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TDC1000, TDC1000-Q1
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
TDC1000 用于液位感测、流量感测、浓度感测以及接近传感应用的超声波
感测模拟前端 (AFE)
1 特性
•
•
•
•
1
•
•
•
符合汽车级 AEC-Q100 标准 (TDC1000-Q1)
测量范围：高达 8ms
工作电流：1.8µA (2 SPS)
发送器通道 TX1/TX2：
– 支持单传感器或双传感器应用
– 可编程激励：31.25kHz 至 4MHz，多达 31 个
脉冲
接收器通道 RX1/RX2：
– STOP 逐周期抖动：50psRMS
– 低噪声、可编程增益放大器
– 可访问外部滤波器的信号链设计
– 针对回声质检的可编程阈值比较器
– 针对差动飞行时间 (TOF) 测量自动交换通道
– 针对较长 TOF 测量的可编程低功耗模式
温度测量
– 2 个 PT1000/500 RTD 接口
– RTD 间的匹配精度为 0.02°CRMS
工作温度范围：-40℃ 至 125℃
3 说明
TDC1000 是一款完全集成的超声波感测模拟前端
(AFE)，常用于汽车、工业、医疗和消费品市场中的液
位、液体鉴别/浓度、流量以及接近传感/远距感测应
用。 与 MSP430/C2000 MCU、电源、无线网络和源
代码配套使用时，TI 可提供完整的超声波感测解决方
案。
TI 的超声波 AFE 可编程且具有灵活性，可适应广泛的
应用和终端设备。 TDC1000 可针对多种发射脉冲和频
率、增益和信号阈值进行配置，以便在多种传感器频率
（31.25kHz 至 4MHz）和 Q 系数下使用。 同样，接
收路径可编程设定，因此在更远的距离/更大的箱体尺
寸范围内也能够检测到通过多种介质传播的超声波。
TDC1000 可选择不同的工作模式，并且针对低功耗进
行了优化，
这使得它成为电池供电流量计，
液位测量仪以及距离/接近传感测量装置的理想选择。
低噪声放大器和比较器产生的抖动极低，可实现零流量
和低流量测量的皮秒级分辨率和精度.
2 应用范围
•
•
•
不同材料箱中的各项测量：
– 液位
– 液体鉴别/浓度
流量计量：水、气体、热量
远距/接近传感
器件信息(1)
部件号
封装
封装尺寸（标称值）
TDC1000
TSSOP (28) PW
9.70mm x 4.40mm
TDC1000-Q1
TSSOP (28) PW
9.70mm x 4.40mm
(1) 要了解所有可用封装，请见数据表末尾的可订购产品附录。
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.
English Data Sheet: SNAS648
TDC1000, TDC1000-Q1
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
www.ti.com.cn
目录
1
2
3
4
5
6
7
8
特性 ..........................................................................
应用范围...................................................................
说明 ..........................................................................
修订历史记录 ...........................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
4
4
4
5
6
8
8
9
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Timing Requirements ................................................
Switching Characteristics ..........................................
Typical Characteristics ..............................................
Parameter Measurement Information ................ 11
Detailed Description ............................................ 12
8.1 Overview ................................................................. 12
8.2 Functional Block Diagram ....................................... 12
8.3 Feature Description................................................. 13
8.4 Device Functional Modes........................................ 20
8.5 Programming .......................................................... 31
8.6 Register Maps ......................................................... 32
9
Application and Implementation ........................ 41
9.1 Application Information............................................ 41
9.2 Typical Applications ................................................ 41
10 Power Supply Recommendations ..................... 51
11 Layout................................................................... 52
11.1 Layout Guidelines ................................................. 52
11.2 Layout Example .................................................... 52
12 器件和文档支持 ..................................................... 53
12.1
12.2
12.3
12.4
12.5
12.6
12.7
器件支持................................................................
文档支持................................................................
相关链接................................................................
社区资源................................................................
商标 .......................................................................
静电放电警告.........................................................
Glossary ................................................................
53
53
53
53
53
53
53
13 机械、封装和可订购信息 ....................................... 54
4 修订历史记录
注意：前一修订版的页码可能与当前版本的页码不同。
Changes from Revision A (December 2014) to Revision B
Page
•
已添加 整个文档中 PW 封装的命名法 .................................................................................................................................... 1
•
Changed programmed threshold in Figure 35, Multiple Echo Receive Mode (Zoom-in) .................................................... 25
•
Added trigger to START time description ............................................................................................................................ 26
•
Changed notes on Figure 37, Short TOF Measurement ..................................................................................................... 27
•
Changed note A on Figure 38, Standard TOF Measurement ............................................................................................. 28
•
Changed note A on Figure 39, Standard TOF Measurement with Blanking Enabled ......................................................... 29
•
Changed Equation 9, downstream TOF ............................................................................................................................... 48
Changes from Original (October 2014) to Revision A
Page
•
已添加 引脚配置和功能部分，规范部分，参数测量信息部分，详细说明部分，应用和实施部分，电源相关建议部分以
及布局部分.............................................................................................................................................................................. 1
•
已更改 器件和文档支持部分.................................................................................................................................................... 1
2
Copyright © 2014–2015, Texas Instruments Incorporated
TDC1000, TDC1000-Q1
www.ti.com.cn
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
5 Pin Configuration and Functions
TSSOP
28 Pin PW
Top View
RX1
RX2
VCOM
LNAOUT
PGAIN
COMPIN
RTD1
RTD2
RREF
CHSEL
ERRB
START
STOP
5
6
7
8
9
10
11
12
13
14
TDC1000
PGAOUT
1
2
3
4
28
27
26
25
24
23
22
21
20
19
18
17
16
15
TX1
TX2
GND
CLKIN
VDD
VDD
VIO
SDO
SDI
CSB
SCLK
RESET
TRIGGER
EN
Pin Functions
PIN
NAME
NO.
TYPE (1)
DESCRIPTION
RX1
1
I
Receive input 1
RX2
2
I
Receive input 2
VCOM
3
P
Output common mode voltage bias
LNAOUT
4
O
Low noise amplifier output (for ac decoupling capacitor)
PGAIN
5
I
Programmable gain amplifier input
PGAOUT
6
O
Programmable gain amplifier output
COMPIN
7
I
Echo qualification and zero-crossing detector input
RTD1
8
O
Resistance temperature detector channel 1
RTD2
9
O
Resistance temperature detector channel 2
RREF
10
O
Reference resistor for temperature measurement
CHSEL
11
I
External channel selection
ERRB
12
O
Error flag (open drain)
START
13
O
Start pulse output
STOP
14
O
Stop pulse output
EN
15
I
Enable (active high; when low the TDC1000 is in SLEEP mode)
TRIGGER
16
I
Trigger input
RESET
17
I
Reset (active high)
SCLK
18
I
Serial clock for the SPI interface
CSB
19
I
Chip select for the SPI interface (active low)
SDI
20
I
Serial data input for the SPI interface
SDO
21
O
Serial data output for the SPI interface
VIO
22
P
Positive I/O supply
VDD (2)
23, 24
P
Positive supply; all VDD supply pins must be connected to the supply.
CLKIN
25
I
Clock input
GND
26
G
Negative supply
(1)
(2)
G = Ground, I = Input, O = Output, P = Power
Place a 100-nF bypass capacitor to ground in closest proximity of the pin
Copyright © 2014–2015, Texas Instruments Incorporated
3
TDC1000, TDC1000-Q1
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
www.ti.com.cn
Pin Functions (continued)
PIN
NAME
NO.
TYPE (1)
DESCRIPTION
TX2
27
O
Transmit output 2
TX1
28
O
Transmit output 1
6 Specifications
6.1 Absolute Maximum Ratings
Over operating free-air temperature range (unless otherwise noted)
(1) (2)
MIN
MAX
UNIT
VDD
Analog supply voltage, VDD pins
–0.3
6.0
V
VIO
I/O supply voltage (VIO must always be lower than or equal to VDD supply)
–0.3
6.0
V
–0.3
VDD + 0.3
V
–0.3
VIO + 0.3
V
5
mA
(3)
VI
Voltage on any analog input pin
VI
Voltage on any digital input pin (3)
II
Input current at any pin
TJ
Operating junction temperature
–40
125
°C
Tstg
Storage temperature range
–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.
All voltages are with respect to ground, unless otherwise specified.
When the input voltage at a pin exceeds the power supplies, the current at that pin must not exceed 5 mA and the voltage (VI) at that
pin must not exceed 6.0 V.
6.2 ESD Ratings
VALUE
Human-body model (HBM), per AEC A100-002 (1)
V(ESD)
(1)
Electrostatic discharge
Charged-device model (CDM), per AEC
Q100-011
UNIT
±2000
All pins
±500
Corner pins (1, 14, 15
and 28)
±750
V
AEC Q100-002 indicates HBM stressing is done in accordance with the ANSI/ESDA/JEDEC JS-001 specification.
6.3 Recommended Operating Conditions
Over operating free-air temperature range (unless otherwise noted)
MIN
MAX
UNIT
2.7
5.5
V
1.8
VDD
V
GND
VDD
V
VIO
V
0.06
16
MHz
–40
125
°C
VDD
Analog supply voltage, VDD pins
VIO
Digital supply voltage, (VIO must always be lower than or equal to VDD supply)
VI
Voltage on any analog input pin
VI
Voltage on any digital input pin
GND
ƒCLKIN
Operating frequency
TJ
Operating junction temperature
4
Copyright © 2014–2015, Texas Instruments Incorporated
TDC1000, TDC1000-Q1
www.ti.com.cn
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
6.4 Thermal Information (1)
THERMAL METRIC
RθJA
Junction-to-ambient thermal resistance
TDC1000
TSSOP
(28 PINS) PW
83.5
RθJC(top) Junction-to-case (top) thermal resistance
29.9
RθJB
Junction-to-board thermal resistance
40.8
ψJT
Junction-to-top characterization parameter
2.4
ψJB
Junction-to-board characterization parameter
40.3
(1)
UNIT
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
Copyright © 2014–2015, Texas Instruments Incorporated
5
TDC1000, TDC1000-Q1
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
www.ti.com.cn
6.5 Electrical Characteristics
The electrical ratings specified in this section apply to all specifications in this document, unless otherwise noted. These
specifications are interpreted as conditions that do not degrade the device parametric or functional specifications for the life of
the product containing it. TA = 25°C, VDD = VIO = 3.7 V, VCOM = VCM = VDD / 2, CVCOM = 10 nF (unless otherwise noted).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
TRANSMITTER SIGNAL PATH (TX)
HIGH
VDD – 0.32
LOW
0.32
VOUT(TX)
Output voltage swing
ƒout = 1 MHz, RL = 75 Ω to VCM
IOUT(TX)
Output drive current
ƒout = 1 MHz, RL = 75 Ω to VCM
ƒOUT(TX)
Output TX frequency
ƒCLKIN = 8 MHz, divide-by-2 (programmable;
see Transmitter Signal Path)
V
V
22
mARMS
4
MHz
RECEIVER SIGNAL PATH (RX)
STOP cycle-to-cycle
jitter
LNA capacitive feedback, GPGA = 6 dB, ƒIN = 1
MHz, VIN = 100 mVPP, CVCOM = 1 µF and
Figure 14
50
psRMS
GLNA
LNA gain
Capacitive feedback, CIN = 300 pF, ƒIN = 1
MHz, RL = 100 kΩ to VCM, CVCOM = 1 µF
20
dB
enLNA
LNA input referred
noise density
Capacitive feedback, CIN = 300 pF, ƒ = 1 MHz,
VDD = 3.1 V, VIN = VCM, RL = ∞, CVCOM = 1 µF
2
nV/√Hz
VIN(LNA)
Input voltage range
Resistive feedback, RL = 1 kΩ to
VCM, CVCOM = 1 µF
HIGH
VCM + (VCM – 0.24) / (GLNA)
V
LOW
VCM – (VCM – 0.24) / (GLNA)
V
Output voltage range
Resistive feedback, RL = 1 kΩ to
VCM, CVCOM = 1 µF
HIGH
VDD – 0.24
V
LOW
GND + 0.24
V
SRLNA
Slew rate (1)
Resistive feedback, RL = 1 kΩ to VCM, 100mV
step, CVCOM = 1 µF
9
XTK
MUX ch-to-ch crosstalk
Capacitive feedback, ƒ = 1 MHz, RL = 100 kΩ
to VCM, CVCOM = 1 µF
–57
BWLNA
–3-dB bandwidth
Capacitive feedback, CIN = 300 pF, RL= 100 kΩ
to VCM, CVCOM = 1 µF
VOS(LNA)
LNA input offset
voltage
Resistive mode, VIN = VCM, RL = ∞
ΔtSTOP
LNA
VOUT(LNA)
5
V/μs
dB
MHz
±320
µV
VCM
V
VCOM
VCOM
VCOM output voltage
VCOM output error
CVCOM = 1 µF
0.5%
PGA
RL = 100 kΩ to VCM, CL = 10 pF
to GND
HIGH
VCM + (VCM – 0.06) / (GPGA)
LOW
VCM – (VCM – 0.06) / (GPGA)
V
VIN(PGA)
PGA input range
GPGAMIN
PGA min gain
GPGAMAX
PGA max gain
ΔGPGA
PGA gain step size
GE(PGA)
PGA gain error
DC, GPGA = 0 dB, RL = ∞, CL = 10 pF
5%
TCGPGA
PGA gain temperature
coefficient
DC, GPGA = 0 dB, RL = ∞, CL = 10 pF
170
ppm/°C
enPGA
PGA input referred
noise density
GPGA = 21 dB, ƒ = 1 MHz, VDD = 3.1V, VIN =
VCM, RL = ∞, CVCOM = 1 µF
3.1
nV/√Hz
VOUT(PGA)
Output range
RL = 100 kΩ to VCM, CL = 10 pF
to GND
BWPGA
–3-db bandwidth
SRPGA
Slew rate (1)
(1)
6
DC, RL = ∞, CL = 10 pF
V
0
dB
21
dB
3
dB
HIGH
VDD – 0.06
LOW
60
mV
V
GPGA = 21 dB, RL = 100 kΩ to VCM, CL = 10
pF, CVCOM = 1 µF
5
MHz
GPGA = 21 dB, RL = 100 kΩ to VCM, CL = 10
pF, CVCOM = 1 µF
12.5
V/µs
The slew rate is measured from 10% to 90% and is represented by the average of the rising and falling slew rates.
