Datasheet

EVM Operation

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7.1.2 S2: AIN2-3 Input Select

These switches control which lines are routed to the ADS1256 AIN2 through AIN3 inputs. The positions of

the switches are described in Table 9.

Table 9. AIN2-3 Input Select Switch (S2)

Board Marking Switch Position Input Source AIN0 Connection AIN1 Connection

EXT Left External J1.4 J1.3

REF Middle Reference voltage +2.5V AGND

ZERO Right Zero (shorted to +2.5V +2.5V

reference)

In the EXT position, J1 pins 3 and 4 are connected to the ADS1256 AIN3 and AIN2 pins, respectively. In

the REF position, the reference is connected across the ADS1256 AIN2 and AIN3 pins. In the ZERO

position, both AIN2 and AIN3 are connected to the reference. This configuration gives a zero-scale

reading across AIN2 and AIN3.

The REF and ZERO positions are useful for noise tests.

7.1.3 Input Filtering Capacitors

The ADS1256EVM has pads for filtering capacitors on every input pair and for the reference input. Each

input pair has pads for two common-mode capacitors and one differential capacitor.

The ADS1256 has a flexible input multiplexer, so these capacitors do not always function as

common-mode and differential signal filters. For example, when measuring a single-ended input, the

common-mode capacitors act to filter the signal.

The ADS1256EVM is shipped with only some of the capacitor pads populated. This configuration allows

the board to be immediately used to measure both differential and single-ended inputs. As shipped, inputs

AIN0 through AIN7 have 10nF differential mode capacitors installed. A differential 1mF capacitor is

connected to the reference near the reference pins.

The input filtering capacitors are in relatively large 1210-size packages, in contrast to most of the other

passives on the board. These capacitors were designed to be large so that you can easily remove them or

replace them with other values. By exercising appropriate care, you can even solder leaded devices to

these large pads.

7.2 Digital Control

The digital control signals can be applied directly to J6 (top or bottom side). The modular ADS1256EVM

can also be connected directly to a DSP or microcontroller interface board, such as the 5-6K Interface or

HPA-MCU Interface boards available from Texas Instruments, or the MMB0 if purchased as part of the

ADS1256EVM-PDK. For a list of compatible interface and/or accessory boards for the EVM or the

ADS1256, see the relevant product folder on the TI web site.

7.3 ADS1256EVM-PDK Power Supply

The analog portion of the ADS1256EVM can either be powered by a 5V source generated via ac adapter,

or by applying the +5VA to the connector on the MMB0 board. The MMB0 board will provide the digital 5V

and 3.3V to the ADS1256EVM. To provide +5VA to the ADS1256EVM from the MMB0 board, make sure

the jumper at J13 (on the MMB0) is closed from +5V to +5VA.

ADS1256EVM and ADS1256EVM-PDK SBAU090C–November 2003–Revised July 2010