Sample & Buy Product Folder Support & Community Tools & Software Technical Documents LDC1051 SNOSCY0 – MARCH 2014 LDC1051: 8-bit Rp only Inductance-to-Digital Converter with SPI 1 Features • 1 • • • • • • • • • Axial Distance Sensing Application Remote Sensor Placement (Decoupling The LDC From Harsh Environments) High Durability (By Virtue Of Contactless Operation) Higher Flexibility For System Design (Using Coils Or Springs As Sensors) Insensitive to Non-conductive Environmental Interferers (such As Dirt, Dust, Oil etc.) Magnet-free Operation Supply Voltage: 5 V, typ Supply Voltage, IO: 1.8V to 5.5V Stand-by Current: 250uA, typ Rp Resolution: 8-bit LC Frequency Range: 5kHz to 5MHz Application Schematic 5V 2 Applications • • • VIO 5V LDO Proximity Sensing Level Sensing Lateral Position Sensing VIO VDD MOSI SDI INA MISO SDO SCLK SCLK GPIO CSB INT/GPIO INTB VIO MCU 3 Description Sensor CFA CFB Inductive sensing is a contactless, short-range sensing technology enabling high-resolution and lowcost position sensing of conductive targets, even in harsh environments. Using a coil or spring as a sensor, the LDC1051 inductance-to-digital converter provides system designers a way to achieve high performance and reliability at a lower system cost than other competing solutions. The LDC1051 is available in a 5mm x 4mm WSON16 package. Device programming via SPI allows for easy configuration using a microcontroller. Device Information PACKAGE DGND GND DGND CLDO DAP DGND AGND DGND Rp vs Distance With 14mm PCB Coil 14 12 10 Rp (k The LDC1051 is pin compatible with the LDC1000 (16-bit Rp/24-bit L) and the LDC1041 (8-bit Rp/24-bit L). This family of devices offers system designers different resolution options based on their application and system requirements. ORDER NUMBER INB LDC1051 8 6 4 2 0 BODY SIZE LDC1051NHRT WSON (16) 5 mm × 4 mm LDC1051NHRR WSON (16) 5 mm × 4 mm LDC1051NHRJ WSON (16) 5 mm × 4 mm 0 1 2 3 4 5 Distance (mm) 6 7 8 C002 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. LDC1051 SNOSCY0 – MARCH 2014 www.ti.com Table of Contents 1 2 3 4 5 6 7 Features .................................................................. Applications ........................................................... Description ............................................................. Revision History..................................................... Terminal Configuration and Functions................ Specifications......................................................... 1 1 1 2 3 4 6.1 6.2 6.3 6.4 6.5 6.6 6.7 4 4 4 4 5 6 7 Absolute Maximum Ratings ...................................... Handling Ratings....................................................... Recommended Operating Conditions....................... Thermal Information .................................................. Electrical Characteristics........................................... Timing Requirements ................................................ Typical Characteristics .............................................. 7.3 7.4 7.5 7.6 8 Feature Description................................................... 8 Device Functional Modes........................................ 11 Programming........................................................... 14 Register Map and Description................................. 15 Applications and Implementation ...................... 20 8.1 Application Information............................................ 20 8.2 Typical Applications ................................................ 21 9 Power Supply Recommendations...................... 25 10 Layout................................................................... 25 10.1 Layout Guidelines ................................................. 25 10.2 Layout Example .................................................... 26 11 Device and Documentation Support ................. 27 11.1 Trademarks ........................................................... 27 11.2 Electrostatic Discharge Caution ............................ 27 11.3 Glossary ................................................................ 27 Detailed Description .............................................. 8 7.1 Overview ................................................................... 8 7.2 Functional Block Diagram ......................................... 8 12 Mechanical, Packaging, and Orderable Information ........................................................... 27 4 Revision History 2 DATE REVISION NOTES March 2014 * Initial release. Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 5 Terminal Configuration and Functions WSON-16 Top View SCLK 1 16 INTB CSB 2 15 N/C SDI 3 14 N/C VIO 4 13 CLDO SDO 5 12 VDD DGND 6 11 GND CFB 7 10 INB CFA 8 9 INA DAP (GND) Terminal Functions TERMINAL NAME TERMINAL NO. TERMINAL TYPE DESCRIPTION SCLK 1 DO SPI clock input. SCLK is used to clock-out/clock-in the data from/into the chip CSB 2 DI SPI CSB(Chip Select Bar). Multiple devices can be connected on the same SPI bus and CSB can be used to select the device to be communicated with SDI 3 DI SPI Slave Data In (Master Out Slave In). This should be connected to the Master Out Slave In of the master VIO 4 P Digital IO Supply SDO 5 DO DGND 6 P SPI Slave Data Out (Master In Slave Out).It is high impedance when CSB is high Digital ground CFB 7 A LDC filter capacitor CFA 8 A LDC filter capacitor INA 9 A External LC Tank. Connect to external LC tank INB 10 A External LC Tank. Connect to external LC tank GND 11 P Analog ground VDD 12 P Analog supply CLDO 13 A LDO bypass capacitor. A 56nF capacitor should be connected from this Terminal to GND N/C 14 N/C No Connection N/C 15 N/C No Connection INTB 16 DO Configurable interrupt. This Terminal can be configured to behave in 3 different ways by programing the INT Terminal mode register. Either threshold detect, wakeup, or DRDYB DAP 17 P Connect to GND Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 3 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com 6 Specifications 6.1 Absolute Maximum Ratings MAX UNIT Analog Supply Voltage (VDD – GND) MIN 6 V IO Supply Voltage (VIO – GND) 6 V V Voltage on any Analog Terminal –0.3 VDD + 0.3 Voltage on any Digital Terminal –0.3 VIO + 0.3 V 8 mA 150 °C Input Current on INA and INB Junction Temperature, TJ 6.2 Handling Ratings MIN MAX UNIT Tstg Storage Temperature range -65 150 °C VESD Human Body Model (HBM) ESD stress voltage 1k 1k V 250 250 V Charge Device Model (CDM) ESD stress voltage 6.3 Recommended Operating Conditions over operating free-air temperature range (unless otherwise noted) Analog Supply Voltage (VDD – GND) IO Supply Voltage (VIO – GND) MIN MAX UNIT 4.75 5.25 V 1.8 5.25 V 125 °C VDD-VIO 0 Operating Temperature, TA -40 V 6.4 Thermal Information THERMAL METRIC (1) θJA (1) 4 Junction-to-ambient thermal resistance NHR (16-TERMINALS) UNIT 28 °C/W For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953. Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 6.5 Electrical Characteristics (1) Unless otherwise specified, all limits ensured for TA = TJ = 25°C, VDD = 5 V, VIO = 3.3 V PARAMETER TEST CONDITIONS MIN (2) TYP (3) MAX (2) 4.75 5 5.25 1.8 3.3 5.25 V 1.7 2.3 mA 14 µA UNIT POWER VDD Analog supply voltage VIO IO supply voltage IDD Supply current, VDD Does not include sensor current. (4) IVIO IO supply current Static current IDD_LP Stand-by mode supply current tSTART Start-Up Time VIO≤VDD From POR to ready-to-convert. V 250 µA 2 ms LDC ƒsensor_MIN Minimum sensor frequency 5 kHz ƒsensor_MAX Maximum sensor frequency 5 MHz Asensor_MIN Minimum sensor amplitude 1 VPP Asensor_MAX Maximum sensor amplitude 4 VPP 10 1/fsensor tREC Oscillation start-up time after Rp underrange condition Recovery time Rp Min Minimum sensor Rp range 798 Ω Rp Max Maximum Sensor Rp range 3.93 MΩ Rp Res Rp measurement resolution 8 Bits tS_MIN Minimum response time Minimum programmable settling time of digital filter tS_MAX Maximum response time Maximum programmable settling time of digital filter 192 × 1 / ƒsensor s 6144 × 1 / ƒsensor s DIGITAL I/O CHARACTERISTICS VIH Logic 1 input voltage VIL Logic 0 input voltage VOH Logic 1 output voltage ISOURCE = 400 µA VOL Logic 0 output voltage ISINK = 400 µA IIOHL Digital IO leakage current (1) (2) (3) (4) 0.8 × VIO V 0.2 × VIO V VIO – 0.3 –500 V 0.3 V 500 nA Electrical Characteristics Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very limited self-heating of the device such that TJ = TA. No specification of parametric performance is indicated in the electrical tables under conditions of internal self-heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond which the device may be permanently degraded, either mechanically or electrically. Limits are specified by testing, design, or statistical analysis at 25°C. Limits over the operating temperature range are specified through correlations using statistical quality control (SQC) method. Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary over time and will also depend on the application and configuration. The typical values are not tested and are not specified on shipped production material. LC tank current depends on the Q-factor of the tank, distance and material of the target. Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 5 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com 6.6 Timing Requirements Unless otherwise noted, all limits specified at TA = 25°C, VDD = 5, VIO = 3.3, 10 pF capacitive load in parallel with a 10 kΩ load on the SDO terminal. Specified by design; not production tested. PARAMETER MIN TYP MAX UNIT 4 MHz ƒSCLK Serial Clock Frequency tPH SCLK Pulse Width High ƒSCLK = 4 MHz 0.4 / ƒSCLK tPL SCLK Pulse Width Low ƒSCLK = 4 MHz 0.4 / ƒSCLK s tSU SDI Setup Time 10 ns tH SDI Hold Time 10 ns tODZ SDO Driven-to-Tristate Time Measured at 10% / 90% point 20 ns tOZD SDO Tristate-to-Driven Time Measured at 10% / 90% point 20 ns tOD SDO Output Delay Time 20 ns tCSS CSB Setup Time 20 ns tCSH CSB Hold Time 20 ns tIAG Inter-Access Gap 100 ns tDRDYB Data ready pulse width s Data ready pulse at every 1 / ODR if no data is read 1 / ƒsensor s Unless otherwise noted, all limits specified at TA = 25°C, VDD=5.0, VIO=3.3, 10pF capacitive load in parallel with a 10kΩ load on SDO. Specified by design; not production tested. ttPLt ttPHt 16th Clock SCLK ttSUt ttHt Valid Data SDI Valid Data Figure 1. Write Timing Diagram 1st Clock 8th Clock 16th Clock SCLK t t CSHt t t CSSt t tCSHt t t CSSt CSB tOZD SDI tOD D7 D1 ttHt D0 Figure 2. Read Timing Diagram 6 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 6.7 Typical Characteristics 14 60 12 50 Code (decimal) Rp (k 10 8 6 4 40 30 20 10 2 0 0 0 1 2 3 4 5 6 Distance (mm) Sensor Details: Target Material: 7 8 0 1 2 Table 16 Rp_MIN: 1.347 kΩ Stainless Steel Rp_MAX: 38.785 kΩ 3 4 5 6 7 Distance (mm) C002 Sensor Details: Target Material: Figure 3. Rp vs Distance 8 C003 Table 16 Rp_MIN: 1.347 kΩ Stainless Steel Rp_MAX: 38.785 kΩ Figure 4. Proximity Data vs Distance Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 7 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com 7 Detailed Description 7.1 Overview The LDC1051 is an Inductance-to-Digital Converter that measures the parallel impedance of an LC resonator. It accomplishes this task by regulating the oscillation amplitude in a closed loop configuration to a constant level, while monitoring the energy dissipated by the resonator. By monitoring the amount of power injected into the resonator, the LDC1051 can determine the value of Rp; it returns this as a digital value which is inversely proportional to Rp. The threshold detector block provides a comparator with hysteresis, with the threshold registers programed and comparator enabled, proximity data register is compared with threshold registers and INTB terminal indicates the output. The device has a simple 4-wire SPI interface. The INTB terminal provides multiple functions which are programmable with SPI. The device has separate supplies for Analog and I/O, with analog operating at 5V and I/O at 1.8-5V. The integrated LDO needs a 56nF capacitor connected from CLDO terminal to GND. 7.2 Functional Block Diagram CFA CFB Threshold Detector L INA Proximity Data Register LDC C INB SCLK 4-Wire Serial Interface SDI SDO CS INTB Rs Power VDD GND VIO DGND CLDO 7.3 Feature Description 7.3.1 Inductive Sensing An AC current flowing through a coil will generate an AC magnetic field. If a conductive material, such as a metal target, is brought into the vicinity of the coil, this magnetic field will induce circulating currents (eddy currents) on the surface of the target. These eddy currents are a function of the distance, size, and composition of the target. The eddy currents then generate their own magnetic field, which opposes the original field generated by the coil. This mechanism is best compared to a transformer, where the coil is the primary core and the eddy current is the secondary core. The inductive coupling between both cores depends on distance and shape. Hence the resistance and inductance of the secondary core (eddy current), shows up as a distant dependent resistive and inductive component on the primary side (coil). The figures(Figure 5 to Figure 8) below show a simplified circuit model. 8 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 Feature Description (continued) d Metal Target Figure 5. Inductor With A Metal Target Eddy currents generated on the surface of the target can be modeled as a transformer as shown in Figure 6. The coupling between the primary and secondary coils is a function of the distance and the conductor’s characteristics. In Figure 6, the inductance Ls is the coil’s inductance, and Rs is the coil’s parasitic series resistance. The inductance L(d), which is a function of distance d, is the coupled inductance of the metal target. Likewise, R(d) is the parasitic resistance of the eddy currents and is also a function of distance. Eddy Currents Ls + L(d) Conductance of Metal Target Metal Surface Distance d Rs + R(d) Figure 6. Metal Target Modeled As L And R With Circulating Eddy Currents Generating an alternating magnetic field with just an inductor will consume a large amount of power. This power consumption can be reduced by adding a parallel capacitor, turning it into a resonator as shown in Figure 7. In this manner the power consumption is reduced to the eddy and inductor losses Rs+R(d) only. L(d) C Oscillator Rs(d) Figure 7. LC Tank Connected To