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TDC7200
SNAS647D – FEBRUARY 2015 – REVISED MARCH 2016
TDC7200 Time-to-Digital Converter for Time-of-Flight Applications in LIDAR,
Magnetostrictive and Flow Meters
1 Features
•
•
•
1
•
•
•
•
•
•
Resolution: 55 ps
Standard Deviation: 35 ps
Measurement Range:
– Mode 1: 12 ns to 500 ns
– Mode 2: 250 ns to 8 ms
Low Power Consumption: 0.5 µA (2 SPS)
Supports up to 5 STOP Signals
Autonomous Multi-Cycle Averaging Mode for Low
Power Consumption
Supply Voltage: 2 V to 3.6 V
Operating Temperature –40°C to 85°C
SPI Host Interface for Configuration and Register
Access
2 Applications
•
•
•
•
Flow Meter: Water Meter, Gas Meter, Heat Meter
Magnetostrictive Position/Level Sensing
Time-of-Flight in Drones (LIDAR, SONAR),
metering equipment and projectors
Heat Cost Allocators
3 Description
The Time to Digital Converter (TDC) performs the
function of a stopwatch and measures the elapsed
time (time-of-flight or TOF) between a START pulse
and up to five STOP pulses. The ability to measure
from START to multiple STOPs gives users the
flexibility to select which STOP pulse yields the best
echo performance.
The device has an internal self-calibrated time base
which compensates for drift over time and
temperature. Self-calibration enables time-to-digital
conversion accuracy in the order of picoseconds. This
accuracy makes the TDC7200 ideal for flow meter
applications, where zero and low flow measurements
require high accuracy.
When placed in the Autonomous Multi-Cycle
Averaging Mode, the TDC7200 can be optimized for
low system power consumption, making it ideal for
battery powered flow meters. In this mode, the host
can go to sleep to save power, and it can wake up
when interrupted by the TDC upon completion of the
measurement sequence.
Device Information(1)
PART NUMBER
TDC7200
PACKAGE
TSSOP (14)
BODY SIZE (NOM)
5.00 mm × 4.40 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
The TDC7200 is a Time-to-Digital Converter (TDC)
for ultrasonic sensing measurements such as water
flow meter, gas flow meter, and heat flow meter.
When paired with the TDC1000 (ultrasonic analogfront-end), the TDC7200 can be a part of a complete
TI ultrasonic sensing solution that includes the
MSP430, power, wireless, and source code.
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
TDC7200
SNAS647D – FEBRUARY 2015 – REVISED MARCH 2016
www.ti.com
Table of Contents
1
2
3
4
5
6
7
8
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Companion Device.................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
5
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
5
5
5
6
7
7
7
9
Absolute Maximum Ratings ......................................
ESD Ratings ............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Timing Requirements ................................................
Switching Characteristics ..........................................
Typical Characteristics ..............................................
Detailed Description ............................................ 12
8.1 Overview ................................................................. 12
8.2 Functional Block Diagram ....................................... 12
8.3 Feature Description................................................. 12
8.4 Device Functional Modes........................................ 14
8.5 Programming........................................................... 21
8.6 Register Maps ......................................................... 24
9
Application and Implementation ........................ 35
9.1
9.2
9.3
9.4
Application Information............................................
Typical Application .................................................
Post Filtering Recommendations ............................
CLOCK Recommendations.....................................
35
35
39
39
10 Power Supply Recommendations ..................... 41
11 Layout................................................................... 41
11.1 Layout Guidelines ................................................. 41
11.2 Layout Example .................................................... 42
12 Device and Documentation Support ................. 43
12.1
12.2
12.3
12.4
12.5
Documentation Support .......................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
43
43
43
43
43
13 Mechanical, Packaging, and Orderable
Information ........................................................... 43
4 Revision History
Changes from Revision C (August 2015) to Revision D
Page
•
Added EN = HIGH ................................................................................................................................................................. 7
•
update equation ................................................................................................................................................................... 14
•
Changed 3818 TO 318 ........................................................................................................................................................ 18
Changes from Revision B (June 2015) to Revision C
•
Page
Changed the data sheet title From: TDC7200 Time-to-Digital Converter for Water and Gas Flow Sensing,
Magnetostrictive Position Sensing, and LIDAR Metering Applications To: TDC7200 Time-to-Digital Converter for
Time-of-Flight applications in LIDAR, Magnetostrictive and Flow Meters ............................................................................. 1
Changes from Revision A (March 2015) to Revision B
Page
•
Changed the data sheet title From: TDC7200 Time-to-Digital Converter for Water, Gas, Heat Flow Metering
Applications To: TDC7200 Time-to-Digital Converter for Water and Gas Flow Sensing, Magnetostrictive Position
Sensing, and LIDAR Metering Applications............................................................................................................................ 1
•
Changed the Applications list to include: "Magnetostrictive Position Sensing", and "LIDAR Metering"................................. 1
Changes from Original (February 2015) to Revision A
Page
•
Changed From: 1-page Product Preview To: Full data sheet ............................................................................................... 1
•
Changed ESD Ratings table................................................................................................................................................... 5
2
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SNAS647D – FEBRUARY 2015 – REVISED MARCH 2016
5 Companion Device
PART NO.
TDC1000
TITLE
Ultrasonic Sensing Analog Front End for Level, Concentration, Flow and Proximity Sensing
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SNAS647D – FEBRUARY 2015 – REVISED MARCH 2016
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6 Pin Configuration and Functions
PW Package
14-Pin TSSOP
Top View
Pin Functions
PIN
NAME
NO.
I/O
DESCRIPTION
ENABLE
1
Input
Enable signal to TDC
TRIGG
2
Output
Trigger output signal
START
3
Input
START signal to TDC
STOP
4
Input
STOP signal to TDC
CLOCK
5
Input
Clock Input to TDC
N.C.
6
–
GND
7
Ground
Ground
INTB
8
Output
Interrupt to MCU, active low (open drain)
DOUT
9
Output
SPI Data Output
DIN
10
Input
SPI Data Input
CSB
11
Input
SPI Chip Select, active low
SCLK
12
Input
SPI clock
VREG
13
Output
LDO Output terminal for external decoupling cap
VDD
14
Power
Supply input
4
Not Connected
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7 Specifications
7.1 Absolute Maximum Ratings
TA = 25°C , VDD = 3.3V, GND = 0V (unless otherwise noted). (1) (2) (3)
MIN
MAX
UNIT
VDD
Supply voltage
–0.3
3.9
V
VI
Terminal input voltage
–0.3
VDD+0.3
V
VDIFF_IN
|Voltage differential| between any two input terminals
3.9
V
VIN_GND_V
|Voltage differential| between any input terminal and GND or VDD
3.9
V
DD
II
Input current at any pin
–5
5
mA
TA
Ambient temperature
-40
125
°C
Tstg
Storage temperature
–65
150
°C
(1)
(2)
(3)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
The algebraic convention, whereby the most negative value is a minimum and the most positive value is a maximum
All voltages are with respect to ground, unless otherwise specified.
7.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±1000
Charged-device model (CDM), per JEDEC specification JESD22C101 (2)
±250
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
7.3 Recommended Operating Conditions
TA = 25°C , VDD = 3.3V, GND = 0V (unless otherwise noted).
MIN
NOM
MAX
UNIT
VDD
Supply voltage
2
3.6
V
VI
Terminal voltage
0
VDD
V
VIH
Voltage input high
0.7 × VDD
3.6
V
VIL
Voltage input low
0
0.3 × VDD
FCALIB_CLK
Frequency (Reference/Calibration Clock)
DUTYCLOCK
Input clock duty cycle
1
(1)
8
16
V
MHz
50%
TIMING REQUIREMENTS: Measurement Mode 1
(1)
T1STARTSTOP_Min
Minimum Time between Start and Stop Signal
12
ns
T1STOPSTOP_Min
Minimum Time between 2 Stop Signals
67
ns
T1STARTSTOP_Max
Maximum time bet. Start and Stop Signal
500
ns
T1STOPSTOP_Max
Maximum time bet. Start and last Stop Signal
500
ns
TIMING REQUIREMENTS: Measurement 2
(1)
T2STARTSTOP_Min
Minimum Time between Start and Stop Signal
2×tCLOCK
T2STOPSTOP_Min
Minimum Time between 2 Stop Signals
2×tCLOCK
s
T2STARTSTOP_Max
Maximum time bet. Start and Stop Signal
(216-2)×tCLOCK
s
T2STOPSTOP_Max
Maximum. time bet. Start and last Stop Signal
(216-2)×tCLOCK
s
s
TIMING REQUIREMENTS: ENABLE INPUT
TREN
Rise Time for Enable Signal (20%-80%)
1 to 100
ns
TFEN
Fall Time for Enable Signal (20%-80%)
1 to 100
ns
(1)
Specified by design.
