LTC1278-5ISW#TRPBF

DDC DD C11 2 112 DDC112 ® ® SBAS085B – JANUARY 2000 – REVISED OCTOBER 2004 Dual Current Input 20-Bit ANALOG-TO-DIGITAL CONVERTER FEATURES DESCRIPTION ● MONOLITHIC CHARGE MEASUREMENT A/D CONVERTER ● DIGITAL FILTER NOISE REDUCTION: 3.2ppm, rms ● INTEGRAL LINEARITY: ±0.005% Reading ±0.5ppm FSR ● HIGH PRECISION, TRUE INTEGRATING FUNCTION ● PROGRAMMABLE FULL-SCALE ● SINGLE SUPPLY ● CASCADABLE OUTPUT The DDC112 is a dual input, wide dynamic range, chargedigitizing analog-to-digital (A/D) converter with 20-bit resolution. Low-level current output devices, such as photosensors, can be directly connected to its inputs. Charge integration is continuous as each input uses two integrators; while one is being digitized, the other is integrating. APPLICATIONS To provide single-supply operation, the internal A/D converter utilizes a differential input, with the positive input tied to V REF. When the integration capacitor is reset at the beginning of each integration cycle, the capacitor charges to V REF. This charge is removed in proportion to the input current. At the end of the integration cycle, the remaining voltage is compared to VREF. ● ● ● ● ● ● For each of its two inputs, the DDC112 combines current-tovoltage conversion, continuous integration, programmable full-scale range, A/D conversion, and digital filtering to achieve a precision, wide dynamic range digital result. In addition to the internal programmable full-scale ranges, external integrating capacitors allow an additional user-settable full-scale range of up to 1000pC. DIRECT PHOTOSENSOR DIGITIZATION CT SCANNER DAS INFRARED PYROMETER PRECISION PROCESS CONTROL LIQUID/GAS CHROMATOGRAPHY BLOOD ANALYSIS The high-speed serial shift register which holds the result of the last conversion can be configured to allow multiple DDC112 units to be cascaded, minimizing interconnections. The DDC112 is available in an SO-28 or TQFP-32 package and is offered in two performance grades. Protected by US Patent #5841310 AVDD CAP1A CAP1A AGND VREF DVDD DGND CHANNEL 1 DCLK IN1 CAP1B CAP1B CAP2A CAP2A Dual Switched Integrator ∆Σ Modulator Digital Filter DVALID DXMIT DOUT DIN CHANNEL 2 IN2 CAP2B CAP2B Digital Input/Output RANGE2 RANGE1 RANGE0 Control Dual Switched Integrator TEST CONV CLK Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. Copyright © 2000-2004, Texas Instruments Incorporated PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. www.ti.com ABSOLUTE MAXIMUM RATINGS(1) AVDD to DVDD ....................................................................... –0.3V to +6V AVDD to AGND ..................................................................... –0.3V to +6V DVDD to DGND ..................................................................... –0.3V to +6V AGND to DGND ............................................................................... ±0.3V VREF Voltage to AGND ........................................... –0.3V to AVDD + 0.3V Digital Input Voltage to DGND .............................. –0.3V to DVDD + 0.3V Digital Output Voltage to DGND ........................... –0.3V to DVDD + 0.3V Package Power Dissipation ............................................. (TJMAX – TA)/θJA Maximum Junction Temperature (TJMAX) ...................................... +150°C Thermal Resistance, SO, θJA .................................................... +150°C/W Thermal Resistance, TQFP, θJA ................................................ +100°C/W Lead Temperature (soldering, 10s) ............................................... +300°C NOTE: (1) Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to absolute maximum conditions for extended periods may affect device reliability. ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. PACKAGE/ORDERING INFORMATION(1) PRODUCT MAXIMUM INTEGRAL LINEARITY ERROR SPECIFICATION TEMPERATURE RANGE PACKAGE-LEAD PACKAGE DESIGNATOR DDC112U ±0.025% Reading ±1.0ppm FSR –40°C to +85°C SO-28 DW DDC112U Rails " " " " " DDC112U/1K Tape and Reel ORDERING NUMBER(2) TRANSPORT MEDIA ±0.025% Reading ±1.0ppm FSR 0°C to +70°C SO-28 DW DDC112UK Rails " " " " " DDC112UK/1K Tape and Reel DDC112Y ±0.025% Reading ±1.0ppm FSR –40°C to +85°C TQFP-32 PJT DDC112Y/250 Tape and Reel " " " " " DDC112Y/2K Tape and Reel ±0.025% Reading ±1.0ppm FSR 0°C to +70°C TQFP-32 PJT DDC112YK/250 Tape and Reel " " " " DDC112YK/2K Tape and Reel DDC112UK DDC112YK " NOTES: (1) For the most current package and ordering information, see the Package Option Addendum located at the end of this data sheet. (2) Models with a slash (/) are available only in Tape and Reel in the quantities indicated (/1K indicates 1000 devices per reel). Ordering 1000 pieces of DDC112U/1K will get a single 1000piece Tape and Reel. 2 DDC112 www.ti.com SBAS085B ELECTRICAL CHARACTERISTICS At TA = +25°C, AVDD = DVDD = +5V, DDC112U, Y: TINT = 500µs, CLK = 10MHz, DDC112UK, YK: TINT = 333.3µs, CLK = 15MHz, VREF = +4.096V, continuous mode operation, and internal integration capacitors, unless otherwise noted. DDC112U, Y PARAMETER CONDITIONS ANALOG INPUTS External, Positive Full-Scale Range 0 Internal, Positive Full-Scale Range 1 Range 2 Range 3 Range 4 Range 5 Range 6 Range 7 Negative Full-Scale Input TYP CSENSOR(2) = 0pF, Range 5 (250pC) CSENSOR = 25pF, Range 5 (250pC) CSENSOR = 50pF, Range 5 (250pC) Differential Linearity Error Integral Linearity Error(4) No Missing Codes Input Bias Current Range Error Range Error Match(5) Range Sensitivity to VREF Offset Error Offset Error Match(5) DC Bias Voltage(6) (Input VOS) Power-Supply Rejection Ratio Internal Test Signal Internal Test Accuracy TA = +25°C Range 5 (250pC) All Ranges VREF = 4.096 ±0.1V Range 5, (250pC) DIGITAL INPUT/OUTPUT Logic Levels VIH VIL VOH VOL Input Current, IIN Data Format(9) 10 POWER-SUPPLY REQUIREMENTS Power-Supply Voltage Supply Current Analog Current Digital Current Total Power Dissipation TEMPERATURE RANGE Specified Performance Storage 12 12 ✻ ✻ ✻ ✻ ✻ ✻ ✻ 333.3 ✻ ✻ ±0.5 ±0.2 3 0.01 2 25 ±0.05 4.000 4.0 –0.3 4.5 ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ DVDD + 0.3 +0.8 ✻ ✻ ✻ AVDD = +5V DVDD = +5V –40 –60 pC ✻ ✻ ✻ ✻ ✻ ✻ ✻ pC pC pC pC pC pC pC pC 3 ✻ 15 15 kHz µs µs MHz MHz 7 ppm of FSR(3), rms ppm of FSR, rms ppm of FSR, rms ✻ 225 ✻ ✻ ✻ ±600 ✻ ✻ ±3(10) ±0.7(10) ✻ ✻ 50(10) Bits pA % of FSR % of FSR ppm of FSR ppm of FSR mV ppm of FSR/V pC % ppm of FSR/°C ppm of FSR/minute µV/°C pA/°C pA ppm/°C ppm/°C ✻ 275 V µA ✻ ✻ ✻ ✻ V V V V µA ✻ V 130 mA mA mW +70 ✻ °C °C ✻ 5.25 14.8 1.2 80 ✻ ±1 ✻ ✻ 25 ✻ ✻ Straight Binary 4.75 ✻ ✻ ✻ ✻ 4.200 0.4 +10 ✻ UNITS ✻ 0 4.096 150 ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ MAX ✻ 1(10) 50(10) –10 