Oscillator The LDC1051 doesn’t measure the series resistance directly; instead it measures the equivalent parallel resonance impedance Rp (see Figure 8). This representation is equivalent to the one shown in Figure 8, where the parallel resonance impedance Rp(d) is given by: Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 9 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com Feature Description (continued) Rp(d) Ls L(d) [Rs R(d)] u C (1) L(d) C Rp(d) Oscillator Figure 8. Equivalent Resistance Of Rs in Parallel With LC Tank Figure 9 below shows the variation in Rp as a function of distance for a 14mm diameter PCB coil (Sensor Details:Table 16). The target in this example is a section of a 2mm thick stainless steel disk. 14 12 Rp (k 10 8 6 4 2 0 0 1 2 3 4 5 Distance (mm) 6 7 8 C002 Figure 9. Typical Rp vs Distance With 14mm PCB Coil 7.3.2 Measuring Rp with LDC1051 The LDC1051 supports a wide range of LC combinations, with oscillation frequencies ranging from 5kHz to 5MHz and Rp ranging from 798Ω to 3.93MΩ. This range of Rp can be viewed as the maximum input range of an ADC. As illustrated in Figure 9, the range of Rp is typically much smaller than the maximum input range supported by the LDC1051. To get better resolution in the desired sensing range, the LDC1051 offers a programmable input range through the Rp_MIN and Rp_MAX registers. Refer to Calculation of Rp_MIN and Rp_MAX below for how to set these registers. When the sensor’s resonance impedance Rp drops below the programed Rp_MIN, the LDC’s Rp output will clip at its full scale output. This situation could, for example, happen when a target comes too close to the coil. 10 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 Feature Description (continued) 60 Code (decimal) 50 40 30 20 10 0 0 1 2 3 4 5 Distance (mm) 6 7 8 C003 Figure 10. Transfer Characteristics Of LDC1051 With Rp_MIN= 1.347 kΩ And Rp_MAX= 38.785 kΩ The resonance impedance can be calculated from the digital output code as follows: Rp _ MAX u Rp _ MIN Rp Rp _ MIN u (1 Y) Rp _ MAX u Y Where: • • • Y=Proximity Data/27 Rp_MAX and Rp_MIN are the maximum and minimum Rp values selected in the respective registers Proximity data is the LDC output, register address 0x22. (2) Example: If Proximity data (address 0x22) is 50, Rp_MIN is 2.394 kΩ, and Rp_MAX is 38.785 kΩ, the resonance impedance is given by: Y=50/27 = 0.3906 Rp=(38785*2394)/(2394×(1-0.3906) + 38785×0.3906) =(92851290)/(15149.421 + 1458.9036) Rp = 5.59 kΩ 7.4 Device Functional Modes 7.4.1 Power Modes The LDC1051 has two power modes: • • Active Mode : In this mode the Proximity data conversion is enabled. Stand-by Mode: This is the default mode on device power-up. In this mode conversion is disabled. 7.4.2 INTB terminal Modes The INTB terminal is a configurable output terminal which can be used to drive an interrupt on an MCU. The LDC1051 provides three different modes on INTB terminal: 1. Comparator Mode 2. Wake-Up Mode 3. DRDY Mode LDC1051 has built-in High and Low trigger threshold registers which can be used as a comparator with programmable hysteresis or in a special mode which can be used to wake-up an MCU. These modes are explained in detail below. Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 11 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com Device Functional Modes (continued) 7.4.2.1 Comparator Mode In the Comparator mode, the INTB terminal is asserted or deasserted when the proximity register value increases above Threshold High or decreases below Threshold Low registers respectively. In this mode, the LDC1051 essentially behaves as a proximity switch with programmable hysteresis. Threshold High Rp Data Threshold Low INTB t Figure 11. Behavior Of INTB Terminal In Comparator Mode 7.4.2.2 Wake-Up Mode In Wake-Up mode, the INTB terminal is asserted when proximity register value increases above Threshold High and de-asserted when wake-up mode is disabled in INTB terminal mode register. This mode can be used to wake-up an MCU from sleep, to conserve power. Threshold High Rp Data Threshold Low INTB CSB SPI SPI: INTB Pin Mode Changed to DRDYB t Figure 12. Behavior Of INTB Terminal In Wake-Up Mode 7.4.2.3 DRDYB Mode In DRDY(Data Ready) mode, the INTB terminal is asserted every time the conversion data is available and deasserted once the read command on register 0x22 is registered internally; if the read is in progress, the terminal is pulsed instead. The valid condition for new data availability is CSB high and DRDYB falling edge. 12 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 Device Functional Modes (continued) t1/ODRt INTB New Data available to Read CSB CMD: Read 0x22 SPI Data Read CMD: Read 0x22 t Figure 13. Behavior of INTB Terminal in DRDYB Mode with SPI Extending Beyond Subsequent Conversions ODRt t INTB CSB SPI CMD: Read 0x22 Data Read t Figure 14. Behavior Of INTB Terminal In DRDYB Mode with SPI Reading The Data Within Subsequent Conversion Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 13 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com 7.5 Programming The LDC1051 utilizes a 4-wire SPI to access control and data registers. The LDC1051 is an SPI slave device and does not initiate any transactions. 