Copyright © 2014–2015, Texas Instruments Incorporated
TDC1000, TDC1000-Q1
www.ti.com.cn
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
Electrical Characteristics (continued)
The electrical ratings specified in this section apply to all specifications in this document, unless otherwise noted. These
specifications are interpreted as conditions that do not degrade the device parametric or functional specifications for the life of
the product containing it. TA = 25°C, VDD = VIO = 3.7 V, VCOM = VCM = VDD / 2, CVCOM = 10 nF (unless otherwise noted).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
ZERO CROSS COMPARATOR
VOS(COMP)
Input offset voltage (2)
Referred to VCOM
enCOMP
Zero crossing
comparator input
referred noise (2)
1 MHz
HYSTCOMP
Hysteresis
(2)
±115
µV
5
Referred to VCOM
nV/√Hz
-10
mV
ECHO_QUAL_THLD = 0h, VCOM referred
–35
mV
ECHO_QUAL_THLD = 7h, VCOM referred
–1.5
V
1
°C
0.5
°C
THRESHOLD DETECTOR
VTHDET
Threshold level
TEMPERATURE SENSOR INTERFACE
TERROR
RREF = 1 kΩ, PT1000 range: –40 to 125°C (4)
Temperature
measurement accuracy RREF = 1 kΩ, PT1000 range: –15°C to 85°C (4)
Relative accuracy
TGE
(3)
RREF = 1 kΩ, RRTD1 = RRTD2 = 1.1 kΩ
Gain error
0.02
°CRMS
5.8
m°C/°C
0.61
µA
POWER SUPPLY
Sleep (EN = CLKIN = TRIGGER = low)
Continuous receive mode, LNA and PGA
bypassed
IDD
VDD supply current
Continuous receive mode, LNA and PGA active
Temp. measurement only (PT1000 mode)
(5)
Temp. measurement (PT500 mode) (6)
VIO supply sleep
current (2)
IIO
Sleep (EN = CLKIN = TRIGGER = low)
2.8
3
mA
6.2
7.5
mA
370
400
µA
500
540
µA
2
nA
DIGITAL INPUT/OUTPUT CHARACTERISTICS
VIL
Input logic low
threshold
VIH
Input logic high
threshold
Output logic low
threshold
VOL
0.2 × VIO
0.8 × VIO
V
SDO pin, 100-μA current
0.2
V
SDO pin, 1.85-mA current
0.4
V
START and STOP pins, 100-μA current
0.5
V
START and STOP pins, 1.85-mA current
0.6
V
ERRB pin, 100-μA current
0.2
V
0.4
V
ERRB pin, 1.85-mA current
Output logic high
threshold
VOH
IOMAX
(2)
(3)
(4)
(5)
(6)
V
SDO pin, 100-μA current
VIO – 0.2
V
SDO pin, 1.85-mA current
VIO – 0.6
V
START and STOP pins, 100-μA current
VIO – 0.5
V
START and STOP pins, 1.85-mA current
VIO – 0.6
V
ERRB pin, 0-µA current
VIO – 0.2
V
Maximum output
current for SDO,
START and STOP
1.85
mA
Specified by design.
With ideal external components. For more detail see Temp Sensor Measurement section.
PT1000 RTD approximate resistance: 800 Ω ≡ –52°C, 931 Ω ≡ –18°C, 1.10 kΩ ≡ 26°C, 1.33 kΩ ≡ 86°C and 1.48 kΩ ≡ 125°C.
Specified currents include 120μA which flows through the RTD sensor in PT1000 mode (TEMP_RTD_SEL = 0).
Specified currents include 240μA which flows through the RTD sensor in PT500 mode (TEMP_RTD_SEL = 1).
Copyright © 2014–2015, Texas Instruments Incorporated
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TDC1000, TDC1000-Q1
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
www.ti.com.cn
6.6 Timing Requirements
TA = 25°C, VDD = VIO = 3.7 V and ƒSCLK = 1 MHz (unless otherwise noted).
MIN
TYP
MAX
UNIT
26
MHz
ƒSCLK
Serial clock frequency
t1
High period, SCLK
16
ns
t2
Low period, SCLK
16
ns
t3
Set-up time, nCS to SCLK
10
ns
t4
Set-up time, SDI to SCLK
12
ns
t5
Hold time, SCLK to SDI
12
ns
t6
SCLK transition to SDO valid time
16
ns
t7
Hold time, SCLK transition to nCS rising
edge
10
ns
t8
nCS inactive
17
ns
t9
Hold time, SCLK transition to nCS falling
edge
10
ns
tr / tf
(1)
Signal rise and fall times
(1)
1.8
ns
The slew rate is measured from 10% to 90% and is represented by the average of the rising and falling slew rates.
SCLK
t9
t7
t1
t2
t3
CSB
t4
t8
t5
D0
D14
D15
t6
Prior D15
90%
Prior D1
10%
90%
10%
Prior D0
tr
tf
Figure 1. SPI Timing Diagram
6.7 Switching Characteristics
TA = 25°C, VDD = VIO = 3.7 V, ƒCLKIN = 8 MHz.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
START, STOP, ENABLE, CHSEL, RESET, CLOCKIN, TRIGGER, ERR
TX_FREQ_DIV = 2h, NUM_TX = 1
1
μs
PWSTART
Pulse width for START signal TX_FREQ_DIV = 2h, NUM_TX = 2
2
μs
TX_FREQ_DIV = 2h, NUM_TX ≥ 3
3
μs
tr / tf
Rise/fall time for START
signal
20% to 80%, 20-pF load
0.25
ns
tr / tf STOP Rise/fall time for STOP signal 20% to 80%, 20-pF load
0.25
ns
START
ƒCLKIN
Maximum CLKIN input
frequency
tr / tf CLKIN CLKIN input rise/fall time (1)
tr / tf TRIG
TRIGGER input rise/fall
time (1)
Enable to trigger wait time
tRES_TRIG
Reset to trigger wait time (1)
8
MHz
20% to 80%
10
ns
20% to 80%
10
ns
50
ns
3.05
μs
(1)
tEN_TRIG
(1)
16
TX_FREQ_DIV = 2h (see TX/RX Measurement
Sequencing and Timing)
Specified by design.
Copyright © 2014–2015, Texas Instruments Incorporated
TDC1000, TDC1000-Q1
www.ti.com.cn
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
6.8 Typical Characteristics
At TA = 25°C, unless otherwise noted.
500
Output Impedance Magnitude (|Ÿ_
Output Impedance Magnitude (|Ÿ|)
500
400
300
200
100
0
±100
400
300
200
100
0
±100
100
1k
10k
100k
1M
10M
Frequency (Hz)
VDD = VIO = 3.7V
100
Capacitive
Feedback Mode
RL = 1kΩ
VDD = VIO = 3.7V
Figure 2. LNA ZOUT vs Frequency
10k
100k
1M
10M
C002
Gain of 21dB
RL = 1kΩ
Figure 3. PGA ZOUT vs Frequency
10
10
9
9
Input-referred Noise (nV/O,Ì•
Input-referred Noise (nV/O,Ì•
1k
Frequency (Hz)
C001
8
7
6
5
4
3
2
1
8
7
6
5
4
3
2
1
0
0
5k
50k
500k
2M
Frequency (Hz)
VDD = VIO = 3.1V
5k
RL = ∞
Capacitive
Feedback Mode
50k
500k
Frequency (Hz)
C013
VDD = VIO = 3.7V
Figure 4. LNA Input-referred Noise vs Frequency
Gain of 21dB
C014
RL = ∞
Output Voltage (250mV/DIV)
Output Voltage (250mV/DIV)
Figure 5. PGA Input-referred Noise vs Frequency
Time (1 s/DIV)
Time (1 s/DIV)
C005
VDD = VIO = 3.7V
VIN = 100mV
2M
Resistive Feedback
Mode
Figure 6. LNA Response
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fIN
RL = 1kΩ
= 100kHz
C006
VDD = VIO = 3.7V
VIN = 100mV
Gain of 21dB
RL = 100kΩ
fIN = 100kHz
Figure 7. PGA Response
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Typical Characteristics (continued)
30
30
20
20
10
10
Gain (dB)
Gain (dB)
At TA = 25°C, unless otherwise noted.
0
0
±10
±10
±20
±20
±30
±30
10k
100k
1M
10M
Frequency (Hz)
VDD = VIO = 3.7V
10k
100k
Capacitive
Feedback Mode
RL = 100kΩ
1M
10M
Frequency (Hz)
C007
VDD = VIO = 3.7V
C008
Gain of 21dB
RL = 100kΩ
CIN = 300 pF
Figure 9. PGA Gain vs Frequency
18
18
16
16
14
14
10
Time (ps)
PGA Gain of 6dB
fIN = 1MHz
Count >= 10000
18
18
16
16
14
14
8
LNA Capacitive
Feedback Mode
(See Figure 14)
-300
300
200
0
100
2
0
0
4
2
-100
6
4
-200
6
Time (ps)
C011
PGA Gain of 6dB
fIN = 1MHz
Count >= 10000
Figure 12. RX Jitter Histrogam
10
10
VDD = VIO = 3.7V
VIN = 100mV
TA = 125C°
LNA Capacitive
Feedback Mode
(See Figure 14)
300
8
12
200
10
100
12
VDD = VIO = 3.7V
VIN = 100mV
TA = -40C°
(See Figure 14)
0
Count (%)
20
Time (ps)
PGA Gain of 6dB
fIN = 1MHz
Count >= 10000
Figure 11. RX Jitter Histogram
20
-300
Count (%)
Figure 10. RX Jitter Histogram
C010
LNA Capacitive
Feedback Mode
-100
(See Figure 14)
VDD = VIO = 3.7V
VIN = 100mV
TA = 25C°
300
-300
Time (ps)
C009
LNA Capacitive
Feedback Mode
-200
VDD = VIO = 5V
VIN = 100mV
300
200
100
0
0
2
0
-100
4
2
-200
6
4
200
8
6
100
8
12
0
10
-100
12
-200
Count (%)
20
-300
Count (%)
Figure 8. LNA Gain vs Frequency
20
C012
PGA Gain of 6dB
fIN = 1MHz
Count >= 10000
Figure 13. RX Jitter Histogram
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7 Parameter Measurement Information
CIN = 300 pF
INPUT
LNAIN
CF1 = 1 nF
LNAOUT
RF1 = 1 NŸ
PGAIN
CF2 = 51 pF
COMPIN
PGAOUT
RF2 = 5.1 NŸ
CF3 = 51 pF
GND
VCOM
Figure 14. External Circuits for Jitter Measurement
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8 Detailed Description
8.1 Overview
The main functional blocks of TDC1000 are the Transmit (TX) and the Receive (RX) Channels. The transmitter
supports flexible settings for driving various ultrasonic transducers, and the receiver provides configurable blocks
with a wide range of settings for signal conditioning in various applications. The receive signal chain consists of
an LNA (Low Noise Amplifier), a PGA (Programmable Gain Amplifier), and two auto-zeroed comparators for
echo qualification and STOP pulse generation.