AVDD and DVDD TYP ✻ ✻ ✻ 3.2 3.8 4.2 6.0 ±0.005% Reading ±0.5ppm FSR (max) ±0.005% Reading ±0.5ppm FSR (typ) ±0.025% Reading ±1.0ppm FSR (max) 20 0.1 10 5 0.1 0.5 1:1 ±200 ±100 ±0.05 ±2 ±25 ±200 13 ±10 TINT = 500µs IOH = –500µA IOL = 500µA 52.5 105 157.5 210 262.5 315 367.5 FS 2 1,000,000 500 50 1 PERFORMANCE OVER TEMPERATURE Offset Drift Offset Drift Stability DC Bias Voltage Drift Applied to Sensor Input Input Bias Current Drift +25°C to +45°C Input Bias Current TA = +75°C (7) Range Drift Range 5 (250pC) (5) Range Drift Match Range 5 (250pC) REFERENCE Voltage Input Current(8) MIN 1000 47.5 50 95 100 142.5 150 190 200 237.5 250 285 300 332.5 350 –0.4% of Positive Continuous Mode Non-Continuous Mode DDC112UK, YK MAX CEXT = 250pF DYNAMIC CHARACTERISTICS Conversion Rate Integration Time, TINT Integration Time, TINT System Clock Input (CLK) Data Clock (DCLK) ACCURACY Noise, Low-Level Current Input(1) MIN ✻ 15.2 1.8 85 100 +85 +100 0 ✻ ✻ Specifications same as DDC112U, Y. NOTES: (1) Input is less than 1% of full scale. (2) CSENSOR is the capacitance seen at the DDC112 inputs from wiring, photodiode, etc. (3) FSR is Full-Scale Range. (4) A best-fit line is used in measuring linearity. (5) Matching between side A and side B, not input 1 to input 2. (6) Voltage produced by the DDC112 at its input which is applied to the sensor. (7) Range drift does not include external reference drift. (8) Input reference current decreases with increasing TINT (see the Voltage Reference section). (9) Data format is Straight Binary with a small offset (see the Data Retrieval section). (10) Ensured by design but not production tested. DDC112 SBAS085B www.ti.com 3 PIN CONFIGURATION PIN DESCRIPTIONS Top View SO IN1 1 28 IN2 AGND 2 27 AGND CAP1B 3 26 CAP2B CAP1B 4 25 CAP2B CAP1A 5 24 CAP2A CAP1A 6 23 CAP2A AVDD 7 22 VREF 21 AGND RANGE2 (MSB) PIN LABEL 1 IN1 2 AGND Analog Ground 3 CAP1B External Capacitor for Integrator 1B 4 CAP1B External Capacitor for Integrator 1B 5 CAP1A External Capacitor for Integrator 1A 6 CAP1A 7 AVDD Analog Supply, +5V Nominal 8 TEST Test Control Input. When HIGH, a test charge is applied to the A or B integrators on the next CONV transition. 9 CONV Controls which side of the integrator is connected to input. In continuous mode; CONV HIGH → side A is integrating, CONV LOW → side B is integrating. CONV must be synchronized with CLK (see Figure 2). CONV 4 8 9 20 External Capacitor for Integrator 1A 10 CLK 11 DCLK Serial Data Clock Input. This input operates the serial I/ O shift register. 12 DXMIT Serial Data Transmit Enable Input. When LOW, this input enables the internal serial shift register. 13 DIN Serial Digital Input. Used to cascade multiple DDC112s. 14 DVDD Digital Supply, +5V Nominal 15 DGND Digital Ground 16 DOUT Serial Data Output, Hi-Z when DXMIT is HIGH 17 DVALID Data Valid Output. A LOW value indicates valid data is available in the serial I/O register. Range Control Input 0 (least significant bit) DDC112U TEST DESCRIPTION Input 1: analog input for Integrators 1A and 1B. The integrator that is active is set by the CONV input. System Clock Input, 10MHz Nominal CLK 10 19 RANGE1 DCLK 11 18 RANGE0 (LSB) DXMIT 12 17 DVALID 18 RANGE0 DIN 13 16 DOUT 19 RANGE1 Range Control Input 1 DVDD 14 15 DGND 20 RANGE2 Range Control Input 2 (most significant bit) 21 AGND 