Datasheet

ADS1198
- V to
+1/2V
1/2
REF
REF
Common
Voltage
Single-EndedInput
ADS1198
V
peak-to-peak
REF
V
peak-to-peak
REF
Common
Voltage
DifferentialInput
CM+1/2V
REF
+1/2V
REF
- V
REF
1/2
Single-EndedInputs
t
INP
CMVoltage
CM V-
REF
1/2
CM+1/2V
REF
DifferentialInputs
t
INP
INN
CMVoltage
CM 1/2V
REF
-
+V
REF
-V
REF
Common-ModeVoltage(DifferentialMode)=
(INP)+(INN)
2
,Common-ModeVoltage(Single-EndedMode)= INN.
INN=CMVoltage
InputRange(DifferentialMode)=(AINP AINN)=V ( V )=2V .-
REF REF
- -
REF
ADS1194, ADS1196
ADS1198
www.ti.com SBAS471C –APRIL 2010– REVISED NOVEMBER 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 4, (MVDDP – MVDDN) is
DVDD/2. Note that to avoid saturating the PGA while measuring power supplies, the gain must be set to '1'.
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 ADS1198 is fully differential. Assuming PGA = 1, the differential input (INP – INN) can
span between –V
REF
to +V
REF
. Note that the absolute range for INP and INN must be between AVSS – 0.3 V and
AVDD + 0.3 V. Refer to Table 6 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 ADS1198: single-ended or differential,
as shown in Figure 17 and Figure 18. 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 + 1/2V
REF
) and the (common-mode – 1/2V
REF
). When the input is differential,
the common-mode is given by (INP + INN)/2. Both the INP and INN inputs swing from (common-mode + 1/2V
REF
to common-mode – 1/2V
REF
). For optimal performance, it is recommended that the ADS1198 be used in a
differential configuration.
Figure 17. Methods of Driving the ADS1198: Single-Ended or Differential
Figure 18. Using the ADS1198 in the Single-Ended and Differential Input Modes
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Product Folder Link(s): ADS1194 ADS1196 ADS1198