The TDC1000 provides three modes of operation: Mode 0, Mode 1 and Mode 2. Each mode is intended for one
or more applications such as flow/concentration measurement, container level measurement, proximity detection,
distance measurement, and a range of other applications where a precision measurement of Time-of-Flight
(TOF) is required.
A measurement cycle is initiated with a trigger signal on the TRIGGER pin of the device. After a trigger signal is
asserted, an output pulse is generated on the START pin. This signal is used as the time reference to begin a
TOF measurement. The transmitter generates programmable TX pulses, synchronous to the rising edge of the
START pulse, to drive an ultrasonic transducer and generate an ultrasonic wave that is shot through an acoustic
medium. The receiver detects the ultrasound wave that traveled through the medium and generates STOP
signals. Whether the ultrasound wave is received directly or from a reflection will depend on the system
configuration. The STOP signals are used by an external Time-to-Digital Converter (TDC), which functions as a
very accurate stopwatch. The system must include a TDC to measure the TOF based on the interval between
the START and STOP pulses. In some applications with medium-range accuracy requirements (ns range), a
microcontroller can be used to measure the TOF duration. In applications with high-range accuracy requirements
(ps range), TI recommends using the TDC7200 time-to-digital converter to measure the TOF duration.
In each application, the TDC1000 has to be configured by a serial interface (SPI) for one of the three modes of
operation available. In addition, the device must be programmed to various application-specific parameters that
are explained in the following sections.
TX1
Tx
Generator
SM Control
Unit
CSB
SCLK
SDI
SDO
ERRB
CHSEL
RESET
EN
Clock
Divider
TRIGGER
CLKIN
VIO
VDD
VDD
8.2 Functional Block Diagram
Serial
Interface
enable
RX1
MUX
RX2
Event
Manager
DAC
+
PGA
±
LNA
+
20 dB
VCOM
Threshold Detect
MUX
Channel
Select
START
MUX
TX2
STOP
±
0 to 21 dB
VCOM
Analog Bias
Temp. Sense
TDC1000
Zero-Cross Detect
RTD1
RTD2
RREF
VCOM
COMPIN
PGAOUT
PGAIN
LNAOUT
GND
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8.3 Feature Description
8.3.1 Transmitter Signal Path
The Transmitter (TX) path consists of a Clock Divider block and a TX Generator block. The clock divider allows
the TDC1000 to divide the clock source that is connected to the CLKIN pin down to the resonant frequency (ƒR)
of the transducer used. The clock divider allows division factors in powers of 2. The division factor of the clock
divider can be programmed with the TX_FREQ_DIV field in the CONFIG_0 register.
The TX Generator block can drive a transducer with a programmable number of TX pulses. The frequency of
these pulses is defined as ƒCLKIN/(2TX_FREQ_DIV+1), and should match the ƒR of the transducer. The number of
pulses is configured by programming the NUM_TX field in the CONFIG_0 register.
For example, for ƒCLKIN = 8 MHz and TX_FREQ_DIV = 2h (divide by 8), the divided clock frequency is 1 MHz.
In addition to the programmable number of pulses, the TX Generator also provides options to introduce a 180⁰
pulse shift at pulse position n or damping the last TX pulse. In some situations, damping can reduce the ringing
of the transducer for very short TOF measurements. These features are further described in the TRANSMIT
Operation section of the datasheet.
8.3.2 Receiver Signal Path
The RX signal path consists of a channel selection multiplexer followed by an LNA. The output of the LNA can
then be sent to the PGA for additional amplification if needed. Finally, the signal is fed into a set of comparators
which generate pulses on the STOP pin based on the programmed threshold levels. The block diagram for the
receiver path can be seen in Figure 15.
If the 20-dB to 41-dB of gain provided by the TDC1000 is insufficient, additional gain can be added prior to the
COMPIN pin. Likewise, with a strong received signal, if the gain from the LNA or PGA is not be needed, they can
be bypassed and the transducer signal could be directly connected to the COMPIN pin.
A band-pass filter centered on the transducer’s response can be used between each stage of the receiver path
to reduce the noise; note that the inputs of the LNA, PGA and comparators should be biased to the VCOM pin’s
potential. The comparators connected to the COMPIN pin are used for echo qualification and generation of
STOP pulses that correspond to the zero-crossings of the echo signal. The STOP pulses are used with a START
pulse to calculate the TOF of the echo in the medium.
Channel
Select
enable
MUX
+
PGA
VCOM
MUX
Event
Manager
DAC
±
LNA
+
20dB
Threshold Detect
STOP
±
0 to 21 dB
VCOM
Analog Bias
Temp. Sense
TDC1000
Zero-Cross Detect
RTD1
RTD2
RREF
VCOM
COMPIN
PGAOUT
PGAIN
LNAOUT
GND
Figure 15. TDC1000 Receiver Path
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Feature Description (continued)
8.3.3 Low Noise Amplifier (LNA)
The LNA in the TDC1000’s front-end limits the input-referred noise and ensures timing accuracy for the
generated STOP pulses. The LNA is an inverting amplifier designed for a closed-loop gain of 20 dB with the aid
of an external input capacitor or resistor, and it can be programmed for two feedback configurations. The bandpass configuration, referred to as capacitive feedback mode, must be combined with an input capacitor. The lowpass configuration, referred to as resistive feedback mode, must be combined with an input resistor. The
recommended values for the input components are 300 pF and 900 Ω respectively.
The LNA can be configured in capacitive feedback mode for transducers with resonant frequencies in the order
of a couple of MHz. This is done by clearing the LNA_FB bit in the TOF_1 register to 0. As shown in Figure 16,
the external capacitor, CIN, should be placed between the transducer and the corresponding input pin. This
provides an in-band gain of CIN/CF, where CF is the on-chip 30-pF feedback capacitor. Provided that CIN = 300
pF, the in-band gain of the LNA circuit is:
CIN 300 pF
Gainin band
10
CF
30 pF
(1)
Transducer
CIN
300 pF
CF
30 pF
RF
9 lQ
MUX
RX1
t
LNAOUT
LNA
RX2
+
300 pF
CIN
VCOM
Figure 16. LNA Capacitive Feedback Configuration
The capacitive feedback configuration of the LNA has a band-pass frequency response. The high-pass corner
frequency is set by the internal feedback components RF (9 kΩ) and CF (30 pF), and is approximately 590 kHz.
The in-band gain is set by the capacitor ratio and the LNA’s 50-MHz gain-bandwidth product sets the low-pass
corner of the frequency response. For example, an in-band gain of 10 results in a bandpass response between
590 kHz and 5 MHz.
The LNA can be configured in resistive feedback mode for transducers with resonant frequencies in the order of
a couple of hundreds of kHz. This is done by setting the LNA_FB bit in the TOF_1 register to 1. In this
configuration, the internal feedback capacitor CF is disconnected (see Figure 17), and the DC gain of the LNA
circuit is determined by the ratio between the internal feedback resistor RF (9 kΩ) and an external resistor RIN.
For RIN = 900 Ω, the gain of the circuit is 10.
RF
9 lQ
MUX
RIN
Transducer 900 Q
RX1
t
LNA
RX2
900 Q
RIN
LNAOUT
+
VCOM
Figure 17. LNA Resistive Feedback Configuration
The LNA can be bypassed and disabled by writing a 1 to the LNA_CTRL bit in the TOF_1 register.
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Feature Description (continued)
8.3.4 Programmable Gain Amplifier (PGA)
The PGA, shown in Figure 18, is an inverting amplifier with an input resistance of RIN = 500 Ω and a
programmable feedback resistor RFB that can be programmed to set a 0-dB to 21-dB gain in 3-dB steps. This
can be done by programming the PGA_GAIN field in the TOF_1 register. The bandwidth of the PGA is scaled
based on its programmed gain. The typical bandwidth of the PGA with a 100-kΩ load to VCM and a 10-pF
capacitor to ground are listed in Table 1.
Table 1. Typical PGA Bandwidth
PGA_GAIN (Hex)
Gain (dB)
Bandwidth (MHz)
0h
0
19.0
1h
3
16.8
2h
6
14.4
3h
9
12.3
4h
12
10.0
5h
15
8.2
6h
18
6.6
7h
21
5.0
The PGA can be bypassed and disabled by writing a 1 to the PGA_CTRL bit in the TOF_1 register. The output of
the PGA should not be loaded directly with capacitances greater than 10 pF.
RFB
PGA_IN
RIN 500 :
PGA_OUT
PGA
VCOM
Figure 18. TDC1000 Programmable Gain Amplifier
8.3.5 Receiver Filters
It is recommended to place two filters in the RX path to minimize the receive path noise and obtain maximum
timing accuracy. As shown in Figure 19, one filter is placed between the LNAOUT and the PGAIN pins, and
another filter is placed between the PGAOUT and the COMPIN pins.
With an in-band gain of 10, the LNA has a bandwidth of 5 MHz. For most applications, a low-pass filter between
the LNAOUT and PGAIN pins is sufficient.
As shown in Figure 19, the second filter stage can use a cascade of a low-pass filter (RF1 and CF3) followed by a
high-pass filter (CF2 and RF2) referenced to VCOM. Design of the filter is straightforward. The RF1 and CF2 can be
chosen first. A reasonable set of values for RF1 and CF2 could be: RF1 = 1 kΩ ± 10% and CF2 = 50pF ± 10%.
Given the center frequency of interest to be ƒC and the filter bandwidth to be ƒB, the value of CF3 can be
calculated as:
CF3
1
2 S R F1 fC
fB
(2)
RF2 and CF2 determine the high-pass corner of the filter. RF2 should be referenced to VCOM to maintain the DC
bias level at the comparator input during the echo receive time. For values of RF2 larger than RF1, there will be
limited loading effect from the high-pass filter to the low-pass filter resulting in more accurate corner frequencies.
The chosen values shown in the figure below result in a high-pass corner frequency of about 600 kHz and a lowpass corner frequency of about 3 MHz.
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More complex filters can be used; external gain is acceptable if the signal amplitude is too low. If the pass-band
of the filter is wider than an octave, it is recommended to use a filter design which has linear group delay.
RF1 = 1 NŸ
CF1 = 1 nF
LNAOUT
PGAIN
CF2 = 50 pF
COMPIN
PGAOUT
RF2 = 5 NŸ
CF3 = 53 pF
GND
VCOM
Figure 19. Filter for a 1-MHz Operation
8.3.6 Comparators for STOP Pulse Generation
The STOP pulse generation block of the TDC1000 contains two auto-zeroed comparators (a zero-cross detect
and a threshold-detect comparator), a threshold setting DAC, and an event manager.
Comparator auto-zero periods occur at the beginning of every TOF receive cycle. During these periods, the
comparator’s input offset is stored in an internal 2.5-pF capacitor, and it is subtracted from the input signal during
the echo processing phase. The duration of auto-zero period is configured with the AUTOZERO_PERIOD field
located in the CLOCK_RATE register.