7.5.1 SPI Description A typical serial interface transaction begins with an 8-bit instruction, which is comprised of a read/write bit (MSB, R=1) and a 7 bit address of the register, followed by a data field which is typically 8 bits. However, the data field can be extended to a multiple of 8 bits by providing sufficient SPI clocks. Refer to the Extended SPI Transactions section below. 1 2 3 4 5 C7 C6 C5 C4 C3 R/Wb A6 A5 A4 A3 6 7 8 C2 C1 C0 A2 A1 A0 9 10 11 D7 D6 (MSB) D5 12 13 14 15 16 D2 D1 D0 (LSB) D2 D1 D0 (LSB) 17 SCLK CSB tCOMMAND FIELDt SDI R/Wb = Read/Write 0: Write Data 1: Read Data SDO Address (7-bits) tDATA FIELDt D4 D3 Write DATA D7 D6 (MSB) D5 High-Z D4 D3 Read DATA Data (8-bits) tSingle Access Cyclet Figure 15. Serial Interface Protocol Each assertion of CSB starts a new register access. The R/Wb bit in the command field configures the direction of the access; a value of 0 indicates a write operation and a value of 1 indicates a read operation. All output data is driven on the falling edge of the serial clock (SCLK), and all input data is sampled on the rising edge of the serial clock (SCLK). Data is written into the register on the rising edge of the 16th clock. It is required to deassert CSB after the 16th clock; if CSB is deasserted before the 16th clock, no data write will occur. 7.5.1.1 Extended SPI Transactions A transaction may be extended to multiple registers by keeping the CSB asserted beyond the initial 16 clocks. In this mode, the register addresses increment automatically. CSB must be asserted during 8*(1+N) clock cycles of SCLK, where N is the amount of bytes to write or read during the transaction. During an extended read access, SDO outputs the register contents every 8 clock cycles after the initial 8 clocks of the command field. During an extended write access, the data is written to the registers every 8 clock cycles after the initial 8 clocks of the command field. 14 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 7.6 Register Map and Description Table 1. Register Map (1) (2) (3) Register Name Address Direction Default Device ID 0x00 RO 0x84 Device ID Rp_MAX 0x01 R/W 0x0E Rp Maximum Rp_MIN 0x02 R/W 0x14 Rp Minimum Watchdog Timer Frequency 0x03 R/W 0x45 Min Sensor Frequency LDC Configuration 0x04 R/W 0x1B Reserved 0x05 RO 0x01 Reserved 0x06 R/W 0xFF ?? Comparator Threshold High MSB 0x07 R/W 0xFF Reserved 0x08 R/W 0x00 ?? Comparator Threshold Low MSB 0x09 R/W 0x00 INTB Terminal Configuration 0x0A R/W 0x00 Power Configuration 0x0B R/W 0x00 Status 0x20 RO Reserved 0x21 RO Reserved(00000000) Proximity Data 0x22 RO Proximity Data Reserved 0x23 RO Reserved Reserved 0x24 RO Reserved Reserved 0x25 RO Reserved (1) (2) (3) Bit 7 Bit 6 Bit 5 Bit 4 Reserved(000) Bit 3 Amplitude Bit 2 Bit 1 Bit 0 Response Time Reserved(00000001) Reserved Threshold High MSB Reserved Threshold Low MSB Reserved(00000) INTB_MODE Reserved(0000000) OSC Dead DRDYB Wake-up Compara tor PWR_M ODE Do Not Care Values of register fields which are unused should be set to default values only. Registers 0x01 through 0x05 are Read Only when the part is awake (PWR_MODE bit is SET) R/W: Read/Write. RO: Read Only. WO: Write Only. Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 15 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com Table 2. Revision ID Address = 0x00, Default=0x84, Direction=RO Bit Field Field Name 7:0 Revision ID Description Revision ID of Silicon. Table 3. Rp_MAX Address = 0x01, Default=0x0E, Direction=R/W Bit Field Field Name 7:0 Rp Maximum Description Maximum Rp that LDC1051 needs to measure. Configures the input dynamic range of LDC1051. See Table 4 for register settings. Table 4. Register Settings for Rp_MAX 16 Register setting Rp (kΩ) 0x00 3926.991 0x01 3141.593 0x02 2243.995 0x03 1745.329 0x04 1308.997 0x05 981.748 0x06 747.998 0x07 581.776 0x08 436.332 0x09 349.066 0x0A 249.333 0x0B 193.926 0x0C 145.444 0x0D 109.083 0x0E 83.111 0x0F 64.642 0x10 48.481 0x11 38.785 0x12 27.704 0x13 21.547 0x14 16.160 0x15 12.120 0x16 9.235 0x17 7.182 0x18 5.387 0x19 4.309 0x1A 3.078 0x1B 2.394 0x1C 1.796 0x1D 1.347 0x1E 1.026 0x1F 0.798 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 Table 5. Rp_MIN Address = 0x02, Default=0x14, Direction=R/W (1) Bit Field Field Name 7:0 Rp Minimum Description Minimum Rp that LDC1051 needs to measure. Configures the input dynamic range of LDC1051. See Table 6 for register settings. (1) This