ADS1292 datasheet(19/69 Pages) TI

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AVDD

AVSS

Temperature Sensor Monitor

To MUX TEMPP

To MUX T

EMP

Temperature( C)=

TemperatureReading( V)

145,300 V

490 V/ C

+25 C

ADS1291

ADS1292

ADS1292R

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SBAS502A – DECEMBER 2011 – REVISED MARCH 2012

Auxiliary Differential Input (RESP_MODN/IN3N, RESP_MODN/IN3P)

applications

where

the

respiration

modulator

output

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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