Zero Cross Detect
VCOM
±
COMPIN
+
Threshold
Detect
ECHO_QUAL_THLD
STOP
Event Manager
±
+
DAC
VTHLD
±
+
RECEIVE_MODE
NUM_RX
Figure 20. STOP Pulse Generation Circuit
8.3.6.1 Threshold Detector and DAC
The threshold detect comparator in Figure 20 compares the echo amplitude with a programmable threshold level
(VTHLD) controlled by a DAC. The DAC voltage is set by the ECHO_QUAL_THLD field in register CONFIG_3 and
provides 8 programmable threshold levels, VTHLD. The typical levels are summarized in Table 2:
Table 2. Echo Qualification Threshold Levels
ECHO_QUAL_THLD
0h
1h
2h
3h
4h
5h
6h
7h
Typical VTHLD (mV)
–35
–50
–75
–125
–220
–410
–775
–1500
8.3.6.2 Zero-cross Detect Comparator
The zero-cross detect comparator compares the amplified echo signal at COMPIN with its reference voltage,
which is VCOM. As shown in Figure 21, the comparator produces a low-to-high transition when the amplitude of
the echo signal rises above VCOM. The comparator produces a high-to-low transition when the echo amplitude
falls below VCOM – VHYST. The built-in negative-sided hysteresis of 10 mV in reference to VCOM ensures accurate
zero-cross time instances associated with the rising edges of the echo signal and immunity of the comparator
output to noise.
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Signal into
COMPIN
VCOM
VHYST = 10 mV
Zero Cross
Detect Output
Figure 21. Zero-Cross Detector Output Signal
The output of the zero-cross detect comparator is passed to the event manager, where depending on the
decision of the threshold-detect comparator.
8.3.6.3 Event Manager
The event manager is a digital state machine in the STOP pulse generation circuit of the TDC1000. The event
manager controls the maximum number of STOP pulses to generate on the STOP pin and the receive mode for
the STOP pulse generation. The number of STOP pulses is configured in the NUM_RX field in the CONFIG_1
register. The receive mode is selected in the RECEIVE_MODE bit of the CONFIG_4 register. See sections
Single Echo Receive Mode and Multiple Echo Receive Mode for details about the receiver modes of the
TDC1000.
An example for NUM_RX = 2h and RECEIVE_MODE = 0 is shown in Figure 22. When the echo signal amplitude
exceeds values smaller than VTHLD, the threshold detect comparator indicates to the event manager to qualify the
next zero-cross event as valid. When the qualified zero-cross is detected by the zero-cross detect comparator,
the event manager passes the pulse to the STOP pin until the number of receive events programmed in
NUM_RX is reached.
STOP
COMPIN
VCOM
VTHLD
GND
Passes VTHLD
Passes VTHLD
Qualified for
zero-cross
Qualified for
zero-cross
Figure 22. Signal Qualification, Zero-cross Detection and STOP Pulse Generation
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8.3.7 Common-mode Buffer (VCOM)
The output of the internal common-mode buffer is present at the VCOM pin. This pin should be bypassed to
ground with a low-leakage 10-nF capacitor and it should not be loaded with more than 20 µA. The commonmode buffer can be disabled with the VCOM_SEL bit in the CONFIG_2 register. If disabled, an external
reference voltage must be applied to the VCOM pin.
During a time-of-flight measurement, the common-mode reference will take approximately 16 µs to settle if
starting from zero initial conditions. Using a larger capacitor will increase the settling time of the internal commonmode reference. The implications of a larger VCOM capacitor are further explored in the Common-mode
Reference Settling Time section.
8.3.8 Temperature Sensor
TDC1011
MEAS_MODE
tof_start
MUX
START
MEAS_MODE
tof_stop
MUX
STOP
RREF
Temp
Sensor
RTD1
RTD2
RTD1
(external)
RTD2
(external)
Figure 23. Temperature Sensor Measurement
Accurate measurements of flow, level, and concentration require compensation for the temperature dependency
of the speed of sound in the medium. The TDC1000 provides two temperature sensor connections, allowing to
measure up to two locations with RTDs, as shown in Figure 23.
The temperature sensor block supports PT1000 or PT500 sensors. The type of RTD used must be selected in
the TEMP_RTD_SEL bit of the CONFIG_3 register. The system requires a temperature-stable external reference
resistor (RREF). If the RTD type is PT500, then RREF should be 500 Ω. If the RTD type is PT1000, then RREF
should be 1 kΩ. The reference resistor needs to have either a low temperature coefficient or be calibrated for
temperature shift.
The logic timing in a temperature measurement is controlled by the TEMP_CLK_DIV bit in the CONFIG_3
register. As shown in Figure 24, the external clock can be divided by 8 or by the value resulting from the
TX_FREQ_DIV field configuration in the CONFIG_0 register. It is recommended to operate the temperature
measurement block at frequencies of 1 MHz or less.
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0x03[4] ± TEMP_CLK_DIV
y8
0
¦CLKIN
CLKIN
¦TEMP
TTEMP =
1
y2
1
¦TEMP
TX_FREQ_DIV+1
0x00[7:5] ± TX_FREQ_DIV
Figure 24. Timing Source for the Temperature Measurement
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 TDC1000 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, RREF, 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 TDC1000 performs three measurements per trigger event
and generates the corresponding pulses on the START and STOP pins.
TRIGGER
Reference
RTD1
td1
START
tREF
RTD2
td2
tRTD1
tRTD2
STOP
Figure 25. Temperature Measurement Output Timing
The resistance of RTD1 and RTD2 can be calculated from the time intervals in Figure 25 as follows:
t
R RTDx R REF u REF
t RTDx
(3)
With a 1-kΩ reference resistor, the tREF interval is approximately 200 μs. The following intervals, tRTD1 and tRTD2,
will depend on the resistance of the RTDs. The time delay between measurements, td1 and td2, can be
approximated as follows:
td1 = (51 × TTEMP) + ( tRTD1 × 0.55 )
td2 = (51 × TTEMP) + ( tRTD2 × 0.55 )
(4)
(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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8.3.8.2 Temperature Measurement with a Single RTD
The temperature sensing block can be configured to measure a single RTD by setting the TEMP_MODE bit in
register CONFIG_3 to 1. When the temperature measurement runs in PT1000 mode (TEMP_RTD_SEL = 0), the
first interval corresponds to RREF, the second interval is a redundant measurement on RREF and should be
neglected, and the third interval corresponds to RTD1. This operation is represented in Figure 26.
Reference
TRIGGER
Discard
td1
START
RTD1
td2
tREF
½ t REF
tRTD1
STOP
Figure 26. Temperature Measurement with a Single PT1000
The resistance of RTD1 can be calculated using Equation 3. The time delay between measurements can be
approximated using Equation 4 and Equation 5, with the exception that in this case, td1 is a function of ½ tREF and
td2 is a function of tRTD1.
If the temperature measurement runs in PT500 mode (TEMP_RTD_SEL = 1), the first interval is a redundant
measurement on RREF and should be neglected, the second interval corresponds to RREF, and the third interval
corresponds to RTD1. This operation is represented in Figure 27.
Discard
TRIGGER
Reference
td1
START
RTD1
td2
tREF
2 u tREF
tRTD1
STOP
Figure 27. Temperature Measurement with a Single PT500
The resistance of RTD1 can be calculated using Equation 3. The time delay between measurements can be
approximated using Equation 4 and Equation 5, with the exception that in this case, td1 is a function of tREF and
td2 is a function of tRTD1.
8.4 Device Functional Modes
8.4.1 Time-of-Flight Measurement Mode
The TOF measurement mode is selected by setting the MEAS_MODE bit in the CONFIG_2 register to 0. The
type of TOF measurement mdoe can be selected with the TOF_MEAS_MODE field in the CONFIG_2 register.
Table 3 lists the available TOF measurement modes with their corresponding channel assignments.
Table 3. TOF Measurement Modes
TOF_MEAS_MODE
Mode 0
00
Mode 1
01
Mode 2
10
Reserved
11
20
CH_SEL
EXT_CHSEL
Active TX Channel
Active RX Channel
Channel 1
0
0
TX1
RX2
Channel 2
1
0
TX2
RX1
Channel 1
0
0
TX1
RX1
Channel 2
1
0
TX2
RX2
Channel 1
0
0
Based on state machine and CH_SWP bit
Channel 2
1
0
Based on state machine and CH_SWP bit
Reserved
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8.4.1.1 Mode 0
Mode 0 is intended for Level and Fluid Identification Measurements applications. The TDC1000 associates each
transducer to complementary TX and RX channels. The transmit/receive pair “TX1/RX2” will act as both
transmitter and receiver for a measurement if CH_SEL = 0 in the CONFIG_2 register. The transmit/receive pair
“TX2/RX1” will act as both transmitter and receiver for the measurement if CH_SEL = 1.
The TDC1000 performs a single TOF measurement after receiving a trigger signal and returns to the SLEEP
mode when the measurement is complete.
8.4.1.2 Mode 1
In Mode 1 the TDC1000 associates each transducer to a single TX and RX channels. The transmit/receive pair
"TX1/RX1" will act as both transmitter and receiver for a measurement if CH_SEL = 0. The transmit/receive pair
"TX2/RX2" will act as both transmitter and receiver for the measurement if CH_SEL = 1.
The TDC1000 performs a single TOF measurement (one direction) and returns to the SLEEP mode when the
measurement is complete.
8.4.1.3 Mode 2
Mode 2 is intended for transit time water flow metering applications (see Water Flow Metering). In this mode, the
channel definitions are the same as for Mode 1: Channel 1 = "TX1/RX1" and Channel 2 = "TX2/RX2". The
TDC1000 will perform one TOF measurement and go into READY state waiting for the next trigger signal.
Mode 2 supports averaging cycles and automatic channel swap. The averaging mode is active if NUM_AVG > 0
and allows for the stopwatch or MCU to perform the average of multiple TOF measurement cycles. In this mode,
the device performs a TOF measurement on one channel (direction) for every trigger pulse until the averaging
count is reached, and if CH_SWP = 1, it will automatically swap channels and perform a TOF measurement on
the other channel (direction) for every trigger pulse until the averaging count is reached.
The number of averages is controlled with the NUM_AVG field found in the CONFIG_1 register. Channel
swapping is controlled with the CH_SWP bit in the CONFIG_2 register. The EXT_CHSEL bit in the CONFIG_2
register must be 0 for automatic channel swap to work. If EXT_CHSEL is 1, the active channel selection is
controlled manually with the CHSEL pin.
NOTE
If an echo measurement times out in averaging mode (indicated by the error flags or
ERRB pin), the state machine should be reset and the error flags should be cleared. The
state machine can be cleared by writing a 1 to bit [1] of the ERROR_FLAGS register and
the error flags can be cleared by writing a 1 to bit [0] of the ERROR_FLAGS register. After
completing these steps, the averaged measurement should be restarted.
8.4.2 State Machine
A state machine in the TDC1000 manages the operation of the various measurement modes (see Figure 28). At
power-on, the state machine is reset and most blocks are disabled. After the power-on sequence is complete, the
device goes into SLEEP mode if the EN pin is low or into READY mode if the EN pin is high. In the SLEEP or
READY state, the TDC1000 is able to receive SPI commands to set registers and configure the device for a
measurement mode.
NOTE
Although the SPI block is always active, it is not recommended to perform configuration
changes while the device is active. Configuration changes should be performed while the
device is in the SLEEP state or in the READY state.
If the EN pin is high and a trigger signal is received, the state machine will begin the execution of the configured
measurement. If the device is configured in Mode 0 or Mode 1, the state machine will return to the SLEEP state
after the measurement is completed. If the device is configured in Mode 2, the state machine returns to the
READY state and waits for the next trigger to continue with the next measurement.
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The device can be forced to exit a measurement by applying a logic high on the RESET pin high or a logic low
on the EN pin.
Timeout=1
SW Reset
EN=Low
HW Reset
SLEEP state
No
EN=High
ERROR_FLAGS register (0x07):
x Writing 1 to bit [1] of the ERROR_FLAGS
register cancels any active measurement
and returns to sleep mode or ready mode
and sets Count to 0 and CH-flag to FALSE.
If averaging: Set Count = 0
If CH_SWP & NOT(EXT_CHSEL):
set CH-flag TRUE
Ready
Trigger
pulse?
TOF_MEAS_MODE = 0h (Mode 0)
= 1h (Mode 1)
Yes
TX Burst
Output START
Pulse
RX Active
Output
STOP pulses
Mode?
TOF_MEAS_MODE = 2h (Mode 2)
Count <
Average?
Yes
Increment Count
Yes
Toggle Channel
Set Count = 0
Set Ch-flag FALSE
No
CH-flag TRUE?