Register needs a mandatory write as it defaults to 0x14. Table 6. Register Settings for Rp_MIN Register setting Rp (kΩ) 0x20 3926.991 0x21 3141.593 0x22 2243.995 0x23 1745.329 0x24 1308.997 0x25 981.748 0x26 747.998 0x27 581.776 0x28 436.332 0x29 349.066 0x2A 249.333 0x2B 193.926 0x2C 145.444 0x2D 109.083 0x2E 83.111 0x2F 64.642 0x30 48.481 0x31 38.785 0x32 27.704 0x33 21.547 0x34 16.160 0x35 12.120 0x36 9.235 0x37 7.182 0x38 5.387 0x39 4.309 0x3A 3.078 0x3B 2.394 0x3C 1.796 0x3D 1.347 0x3E 1.026 0x3F 0.798 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 17 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com Table 7. Watchdog Timer Frequency Address = 0x03, Default=0x45, Direction=R/W Bit Field Field Name 7:0 Min Sensor Frequency Description Sets the watchdog timer. The Watchdog timer is set based on the lowest sensor frequency. N § F · 68.94 u log10 ¨ ¸ © 2500 ¹ where • F is the sensor frequency (3) Example: If Sensor frequency is 1Mhz Min Sensor Frequency=68.94*log10(1M/2500)=Round to nearest integer(179.38)=179 Table 8. LDC Configuration Address = 0x04, Default=0x1B, Direction=R/W Bit Field Field Name Description 7:5 Reserved Reserved to 0 4:3 Amplitude Sets the oscillation amplitude 00:1V 01:2V 10:4V 11:Reserved 2:0 Response Time 000: Reserved 001: Reserved 010: 192 011: 384 100: 768 101: 1536 110: 3072 111: 6144 Table 9. Comparator Threshold High MSB Address = 0x07, Default=0xFF, Direction=R/W Bit Field Field Name 7:0 Threshold High Description Threshold High Register. Table 10. Comparator Threshold Low MSB Address = 0x09, Default=0x00, Direction=R/W 18 Bit Field Field Name 7:0 Threshold Low Description Threshold Low Register. Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 Table 11. INTB Terminal Configuration Address = 0x0A, Default=0x00, Direction=R/W Bit Field Field Name 7:3 Reserved 2:0 Mode Description Reserved to 0 000: All modes disabled 001: Wake-up Enabled on INTB terminal 010: INTB terminal indicates the status of Comparator output 100: DRDYB Enabled on INTB terminal All other combinations are Reserved Table 12. Power Configuration Address = 0x0B, Default=0x00, Direction=R/W Bit Field Field Name 7:1 Reserved 0 PWR_MODE Description Reserved to 0 0:Stand-By mode 1:Active Mode. Conversion is Enabled Refer to Power Modes for more details. Table 13. Status Address = 0x20, Default=NA, Direction=RO Bit Field Field Name 7 OSC status 6 Data Ready Description 1:Indicates oscillator overloaded and stopped 0:Oscillator working 1:No new data available 0:Data is ready to be read 5 Wake-up 4 Comparator 3:0 Do not Care 1:Wake-up disabled 0:Wake-up triggered. Proximity data is more than Threshold High value. 1:Proximity data is less than Threshold Low value 0:Proximity data is more than Threshold High value Table 14. Proximity Data Address = 0x22, Default=NA, Direction=RO Bit Field Field Name 7:0 Proximity data Description Proximity data Conversion data is updated to the proximity register only when a read is initiated on 0x22 register. If the read is delayed between subsequent conversions, these registers are not updated until another read is initiated on 0x22. Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 19 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com 8 Applications and Implementation 8.1 Application Information 8.1.1 Calculation of Rp_MIN and Rp_MAX Different sensing applications may have a different range of the resonance impedance Rp to measure. The LDC1051 measurement range of Rp is controlled by setting 2 registers – Rp_MIN and Rp_MAX. For a given application, Rp must never be outside the range set by these register values, otherwise the measured value will be clipped. For optimal sensor resolution, the range of Rp_MIN to Rp_MAX should not be unnecessarily large. The following procedure is recommended to determine the Rp_MIN and Rp_MAX register values. 8.1.1.1 Setting Rp_MAX Rp_MAX sets the upper limit of the LDC1051 resonant impedance input range. • • • Configure the sensor such that the eddy current losses are minimized. As an example, for a proximity sensing application, set the distance between the sensor and the target to the maximum sensing distance. Measure the resonant impedance Rp using an impedance analyzer. Multiply Rp by 2 and use the next higher value from Table 4. Note that setting Rp_MAX to a value not listed in Table 4 can result in indeterminate behavior. 