADS1278EVM-PDK software checks at startup to
verify that these switches are set correctly, and generates an error message for incorrect settings. The
software cannot detect if the switches are changed after startup.
CAUTION
When using the ADS1x7xEVM-PDK, the DIP switches S1 and S2 must all be
switched down (toward the center of the board). Failure to do so may damage
the EVM.
5.3
Clock Source
The ADS1278 clock can come from one of several sources: the onboard 27MHz crystal oscillator, a clock
supplied by a processor on the TOUT pin (J4.17), or an external clock source connected between J4.17
(TOUT) and J4.18 (DGND).
If the onboard 27MHz oscillator is selected, the device can be run in high-speed mode, high-resolution
mode, low-power mode, or low-speed modes with CLKDIV set to 1.
If the performance of the device must be explored with CLKDIV set to 0 in the low-power and low-speed
modes, an external clock must be provided to the board, either using the TOUT connection or having an
external clock source connected to J18. The same condition is true if frequencies other than the 27MHz
provided by the onboard oscillator must be investigated.
5.4
Analog Headers, J1 and J3
For maximum flexibility, the ADS1278EVM is designed for easy interfacing to multiple analog sources.
These headers/socket provide access to the analog input pins of the ADS1278.
Four of the analog input sources (Channels 1
–
4) connect directly to J3 (top or bottom side) or through
signal-conditioning modules available for the modular EVM system. These inputs have provisions to buffer
the inputs using THS4521 before connecting to the converter. Switches S4-5 and S7-8 provide the
capability to connect either the header directly or through a buffer. When the buffers are not selected, the
op-amps used for buffering can be powered down by shorting JP3.
12
ADS1x7xEVM-PDK
SBAU197
–
February 2012
Copyright
©
2012, Texas Instruments Incorporated