Figure 28. Simplified TDC1000 State Machine Diagram
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8.4.3 TRANSMIT Operation
8.4.3.1 Transmission Pulse Count
The number of TX pulses generated by the TDC1000 to drive an ultrasonic transducer is programmable using
the NUM_TX field located in the CONFIG_0 register.
8.4.3.2 TX 180° Pulse Shift
As shown in Figure 29, the transmitter block can add a 180° shift at a position in the TX signal. The position of
the pulse shift is set by the TX_PH_SHIFT_POS field in the CONFIG_4 register and allows generating a specific
signal pattern.
Generation of 180° burst
for Tx Signature
Figure 29. Transmitter Pulse Signature, 180° Burst
As shown in Figure 30, enabling the TX 180° pulse shift has the effect of decreasing the number of transmitted
pulses by 1.
Normal Operation:
NUM_TX = 0x07
TX_PH_SHIFT_POS = 0x1F
180| Shift:
NUM_TX = 0x07
TX_PH_SHIFT_POS = 0x03
Pos. 0
Pos. 1
Pos. 2
Pos. 3
Pos. 4
Pos. 5
Pos. 6
Figure 30. Transmitter Pulse Signature
In some cases, the 180° pulse shift may help improving the turn-off time of a transducer, and thus suppress the
transmit ringing.
The 180° pulse shift is disabled by setting TX_PH_SHIFT_POS to position 31. Setting the 180° pulse shift to
positions 0 or 1 is not recommended.
8.4.3.3 Transmitter Damping
The transmitter damping feature allows for improved control over the transducer signal generation. Damping
extends the duration of the last TX pulse to help dissipate ringing and improve the transducer's turn-off time (see
Figure 31 and Figure 32). The accuracy of measurements can be improved by having a faster transducer turn-off
time. Damping is controlled with the DAMPING bit in the CONFIG_2 register.
Damping extends the duration of
the last pulse to dissipate ringing
Figure 31. Transmitter Damping (5 Tx Pulses With a Damping Pulse)
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8.0
Damping disabled
6.0
Damping enabled
Amplitude
4.0
2.0
0.0
-2.0
-4.0
-6.0
-8.0
0.0
2.0
4.0
6.0
8.0
10.0
7LPH
12.0
14.0
16.0
18.0
20.0
V
Figure 32. Transmitter Damped Echo
There are two invalid use combinations of the damping feature that may result in unexpected behavior. First,
damping should not be combined with the 180° pulse shift described in the previous section. Second, damping
should not be enabled if the number of TX pulses is set to 31.
8.4.4 RECEIVE Operation
8.4.4.1 Single Echo Receive Mode
Single Echo mode is suitable for concentration measurements and flow metering applications. The device can be
configured for Single Echo mode by setting the RECEIVE_MODE bit to 0 in the CONFIG_4 register. In Single
Echo mode, the device will generate STOP pulses for every zero-cross qualified by the threshold comparator, up
to the number of expected STOP events configured in the NUM_RX field in the CONFIG_1 register.
The threshold comparator qualifies the next zero-cross after an RX amplitude smaller than the programmed
threshold voltage is detected. The zero-cross detector will provide output pulses corresponding to the rising edge
of the received signal crossing the VCOM level, as shown in Figure 33. The threshold voltage can be set in the
ECHO_QUAL_THDL field in the CONFIG_3 register.
Zero-crossing detected after
threshold exceeded
COMPIN
VCOM
ECHO_QUAL_THLD
Threshold
Signal exceeds threshold
Output on
STOP pin
Maximum number of requested events (5 in this figure)
returned; subsequent events not reported
Figure 33. Single Echo Receive Mode (5 STOP Events)
24
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If the number of expected pulses programmed in NUM_RX is not received or the time-of-flight operation times
out, the TDC1000 will indicate an error condition in the ERROR_FLAGS register and will set the ERRB pin low.
8.4.4.2 Multiple Echo Receive Mode
The Multiple Echo mode is intended for use in level sensing applications and distance/displacement
measurements in which multiple echoes (burst) are received. In this condition, each received echo group will be
treated as a single pulse on the STOP pin. Up to 7 STOP pulses can be generated based on the value of the
NUM_RX field in the CONFIG_1 register. Multi echo mode can be enabled by setting the RECEIVE_MODE bit to
1 in the CONFIG_4 register. A representation of multiple echo STOP pulse generation is shown in Figure 34.
COMPIN
VCOM
Programmed
threshold
Output on
STOP pin
No pulse on STOP
pin because signal did not
exceed threshold
No pulse on STOP pin because
maximum number of programmed events
(5 in this example) already produced.
Figure 34. Multiple Echo Receive Mode (5 STOP Events)
The rising edge of a STOP pulse is generated by a zero-crossing event. As in the Single Echo Receive Mode,
the threshold comparator qualifies the next zero-cross after an RX amplitude smaller than the programmed
threshold voltage is detected. The STOP pulse will extend until a zero-cross after the RX amplitude is no longer
smaller than the threshold voltage (see Figure 35).
Zero-crossing detected
after threshold exceeded
Signal zero-crossing without
exceeding threshold
COMPIN
VCOM
Programmed
threshold
Signal exceeds
threshold
Output on
STOP pin
Figure 35. Multiple Echo Receive Mode (Zoom-in)
If the number of expected pulses programmed in NUM_RX is not received or the time-of-flight operation times
out, the TDC1000 will indicate an error condition in the ERROR_FLAGS register and will set the ERRB pin low.
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8.4.5 Timing
8.4.5.1 Timing Control and Frequency Scaling (CLKIN)
0x09[2] ± CLOCKIN_DIV
CLKIN
y 2CLOCKIN_DIV
¦0
1
T0 = Š
¦0
y 2TX_FREQ_DIV+1
¦1
1
T1 = Š
¦1
¦CLKIN
0x00[7:5] ± TX_FREQ_DIV
Figure 36. External Clock Division Tree
All transmit and receive function sequencing is synchronous to the external clock applied to the CLKIN pin. The
external clock is divided to generate two internal clocks with corresponding time periods denoted as T0 and T1 in
Figure 36. The division factor used to generate T0 is controlled with the CLOCKIN_DIV bit in the CLOCK_RATE
register. The division factor used to generate T1 is controlled with the TX_FREQ_DIV field located in the
CONFIG_0 register.
The SPI block is synchronous with the clock applied to the SCLK pin, and it is independent of the clock applied
to CLKIN. See the Serial Peripheral Interface (SPI) section for a complete description of the SPI block.
8.4.5.2 TX/RX Measurement Sequencing and Timing
The TDC1000 automatically sequences the TX and RX functionality. After receiving a pulse edge on the
TRIGGER pin, the TDC1000 resynchronizes to the CLKIN signal, and sends a TX burst. During the transmission
burst, the RX path is set to the alternate channel to minimize coupled noise.
During resynchronization, the trigger and START edges are aligned to the negative edge of the external clock.
The time between trigger and START is equal to 3 T0 periods plus 2 or 3 T1 periods, depending on the phase
between the received trigger pulse and the external clock. For example, if ƒCLKIN = 8 MHz and TX_FREQ_DIV =
0h2 (divide-by-8), the period T0 is 125 ns and the period T1 is 1 µs, resulting in a time of 2.375 µs or 3.375 µs
between the received trigger signal and the generated START pulse.
The trigger edge polarity is configured to rising edge by default, but it can be changed to falling edge by setting
the TRIG_EDGE_POLARITY bit in the CONFIG4 register to 1.
After a device reset, the system must wait a determined time before sending the next trigger signal. The typical
reset to trigger wait time is 3 × T1 + (50 ns).
8.4.6 Time-of-Flight (TOF) Control
The possible configurations of the TX/RX sequencing during a time-of-flight measurement can be divided into
three cases: Short TOF Measurement, Standard TOF Measurement and Standard TOF Measurement with
Power Blanking. Overall, the cases differ in the order of sequencing, power saving and echo listening windows.
The behavior of each case is described in the sections to follow.
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8.4.6.1 Short TOF Measurement
Analog OFF
Analog ON
(see Note A)
TRIG
Echo listen period
TX
(see Note B)
START
(see Note C)
RX
STOP
READY
COMMON-MODE
AUTOZERO
TRANSMIT
MASK
ECHO LISTEN
END
128 x T0
2AUTOZERO_PERIOD x 64 x T0
NUM_TX x T1
2SHORT_TOF_BLANK_PERIOD x 8 x T0
2TOF_TIMEOUT_CTRL x 128 x T0
1 x T1
A.
Clock alignment (see TX/RX Measurement Sequencing and Timing)
B.
If NUM_TX < 3, the width of the START pulse is equal to NUM_TX × T1. If NUM_TX ≥ 3, the width of the START
pulse is equal to 3 × T1.
C.
Common-mode settling time.
READY
Figure 37. Short TOF Measurement
In a short time of flight measurement, the RX path is activated before the TX burst, as shown in Figure 37. The
input MUX is automatically swapped to the alternate receive channel before and during the TX burst. Swapping
the input prevents the TX burst from being amplified in the RX path. After the TX burst, the input MUX remains
switched to the alternate channel for a masking period determined by the SHORT_TOF_BLANK_PERIOD field in
the TIMEOUT register. Masking the RX path avoids the issue of amplifying the transducer's residual TX ringing in
the RX path.
The short TOF is the default measurement sequence selected at power-on. The short TOF measurement is
selected if the value of the TIMING_REG[9:0] field is less than 30, or if the FORCE_SHORT_TOF bit is set to 1.
The TIMING_REG[9:0] is a 10-bit wide field, with its 2 most significant bits located in the TOF_1 register, and the
8 least significant bits located in the TOF_0 register. The FORCE_SHORT_TOF bit is located in the TIMEOUT
register.
The comparator's input offset is stored in an internal capacitor during the auto-zero period. The length of the
auto-zero period is controlled by the AUTOZERO_PERIOD field in the CLOCK_RATE register.
The length of the window when the comparators are able to qualify and generate STOP pulses is configured by
the TOF_TIMEOUT_CTRL field. A timeout will occur if the number of expected pulses is not received during the
allocated time and an error condition is reported to the ERROR_FLAGS register and the ERRB pin. It is possible
to disable the echo timeout (see TOF Measurement Interval). The TOF_TIMEOUT_CTRL field is located in the
TIMEOUT register.
See the Timing Control and Frequency Scaling (CLKIN) section for the definition of the time periods T0 and T1.
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8.4.6.2 Standard TOF Measurement
Analog OFF
Analog ON
TRIG
Echo listen period
TX
(see Note A)
START
(see Note B)
(see Note C)
RX
STOP
READY
TRANSMIT
COMMON-MODE
AUTOZERO
WAIT / ECHO LISTEN
ECHO LISTEN
END
NUM_TX x T1
128 x T0
2AUTOZERO_PERIOD x 64 x T0
(TIMING_REG ± 30) x 8 x T0
2TOF_TIMEOUT_CTRL x 128 x T0
1 x T1
A.
Clock alignment (see TX/RX Measurement Sequencing and Timing)
B.
If NUM_TX < 3, the width of the START pulse is equal to NUM_TX × T1. If NUM_TX ≥ 3, the width of the START
pulse is equal to 3 × T1.
C.
Common-mode settling time.
READY
Figure 38. Standard TOF Measurement
In a standard time of flight measurement, the RX path is activated after the TX burst is completed, as shown in
Figure 38.
The standard TOF measurement sequence is enabled if the value of the TIMING_REG field is greater than or
equal to 30, and only if the FORCE_SHORT_TOF bit is set to 0. The TIMING_REG is a 10-bit wide field, with its
2 most significant bits located in the TOF_1 register, and the 8 least significant bits located in the TOF_0 register.
The FORCE_SHORT_TOF bit is located in the TIMEOUT register.
The comparator's input offset is stored in an internal capacitor during the auto-zero period. The length of the
auto-zero period is controlled by the AUTOZERO_PERIOD field in the CLOCK_RATE register.
The length of the window when the comparators are able to qualify and generate STOP pulses is configured by a
combination of the TIMING_REG field and the TOF_TIMEOUT_CTRL field. With the addition of the
TIMING_REG in the calculation, the standard TOF measurement allows for a longer wait time and listening
window. A timeout will occur if the number of expected pulses is not received during the allocated time and an
error condition is reported to the ERROR_FLAGS register and the ERRB pin. It is possible to disable the echo
timeout (see TOF Measurement Interval). The TOF_TIMEOUT_CTRL field is located in the TIMEOUT register.