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Recommended Operating Conditions (continued)
TA = 25°C , VDD = 3.3V, GND = 0V (unless otherwise noted).
MIN
NOM
MAX
UNIT
TIMING REQUIREMENTS: START, STOP, CLOCK
TRST, TFST
Maximum rise, fall time for START, STOP signals (20%80%)
1
ns
TRXCLK, TFXCLK
Maximum rise, fall time for external CLOCK (20%-80%)
1
ns
5
ns
TIMING REQUIREMENTS: TRIGG
TTRIGSTART
Time from TRIG to START
TEMPERATURE
TA
Ambient temperature
–40
85
°C
TJ
Junction temperature
–40
85
°C
7.4 Thermal Information
TDC7200
THERMAL METRIC (1)
PW [TSSOP]
UNIT
14 PINS
RθJA
Junction-to-ambient thermal resistance
RθJC(top)
Junction-to-case (top) thermal resistance
RθJB
Junction-to-board thermal resistance
76.8
ψJT
Junction-to-top characterization parameter
12.4
ψJB
Junction-to-board characterization parameter
76.2
θJA
Package thermal impedance
113
(1)
6
134.9
63
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
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7.5 Electrical Characteristics
TA = 25°C , VDD = 3.3 V, GND = 0 V (unless otherwise noted).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
TDC CHARACTERISTICS
LSB
Resolution
TACC-2
Accuracy (Mode 2)
TSTD-2
(1)
Standard Deviation (Mode 2)
Single shot measurement
55
ps
CLOCK = 8 MHz
28
ps
Measured time = 100 µs
50
ps
Measured time = 1 µs
35
ps
2.95
V
OUTPUT CHARACTERISTICS: TRIGG, INTB, DOUT
VOH
Output voltage high
Isource = -2 mA
VOL
Output voltage low
Isink = 2 mA
2.31
0.35
0.99
V
INPUT CHARACTERISTICS: ENABLE, START, STOP, CLOCK, DIN, CSB,SCLK
Cin
Input capacitance
(2)
3
pF
POWER CONSUMPTION (see Measurement Mode 1 and Measurement Mode 2)
Ish
Shutdown current
EN = LOW
IQA
Quiescent Current A
EN = HIGH; TDC running
IQB
Quiescent Current B
IQC
IQD
(1)
(2)
0.3
2
µA
1.35
mA
EN = HIGH; TDC OFF, Clock Counter running
71
µA
Quiescent Current C
EN = HIGH; measurement stopped, SPI
communication only
87
µA
Quiescent Current D
EN = HIGH, TDC OFF, counter stopped, no
communication
50
µA
Accuracy is defined as the systematic error in the output signal; the error of the device excluding noise.
Specified by design.
7.6 Timing Requirements
MIN
NOM
MAX
UNIT
TIMING REQUIREMENTS: START, STOP INPUTS, CLOCK
PWSTART
Pulse width for Start Signal
10
ns
PWSTOP
Pulse width for Stop Signal
10
ns
SERIAL INTERFACE TIMING CHARACTERISTICS (VDD = 3.3 V, fSCLK = 20 MHz) (See Figure 1)
fSCLK
SCLK Frequency
20
t1
SCLK period
50
ns
t2
SCLK High Time
16
ns
t3
SCLK Low Time
16
ns
t4
DIN setup time
4
ns
t5
DIN hold time
4
ns
t6
CSB fall to SCLK rise
6
ns
t7
Last SCLK rising edge to CSB rising edge
6
ns
t8
Minimum pause time (CSB high)
t9
Clk fall to DOUT bus transition
40
MHz
ns
12
ns
7.7 Switching Characteristics
TA = 25°C , VDD = 3.3 V, GND = 0 V (unless otherwise noted).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
WAKE UP TIME
TWAKEUP_PERIOD
Time to be ready for
Measurement
LSB within 0.3% of settled value
300
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Figure 1. SPI Register Write: 8 bit Register Example
8
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7.8 Typical Characteristics
50.000045
50.00003
50.000040
50.00002
Time-of-Flight at 50 µs (µs)
Time-of-Flight at 50 µs (µs)
TA = 25°C , VDD = 3.3 V, GND = 0 V, CLOCK = 8 MHz, CALIBRATION2_PERIODS = 10, AVG_CYCLES = 1 Measurement,
NUM_STOP = Single STOP, Measurement Mode 2 (unless otherwise noted).
50.000035
50.000030
50.000025
50.000020
50.000015
50.000010
50.00001
50
49.99999
49.99998
49.99997
49.99996
49.99995
49.99994
50.000005
49.99993
2
3.3
VDD (V)
3.6
-40
D001
Figure 2. Time-of-Flight (TOF) vs. VDD (Measurement Mode
2)
25
Temperature (°C)
85
D002
Figure 3. TOF vs. Temperature (Measurement Mode 2)
250.25
250.05
Time-of-Flight at 250 ns (ns)
Time-of-Flight at 250 ns (ns)
250.2
250
249.95
249.9
249.85
249.8
250.15
250.1
250.05
250
249.95
249.9
249.85
249.8
249.75
2
3.3
VDD (V)
-40
3.6
D004
85
D005
Figure 5. TOF vs. Temperature (Measurement Mode 1)
70
59
65
58
60
57
Resolution [LSB] (ps)
Resolution [LSB] (ps)
Figure 4. TOF vs. VDD (Measurement Mode 1)
25
Temperature (°C)
55
50
45
40
35
56
55
54
53
52
30
2
2.2
2.4
2.6
2.8
VDD (V)
3
3.2
3.4
3.6
51
-60
-40
D006
Figure 6. Resolution (LSB) vs. VDD
-20
0
20
40
Temperature (°C)
60
80
100
D007
Figure 7. Resolution (LSB) vs. Temperature
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Typical Characteristics (continued)
TA = 25°C , VDD = 3.3 V, GND = 0 V, CLOCK = 8 MHz, CALIBRATION2_PERIODS = 10, AVG_CYCLES = 1 Measurement,
NUM_STOP = Single STOP, Measurement Mode 2 (unless otherwise noted).
100
1353
IQB
IQC
IQD
90
1351
Operating Current (µA)
Operating Current [IQA] (µA)
1352
1350
1349
1348
1347
1346
80
70
60
50
1345
40
1344
2
3.3
VDD (V)
2
3.6
Figure 8. Operating Current (IQA) vs. VDD
Operating Current [IQA] (µA)
Shutdown Current (µA)
D009
Figure 9. Operating Currents (IQB, IQC, IQD) vs. VDD
0.31
0.3
0.29
0.28
0.27
0.26
0.25
1380
1360
1340
1320
1300
1280
0.24
1260
0.23
2
3.3
VDD (V)
-40
3.6
D010
Figure 10. Shutdown Current (ISH) vs. VDD
1.2
90
1
80
70
60
IQB
IQC
IQD
50
25
Temperature (°C)
85
D011
Figure 11. Operating Current (IQA) vs. Temperature
100
Shutdown Current (µA)
Operating Current (µA)
3.6
1400
0.32
0.8
0.6
0.4
0.2
40
0
-40
25
Temperature (°C)
85
-40
D012
Figure 12. Operating Currents (IQB, IQC, IQD) vs.
Temperature
10
3.3
VDD (V)
D008
25
Temperature (°C)
85
D013
Figure 13. Shutdown Current (ISH) vs. Temperature
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Typical Characteristics (continued)
TA = 25°C , VDD = 3.3 V, GND = 0 V, CLOCK = 8 MHz, CALIBRATION2_PERIODS = 10, AVG_CYCLES = 1 Measurement,
NUM_STOP = Single STOP, Measurement Mode 2 (unless otherwise noted).
Number of Instances
10000
1000
100
10
Measured Time (ps)
1600
1200
800
400
0
-400
-800
-1200
-1600
-2000
1
D014
Figure 14. Standard Time-of-Flight Histogram (Normalized)
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8 Detailed Description
8.1 Overview
The TDC7200 is a stopwatch IC used to measure time between a single event (edge on START pin) and multiple
subsequent events (edge on STOP pin). An event from a START pulse to a STOP pulse is also known as timeof-flight, or TOF for short. The device has an internal time base that is used to measure time with accuracy in the
order of picoseconds. This accuracy makes the TDC7200 ideal for application such as flow meter, where zero
and low flow measurements require high accuracy in the picoseconds range.
