ADS1294 datasheet(25/88 Pages) TI

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ADS1298

+1/2V

REF

1/2

Common

Voltage

Single-EndedInput

ADS1298

peak-to-peak

REF

peak-to-peak

REF

Common

Voltage

DifferentialInput

CM+1/2V

REF

+1/2V

REF

1/2

Single-EndedInputs

INP

CMVoltage

REF

1/2

CM+1/2V

REF

DifferentialInputs

INP

INN

CMVoltage

1/2V

REF

Common-ModeVoltage(DifferentialMode)=

(INP)+(INN)

,Common-ModeVoltage(Single-EndedMode)= INN.

INN=CMVoltage

InputRange(DifferentialMode)=(AINP

AINN)=V

( V

)=2V

REF

ADS1294, ADS1294R

ADS1296, ADS1296R

ADS1298, ADS1298R

www.ti.com

SBAS459H

– JANUARY 2010 – REVISED OCTOBER 2011

Supply Measurements (MVDDP, MVDDN)

Setting CHnSET[2:0] = 011 sets the channel inputs to different supply voltages of the device. For channels 1, 2,

5, 6, 7, and 8, (MVDDP

– MVDDN) is [0.5 × (AVDD – AVSS)]; for channel 3 and for channel 4, (MVDDP –

MVDDN) is DVDD/4. Note that to avoid saturating the PGA while measuring power supplies, the gain must be

set to '1'. For example, if AVDD = 2.5V and AVSS =

–2.5V, then the measurement result would be 2.5V.

Lead-Off Excitation Signals (LoffP, LoffN)

The lead-off excitation signals are fed into the multiplexer before the switches. The comparators that detect the

lead-off condition are also connected to the multiplexer block before the switches. For a detailed description of

the lead-off block, refer to the Lead-Off Detection subsection in the ECG-Specific Functions section.

Auxiliary Single-Ended Input

The RLD_IN pin is primarily used for routing the right leg drive signal to any of the electrodes in case the right leg

drive electrode falls off. However, the RLD_IN pin can be used as a multiple single-ended input channel. The

signal at the RLD_IN pin can be measured with respect to the voltage at the RLD_REF pin using any of the eight

channels. This measurement is done by setting the channel multiplexer setting to '010' and the RLD_MEAS bit of

the CONFIG3 register to '1'.

ANALOG INPUT

The analog input to the ADS1298 is fully differential. Assuming PGA = 1, the input (INP

– INN) can span

between

–VREF to +VREF. Refer to Table 8 for an explanation of the correlation between the analog input and the

digital codes. There are two general methods of driving the analog input of the ADS1298: single-ended or

differential, as shown in Figure 26 and Figure 27. Note that INP and INN are 180

°C out-of-phase in the

differential input method. When the input is single-ended, the INN input is held at the common-mode voltage,

preferably at mid-supply. The INP input swings around the same common voltage and the peak-to-peak

amplitude is the (common-mode + 1/2VREF) and the (common-mode – 1/2VREF). When the input is differential,

the common-mode is given by (INP + INN)/2. Both the INP and INN inputs swing from (common-mode + 1/2VREF

to common-mode

– 1/2VREF). For optimal performance, it is recommended that the ADS1298 devices be used in

a differential configuration.

Figure 26. Methods of Driving the ADS1298: Single-Ended or Differential

Figure 27. Using the ADS1298 in the Single-Ended and Differential Input Modes

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Product Folder Link(s): ADS1294 ADS1294R ADS1296 ADS1296R ADS1298 ADS1298R

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