NOTE
If the FORCE_SHORT_TOF bit = 1, the measurement sequencing will behave as a Short
TOF Measurement, thus overriding the setting of the TIMING_REG field.
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8.4.6.3 Standard TOF Measurement with Power Blanking
Analog OFF
Analog ON
TRIG
Echo listen period
TX
(see Note A)
START
(see Note B)
(see Note C)
RX
STOP
READY
TRANSMIT
WAIT
COMMON-MODE
AUTOZERO
ECHO LISTEN
END
NUM_TX x T1
(TIMING_REG ± 30) x 8 x T0
128 x T0
2AUTOZERO_PERIOD x 64 x T0
2TOF_TIMEOUT_CTRL x 128 x T0
1 x T1
A.
Clock alignment (see TX/RX Measurement Sequencing and Timing)
B.
If NUM_TX < 3, the width of the START pulse is equal to NUM_TX × T1. If NUM_TX ≥ 3, the width of the START
pulse is equal to 3 × T1.
C.
Common-mode settling time.
READY
Figure 39. Standard TOF Measurement with Blanking Enabled
The power blanking sequence is a variation to the standard TOF measurement sequence, and can be enabled
by setting the BLANKING bit to 1. In addition, all other conditions described in the Standard TOF Measurement
should be met. The BLANKING bit can be found in the CONFIG_3 register.
Power blanking allows the device to remain in a low-power state while the TX signals propagate to the RX
transducer in situations when the expected time-of-flight is long. Power blanking uses the TIMING_REG to
control a wait time between the transmit sequence and the receive sequence, during which, the complete RX
chain is disabled, as shown in Figure 39. The TIMING_REG is a 10-bit wide field, with its 2 most significant bits
located in the TOF_1 register, and the 7 least significant bits located in the TOF_0 register.
8.4.6.4 Common-mode Reference Settling Time
The duration of the common-mode settling time is defined by the VCOM capacitor. With a 10-nF VCOM
capacitor, the common-mode reference requires 16 µs to settle. On the other hand, the duration of the commonmode settling window is defined as 128 × T0, where the time unit T0 is determined by the external clock
frequency and the value of the CLOCKIN_DIV bit, as explained in the Timing Control and Frequency Scaling
(CLKIN) section.
A frequency of 8 MHz will result in a settling window of 128 × 1 / 8 MHz, which equals to 16 µs. Increasing the
value of the VCOM capacitor will increase the common-mode settling time, but for the same 8-MHz frequency,
the duration of the common-mode settling window will remain at 16 µs. In such situation, the common-mode
reference will take multiple TOF cycles to reach its final value when starting from zero initial conditions.
8.4.6.5 TOF Measurement Interval
The comparators in the TDC1000's RX path can qualify and generate STOP pulses from a received echo within
an interval set by the TOF_TIMEOUT_CTRL field in the TIMEOUT register. The listening interval can be
extended in the standard TOF measurement (without blanking) by a period controlled with the TIMING_REG field
(see Standard TOF Measurement).
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If the number of STOP events programmed in the NUM_RX field is not received within the listening interval, a
timeout event will occur and the device will return to the READY state. In addition, an error will be reported to the
ERROR_FLAGS register and the ERRB pin will be driven low.
The echo timeout can be disabled by setting the ECHO_TIMEOUT bit to 1 in the TIMEOUT register. If the echo
timeout is disabled, the device will not exit from the receive state until the expected number of STOP events set
in NUM_RX occur. If the number of events does not occur, the device can be forced out of the receive state by
writing a value of 0x03 to the ERROR_FLAGS register, or by de-asserting the EN pin, or asserting the RESET
pin.
NOTE
Writing a logic 1 to bit [1] of the ERROR_FLAGS register clears the state machine. Writing
a logic 1 to bit[0] clears the error flags.
NOTE
It is not recommended to hold the RX in an active state for intervals longer than 100ms, as
the comparator auto-zero may no longer be accurate.
8.4.7 Averaging and Channel Selection
The TDC1000 supports averaging when configured in measurement Mode 2 (see Time-of-Flight Measurement
Mode). Averaging is controlled with the NUM_AVG field located in the CONFIG_1 register. In Mode 2, the
TDC1000 will remain on the channel indicated by CH_SEL for 2NUM_AVG trigger cycles. If CH_SWP is enabled in
the CONFIG_2 register, the TDC1000 will automatically swap the active channel and repeat the averaging cycle.
NOTE
If the bit [1] in the ERROR_FLAGS register is written to 1, the TDC1000 will reset its
internal averaging counter and the software channel selection.
8.4.8 Error Reporting
The TDC1000 will report an error when the receive signals do not match the expected configuration. The ERRB
pin will go low to indicate the presence of an error condition. Reading the ERROR_FLAGS register provides
information about the condition(s) that caused the error.
The ERR_SIG_WEAK bit indicates that the number of received and qualified zero-crossings was less than the
expected number set in the NUM_RX register field and a timeout occurred. This error is cleared when bit [0] is
written to 1.
The ERR_NO_SIG bit indicates that no signals were received and a timeout occurred. Writing a 1 to this bit
resets the state machine, halts active measurements and returns the device to SLEEP or READY mode and
resets the average counter and automatic channel selection in measurement Mode 2. This error is cleared when
bit [0] is written to 1.
The ERR_SIG_HIGH bit indicates that the received echo amplitude exceeds the largest echo qualification
threshold at the input of the comparators. The ERR_SIG_HIGH error is only reported when the
ECHO_QUAL_THDL register field is set to 7h. Writing a 1 to this bit will reset all the error flags and reset the
ERRB pin to high.
NOTE
It is recommended to reset the state machine when the error flags are cleared. This can
be done simultaneously by writing a value of 0x03 to the ERROR_FLAGS register.
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8.5 Programming
8.5.1 Serial Peripheral Interface (SPI)
The serial interface consists of serial data input (SDI), serial data output (SDO), serial interface clock (SCLK) and
chip select bar (CSB). The serial interface is used to configure the TDC1000 parameters available in various
configuration registers. All the registers are organized into individually addressable byte-long registers with a
unique address.
The communication on the SPI bus normally 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 SCLK cycles. The write and read command bytes consist of 1 reserved bit, a 1-bit instruction,
and a 6-bit register address. Figure 40 shows the SPI protocol for a transaction involving one byte of data (read
or write).
CSB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
SCK
COMMAND FIELD
DATA FIELD
MSB
SDI
c7
c6
resvd
R/W
c5
c4
c3
c2
c1
c0
d7
LSB
d6
d5
Address (6 bits)
d4
d3
d2
d1
Write Data (8-bits)
MSB
SDO
d0
d7
LSB
d6
d5
R/W = Instruction
0: Read
1: Write
Note: Specifying any value other than zero in bit[7] of the command byte is prohibited.
d4
d3
d2
d1
d0
Read Data (8-bits)
Figure 40. SPI Protocol
8.5.1.1 Chip Select Bar (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 Serial Clock (SCLK)
SCLK 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 Serial Data Input (SDI)
SDI is driven by the SPI master by sending the command and the data byte to configure the AFE.
8.5.1.4 Serial Data Output (SDO)
SDO is driven by the AFE when the SPI master initiates a read transaction.
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8.6 Register Maps
•
•
•
NOTE
Reserved bits must be written to 0 unless otherwise indicated.
Read-back value of reserved bits and registers is unspecified and should be discarded.
Recommended values must be programmed and forbidden values must not be
programmed where they are indicated to avoid unexpected results.
8.6.1 TDC1000 Registers
Table 4 list the memory-mapped registers for the TDC1000. All register addresses not listed in Table 4 should be
considered as reserved locations and the register contents should not be modified.
Table 4. TDC1000 REGISTERS
Address (Hex)
Acronym
Register Name
Reset Value
Section
0h
CONFIG_0
Config-0
45h
See here
1h
CONFIG_1
Config-1
40h
See here
2h
CONFIG_2
Config-2
0h
See here
3h
CONFIG_3
Config-3
3h
See here
4h
CONFIG_4
Config-4
1Fh
See here
5h
TOF_1
TOF-1
0h
See here
6h
TOF_0
7h
ERROR_FLAGS
8h
TIMEOUT
9h
CLOCK_RATE
TOF-0
0h
See here
Error Flags
0h
See here
Timeout
19h
See here
Clock Rate
0h
See here
8.6.1.1 CONFIG_0 Register (address = 0h) [reset = 45h] (map)
Figure 41. CONFIG_0 Register
(MSB) 7
6
TX_FREQ_DIV
R/W-2h
5
4
3
2
NUM_TX
R/W-5h
1
0 (LSB)
LEGEND: R/W = Read or write; R = Read only; R/W1C = Read or write 1 to clear
Table 5. CONFIG_0 Register Field Descriptions
Bit
Field
Type
Reset
Description
Frequency divider for TX clock and T1
0h: Divide by 2
1h: Divide by 4
2h: Divide by 8 (default)
[7:5]
TX_FREQ_DIV (1)
R/W
2h
3h: Divide by 16
4h: Divide by 32
5h: Divide by 64
6h: Divide by 128
7h: Divide by 256
[4:0]
NUM_TX
R/W
5h
Number of TX pulses in a burst, ranging from 0 to 31.
5h: 5 pulses (default)
(1)
32
See Timing Control and Frequency Scaling (CLKIN) for the definition of the time period T1.
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8.6.1.2 CONFIG_1 Register (address = 1h) [reset = 40h] (map)
Figure 42. CONFIG_1 Register
(MSB) 7
6
RESERVED
R/W-1h
5
4
NUM_AVG
R/W-0h
3
2
1
NUM_RX
R/W-0h
0 (LSB)
LEGEND: R/W = Read or write; R = Read only; R/W1C = Read or write 1 to clear
Table 6. CONFIG_1 Register Field Descriptions
Bit
[7:6]
Field
Type
Reset
Description
RESERVED
R/W
1h
1h: Reserved (default)
Number of measurement cycles to average in stopwatch/MCU
0h: 1 measurement cycle (default)
1h: 2 measurement cycles
2h: 4 measurement cycles
[5:3]
NUM_AVG
R/W
0h
3h: 8 measurement cycles
4h: 16 measurement cycles
5h: 32 measurement cycles
6h: 64 measurement cycles
7h: 128 measurement cycles
Number of expected receive events
0h: Do not count events (32 STOP pulses output) (default)
1h: 1 event (1 STOP pulse output)
2h: 2 events (2 STOP pulses output)
[2:0]
NUM_RX
R/W
0h
3h: 3 events (3 STOP pulses output)
4h: 4 events (4 STOP pulses output)
5h: 5 events (5 STOP pulses output)
6h: 6 events (6 STOP pulses output)
7h: 7 events (7 STOP pulses output)
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8.6.1.3 CONFIG_2 Register (address = 2h) [reset = 0h] (map)
Figure 43. CONFIG_2 Register
(MSB) 7
VCOM_SEL
R/W-0h
6
MEAS_MODE
R/W-0h
5
DAMPING
R/W-0h
4
CH_SWP
R/W-0h
3
EXT_CHSEL
R/W-0h
2
CH_SEL
R/W-0h
1
0 (LSB)
TOF_MEAS_MODE
R/W-0h
LEGEND: R/W = Read or write; R = Read only; R/W1C = Read or write 1 to clear
Table 7. CONFIG_2 Register Field Descriptions
Bit
Field
Type
Reset
[7]
VCOM_SEL
R/W
0h
Description
Common-mode voltage reference control
0h: Internal (default)
1h: External
AFE measurement type
[6]
MEAS_MODE
R/W
0h
0h: Time-of-flight measurement (default)
1h: Temperature measurement
TX burst damping
[5]
DAMPING
R/W
0h
0h: Disable damping (default)
1h: Enable damping
[4]
CH_SWP
R/W
0h
Automatic channel swap in Mode 2 of operation. The setting is
ignored if EXT_CHSEL = 1.
0h: Disable automatic channel swap (default)
1h: Enable automatic channel swap
External channel select by CHSEL pin
[3]
EXT_CHSEL
R/W
0h
0h: Disable external channel select (default).