8.2 Functional Block Diagram
8.3 Feature Description
8.3.1 LDO
The LDO (low-dropout) is an internal supply voltage regulator for the TDC7200. No external circuitry needs to be
connected to the output of this regulator other than the mandatory external decoupling capacitor.
Recommendations for the decoupling capacitor parameters:
• Type: ceramic
• Capacitance: 0.4 µF–2.7 µF (1 µF typical). If using a capacitor value outside the recommended range, the
part may malfunction and can be damaged.
• ESR: 100 mΩ (max)
12
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Feature Description (continued)
8.3.2 CLOCK
TDC7200 needs an external reference clock connected to the CLOCK pin. The external CLOCK is used to
calibrate the internal time base accurately and therefore, the measurement accuracy is heavily dependent on the
external CLOCK accuracy. This reference clock is also used by all digital circuits inside the device; thus, CLOCK
has to be available and stable at all times when the device is enabled (ENABLE = HIGH).
Figure 15 shows the typical effect of the external CLOCK frequency on the measurement uncertainty. With a
reference clock of 1MHz, the standard deviation of a set of measurement results is approximately 243ps. As the
reference clock frequency is increased, the standard deviation (or measurement uncertainty) reduces. Therefore,
using a reference clock of 16MHz is recommended for optimal performance.
Standard Deviation (ps)
400
100
40
0
2
4
6
8
10
12
Clock Period (MHz)
14
16
18
D018
Figure 15. Standard Deviation vs. CLOCK
8.3.3 Counters
8.3.3.1 Coarse and Clock Counters Description
Time measurements by the TDC7200 rely on two counters: the Coarse Counter and the Clock Counter. The
Coarse Counter counts the number of times the ring oscillator (the TDC7200’s core time measurement
mechanism) wraps, which is used to generate the results in the TIME1 to TIME6 registers.
The Clock Counter counts the number of integer clock cycles between START and STOP events and is used in
Measurement Mode 2 only. The results for the Clock Counter are displayed in the CLOCK_COUNT1 to
CLOCK_COUNT5 registers.
8.3.3.2 Coarse and Clock Counters Overflow
Once the coarse counter value has reached the corresponding value of the Coarse Counter Overflow registers,
then its interrupt bit will be set to 1. In other words, if (TIMEn / 63) ≥ COARSE_CNTR_OVF, then
COARSE_CNTR_OVF_INT = 1 (this interrupt bit is located in the INT_STATUS register). COARSE_CNTR_OVF
= (COARSE_CNTR_OVF_H x 28 + COARSE_CNTR_OVF_L), and TIMEn refers to the TIME1 to TIME6
registers.
Similarly, once the clock counter value has reached the corresponding value of the Clock Counter Overflow
registers, then its interrupt bit will be set to 1. In other words, if CLOCK_COUNTn > CLOCK_CNTR_OVF, then
CLOCK_CNTR_OVF_INT = 1 (this interrupt bit is located in the INT_STATUS register). CLOCK_CNTR_OVF =
(CLOCK_CNTR_OVF_H x 28 + CLOCK_CNTR_OVF_L), and CLOCK_COUNTn refers to the CLOCK_COUNT1
to CLOCK_COUNT5 registers.
As soon as there is an overflow detected, the running measurement will be terminated immediately.
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Feature Description (continued)
8.3.3.3 Clock Counter STOP Mask
The value in the Clock Counter STOP Mask registers define the end of the mask window. The Clock Counter
STOP Mask value will be referred to as CLOCK_CNTR_STOP_MASK = (CLOCK_CNTR_STOP_MASK_H x 28
+ CLOCK_CNTR_STOP_MASK_L).
The Clock Counter is started by the first rising edge of the external CLOCK after the START signal (see
Figure 18). All STOP signals occurring before the value set by the CLOCK_CNTR_STOP_MASK registers will be
ignored. This feature can be used to help suppress wrong or unwanted STOP trigger signals.
For example, assume the following values:
• The first time-of-flight (TOF1), which is defined as the time measurement from the START to the 1st STOP =
19 μs.
• The second time-of-flight (TOF2), which is defined as the time measurement from the START to the 2nd
STOP = 119 μs.
• CLOCK = 8 MHz
In this example, the TDC7200 will provide a CLOCK_COUNT1 of approximately 152 (19 μs / tCLOCK), and
CLOCK_COUNT2 of approximately 952 (119 μs / tCLOCK). If the user sets CLOCK_CNTR_STOP_MASK
anywhere between 152 and 952, then the 1st STOP will be ignored and 2nd STOP will be measured.
The Clock Counter Overflow value (CLOCK_CNTR_OVF_H x 28 + CLOCK_CNTR_OVF_L) should always be
higher than the Clock Counter STOP Mask value (CLOCK_CNTR_STOP_MASK_H x 28 +
CLOCK_CNTR_STOP_MASK_L). Otherwise, the Clock Counter Overflow Interrupt will be set before the STOP
mask time expires, and the measurement will be halted.
8.3.3.4 ENABLE
The ENABLE pin is used as a reset to all digital circuits in the TDC7200. Therefore, it is essential that the
ENABLE pin sees a positive edge after the device has powered up. It is also important to ensure that there are
no transients (glitches, etc.) on the ENABLE pin; such glitches could cause the device to RESET.
8.4 Device Functional Modes
8.4.1 Calibration
The time measurements performed by the TDC7200 are based on an internal time base which is represented as
the LSB value of the TIME1 to TIME6 results registers. The typical LSB value can be seen in Electrical
Characteristics. However, the actual value of the LSB can vary depending on environmental variables
(temperature, systematic noise, etc.). This variation can introduce significant error into the measurement result.
There is also an offset error in the measurement due to certain internal delays in the device.
In order to compensate for these errors and to calculate the actual LSB value, calibration needs to be performed.
The TDC7200 calibration consists of two measurement cycles of the external CLOCK. The first is a
measurement of a single clock cycle period of the external clock; the second measurement is for the number of
external CLOCK periods set by the CALIBRATION2_PERDIOS in the CONFIG2 register. The results from the
calibration measurements are stored in the CALIBRATION1 and CALIBRATION2 registers.
The two-point calibration is used to determine the actual LSB in real time in order to convert the TIME1 to TIME6
results from number of delays to a real time-of-flight (TOF) number. As discussed in the next sections, the
calibrations will be used for calculating time-of-flight (TOF) in measurement modes 1 and 2.
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Device Functional Modes (continued)
8.4.2 Measurement Modes
8.4.2.1 Measurement Mode 1
In measurement mode 1 as shown in Figure 16, the TDC7200 performs the entire counting from START to the
last STOP using its internal ring oscillator plus coarse counter. This method is recommended for measuring
shorter time durations of < 500 ns. Using measurement mode 1 for measuring time > 500ns decreases accuracy
of the measurement (as shown in Figure 17), and is not recommended.
Figure 16. Measurement Mode 1
Standard Deviation (ps)
400
100
20
0
200
400
600
800 1000 1200 1400 1600 1800 2000
Time Measured (ns)
D019
Figure 17. Measurement Mode 1 Standard Deviation vs. Measured Time-of-Flight
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Device Functional Modes (continued)
8.4.2.1.1 Calculating Time-of-Flight (Measurement Mode 1)
For measurement mode 1, the time-of-flight (TOF) between the START to the nth STOP can be calculated using
Equation 1:
where
•
•
•
•
•
•
•
TOFn [sec] = time-of-flight measurement from the START to the nth STOP
TIMEn = nth TIME measurement given by the TIME1 to TIME6 registers
normLSB [sec] = normalized LSB value from calibration
CLOCKperiod [sec] = external CLOCK period
CALIBRATION1 [count] = TDC count for first calibration cycle
CALIBRATION2 [count] = TDC count for second calibration cycle
CALIBRATION2_PERIODS = setting for the second calibration cycle; located in register CONFIG2
For example, assume the time-of-flight between the START to the 1
readouts were obtained:
• CALIBRATION2 = 21121 (decimal)
• CALIBRATION1 = 2110 (decimal)
• CALIBRATION2_PERIODS = 10
• CLOCK = 8MHz
• TIME1 = 4175 (decimal)
st
(1)
STOP is desired, and the following
Therefore, the calculation for time-of-flight is:
• calCount = (21121 – 2110) / (10 – 1) = 2112.33
• normLSB = (1/8MHz) / (2112.33) = 5.917 x 10-11
• TOF1 = (4175)(5.917 x 10-11) = 247.061 ns
8.4.2.2 Measurement Mode 2
In measurement mode 2, the internal ring oscillator of the TDC7200 is used only to count fractional parts of the
total measured time. As shown in Figure 18, the internal ring oscillator starts counting from when it receives the
START signal until the first rising edge of the CLOCK. Then, the internal ring oscillator switches off, and the
Clock counter starts counting the clock cycles of the external CLOCK input until a STOP pulse is received. The
internal ring oscillator again starts counting from the STOP signal until the next rising edge of the CLOCK.