8.1.1.2 Setting Rp_MIN Rp_MIN sets the lower limit of the LDC1051 resonant impedance input range. • • • Configure the sensor such that the eddy current losses are maximized. As an example, for a proximity sensing application, set the distance between the sensor and the metal target to the minimum sensing distance. Measure the resonant impedance Rp using an impedance analyzer. Divide the Rp value by 2 and then select the next lower Rp value from Table 6. Note that setting Rp_MIN to a value not listed on Table 6 can result in indeterminate behavior. In addition, Rp_MIN powers on with a default value of 0x14 which must be set to a value from Table 6 prior to powering on the LDC. 8.1.2 Output Data Rate Output data rate of LDC1051 depends on the sensor frequency, fsensor and 'Response Time' field in LDC Configuration register(Address:0x04). fsensor Output Data Rate § Response time · ¨ ¸ 3 © ¹ (4) 8.1.3 Choosing Filter Capacitor (CFA and CFB Terminals) The Filter capacitor is critical to the operation of the LDC1051. The capacitor should be low leakage, temperature stable, and it must not generate any piezoelectric noise (the dielectrics of many capacitors exhibit piezoelectric characteristics and any such noise is coupled directly through Rp into the converter). The optimal capacitance values range from 20pF to 100nF. The value of the capacitor is based on the time constant and resonating frequency of the LC tank. If a ceramic capacitor is used, then a C0G (or NP0) grade dielectric is recommended; the voltage rating should be ≥10V. The traces connecting CFA and CFB to the capacitor should be as short as possible to minimize any parasitics. For optimal performance, the chosen filter capacitor, connected between terminals CFA and CFB, needs to be as small as possible, but large enough such that the active filter does not saturate. The size of this capacitor depends on the time constant of the sense coil, which is given by L/Rs, (L=inductance, Rs=series resistance of the inductor at oscillation frequency). The larger this time constant, the larger filter capacitor is required. Hence, this time constant reaches its maximum when there is no target present in front of the sensing coil. 20 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 Application Information (continued) The following procedure can be used to find the optimal filter capacitance: 1. Start with a large filter capacitor. For a ferrite core coil, 10nF is usually large enough. For an air coil or PCB coil, 100pF is usually large enough. 2. Power on the LDC and set the desired register values. Minimize the eddy currents losses. This is done by minimizing the amount of conductive target covering the sensor. For an axial sensing application, the target should be at farthest distance from coil. For a lateral or angular position sensing application, the target coverage of the coil should be minimized. 3. Observe the signal on the CFB terminal using a scope. Since this node is very sensitive to capacitive loading, it is recommended to use an active probe. As an alternative, a passive probe with a 1kΩ series resistance between the tip and the CFB terminal can be used. 4. Vary the values of the filter capacitor until that the signal observed on the CFB terminal has an amplitude of approximate 1V peak-to-peak. This signal scales linearly with the reciprocal of the filter capacitance. For example, if a 100pF filter capacitor is applied and the signal observed on the CFB terminal has a peak-topeak value of 200mV, the desired 1V peak-to-peak value is obtained using a 200mV / 1V * 100pF = 20pF filter capacitor. 8.2 Typical Applications 8.2.1 Axial Distance Sensing Using a PCB Sensor with LDC1051 LDC10xx NHR 18uH Figure 16. Typical Application Schematic, LDC10xx 8.2.1.1 Design Requirements For this design example, use the following as the input parameters. Table 15. Design Parameters DESIGN PARAMETER EXAMPLE VALUE Minimum sensing distance 1 mm Maximum sensing distance 8 mm Output data rate 78 KSPS (Max data rate with LDC10xx series) Number of PCB layers for sensor 2 layers Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 21 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com 8.2.1.2 Detailed Design Procedure 8.2.1.2.1 Sensor and Target In this example, consider a sensor with the below characteristics. Table 16. Sensor Characteristics PARAMETER VALUE Layers 2 Thickness of copper 1 Oz Coil shape Circular Number of turns 23 Trace thickness 4 mil Trace spacing 4 mil PCB core material FR4 Rp @ 1 mm 5 kΩ Rp @ 8 mm 12.5 kΩ Nominal Inductance 18 µH Target material used is stainless steel 8.2.1.2.2 Calculating Sensor Capacitor Sensor frequency depends on various factors in the application. In this example since one of the design parameter is to achieve output data rate of 78 KSPS, sensor frequency can be calculated as below. fsensor Output Data Rate § Response time · ¨ ¸ 3 © ¹ (5) With the lowest Response time of 192 and output data rate of 78 KSPS, sensor frequency calculated using the above formula is 4.99 MHz. Now, using the below formula sensor capacitor is calculated to be 55 pF with a sensor inductance of 18 µH 1 L C u (2S u fsensor )2 (6) 8.2.1.2.3 Choosing Filter Capacitor Using the