Datasheet

Temperature( C)=°
TemperatureReading( V) 145,300 Vm - m
490 V/ Cm °
+25 C°
2x
1x
1x
8x
AVDD
AVSS
Temperature Sensor Monitor
To MUX TEMPP
To MUX T NEMP
ADS1291
ADS1292
ADS1292R
www.ti.com SBAS502B –DECEMBER 2011–REVISED SEPTEMBER 2012
Auxiliary Differential Input (RESP_MODN/IN3N, RESP_MODN/IN3P)
In applications where the respiration modulator output is not used, the RESP_MODN/IN3N and
RESP_MODN/IN3P signals can be used as a third multiplexed differential input channel. These inputs can be
multiplexed to either of the ADC channels.
Temperature Sensor (TEMPP, TEMPN)
The ADS1291, ADS1292, and ADS1292R contain an on-chip temperature sensor. This sensor uses two internal
diodes with one diode having a current density 16x that of the other, as shown in Figure 20. The difference in
diode current densities yields a difference in voltage that is proportional to absolute temperature.
Figure 20. Temperature Sensor Measurement in the Input
As a result of the low thermal resistance of the package to the printed circuit board (PCB), the internal device
temperature tracks the PCB temperature closely. Note that self-heating of the ADS1291, ADS1292, and
ADS1292R causes a higher reading than the temperature of the surrounding PCB.
The scale factor of Equation 4 converts the temperature reading to °C. Before using this equation, the
temperature reading code must first be scaled to μV.
(4)
Supply Measurements (MVDDP, MVDDN)
Setting CHnSET[3:0] = 0011 sets the channel inputs to different supply voltages of the device. For channel 1
(MVDDP – MVDDN) is [0.5(AVDD + AVSS)]; for channel 2 (MVDDP – MVDDN) is DVDD / 4. 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 RLDIN/RLDREF 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 RLDIN/RLDREF pin can be used as a multiple single-ended input
channel. The signal at the RLDIN/RLDREF pin can be measured with respect to the midsupply [(AVDD + AVSS)
/ 2]. This measurement is done by setting the channel multiplexer setting MUXn[3:0] to '0010' in the CH1SET and
CH2SET registers.
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Product Folder Links: ADS1291 ADS1292 ADS1292R