16
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Device Functional Modes (continued)
Figure 18. Measurement Mode 2
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Device Functional Modes (continued)
8.4.2.2.1 Calculating Time-of-Flight (TOF) (Measurement Mode 2)
The time-of-flight (TOF) between the START to the nth STOP can be calculated using Equation 2:
TOFn normLSB TIME1 TIMEn 1
CLOCK _ COUNTn CLOCKperiod
normLSB
calCount
CLOCKperiod
calCount
CALIBRATION2 CALIBRATION1
CALIBRATION2 _ PERIODS 1
where
•
•
•
•
•
•
•
•
•
TOFn [sec] = time-of-flight measurement from the START to the nth STOP
TIME1 = time 1 measurement given by the TDC7200 register address 0x10
TIME(n+1) = (n+1) time measurement, where n = 1 to 5 (TIME2 to TIME6 registers)
normLSB [sec] = normalized LSB value from calibration
CLOCK_COUNTn = nth clock count, where n = 1 to 5 (CLOCK_COUNT1 to CLOCK_COUNT5)
CLOCKperiod [sec] = external CLOCK period
CALIBRATION1 [count] = TDC count for first calibration cycle
CALIBRATION2 [count] = TDC count for second calibration cycle
CALIBRATION2_PERIODS = setting for the second calibration; located in register CONFIG2
For example, assume the time-of-flight between the START to the 1
readouts were obtained:
• CALIBRATION2 = 23133 (decimal)
• CALIBRATION1 = 2315 (decimal)
• CALIBRATION2_PERIODS = 10
• CLOCK = 8MHz
• TIME1 = 2147 (decimal)
• TIME2 = 201 (decimal)
• CLOCK_COUNT1 = 318 (decimal)
st
(2)
STOP is desired, and the following
Therefore, the calculation for time-of-flight is:
CALIBRATION2 CALIBRATION1 (23133 2315)
calCount
2313.11
(CALIBRATION2 _ PERIODS) 1
(10 1)
(CLOCKperiod) (1/ 8MHz)
normLSB
5.40 10 11
(calCount)
2313.11
TOF1 (TIME1)(normLSB) (CLOCK _ COUNT1)(CLOCKperiod) (TIME2)(normLSB)
TOF1
2147 5.40 10
11
(318)(1/ 8MHz) (201)(5.40 10
11
TOF1 39.855Ps
18
)
(3)
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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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Device Functional Modes (continued)
8.4.6 Measurement Sequence
The TDC7200 is a stopwatch IC that measures time between a START and multiple STOP events. The
measurement sequence of the TDC7200 is as follows:
1. After powering up the device, the EN pin needs to be low. There is one low to high transition required while
VDD is supplied for correct initialization of the device.
2. MCU software requests a new measurement to be initiated via the SPI™ interface.
3. After the start new measurement bit START_MEAS has been set in the CONFIG1 register, the TDC7200
generates a trigger signal on the TRIGG pin, which is typically used by the corresponding ultrasonic analogfront-end (such as the TDC1000) as start trigger for a measurement (for example, transmit signal for the
ultrasonic burst)
4. Immediately after sending the trigger, the TDC7200 enables the START pin and waits to receive the START
pulse edge
5. After receiving a START, the TDC resets the TRIGG pin
6. The Clock counter is started after the next rising edge of the external clock signal (Measurement Mode 2).
The
Clock
Counter
STOP
Mask
registers
(CLOCK_CNTR_STOP_MASK_H
and
CLOCK_CNTR_STOP_MASK_L) determine the length of the STOP mask window.
7. After reaching the Clock Counter STOP Mask value, the STOP pin waits to receive a single or multiple STOP
trigger signal from the analog-front-end (for example, detected echo signal of the ultrasonic burst signal)
8. After the last STOP trigger has been received, the TDC will signal to the MCU via interrupt (INTB pin) that
there are new measurement results waiting in the registers. START, STOP and TRIGG pin are disabled (in
Multi-Cycle Averaging Mode, the TDC will start the next cycle automatically by generating a new TRIGG
signal). Note: INTB must be utilized to determine TDC measurement completion; polling the INT_STATUS
register to determine measurement completion is NOT recommended as it will interfere with the TDC
measurement.
9. After the results are retrieved, the MCU can then start a new measurement with the same register settings.
This is done by just setting the START measurement bit via SPI. It is not required to drive the ENABLE pin
low between measurements.
10. The ENABLE pin can be taken low, if the time duration between measurements is long, and it is desired to
put the TDC7200 in its lowest power state. However, upon taking ENABLE high again, the device will come
up with its default register settings and will need to be configured via SPI.
8.4.7 Wait Times for TDC7200 Startup
The required wait time following the rising edge of the ENABLE pin of the TDC7200 is defined by three key
times, as shown in Figure 20. All three times relate to the startup of the TDC7200’s internal LDO, which is power
gated when the device is disabled for optimal power consumption. The first parameter, T1SPI_RDY, is the time after
which the SPI interface is accessible. The second (T2LDO_SET1) parameter and third (T3LDO_SET2) parameter are
related to the performance of a measurement made while the internal LDO is settling. The LDO supplies the
TDC7200’s time measurement device, and a change in voltage on its supply during a measurement translates
directly to an inaccuracy. It is therefore recommended to wait until the LDO is settled before time measurement
begins.
The first time period relating to the measurement accuracy is T2LDO_SET1, the LDO settling time 1. This is the time
after which the LDO has settled to within 0.3% of its final value. A 0.3% error translates to a worst case time
error (due to the LDO settling) of 0.3% x tCLOCK, which is 375ps in the case of an 8MHz reference clock, or
187.5ps if a 16MHz clock is used. Finally, the time T3LDO_SET2 is the time after which the LDO has settled to its
final value. For best performance, it is recommended that a time measurement is not started before T3LDO_SET2 to
allow the LDO to fully settle. Typical times for T1SPI_RDY is 100 µs, for T2LDO_SET1 is 300 µs, and for T3LDO_SET2 is
1.5 ms.
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Device Functional Modes (continued)
Figure 20. VREG Startup Time
8.5 Programming
8.5.1 Serial Peripheral Interface (SPI)
The serial interface consists of data input (DIN), data output (DOUT), serial interface clock (SCLK), and chip
select bar (CSB). The serial interface is used to configure the TDC7200 parameters available in various
configuration registers.
The communication on the SPI bus supports write and read transactions. A write transaction consists of a single
write command byte, followed by single data byte. A read transaction consists of a single read command byte
followed by 8 or 24 SCLK cycles. The write and read command bytes consist of a 1-bit auto-increment bit, a 1-bit
read or write instruction, and a 6-bit register address. Figure 21 shows the SPI protocol for a transaction
involving one byte of data (read or write).
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Programming (continued)
Figure 21. SPI Protocol
8.5.1.1 CSB
CSB is an active-low signal and needs to be low throughout a transaction. That is, CSB should not pulse
between the command byte and the data byte of a single transaction.
De-asserting CSB always terminates an ongoing transaction, even if it is not yet complete. Re-asserting CSB will
always bring the device into a state ready for the next transaction, regardless of the termination status of a
previous transaction.
8.5.1.2 SCLK
SPI clock can idle high or low. It is recommended to keep SCLK as clean as possible to prevent glitches from
corrupting the SPI frame.
8.5.1.3 DIN
Data In (DIN) is driven by the SPI master by sending the command and the data byte to configure the TDC7200.
8.5.1.4 DOUT
Data Out (DOUT) is driven by the TDC7200 when the SPI master initiates a read transaction. When the
TDC7200 is not being read out, the DOUT pin is in high impedance mode and is undriven.
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Programming (continued)
8.5.1.5 Register Read/Write
Access to the internal registers can be done through the serial interface formed by pins CSB (Chip Select - active
low), SCLK (serial interface clock), DIN (data input), and DOUT (data out).
Serial shift of bits into the device is enabled when CSB is low. Serial data DIN is latched (MSB received first,
LSB received last) at every rising edge of SCLK when CSB is active (low). The serial data is loaded into the
register with the last data bit SCLK rising edge when CSB is low. In the case that the word length exceeds the
register size, the excess bits are ignored. The interface can work with SCLK frequency from 20MHz down to very
low speeds (a few Hertz) and even with a non-50% duty-cycle SCLK.