steps given in Choosing Filter Capacitor (CFA and CFB Terminals) filter capacitor for the example sensor is 20 pF. Below waveform shows the pattern on CFB terminal with 100 pF and 20 pF filter capacitor. Figure 17. Waveform On CFB With 100pf 22 Submit Documentation Feedback Figure 18. Waveform On CFB With 20pf Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 8.2.1.2.4 Setting Rp_MIN and Rp_MAX Calculating value for Rp_MAX Register : Rp at 8mm is 12.5kΩ, 12500×2 = 25000. In Table 4, then 27.704 kΩ is the nearest value larger than 25kΩ; this corresponds to Rp_MAX value of 0x12 Calculating value for Rp_MIN Register : Rp at 1mm is 5kΩ, 5000/2 = 2500. In Table 6, 2.394kΩ is the nearest value lower than 2.5kΩ; this corresponds to Rp_MIN value of 0x3B 8.2.1.2.5 Calculating Minimum Sensor Frequency Using, N § F · 68.94 u log10 ¨ ¸ © 2500 ¹ (7) N is 227.51, round off to 228 decimal. This value has to be written into Watchdog Timer Register, which is used to wake up the internal circuit when the sensor is saturated. 8.2.1.3 Application Curves 14 12 Rp (k 10 8 6 4 2 0 0 1 2 3 4 5 6 Distance (mm) 7 8 C002 Figure 19. Rp vs Distance Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 23 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com 8.2.2 Lateral Position Sensing Application Diagram Figure 20. Linear Position Sensing 8.2.3 Angular Position Sensing Application Diagram Figure 21. Angular Position Sensing 24 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 9 Power Supply Recommendations The LDC1051 is designed to operate from an analog supply range of 4.75 V to 5.25 V and digital I/O supply range of 1.8V to 5.25V. The analog supply voltage should be greater than or equal to the digital supply voltage for proper operation of the device. The supply voltage should be well regulated. If the supply is located more than a few inches from the LDC1051 additional bulk capacitance may be required in addition to the ceramic bypass capacitors. An electrolytic capacitor with a value of 10uF is a typical choice. 10 Layout 10.1 Layout Guidelines • • • • • The VDD and VIO terminal should be bypassed to ground with a low ESR ceramic bypass capacitor. The typical recommended bypass capacitance is 0.1uF ceramic with a X5R or X7R dielectric. The optimum placement is closest to the VDD/VIO and GND/DGND terminals of the device. Care should be taken to minimize the loop area formed by the bypass capacitor connection, the VDD/VIO terminal, and the GND/DGND terminal of the IC. See Figure 22 for a PCB layout example. The CLDO terminal should be bypassed to digital ground (DGND) with a 56nF ceramic bypass capacitor. The filter capacitor selected for the application using the procedure described in section Choosing Filter Capacitor (CFA and CFB Terminals) is connected between CFA and CFB terminals. Place the filter capacitor close to the CFA and CFB terminals. Do not use any ground/power plane below the capacitor and the trace connecting the capacitor and the CFA /CFB terminals. Use of two separate ground plane for GND and DGND is recommended with a start connection. See Figure 22 for a PCB layout example. Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 25 LDC1051 SNOSCY0 – MARCH 2014 www.ti.com 10.2 Layout Example Figure 22. LDC10xx Board Layout 26 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 LDC1051 www.ti.com SNOSCY0 – MARCH 2014 11 Device and Documentation Support 11.1 Trademarks All trademarks are the property of their respective owners. 11.2 Electrostatic Discharge Caution These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. 11.3 Glossary SLYZ022 — TI Glossary. This glossary lists and explains terms, acronyms and definitions. 12 Mechanical, Packaging, and Orderable Information The following pages include mechanical packaging and orderable information. This information is the most current data available for the designated devices. This data is subject to change without notice and revision of this document. For browser-based versions of this data sheet, refer to the left-hand navigation. Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated Product Folder Links: LDC1051 27 PACKAGE OPTION ADDENDUM www.ti.com 17-May-2014 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (°C) Device Marking (4/5) LDC1051NHRJ ACTIVE WSON NHR 16 4500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LDC1051 LDC1051NHRR ACTIVE WSON NHR 16 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LDC1051 LDC1051NHRT ACTIVE WSON NHR 16 250 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LDC1051 (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) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish value exceeds the maximum column width. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. 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