1h: Enable external channel select
EXT_CHSEL = 1 overrides the CH_SWP and CH_SEL settings.
Active TX/RX channel pair.
0h: Channel 1 (default)
[2]
CH_SEL
R/W
0h
1h: Channel 2
See Time-of-Flight Measurement Mode for channel definitions.
The setting is ignored if EXT_CHSEL = 1.
Time-of-flight measurement mode
0h: Mode 0 (default)
[1:0]
TOF_MEAS_MODE
R/W
0h
1h: Mode 1
2h: Mode 2
3h: Reserved
34
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8.6.1.4 CONFIG_3 Register (address 3h) [reset = 3h] (map)
Figure 44. CONFIG_3 Register
(MSB) 7
RESERVED
R/W-0h
6
TEMP_MODE
R/W-0h
5
TEMP_RTD_SEL
R/W-0h
4
TEMP_CLK_DIV
R/W-0h
3
BLANKING
R/W-0h
2
1
0 (LSB)
ECHO_QUAL_THLD
R/W-3h
LEGEND: R/W = Read or write; R = Read only; R/W1C = Read or write 1 to clear
Table 8. CONFIG_3 Register Field Descriptions
Bit
Field
Type
Reset
Description
[7]
RESERVED
R/W
0h
0h: Reserved (default)
[6]
TEMP_MODE
R/W
0h
Temperature measurement channels
0h: Measure REF, RTD1 and RTD2 (default)
1h: Measure REF and RTD1
RTD type
[5]
TEMP_RTD_SEL
R/W
0h
0h: PT1000 (default)
1h: PT500
Clock divider for temperature mode
[4]
TEMP_CLK_DIV
R/W
0h
0h: Divide by 8 (default)
1h: Use TX_FREQ_DIV
[3]
BLANKING
R/W
0h
Power blanking in standard TOF measurements. The blanking
length is controlled with the TIMING_REG field (see Standard
TOF Measurement with Power Blanking).
0h: Disable power blanking (default)
1h: Enable power blanking
Echo qualification DAC threshold level with respect to VCOM
0h: –35 mV
1h: –50 mV
2h: –75 mV
[2:0]
ECHO_QUAL_THLD
R/W
3h
3h: –125 mV (default)
4h: –220 mV
5h: –410 mV
6h: –775 mV
7h: –1500 mV
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8.6.1.5 CONFIG_4 Register (address = 4h) [reset = 1Fh] (map)
Figure 45. CONFIG_4 Register
(MSB) 7
RESERVED
R/W-0h
6
RECEIVE_
MODE
R/W-0h
5
TRIG_EDGE_
POLARITY
R/W-0h
4
3
2
1
0 (LSB)
TX_PH_SHIFT_POS
R/W-1Fh
LEGEND: R/W = Read or write; R = Read only; R/W1C = Read or write 1 to clear
Table 9. CONFIG_4 Register Field Descriptions
Bit
Field
Type
Reset
Description
[7]
RESERVED
R/W
0h
0h: Reserved (default)
[6]
RECEIVE_MODE
R/W
0h
Receive echo mode
0h: Single echo (default)
1h: Multi echo
Trigger edge polarity
[5]
TRIG_EDGE_POLARITY
R/W
0h
0h: Rising edge (default)
1h: Falling edge
TX 180° pulse shift position, ranging from 0 to 31.
[4:0]
TX_PH_SHIFT_POS
R/W
1Fh
1Fh: Position 31 (default)
It is not recommended to set TX_PH_SHIFT_POS to 0 or 1.
36
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8.6.1.6 TOF_1 Register (address = 5h) [reset = 0h] (map)
Figure 46. TOF_1 Register
(MSB) 7
6
PGA_GAIN
R/W-0h
5
4
PGA_CTRL
R/W-0h
3
LNA_CTRL
R/W-0h
2
LNA_FB
R/W-0h
1
0 (LSB)
TIMING_REG[9:8]
R/W-0h
LEGEND: R/W = Read or write; R = Read only; R/W1C = Read or write 1 to clear
Table 10. TOF_1 Register Field Descriptions
Bit
Field
Type
Reset
Description
PGA gain
0h: 0 dB (default)
1h: 3 dB
2h: 6 dB
[7:5]
PGA_GAIN
R/W
0h
3h: 9 dB
4h: 12 dB
5h: 15 dB
6h: 18 dB
7h: 21 dB
PGA control
[4]
PGA_CTRL
R/W
0h
0h: Active (default)
1h: Bypassed and powered off
LNA control
[3]
LNA_CTRL
R/W
0h
0h: Active (default)
1h: Bypassed and powered off
LNA feedback mode
[2]
LNA_FB
R/W
0h
0h: Capacitive feedback (default)
1h: Resistive feedback
[1:0]
TIMING_REG[9:8]
R/W
0h
TIMING_REG field's 2 most-significant bits (see Standard TOF
Measurement and Standard TOF Measurement with Power
Blanking)
0h: 0 (default)
8.6.1.7 TOF_0 Register (address = 6h) [reset = 0h] (map)
Figure 47. TOF_0 Register
(MSB) 7
6
5
4
3
TIMING_REG[7:0]
R/W-0h
2
1
0 (LSB)
LEGEND: R/W = Read or write; R = Read only; R/W1C = Read or write 1 to clear
Table 11. TOF_0 Register Field Descriptions
Bit
[7:0]
Field
Type
Reset
TIMING_REG[7:0]
R/W
0h
Description
TIMING_REG field's 8 least-significant bits (see Standard TOF
Measurement and Standard TOF Measurement with Power
Blanking)
0h: 0 (default)
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8.6.1.8 ERROR_FLAGS Register (address = 7h) [reset = 0h] (map)
Figure 48. ERROR_FLAGS Register
7 (MSB)
6
5
4
3
RESERVED
R-0h
2
ERR_
SIG_WEAK
R-0h
1
ERR_NO_SIG
R/W1C-0
0 (LSB)
ERR_
SIG_HIGH
R/W1C-0
LEGEND: R/W = Read or write; R = Read only; R/W1C = Read or write 1 to clear
Table 12. ERROR_FLAGS Register Field Descriptions (1) (2)
Bit
[7:3]
[2]
Field
Type
Reset
Description
RESERVED
R
0h
0h: Reserved (default)
ERR_SIG_WEAK
R
0h
1h: The number of received and qualified zero-crossings was
less than the expected number set in NUM_RX field and a
timeout occurred.
1h: No signals were received and timeout occurred.
[1]
[0]
ERR_NO_SIG
ERR_SIG_HIGH
R/W1C
R/W1C
0h
0h
Writing a 1 to this field resets the state machine, halts active
measurements and returns the device to the SLEEP or READY
mode and resets the average counter and automatic channel
selection in measurement Mode 2.
1h: The received echo amplitude exceeds the largest echo
qualification threshold at the input of the comparators. The error
is only reported when ECHO_QUAL_THLD = 0x07.
Writing a 1 to this field will reset all the error flags and reset the
ERRB pin to high.
(1)
(2)
38
It is recommended to read the error status register or the ERRB pin before initiating a new measurement.
All error flags should be cleared before initiating a new measurement.
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8.6.1.9 TIMEOUT Register (address = 8h) [reset = 19h] (map)
Figure 49. TIMEOUT Register
(MSB) 7
RESERVED
R/W-0h
6
FORCE_
SHORT_TOF
R/W-0h
5
4
3
SHORT_TOF_BLANK_PERIOD
R/W-3h
2
ECHO_
TIMEOUT
R/W-0h
1
0 (LSB)
TOF_TIMEOUT_CTRL
R/W-1h
LEGEND: R/W = Read or write; R = Read only; R/W1C = Read or write 1 to clear
Table 13. TIMEOUT Register Field Descriptions
Bit
Field
Type
Reset
Description
[7]
RESERVED
R/W
0h
0h: Reserved (default)
[6]
FORCE_SHORT_TOF
R/W
0h
Short time-of-flight control
0h: Disabled (default)
1h: Force a short time-of-flight measurement
Short time-of-flight
Measurement)
blanking
period
(see
Short
TOF
0h: 8 × T0
1h: 16 × T0
[5:3]
SHORT_TOF_BLANK_PERIOD (1)
R/W
3h
2h: 32 × T0
3h: 64 × T0 (default)
4h: 128 × T0
5h: 256 × T0
6h: 512 × T0
7h: 1024 × T0
Echo receive timeout control (see TOF Measurement Interval)
[2]
ECHO_TIMEOUT
R/W
0h
0h: Enable echo timeout (default)
1h: Disable timeout
Echo listening window timeout (see TOF Measurement Interval)
0h: 128 × T0
[1:0]
TOF_TIMEOUT_CTRL (1)
R/W
1h
1h: 256 × T0 (default)
2h: 512 × T0
3h: 1024 × T0
(1)
See Timing Control and Frequency Scaling (CLKIN) for the definition of the time period T0.
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8.6.1.10 CLOCK_RATE Register (address = 9h) [reset = 0h] (map)
Figure 50. CLOCK_RATE Register
(MSB) 7
6
5
RESERVED
R/W-0h
4
3
2
CLOCKIN_DIV
R/W-0h
1
0 (LSB)
AUTOZERO_PERIOD
R/W-0h
LEGEND: R/W = Read or write; R = Read only; R/W1C = Read or write 1 to clear
Table 14. CLOCK_RATE Register Field Descriptions (1)
Bit
[7:3]
Field
Type
Reset
Description
RESERVED
R/W
0h
0h: Reserved (default)
CLOCKIN_DIV (1)
R/W
0h
CLKIN divider to generate T0
[2]
0h: Divide by 1 (default)
1h: Divide by 2
Receiver auto-zero period
0h: 64 × T0 (default)
[1:0]
AUTOZERO_PERIOD (1)
R/W
0h
1h: 128 × T0
2h: 256 × T0
3h: 512 × T0
(1)
40
See Timing Control and Frequency Scaling (CLKIN) for the definition of the time period T0.
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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
The TDC1000 is an analog front-end for ultrasonic sensing applications. The device is typically used for the
driving and sensing of ultrasonic transducers to perform accurate time-of-flight measurements. Ultrasonic time-offlight sensing allows for fluid level measurements, fluid identification or concentration, flow measurements, and
proximity/distance sensing.
9.2 Typical Applications
9.2.1 Level and Fluid Identification Measurements
TX2/RX1
A
RREF
TX1/RX2
B
RTD
TDC1000
EN
RESET
TRIGGER
SPI
ERRB
TX2
TX1
RX1
RX2
START
STOP
OR
Gate
16-MHz CLK
OSC
TMS320F28035
C2000 MCU
Figure 51. Level and Concentration Measurement Application Diagram
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Typical Applications (continued)
9.2.1.1 Design Requirements
Table 15. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Range
2 – 10 cm
Accuracy
0.5% concentration variation
Distance
5.08 cm
Fluid Level
Fluid Identification
9.2.1.2 Detailed Design Procedure
9.2.1.2.1 Level Measurements
For level sensing applications, the total time-of-flight (TOF) of the sound wave in the fluid is measured. The
pulses transmitted by transducer B travel through the fluid, typically from the bottom, to the surface of the fluid.
The discontinuity between the fluid and air generates a reflected wave which returns back to transducer B.
At the beginning of a measurement cycle, the transducer is connected to a transmit channel of the AFE, and the
transmit burst excites the transducer to generate an ultrasound wave. Synchronous to the TX burst, a START
pulse is generated by the TDC1000 to indicate the start of a measurement. After the transmission is completed,
and depending on the device configuration, the transducer is connected to a receive channel of the AFE.
When a valid echo is received, the TDC1000 generates a STOP pulse. Generation of multiple STOP pulses is
possible through register configuration of the device. The START and STOP signal times are compared to
determine the TOF.
The level of the fluid can be determined using the following equation:
@=
61( × ?
2
where
•
•
•
42
d is the fluid level in meters (m)
TOF is the time-of-flight in seconds (s)
c is the speed of sound in the fluid in meters per second (m/s)
(6)
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Trigger
START
TX1
Echo Pulse
received
RX2
TOF
STOP
Figure 52. Relation Between Transmit and Receive Pulses in Level Measurements
Level measurements have 2 main criteria: resolution and range (maximum height). Resolution accuracies of 1-2
mm are achievable but are impractical due to any environmental disturbances, such as tank vibrations, creating
millimeter level surface waves. Ranges of up to 1 m are measurable utilizing VDD level excitation pulses, but
surface disturbances and signal loss over longer distances make the reliable echo reception an issue. Greater
level measurement reception can be achieved by mechanical means (level guide tube) and/or electronic means
(level shifting the TX pulses to greater voltages; see TIDA-00322).