The SPI transaction is divided in two main portions:
• Address and Control: Auto Increment Mode selection bit, Read/Write bit, Address 6 bits
• Data: 8 bit or 24 bit
When writing to a register with unused bits, these should be set to 0.
Address and Control (A7 - A0)
A7
A6
Auto
Increment
A5
A4
A3
A2
RW
Register Address
0: OFF
1: ON
Read = 0
Write = 1
00 h up to 3Fh
A1
A0
8.5.1.6 Auto Increment Mode
When the Auto Increment Mode is OFF, only the register indicated by the Register Address will be accessed, all
cycles beyond the register length will be ignored. When the Auto Increment is ON, the register of the Register
Address is accessed first, then without interruption, subsequent registers are accessed.
The Auto Increment Mode can be either used to access the configuration (CONFIG1 and CONFIG2) and status
(INT_STATUS) registers, or for the Measurement Results registers (TIME1 to TIME6, CLOCK_COUNT1 to
CLOCK_COUNT5, CALIBRATION1, CALIBRATION2). As both register block use registers with different length,
it’s not possible to access all registers of the device within one single access cycle.
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8.6 Register Maps
8.6.1 Register Initialization
After power up (VDD supplied, ENABLE Pin low to high transition) the internal registers are initialized with the
default value. Disabling the part by pulling ENABLE pin to GND will set the device into total shutdown. As the
internal LDO is turned off settings in the register will be lost. The device initializes the registers with default
values with the next enable (ENABLE pin to VDD).
Table 1. Register Summary
REGISTER ADDRESS
24
REGISTER NAME
REGISTER DESCRIPTION
SIZE (BITS)
RESET
VALUE
00h
CONFIG1
Configuration Register 1
8
00h
01h
CONFIG2
Configuration Register 2
8
40h
02h
INT_STATUS
Interrupt Status Register
8
00h
03h
INT_MASK
Interrupt Mask Register
8
07h
04h
COARSE_CNTR_OVF_H
Coarse Counter Overflow Value High
8
FFh
05h
COARSE_CNTR_OVF_L
Coarse Counter Overflow Value Low
8
FFh
06h
CLOCK_CNTR_OVF_H
CLOCK Counter Overflow Value High
8
FFh
07h
CLOCK_CNTR_OVF_L
CLOCK Counter Overflow Value Low
8
FFh
08h
CLOCK_CNTR_STOP_MASK_H
CLOCK Counter STOP Mask High
8
00h
09h
CLOCK_CNTR_STOP_MASK_L
CLOCK Counter STOP Mask Low
8
00h
10h
TIME1
Measured Time 1
24
00_0000h
11h
CLOCK_COUNT1
CLOCK Counter Value
24
00_0000h
12h
TIME2
Measured Time 2
24
00_0000h
13h
CLOCK_COUNT2
CLOCK Counter Value
24
00_0000h
14h
TIME3
Measured Time 3
24
00_0000h
15h
CLOCK_COUNT3
CLOCK Counter Value
24
00_0000h
16h
TIME4
Measured Time 4
24
00_0000h
17h
CLOCK_COUNT4
CLOCK Counter Value
24
00_0000h
18h
TIME5
Measured Time 5
24
00_0000h
19h
CLOCK_COUNT5
CLOCK Counter Value
24
00_0000h
1Ah
TIME6
Measured Time 6
24
00_0000h
1Bh
CALIBRATION1
Calibration 1, 1 CLOCK Period
24
00_0000h
1Ch
CALIBRATION2
Calibration 2, 2/10/20/40 CLOCK
Periods
24
00_0000h
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8.6.2 CONFIG1: Configuration Register 1 R/W (address = 00h) [reset = 0h]
Figure 22. Configuration Register 1
7
FORCE_CAL
R/W-0h
6
PARITY_EN
R/W-0h
5
TRIGG_EDGE
R/W-0h
4
STOP_EDGE
R/W-0h
3
START_EDGE
R/W-0h
2
1
MEAS_MODE
R/W-0h
R/W-0h
0
START_MEAS
R/W-0h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 2. Configuration Register 1 Field Descriptions
Bit
7
Field
Type
Reset
Description
FORCE_CAL
R/W
0
0: Calibration is not performed after interrupted measurement (for example, due
to counter overflow or missing STOP signal)
1: Calibration is always performed at the end (for example, after a counter
overflow)
6
PARITY_EN
R/W
0
0: Parity bit for Measurement Result Registers* disabled (Parity Bit always 0)
1: Parity bit for Measurement Result Registers enabled (Even Parity)
*The Measurement Results registers are the TIME1 to TIME6,
CLOCK_COUNT1 to CLOCK_COUNT5, CALIBRATION1, CALIBRATION2
registers.
5
TRIGG_EDGE
R/W
0
4
STOP_EDGE
R/W
0
3
START_EDGE
R/W
0
[2:1]
MEAS_MODE
R/W
00h
0
START_MEAS
R/W
0
0: TRIGG is output as a Rising edge signal
1: TRIGG is output as a Falling edge signal
0: Measurement is stopped on Rising edge of STOP signal
1: Measurement is stopped on Falling edge of STOP signal
0: Measurement is started on Rising edge of START signal
1: Measurement is started on Falling edge of START signal
00: Measurement Mode 1 (for expected time-of-flight < 500 ns).
01: Measurement Mode 2 (recommended)
10, 11: Reserved for future functionality
Start New Measurement:
This bit is cleared when Measurement is Completed.
0: No effect
1: Start New Measurement. Writing a 1 will clear all bits in the Interrupt Status
Register and Start the measurement (by generating an TRIGG signal) and will
reset the content of all Measurement Results registers (TIME1 to TIME6,
CLOCK_COUNT1 to CLOCK_COUNT5, CALIBRATION1, CALIBRATION2) to
0.
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8.6.3 CONFIG2: Configuration Register 2 R/W (address = 01h) [reset = 40h]
Figure 23. Configuration Register 2
7
6
CALIBRATION2_PERIODS
R/W-0h
R/W-1h
5
R/W-0h
4
AVG_CYCLES
R/W-0h
3
2
R/W-0h
R/W-0h
1
NUM_STOP
R/W-0h
0
R/W-0h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 3. Configuration Register 2 Field Descriptions
Bit
[7:6]
Field
Type
Reset
Description
CALIBRATION2_PERI
ODS
R/W
01h
00: Calibration 2 - measuring 2 CLOCK periods
01: Calibration 2 - measuring 10 CLOCK periods
10: Calibration 2 - measuring 20 CLOCK periods
11: Calibration 2 - measuring 40 CLOCK periods
[5:3]
AVG_CYCLES
R/W
00h
000: 1 Measurement Cycle only (no Multi-Cycle Averaging Mode)
001: 2 Measurement Cycles
010: 4 Measurement Cycles
011: 8 Measurement Cycles
100: 16 Measurement Cycles
101: 32 Measurement Cycles
110: 64 Measurement Cycles
111: 128 Measurement Cycles
[2:0]
NUM_STOP
R/W
00h
000: Single Stop
001: Two Stops
010: Three Stops
011: Four Stops
100: Five Stops
101, 110, 111: No Effect. Single Stop
26
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8.6.4 INT_STATUS: Interrupt Status Register (address = 02h) [reset = 00h]
Figure 24. Interrupt Status Register
7
Reserve
d
6
Reserve
d
5
Reserve
d
R/W-0h
R/W-0h
R/W-0h
4
3
MEAS_COMPLET MEAS_STARTED_FL
E_FLAG
AG
R/W-0h
R/W-0h
2
CLOCK_CNT
R_
OVF_INT
R/W-0h
1
COARSE_CNTR_
OVF_INT
0
NEW_MEAS_
INT
R/W-0h
R/W-0h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 4. Interrupt Status Register Field Descriptions
Bit
Field
Type
Reset
7
Reserved
R/W
0h
6
Reserved
R/W
0h
5
Reserved
R/W
0h
4
MEAS_COMPLETE_FLAG
R/W
0h
Description
Writing a 1 will clear the status
0: Measurement has not completed
1: Measurement
NEW_MEAS_INT)
3
MEAS_STARTED_FLAG
R/W
0h
has
completed
(same
information
as
Writing a 1 will clear the status
0: Measurement has not started
1: Measurement has started (START signal received)
2
CLOCK_CNTR_OVF_INT
R/W
0h
Requires writing a 1 to clear interrupt status
0: No overflow detected
1: Clock overflow detected, running measurement will be
stopped immediately
1
COARSE_CNTR_OVF_INT
R/W
0h
Requires writing a 1 to clear interrupt status
0: No overflow detected
1: Coarse overflow detected, running measurement will be
stopped immediately
0
NEW_MEAS_INT
R/W
0h
Requires writing a 1 to clear interrupt status
0: Interrupt not detected
1: Interrupt detected – New Measurement has been completed
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8.6.5 INT_MASK: Interrupt Mask Register R/W (address = 03h) [reset = 07h]
Figure 25. Interrupt Mask Register
7
Reserve
6
Reserve
5
Reserve
4
Reserve
3
Reserve
2
CLOCK_CNTR
_OVF_MASK
R/W-0h
R/W-0h
R/W-0h
R/W-0h
R/W-0h
R/W-1h
1
COARSE_CNT
R
_OVF_MASK
R/W-1h
0
NEW_MEAS
_MASK
R/W-1h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 5. Interrupt Mask Register Field Descriptions
Bit
Field
Type
Reset
7
Reserve
R/W
0
6
Reserve
R/W
0
5
Reserve
R/W
0
4
Reserve
R/W
0
3
Reserve
R/W
0
2
CLOCK_CNTR_OVF_MASK
R/W
1
1
COARSE_CNTR_OVF_MASK
R/W
1
0
NEW_MEAS_MASK
R/W
1
Description
0: CLOCK Counter Overflow Interrupt disabled
1: CLOCK Counter Overflow Interrupt enabled
0: Coarse Counter Overflow Interrupt disabled
1: Coarse Counter Overflow Interrupt enabled
0: New Measurement Interrupt disabled
1: New Measurement Interrupt enabled
A disabled interrupt will no longer be visible on the device pin (INTB). The interrupt bit in the INT_STATUS
register will still be active.
