TDC1011_15 Datasheet, PDF (18/49 Pages) Texas Instruments – TDC1011 Single Channel Ultrasonic Sensing Analog Front End (AFE) for Level Sensing,Concentration Sensing Applications

TDC1011
SNAS662 – JULY 2015
CLKIN ¦_CLKIN
0x03[4] ± TEMP_CLK_DIV
O8
O 2^{TX_FREQ_DIV+1}
0
1
¦_TEMP
1
T_TEMP = _¦TEMP
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0x00[7:5] ± TX_FREQ_DIV
Figure 24. Timing Source for the Temperature Measurement
See the TDC1011 Temperature Sensing Interface application note listed in the Temperature Measurement with
Multiple RTDs section for details about artifacts in the temperature measurement and how to manage them.
8.3.8.1 Temperature Measurement with Multiple RTDs
The temperature measurement mode is selected by setting the MEAS_MODE bit in the CONFIG_2 register to 1.
A temperature measurement is started by sending a trigger pulse. After the temperature measurement is
complete, the TDC1011 returns to SLEEP mode. To return to TOF measurement mode, reset the MEAS_MODE
bit to 0.
The temperature sensor measurement can be performed without the need of an external ADC. The temperature
sensor block operates by converting the resistance of a reference, R_REF, and up to two RTDs into a series of
START and STOP pulses. The interval between the pulses is proportional to the measured resistance, and
therefore, the temperature. As shown in Figure 25, the TDC1011 performs three measurements per trigger event
and generates the corresponding pulses on the START and STOP pins.
TRIGGER
Reference
RTD1
RTD2
START
STOP
t_d1
t_REF
t_d2
t_RTD1
Figure 25. Temperature Measurement Output Timing
t_RTD2
The resistance of RTD1 and RTD2 can be calculated from the time intervals in Figure 25 as follows:
R _RTDx
 R_REF
K
t_REF
t_RTDx
(3)
With a 1-kΩ reference resistor, the t_REF interval is approximately 200 μs. The following intervals, t_RTD1 and t_RTD2,
will depend on the resistance of the RTDs. The time delay between measurements, t_d1 and t_d2, can be
approximated as follows:
t_d1 = (51 × T_TEMP) + ( t_RTD1 × 0.55 )
(4)
t_d2 = (51 × T_TEMP) + ( t_RTD2 × 0.55 )
(5)
For example, two PT1000 sensors at 0°C will have an approximate resistance of 1 kΩ; the same as the
reference resistor in this example. Given an external 8-MHz clock and the default temperature clock divide-by-8
from the TEMP_CLK_DIV bit, the overall measurement time between the START pulse and the last STOP pulse
is approximately 922 µs.
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