9.2.1.2.2 Fluid Identification
The TDC1000 can be used to measure the time-of-flight for a known distance to calculate the speed of sound
(cmedium) in the fluid. This application utilizes the same circuitry as the level example but a transducer in a
different configuration connected to the second channel. In this example, the speed of sound in the fluid (cmedium)
is measured by using transducer A.
The temperature can also be measured to compensate for the temperature variation of sound. With the known
distance, TOF and temperature, the speed of sound in the fluid can be determined and the identity of the
medium verified.
After measuring the time-of-flight for the fixed distance, the speed of sound can be calculated as follows:
2×@
?IA@EQI =
61(
where
•
•
•
cmedium is the speed of sound in the fluid in meters per second (m/s)
d is the level in meters (m)
TOF is the time of flight in seconds (s)
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The measurement process is identical to the level example above. The speed of sound can be used to uniquely
identify a variety of fluids. In this example, the concentration of diesel exhaust fluid (DEF) is measured with a
desired accuracy resolution of 0.5% of concentration variation. For most fluids, the speed of sound varies over
temperature, so every application will be different. In this example, all samples were all at ambient temperature of
23°C.
9.2.1.3 Application Curves
The data used in the following level and fluid identification graphs was collected using ultrasonic test cells. The
test cells are acrylic plastic containers with width of 2.54 cm and ultrasonic transducers attached to the outside
using cyanoacrylate glue. The transducers in this experiment are STEMiNC 1MHz piezo electric ceramic discs
(SMD10T2R111). Equivalent transducers with the following characteristics could be used:
• Piezo material: SM111
• Dimensions: 10mm diameter x 2mm thickness
• Resonant frequency: 1050 kHz (thickness mode)
1650
150
Speed of sound in medium (m/s)
135
105
90
75
60
45
1600
1575
1550
1525
1500
1475
1450
1425
Figure 53. Time-of-Flight for Fluid Height in Tank
.5
%
32
32
.0
%
D
EF
.5
%
EF
31
D
30
.0
%
D
EF
.0
%
EF
D
D
EF
10
20
er
at
W
EF
Time-of-Flight (µs)
145
131
118
50
35
D
10
er
9
at
8
W
6
7
Height (cm)
Ta
p
Fluid Height in Tank
Full (10 cm)
Full – 1 (9 cm)
Full – 2 (8 cm)
3 cm
2 cm
5
le
d
4
til
3
is
2
.0
%
1400
30
D
Time-of-flight (Ps)
120
1625
Fluid
Distilled water
Tap water
DEF 10.0%
DEF 20.0%
DEF 30.0%
DEF 31.5%
DEF 32.0%
DEF 32.5%
Speed of sound (m/s)
1481.87
1483.13
1530.49
1576.42
1620.00
1627.37
1629.15
1630.00
Figure 54. Speed of Sound for Various Fluids and Diesel
Exhaust Fluid (DEF) Concentration
44
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1632
Speed of sound in medium (m/s)
1483.0
1482.5
1482.0
1481.5
1630
1628
1626
1624
1622
1620
Figure 55. Speed of Sound in Distilled Water and Tap
Water
Copyright © 2014–2015, Texas Instruments Incorporated
Fluid
DEF 30.0%
DEF 31.5%
DEF 32.0%
DEF 32.5%
%
D
EF
32
.0
D
EF
32
.5
%
%
.5
31
EF
D
EF
p
Ta
Speed of sound (m/s)
1481.87
1483.13
30
W
at
.0
er
er
at
W
d
le
til
is
D
Fluid
Distilled water
Tap water
%
1618
1481.0
D
Speed of sound in medium (m/s)
1483.5
Speed of sound (m/s)
1620.00
1627.37
1629.15
1630.00
Figure 56. Speed of Sound of Various Diesel Exhaust Fluid
(DEF) Concentrations
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9.2.2 Water Flow Metering
RREF
RTD
Flow
l
TX1/RX2
B
TX2/RX1
A
TX2
TX1
RX1
TDC1000
START
STOP
TRIGGER
TDC7200
EN
RESET
ERRB
SPI
RX2
8-MHz CLK
OSC
MSP430
MCU
SPI
ENABLE
INT
Figure 57. Water Flow-meter Application Simplified Diagram
9.2.2.1 Design Requirements
The parameters in Table 16 are considered for this example.
Table 16. 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%
9.2.2.2 Detailed Design Procedure
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)
46
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9.2.2.2.1 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 17.
Table 17. 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.
9.2.2.2.2 Transit-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.
Copyright © 2014–2015, Texas Instruments Incorporated
47
TDC1000, TDC1000-Q1
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
www.ti.com.cn
Trigger
START
Echo Pulse from
Transducer 2
Transducer B
TX1/RX2
Echo Pulse from
Transducer 1
Transducer A
TX2/RX1
STOP
Upstream
Downstream
tBA
tAB
Figure 58. Relation Between Transmit and Receive Pulses Upstream/Downstream
In this example, the upstream TOF is defined as:
H
P$# =
:? F R;
where
•
•
•
l is the path length between the two transducers in meters (m)
c is the speed of sound in water in meters per second (m/s)
v is the velocity of the water in the pipe in meters per second (m/s)
(8)
In this example, the downstream TOF is defined as:
H
P#$ =
:? + R;
where
•
•
•
48
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)
(9)
Copyright © 2014–2015, Texas Instruments Incorporated
TDC1000, TDC1000-Q1
www.ti.com.cn
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
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)
(10)
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)
(11)
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)
(12)
9.2.2.2.3 ΔTOF Accuracy Requirement Calculation
Based on the minimum mass flow requirement and accuracy requirements in Table 16, the ΔTOF accuracy
needed can be calculated as follows:
1. Convert the mass flow rate to m3/s:
1D
3 = :0.015 I3 /D; l
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
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.
9.2.2.2.4 Operation
The TDC1000 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.
Copyright © 2014–2015, Texas Instruments Incorporated
49
TDC1000, TDC1000-Q1
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
www.ti.com.cn
A temperature measurement can be performed and the result can be used to correct for temperature
dependency of the speed of sound.
9.2.2.3 Application Curves
The following figures 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
0.3
Delta time-of-flight (ns)
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
0
1000
2000
3000
Samples (n)
4000
5000
6000
Figure 59. Calibrated Raw and Averaged Delta Time-of-Flight Data
1800
1400
1200
1200
Number of hits
1000
800
600
800
600
09
0.
0.
07
03
05
0.
0.
1
01
0.
3
-0
.0
5
-0
.0
-0
.0
Delta time-of-flight (ns)
Figure 60. Raw Calibrated Data Histogram
9
28
0.
0.
22
10
16
0.
0.
2
04
0.
-0
.0
-0
.0
-0
.1
-0
.2
-0
.2
8
0
4
0
0
200
6
200
7
400
400
50
1000
-0
.0
Number of hits
1400
V = 31 ps
-0
.0
1600
1600
V = 82 ps
Delta time-of-flight (ns)
Figure 61. 10x Running Average Data Histogram
Copyright © 2014–2015, Texas Instruments Incorporated
TDC1000, TDC1000-Q1
www.ti.com.cn
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
10 Power Supply Recommendations
The analog circuitry of the TDC1000 is designed to operate from an input voltage supply range between 2.7V
and 5.5V. It is recommended to place a 100nF ceramic bypass capacitor to ground as close as possible to the
VDD pins. In addition, an electrolytic or tantalum capacitor with value greater than 1µF is recommended. The
bulk capacitor does not need to be in close vicinity with the TDC1000 and could be close to the voltage source
terminals or at the output of the voltage regulators powering the TDC1000.
The IO circuitry of the TDC1000 is designed to operate from an input voltage supply range between 1.8V and
5.5V. The IO voltage supply (VIO) can be lower than the analog voltage supply (VDD), but it should not exceed it.
It is also recommended to place a 100nF ceramic bypass capacitor to ground as close as possible to the VIO
pin. If a separate source or regulator is used for VIO, an additional electrolytic or tantalum capacitor with value
greater than 1µF is recommended.
In some cases an additional 10µF bypass capacitor may further reduce the supply noise.
Copyright © 2014–2015, Texas Instruments Incorporated
51
TDC1000, TDC1000-Q1
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
www.ti.com.cn
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 and VIO pins.
The length of the START and STOP traces from the DUT 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.
Match the length of the TX pair from the DUT to the transducers to prevent uneven signal delays from one
channel direction to the other.
Match the length of the RX pair from the transducers to the DUT to prevent uneven signal delays from one
channel direction to the other.
Match the length (or resistance) of the traces leading to the RTD sensors. PCB series resistance will be
added in series to the RTD sensors.
Route the SPI signal traces close together. Place a series resistor at the source of SDO (close to the DUT)
and series resistors at the sources of SDI, SCLK and CSB (close to the master MCU).
11.2 Layout Example
Matched TX pair length to transducers
Matched RX pair length from transducers
VIA to Ground Plane
VIA to Bottom or Internal Layer
Top Layer
GND
Bottom Layer
GND
GND
1
TX1
TX2
VCOM
GND
CLKIN
LNAOUT
PGAIN
RTD1
COMPIN
To RTDs: Match trace
length (resistance)
RTD1
RTD2
GND
RREF
CHSEL
ERRB
RTD2
START
GND
STOP
VDD
TDC1000
PGAOUT
System Clock
GND
VDD
GND
RX1
RX2
VIO
SDO
MCU
SPI Master
SDI
CSB
SCLK
RESET
MCU
I/Os
Trigger:stop
watch/MCU
TRIGGER
EN
Matched
trace
length to
stopwatch
/MCU
MCU
I/Os
Figure 62. TDC1000 Board Layout (Capacitive Feedback Mode)
52
版权 © 2014–2015, Texas Instruments Incorporated
TDC1000, TDC1000-Q1
www.ti.com.cn
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
12 器件和文档支持
12.1 器件支持
12.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
12.1.2 开发支持
相关开发支持请参阅以下文档：
• 《汽车类超声波液位/质量测量参考设计》， TIDA-00322
12.2 文档支持
相关文档请参见以下部分：
• 《TDC1000 温度感测接口》，SNAA218
12.3 相关链接
下面的表格列出了快速访问链接。
问。
范围包括技术文档、支持和社区资源、工具和软件，以及样片或购买的快速访
表 18. 相关链接
部件
产品文件夹
样片与购买
技术文档
工具与软件
支持与社区
TDC1000
请单击此处
请单击此处
请单击此处
请单击此处
请单击此处
TDC1000-Q1
请单击此处
请单击此处
请单击此处
请单击此处
请单击此处
12.4 社区资源
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.
12.5 商标
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
12.6 静电放电警告
这些装置包含有限的内置 ESD 保护。 存储或装卸时，应将导线一起截短或将装置放置于导电泡棉中，以防止 MOS 门极遭受静电损
伤。
12.7 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
版权 © 2014–2015, Texas Instruments Incorporated
53
TDC1000, TDC1000-Q1
ZHCSD54B – OCTOBER 2014 – REVISED AUGUST 2015
www.ti.com.cn
13 机械、封装和可订购信息
以下页中包括机械、封装和可订购信息。 这些信息是针对指定器件可提供的最新数据。 这些数据会在无通知且不
对本文档进行修订的情况下发生改变。 欲获得该数据表的浏览器版本，请查阅左侧的导航栏。
54
版权 © 2014–2015, Texas Instruments Incorporated
PACKAGE OPTION ADDENDUM
www.ti.com
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)
TDC1000PW
ACTIVE
TSSOP
PW
28
48
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
TDC1000PW
TDC1000PWR
ACTIVE
TSSOP
PW
28
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
TDC1000PW
TDC1000QPWQ1
ACTIVE
TSSOP
PW
28
48
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
TDC1000
PWQ1
TDC1000QPWRQ1
ACTIVE
TSSOP
PW
28
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
TDC1000
PWQ1
(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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