8.6.6 COARSE_CNTR_OVF_H: Coarse Counter Overflow High Value Register (address = 04h) [reset =
FFh]
Figure 26. Coarse Counter Overflow Value_H Register
7
6
5
R/W-1h
R/W-1h
R/W-1h
4
3
COARSE_CNTR_OVF_H
R/W-1h
R/W-1h
2
1
0
R/W-1h
R/W-1h
R/W-1h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 6. Coarse Counter Overflow Value_H Register Field Descriptions
28
Bit
Field
Type
Reset
Description
7-0
COARSE_CNTR_OVF_H
R/W
FFh
Coarse Counter Overflow Value, upper 8 Bit
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8.6.7 COARSE_CNTR_OVF_L: Coarse Counter Overflow Low Value Register (address = 05h) [reset =
FFh ]
Figure 27. Coarse Counter Overflow Value_L Register
7
6
5
R/W-1h
R/W-1h
R/W-1h
4
3
COARSE_CNTR_OVF_L
R/W-1h
R/W-1h
2
1
0
R/W-1h
R/W-1h
R/W-1h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 7. Coarse Counter Overflow Value_L Register Field Descriptions
Bit
Field
Type
Reset
Description
7-0
COARSE_CNTR_OVF_L
R/W
FFh
Coarse Counter Overflow Value, lower 8 Bit
Note: Don't set COARSE_CNTR_OVF_L to 1.
8.6.8 CLOCK_CNTR_OVF_H: Clock Counter Overflow High Register (address = 06h) [reset = FFh]
Figure 28. CLOCK Counter Overflow Value_H Register
7
6
5
R/W-1h
R/W-1h
R/W-1h
4
3
CLOCK_CNTR_OVF_H
R/W-1h
R/W-1h
2
1
0
R/W-1h
R/W-1h
R/W-1h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 8. CLOCK Counter Overflow Value_H Register Field Descriptions
Bit
Field
Type
Reset
Description
7-0
CLOCK_CNTR_OVF_H
R/W
FFh
CLOCK Counter Overflow Value, upper 8 Bit
8.6.9 CLOCK_CNTR_OVF_L: Clock Counter Overflow Low Register (address = 07h) [reset = FFh]
Figure 29. CLOCK Counter Overflow Value_L Register
7
6
5
R/W-1h
R/W-1h
R/W-1h
4
3
CLOCK_CNTR_OVF_L
R/W-1h
R/W-1h
2
1
0
R/W-1h
R/W-1h
R/W-1h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 9. CLOCK Counter Overflow Value_L Register Field Descriptions
Bit
Field
Type
Reset
Description
7-0
CLOCK_CNTR_OVF_L
R/W
FFh
CLOCK Counter Overflow Value, lower 8 Bit
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8.6.10 CLOCK_CNTR_STOP_MASK_H: CLOCK Counter STOP Mask High Value Register (address = 08h)
[reset = 00h]
Figure 30. CLOCK Counter STOP Mask_H Register
7
6
5
R/W-0h
R/W-0h
R/W-0h
4
3
CLOCK_CNTR_STOP_MASK_H
R/W-0h
R/W-0h
2
1
0
R/W-0h
R/W-0h
R/W-0h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 10. CLOCK Counter STOP Mask_H Register Field Descriptions
Bit
Field
Type
Reset
Description
7-0
CLOCK_CNTR_STOP_MASK_H
R/W
0
CLOCK Counter STOP Mask, upper 8 Bit
8.6.11 CLOCK_CNTR_STOP_MASK_L: CLOCK Counter STOP Mask Low Value Register (address = 09h)
[reset = 00h]
Figure 31. CLOCK Counter STOP Mask_L Register
7
6
5
R/W-0h
R/W-0h
R/W-0h
4
3
CLOCK_CNTR_STOP_MASK_L
R/W-0h
R/W-0h
2
1
0
R/W-0h
R/W-0h
R/W-0h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 11. CLOCK Counter STOP Mask_L Register Field Descriptions
Bit
Field
Type
Reset
Description
7-0
CLOCK_CNTR_STOP_MASK_L
R/W
0
CLOCK Counter STOP Mask, lower 8 Bit
8.6.12 TIME1: Time 1 Register (address: 10h) [reset = 00_0000h]
Figure 32. TIME1 Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
Measurement Result: 23 bit integer value (Bit 22: MSB, Bit 0: LSB)
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 12. TIME1 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity Bit
R
0
Parity Bit
Measurement Result: 23 bit integer
value (Bit 22: MSB, Bit 0: LSB)
R
0
Measurement Result
22-0
30
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8.6.13 CLOCK_COUNT1: Clock Count Register (address: 11h) [reset = 00_0000h]
Figure 33. CLOCK Count Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
CLOCK_COUNT1 Result
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 13. CLOCK_COUNT1 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity Bit
R
0
Parity Bit
22-16
Not Used
R
0
These bits will be used in Multi-Cycle Averaging Mode in order
to allow higher averaging results.
15-0
CLOCK_COUNT1 Measurement
Result
R
0
CLOCK_COUNT1 Measurement Result
8.6.14
TIME2: Time 2 Register (address: 12h) [reset = 00_0000h]
Figure 34. TIME2 Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
Measurement Result: 23 bit integer value (Bit 22: MSB, Bit 0: LSB)
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 14. TIME2 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity Bit
R
0
Parity Bit
Measurement Result
R
0
Measurement Result
22-0
8.6.15 CLOCK_COUNT2: Clock Count Register (address: 13h) [reset = 00_0000h]
Figure 35. CLOCK_COUNT2 Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
CLOCK_COUNT2
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 15. CLOCK_COUNT2 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity bit
R
0
Parity Bit
22-16
Not Used
R
0
These bits will be used in Multi-Cycle Averaging Mode in order
to allow higher averaging results.
15-0
CLOCK_COUNT2 result
R
0
CLOCK_COUNT2 result
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TIME3: Time 3 Register (address: 14h) [reset = 00_0000h]
Figure 36. TIME3 Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
Measurement Result: 23 bit integer value (Bit 22: MSB, Bit 0: LSB)
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 16. TIME3 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity bit
R
0
Parity Bit
Measurement result
R
0
Measurement Result
22-0
8.6.17 CLOCK_COUNT3: Clock Count Registers (address: 15h) [reset = 00_0000h]
Figure 37. CLOCK_COUNT3 Count Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
CLOCK_COUNT3
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 17. CLOCK_COUNT3 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity bit
R
0
Parity bit
22-16
Not Used
R
0
These bits will be used in Multi-Cycle Averaging Mode in order
to allow higher averaging results.
