TDC7200_15 Datasheet, PDF (19/50 Pages) Texas Instruments – TDC7200 Time-to-Digital Converter for Time-of-Flight Applications in LIDAR,Magnetostrictive and Flow Meters

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TDC7200
SNAS647C – FEBRUARY 2015 – REVISED AUGUST 2015
Device Functional Modes (continued)
8.4.3 Timeout
For one STOP, the TDC performs the measurement by counting from the START signal to the STOP signal. If no
STOP signal is received, either the Clock Counter or Coarse Counter will overflow and will generate an interrupt
(see Coarse and Clock Counters Overflow). If no START signal is received, the timer waits indefinitely for a
START signal to arrive.
For multiple STOPs, the TDC performs the measurement by counting from the START signal to the last STOP
signal. All earlier STOP signals are captured and stored into the corresponding Measurement Results registers
(TIME1 to TIME6, CLOCK_COUNT1 to CLOCK_COUNT5, CALIBRATION1, CALIBRATION2). The minimum
time required between two consecutive STOP signals is defined in the Recommended Operating Conditions
table. The device can be programmed to measure up to 5 STOP signals by setting the NUM_STOP bits in the
CONFIG2 register.
8.4.4 Multi-Cycle Averaging
In the Multi-Cycle Averaging Mode, the TDC7200 will perform a series of measurements on its own and will only
send an interrupt to the MCU (for example, MSP430, C2000, etc) for wake up after the series has been
completed. While waiting, the MCU can remain in sleep mode during the whole cycle (as shown in Figure 19).
Multi-Cycle Averaging Mode Setup and Conditions:
• The number of averaging cycles should be selected (1 to 128). This is done by programming the
AVG_CYCLES bit in the CONFIG2 register.
• The results of all measurements are reported in the Measurement Results registers (TIME1 to TIME6,
CLOCK_COUNT1 to CLOCK_COUNT5, CALIBRATION1, CALIBRATION2 registers). The CLOCK_COUNTn
registers should be right shifted by the log2(AVG_CYCLES) before calculating the time-of-flight (TOF). For
example, if using the multi-cycle averaging mode, Equation 2 should be rewritten as: TOFn = normLSB
[TIME1 - TIME(n+1)] + [CLOCK_COUNTn >> log 2 (AVG_CYCLES)] x [CLOCKperiod]
• Following each average cycle, the TDC generates either a trigger event on the TRIGG pin after the calibration
measurement to commence a new measurement or an interrupt on the INTB pin, indicating that the averaging
sequence has completed.
This mode allows multiple measurements without MCU interaction, thus optimizing power consumption for the
overall system.
Figure 19. Multi-Cycle Averaging Mode Example with 2 Averaging Cycles and 5 STOP Signals
8.4.5 START and STOP Edge Polarity
In order to achieve the highest measurement accuracy, having the same edge polarity for the START and STOP
input signals is highly recommended. Otherwise, slightly different propagation delays due to symmetry shift
between the rising and falling edge configuration will impact the measurement accuracy.
For highest measurement accuracy in measurement mode 2, it’s strongly recommended to choose for the
START and STOP signal the “rising edge”. This is done by setting the START_EDGE and STOP_EDGE bits in
the CONFIG1 register to 0.
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