22 VREF 23 CAP2A External Capacitor for Integrator 2A 24 CAP2A External Capacitor for Integrator 2A 25 CAP2B External Capacitor for Integrator 2B 26 CAP2B External Capacitor for Integrator 2B 27 AGND 28 IN2 Analog Ground External Reference Input, +4.096V Nominal Analog Ground Input 2: analog input for Integrators 2A and 2B. The integrator that is active is set by the CONV input. DDC112 www.ti.com SBAS085B PIN CONFIGURATION 25 CAP2B 26 CAP2B 27 AGND 28 IN2 29 IN1 30 AGND 31 CAP1B TQFP 32 CAP1B Top View CAP1A 1 24 CAP2A CAP1A 2 23 CAP2A AVDD 3 22 VREF NC 4 21 AGND DDC112Y 16 RANGE1 RANGE0 (LSB) 17 15 8 DVALID CLK 14 RANGE2 (MSB) DOUT 18 13 7 DGND CONV 12 NC DVDD 19 11 6 DIN TEST 10 NC DXMIT 20 9 5 DCLK NC PIN DESCRIPTIONS PIN LABEL DESCRIPTION PIN LABEL DESCRIPTION 1 CAP1A External Capacitor for Integrator 1A 15 DVALID 2 CAP1A External Capacitor for Integrator 1A Data Valid Output. A LOW value indicates valid data is available in the serial I/O register. 3 AVDD Analog Supply, +5V Nominal 16 RANGE0 Range Control Input 0 (least significant bit) No Connection 17 RANGE1 Range Control Input 1 No Connection 18 RANGE2 Range Control Input 2. (most significant bit) Test Control Input. When HIGH, a test charge is applied to the A or B integrators on the next CONV transition. 19 NC No Connection 20 NC No Connection 21 AGND 4 NC 5 NC 6 TEST 7 CONV 8 CLK 9 DCLK Analog Ground Controls which side of the integrator is connected to input. In continuous mode; CONV HIGH side A is integrating, CONV LOW side B is integrating CONV must be synchronized with CLK (see text). 22 VREF 23 CAP2A External Capacitor for Integrator 2A 24 CAP2A External Capacitor for Integrator 2A System Clock Input, 10MHz Nominal 25 CAP2B External Capacitor for Integrator 2B Serial Data Clock Input. This input operates the serial I/O shift register. 26 CAP2B External Capacitor for Integrator 2B 27 AGND External Reference Input, +4.096V Nominal Analog Ground 10 DXMIT Serial Data Transmit Enable Input. When LOW, this input enables the internal serial shift register. 28 IN2 Input 2: analog input for Integrators 2A and 2B. The integrator that is active is set by the CONV input. 11 DIN Serial Digital Input. Used to cascade multiple DDC112s. 29 IN1 Input 1: analog input for Integrators 1A and 1B. The integrator that is active is set by the CONV input. 12 DVDD Digital Supply, +5V Nominal 13 DGND Digital Ground 14 DOUT Serial Data Output, Hi-Z when DXMIT is HIGH 30 AGND Analog Ground 31 CAP1B External Capacitor for Integrator 1B 32 CAP1B External Capacitor for Integrator 1B DDC112 SBAS085B www.ti.com 5 TYPICAL CHARACTERISTICS At TA = +25°C, characterization done with Range 5 (250pC), TINT = 500µs, VREF = +4.096, AVDD = DVDD = +5V, and CLK = 10MHz, unless otherwise noted. NOISE vs CSENSOR Noise (ppm of FSR, rms) 50 Range 2 Range 0 (CEXT = 250pF) 40 Noise (ppm of FSR, rms) Range 1 60 NOISE vs TINT 6 70 Range 7 30 20 5 CSENSOR = 50pF 4 CSENSOR = 0pF 3 2 Range 5 1 10 0 0 0 200 400 600 800 0.1 1000 1 10 4.5 8 CSENSOR = 50pF Noise (ppm of FSR, rms) Noise (ppm of FSR, rms) 9 3.5 3 CSENSOR = 0pF 2.5 2 1.5 1 Range 5 0.5 1000 NOISE vs TEMPERATURE NOISE vs INPUT LEVEL 5 4 100 TINT (ms) CSENSOR (pF) Range 1 7 6 Range 2 5 Range 3 4 3 Range 7 2 CSENSOR = 0pF 1 0 0 10 20 30 40 50 60 70 80 90 10 100 –40 –15 Input Level (% of Full-Scale) 