15-0
CLOCK_COUNT3 Result
R
0
CLOCK_COUNT3 Result
8.6.18
TIME4: Time 4 Register (address: 16h) [reset = 00_0000h]
Figure 38. TIME4 Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
Measurement Result: 23 bit integer value (Bit 22: MSB, Bit 0: LSB)
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 18. TIME4 Register Field Descriptions
Bit
Field
Type
Reset
23
Parity bit
R
0
Measurement result
R
0
22-0
32
Description
Measurement result
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8.6.19 CLOCK_COUNT4: Clock Count Register (address: 17h) [reset = 00_0000h]
Figure 39. CLOCK_COUNT4 Count Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
CLOCK_COUNT4
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 19. CLOCK_COUNT4 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity bit
R
0
Parity bit
22-16
Not Used
R
0
These bits will be used in Multi-Cycle Averaging Mode in order
to allow higher averaging results.
15-0
CLOCK_COUNT4 Result
R
0
CLOCK_COUNT4 Result
8.6.20
TIME5: Time 5 Register (address: 18h) [reset = 00_0000h]
Figure 40. TIME5 Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
Measurement Result: 23 bit integer value (Bit 22: MSB, Bit 0: LSB)
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 20. TIME5 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity bit
R
0
Parity Bit
Measurement result
R
0
Measurement result
22-0
8.6.21 CLOCK_COUNT5: Clock Count Register (address: 19h) [reset = 00_0000h]
Figure 41. CLOCK_COUNT5 Count Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
CLOCK_COUNT5
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 21. CLOCK_COUNT5 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity bit
R
0
Parity bit
22-16
Not Used
R
0
These bits will be used in Multi-Cycle Averaging Mode in order
to allow higher averaging results.
15-0
CLOCK_COUNT5 Result
R
0
CLOCK_COUNT5 Result
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TIME6: Time 6 Register (address: 1Ah) [reset = 00_0000h]
Figure 42. TIME6 Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
Measurement Result: 23 bit integer value (Bit 22: MSB, Bit 0: LSB)
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 22. TIME6 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity bit
R
0
Parity Bit
Measurement result
R
0
Measurement result
22-0
8.6.23 CALIBRATION1: Calibration 1 Register (address: 1Bh ) [reset = 00_0000h]
Figure 43. CALIBRATION1 Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
CALIBRATION1
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 23. CALIBRATION1 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity BIt
R
0
Parity Bit
CALIBRATION1
R
0
Calibration 1 Result: 23 bit integer value (Bit 22: MSB, Bit 0:
LSB)
22-0
8.6.24 CALIBRATION2: Calibration 2 Register (address: 1Ch ) [reset = 00_0000h]
Figure 44. CALIBRATION2 Register
23
22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Parity Bit
CALIBRATION2
R-0
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 24. CALIBRATION2 Register Field Descriptions
Bit
Field
Type
Reset
Description
23
Parity BIt
R
0
Parity Bit
CALIBRATION2
R
0
Calibration 2 Result: 23 bit integer value (Bit 22: MSB, Bit 0:
LSB)
22-0
34
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9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
In the Time Of Flight (TOF) method, the upstream flight time as well as the downstream flight time is measured.
The difference between the Downstream and Upstream values is proportional to the flow.
The microcontroller (MCU) configures the TDC and AFE and issues a measurement start command to the TDC
via the SPI interface. The TDC sends a TRIGGER pulse to the AFE which is set up to actuate one of the
transducers and transmit a START signal to the TDC which starts its counter(s). The echo pulse will travel
through the AFE and arrive to the TDC as the STOP signal. The counter will be stopped and after performing
calibration, the counter value is reported as VAL.
Depending on system implementation, the above procedure is repeated for the same direction or opposite
direction.
9.2 Typical Application
RREF
Flow
RTD
l
TX1/RX2
B
TX2/RX1
A
TX2
TX1
RX1
START
STOP
TRIGGER
TDC1000
TDC7200
EN
RESET
ERRB
SPI
RX2
8-MHz CLK
MSP430
MCU
OSC
SPI
ENABLE
INT
Figure 45. System in Time of Flight Mode
9.2.1 Design Requirements
The parameters in this section are considered for this example.
Table 25. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Pipe diameter
15 mm
Distance between transducers
60 mm
Minimum flow rate
0.015 m3/h
Accuracy at minimum flow rate
5%
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•
•
•
•
•
•
•
•
•
•
www.ti.com
The design of flow-meters requires a thorough technical assessment of the system where the device will be
used. The following is a list of areas to consider:
Minimum and maximum flow rate at maximum allowable error in the system
Transitional flow rate
Instantaneous and total quantity pumped over time
Accuracy of the meter within prescribed limits per applicable standards
Pressure in the system
Operating temperature range
The appropriate ultrasonic sensor and the proper electronics for interfacing to the sensor are determined
based on the system requirements. The following is a list of specifications applicable to the senor/assembly
used in the system:
Excitation frequency
Excitation source voltage
Pipe diameter
Distance between the transducers (or reflectors)
9.2.2 Detailed Design Procedure
The following subsections describe the detailed design procedure for a flow meter application.
9.2.2.1 Flow Meter Regulations and Accuracy
If the flow meter is intended for residential applications, it must be designed to meet the required standards. For
example, per the INTERNATIONAL ORGANIZATION OF LEGAL METROLOGY (OIML), the metrological
requirements of water meters are defined by the values of Q1, Q2, Q3 and Q4, which are described in Table 26.
Table 26. Flow-rate Zones per OIML
FLOW-RATE ZONE
DESCRIPTION
Q1
Lowest flow rate at which the meter is to operate within the maximum permissible errors.
Q2
Flow rate between the permanent flow rate and the minimum flow rate that divides the flow
rate range into two zones, the upper flow rate zone and the lower flow rate zone, each
characterized by its own maximum permissible errors.
Q3
Highest flow rate within the rated operating condition at which the meter is to operate within
the maximum permissible errors.
Q4
Highest flow rate at which the meter is to operate for a short period of time within the
maximum permissible errors, while maintaining its metrological performance when it is
subsequently operating within the rated operating conditions.
A water meter is designated by the numerical value of Q3 in m3/h and the ratio Q3/Q1. The value of Q3 and the
ratio of Q3/Q1 are selected from the lists provided in the OIML standards.
Water meters have to be designed and manufactured such that their errors do not exceed the maximum
permissible errors (MPE) defined in the standards. For example, in OIML standards, water meters need to be
designated as either accuracy class 1 or accuracy class 2, according to the requirements.
For class 1 water meters, the maximum permissible error in the upper flow rate zone (Q2 ≤ Q ≤ Q4) is ±1%, for
temperatures from 0.1°C to 30°C, and ±2% for temperatures greater than 30°C. The maximum permissible error
for the lower flow-rate zone (Q1 ≤ Q < Q2) is ±3%, regardless of the temperature range.
For class 2 water meters, the maximum permissible error for the upper flow rate zone (Q2 ≤ Q ≤ Q4) is ±2%, for
temperatures from 0.1°C to 30°C, and ±3% for temperatures greater than 30°C. The maximum permissible error
for the lower flow rate zone (Q1 ≤ Q < Q2) is ±5% regardless of the temperature range.
The flow meter accuracy specified in the standards dictates the required accuracy in the electronics used for
driving the ultrasonic transducers, circuits in the receiver path, and time measurement sub circuits. The stringent
accuracy required at lower flow rates would require a very low noise signal chain in the transmitter and receiver
circuits used in ultrasonic flow meters, as well as the ability to measure picosecond time intervals.
36
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9.2.2.2 Transmit Time in Ultrasonic Flow Meters
Transit-time ultrasonic flow meters works based on the principle that sound waves in a moving fluid travel faster
in the direction of flow (downstream), and slower in the opposite direction of flow (upstream).
The system requires at least two transducers. The first transducer operates as a transmitter during the upstream
cycle and as a receiver during the downstream cycle, and the second transducer operates as a receiver during
the upstream cycle and as a transmitter during the downstream cycle. An ultrasonic flow meter operates by
alternating transmit and receive cycles between the pair of transducers and accurately measuring the time-offlight both directions.
