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TempN
ADS1294, ADS1294R
ADS1296, ADS1296R
ADS1298, ADS1298R
www.ti.com SBAS459I –JANUARY 2010–REVISED JANUARY 2012
Device Noise Measurements
Setting CHnSET[2:0] = 001 sets the common-mode voltage of (AVDD – AVSS)/2 to both inputs of the channel.
This setting can be used to test the inherent noise of the device in the user system.
Test Signals (TestP and TestN)
Setting CHnSET[2:0] = 101 provides internally-generated test signals for use in sub-system verification at
power-up. This functionality allows the entire signal chain to be tested out. Although the test signals are similar to
the CAL signals described in the IEC60601-2-51 specification, this feature is not intended for use in compliance
testing.
Control of the test signals is accomplished through register settings (see the CONFIG2: Configuration Register 2
subsection in the Register Map section for details). TEST_AMP controls the signal amplitude and TEST_FREQ
controls switching at the required frequency.
The test signals are multiplexed and transmitted out of the device at the TESTP_PACE_OUT1 and
TESTN_PACE_OUT2 pins. A bit register (CONFIG2.INT_TEST = 0) deactivates the internal test signals so that
the test signal can be driven externally. This feature allows the calibration of multiple devices with the same
signal. The test signal feature cannot be used in conjunction with the external hardware PACE feature (see the
External Hardware Approach subsection of the ECG-Specific Functions section for details).
Auxiliary Differential Input (TESTP_PACE_OUT1, TESTN_PACE_OUT2)
When hardware PACE detect is not used, the TESTP_PACE_OUT1 and TESPN_PACE_OUT2 signals can be
used as a multiplexed differential input channel. These inputs can be multiplexed to any of the eight channels.
The performance of the differential input signal fed through these pins is identical to the normal channel
performance.
Temperature Sensor (TempP, TempN)
The ADS129x 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 25. The difference in current densities of the
diodes yields a difference in voltage that is proportional to absolute temperature.
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 ADS129x causes a higher reading
than the temperature of the surrounding PCB.
The scale factor of Equation 1 converts the temperature reading to °C. Before using this equation, the
temperature reading code must first be scaled to μV.
(1)
Figure 25. Measurement of the Temperature Sensor in the Input
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