In this example, the upstream TOF is defined as:
H
P$# =
:? F R;
where
•
•
•
l is the path length between the two transducers in meters (m)
c is the speed of sound in water in meters per second (m/s)
v is the velocity of the water in the pipe in meters per second (m/s)
(4)
In this example, the downstream TOF is defined as:
where
•
•
•
l is the path length between the two transducers in meters (m)
c is the speed of sound in water in meters per second (m/s)
v is the velocity of the water in the pipe in meters per second (m/s)
(5)
The difference of TOF is defined as:
¿61( = P$# F P#$
where
•
•
tBA is the upstream TOF from transducer B to transducer A in seconds (s)
tAB is the downstream TOF from transducer A to transducer B in seconds (s)
(6)
After the difference in time-of-flight (ΔTOF) is calculated, the water velocity inside the pipe can be related to the
ΔTOF using the following equation:
¿61( × ? 2
R=
2×H
where
•
•
c is the speed of sound in water in meters per second (m/s)
l is the path length between the two transducers in meters (m)
(7)
Finally, the mass flow rate can be calculated as follows:
3 =G×R×#
where
•
•
•
k is the flow-meter constant
v is the velocity of the water in the pipe in meters per second (m/s)
A is the cross-section area of the pipe in meters-squared (m2)
(8)
9.2.2.3 ΔTOF Accuracy Requirement Calculation
Based on the minimum mass flow requirement and accuracy requirements in Table 25, the ΔTOF accuracy
needed can be calculated as follows:
1. Convert the mass flow rate to m3/s:
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1D
p = 4.167T10F6 I3 /O
3600 O
2. Calculate the flow velocity assuming k = 1:
3
4.167T10F6 I3 /O
R=
=
= 0.0236 I/O
G#
0.015 I 2
A
è@
2
3. Calculate the ΔTOF for the given speed of sound. In this example, a speed of sound c = 1400 m/s is
assumed:
2 × H × R (2)(0.06 I)(0.0236 I/O)
¿61( =
=
= 1.445 JO
?2
1400 I/O 2
3 = :0.015 I3 /D; l
4. The requirement of 5% accuracy for minimum flow will result in a ΔTOF accuracy of:
¿61(ANNKN = :0.05;:1.445 JO; = 72.25 LO
For this reason, this system requires a high accuracy timer/stopwatch that can measure the lower flow rate state.
The TDC1000 ultrasonic analog-front-end is used to drive the transmitter, amplify and filter the received
signal and conditioning the echo for START and STOP pulse generation. The TDC7200 ps-accurate timer is
used to measure the time interval between the rising edge of the START pulse and the rising edge of the
STOP pulse produced by the TDC1000.
The microcontroller should first configure the TDC7200 and the TDC1000 for the measurement. When the
microcontroller issues a start command to the TDC7200 via the SPI interface, the TDC7200 sends a trigger
pulse to the TRIGGER pin of the TDC1000. When the TDC1000 drives the transmit transducer, a
synchronous START pulse is produced on the START pin, which commands the TDC7200 to start its
counters. When a valid echo pulse is received on the receive transducer, the TDC1000 generates a STOP
pulse on the STOP pin, which commands the TDC7200 to stop its counters. This procedure is repeated for
the upstream and downstream cycles.
A temperature measurement can be performed and the result can be used to correct for temperature
dependency of the speed of sound.
9.2.3 Application Curves
Figure 46 , Figure 47, and Figure 48 show data and histograms created with data collected under a zero flow
condition at room temperature. A simple offset calibration has been applied, where the overall average of the
data is subtracted from the data.
0.4
Raw calibrated data
10x running average
Delta time-of-flight (ns)
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
0
1000
2000
3000
Samples (n)
4000
5000
6000
Figure 46. Calibrated Raw and Averaged Delta Time-of-Flight Data
38
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1800
1600
V = 82 ps
1400
1200
1200
Number of hits
1000
800
600
1000
800
600
0.
09
07
0.
03
0.
05
0.
01
0.
-0
.0
1
Delta time-of-flight (ns)
Figure 47. Raw Calibrated Data Histogram
-0
.0
3
0.
28
22
0.
10
0.
16
0.
04
0.
-0
.0
2
-0
.0
8
0
-0
.1
4
0
-0
.2
0
200
-0
.2
6
200
-0
.0
5
400
400
-0
.0
9
Number of hits
1400
V = 31 ps
-0
.0
7
1600
Delta time-of-flight (ns)
Figure 48. 10x Running Average Data Histogram
9.3 Post Filtering Recommendations
For application such as flow meters where conversion results are accumulated over a long period of time, post
filtering is not required. However, for applications where a specific action is taken based on individual conversion
results, post filtering is recommended. One advantage of post filtering is to remove the conversion results that
are outside of the normal distribution.
One such post filtering method commonly applied by an MCU is the Median Filter Method. The median of a finite
number of conversion results can be found by arranging all the conversions from the lowest value to the highest
value, and picking the middle one. For example, a conversion result of {50, 51, 49, 40, 51} can be rearranged
from lowest to highest {40, 49, 50, 51, 51}, and the median value after applying the Median Filter Method is 50.
9.4 CLOCK Recommendations
A stable, known reference clock is crucial to the ability to measure time, regardless of the time measuring device.
Two parameters of a clock source primarily affect the ability to measure time: accuracy and jitter. The following
subsections will discuss recommendations for the CLOCK in order to increase accuracy and reduce jitter.
9.4.1 CLOCK Accuracy
CLOCK sources are typically specified with an accuracy value as the clock period is not exactly equal to the
nominal value specified. For example, an 8 MHz clock reference may have a 20 ppm accuracy. The true value of
the clock period therefore has an error of ±20ppm, and the real frequency is in the range 7.99984 MHz to
8.00016 MHz [8 MHz ± (8 MHz) x (20/106)].
If the clock accuracy is at this boundary, but the reference time used to calculate the time of flight relates to the
nominal 8 MHz clock period, then the time measured will be affected by this error. For example, if the time period
measured is 50 µs, and the 8MHz reference clock has +50ppm of error in frequency, but the time measured
refers to the 125 ns period (1/8 MHz), then the 50 µs time period will have an error of 50µs x 50/1000000 = 2.5
ns.
In summary, a clock inaccuracy translates proportionally to a time measurement error.
9.4.2 CLOCK Jitter
Clock jitter introduces uncertainty into a time measurement, rather than inaccuracy. As shown in Figure 49, the
jitter accumulates on each clock cycle so the uncertainty associated to a time measurement is a function of the
clock jitter and the number of clock cycles measured.
Clock_Jitter_Uncertainty = (√n) x (θJITTER), where n is the number of clock cycles counted, and θJITTER is the
cycle-to-cycle jitter of the clock.
For example, if the time measured is 50 µs using an 8 MHz reference clock, n = 50 µs/(1/8 MHz) = 400 clock
cycles. If the RMS cycle-to-cycle jitter, θJITTER = 10 ps, then the RMS uncertainty introduced in a single
measurement is in the order of (√n) x (θJITTER) = 200 ps.
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CLOCK Recommendations (continued)
Because the effect of jitter is random, averaging or accumulating time results reduces the effect of the
uncertainty introduced. If the time is measured m times and the result is averaged, then the uncertainty is
reduced to: Clock_Jitter_Uncertainty = (√n) x (θJITTER) / (√m).
For example, if 64 averages are performed in the example above, then the jitter-related uncertainty is reduced to
25 ps RMS.
Figure 49. CLOCK Jitter
40
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10 Power Supply Recommendations
The analog circuitry of the TDC7200 is designed to operate from an input voltage supply range between 2 V and
3.6 V. It is recommended to place a 100 nF ceramic bypass capacitor to ground as close as possible to the VDD
pins. In addition, an electrolytic or tantalum capacitor with value greater than 1 µF is recommended. The bulk
capacitor does not need to be in close vicinity with the TDC7200 and could be close to the voltage source
terminals or at the output of the voltage regulators powering the TDC7200.
11 Layout
11.1 Layout Guidelines
•
•
•
•
In a 4-layer board design, the recommended layer stack order from top to bottom is: signal, ground, power
and signal.
Bypass capacitors should be placed in close proximity to the VDD pin.
The length of the START and STOP traces from the TDC7200 to the stopwatch/MCU should be matched to
prevent uneven signal delays. Also, avoid unnecessary via-holes on these traces and keep the routing as
short/direct as possible to minimize parasitic capacitance on the PCB.
Route the SPI signal traces close together. Place a series resistor at the source of DOUT (close to the
TDC7200) and series resistors at the sources of DIN, SCLK, and CSB (close to the master MCU).
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11.2 Layout Example
Figure 50. TDC7200EVM Layout
42
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12 Device and Documentation Support
12.1 Documentation Support
12.1.1 Related Documentation
For related documentation see the following:
•
TDC1000 : Ultrasonic Sensing Analog Front End for Level, Concentration, Flow & Proximity Sensing
Applications.
12.2 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
12.3 Trademarks
E2E is a trademark of Texas Instruments.
SPI is a trademark of Motorola.
All other trademarks are the property of their respective owners.
12.4 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
12.5 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
TDC7200PW
ACTIVE
TSSOP
PW
14
90
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
T7200
TDC7200PWR
ACTIVE
TSSOP
PW
14
2000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
T7200
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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