10 35 60 85 Temperature (°C) RANGE DRIFT vs TEMPERATURE IB vs TEMPERATURE 2000 10 Ranges 1 - 7 (Internal Integration Capacitor) All Ranges 1000 1 500 IB (pA) Range Drift (ppm) 1500 0 0.1 –500 –1000 –1500 0.01 –40 –15 10 35 60 85 25 Temperature (°C) 6 35 45 55 65 75 85 Temperature (°C) DDC112 www.ti.com SBAS085B TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, characterization done with Range 5 (250pC), TINT = 500µs, VREF = +4.096, AVDD = DVDD = +5V, and CLK = 10MHz, unless otherwise noted. OFFSET DRIFT vs TEMPERATURE INPUT VOS vs RANGE 36 100 All Ranges Offset Drift (ppm of FSR) 35 50 VOS (µV) 34 0 33 32 –50 31 30 –100 25 35 45 55 65 75 85 1 2 3 4 5 6 7 Range Temperature (°C) ANALOG SUPPLY CURRENT vs TEMPERATURE DIGITAL SUPPLY CURRENT vs TEMPERATURE 18 1.4 16 1.2 1.0 12 Current (mA) Current (mA) 14 10 8 6 0.8 0.6 0.4 4 0.2 2 0 0 –40 –15 10 35 60 85 –40 –15 10 Temperature (°C) CROSSTALK vs FREQUENCY 60 85 POWER-SUPPLY REJECTION RATIO vs FREQUENCY 600 0 –20 500 Separation Measured Between Inputs 1 and 2 –40 PSRR (ppm of FSR/V) Separation (dB) 35 Temperature (°C) –60 –80 –100 400 300 200 100 –120 0 –140 0 100 200 300 400 500 DDC112 SBAS085B 0 25 50 75 100 Frequency (KHz) Frequency (Hz) www.ti.com 7 THEORY OF OPERATION The DVALID output goes LOW when the shift register contains valid data. The basic operation of the DDC112 is illustrated in Figure 1. The device contains two identical input channels where each performs the function of current-to-voltage integration followed by a multiplexed analog-to-digital (A/D) conversion. Each input has two integrators so that the current-to-voltage integration can be continuous in time. The output of the four integrators are switched to one delta-sigma (∆Σ) converter via a four input multiplexer. With the DDC112 in the continuous integration mode, the output of the integrators from one side of both of the inputs will be digitized while the other two integrators are in the integration mode as illustrated in the timing diagram in Figure 2. This integration and A/D conversion process is controlled by the system clock, CLK. With a 10MHz system clock, the integrator combined with the deltasigma converter accomplishes a single 20-bit conversion in approximately 220µs. The results from side A and side B of each signal input are stored in a serial output shift register. The digital interface of the DDC112 provides the digital results via a synchronous serial interface consisting of a data clock (DCLK), a transmit enable pin (DXMIT), a valid data pin (DVALID), a serial data output pin (DOUT), and a serial data input pin (DIN). The DDC112 contains only one A/D converter, so the conversion process is interleaved between the two inputs, as shown in Figure 2. The integration and conversion process is fundamentally independent of the data retrieval process. Consequently, the CLK frequency and DCLK frequencies need not be the same. DIN is only used when multiple converters are cascaded and should be tied to DGND otherwise. Depending on TINT, CLK, and DCLK, it is possible to daisy-chain over 100 converters. This greatly simplifies the interconnection and routing of the digital outputs in cases where a large number of converters are needed. AVDD CAP1A CAP1A AGND VREF DVDD DGND Input 1 DCLK IN1 CAP1B CAP1B Dual Switched Integrator CAP2A CAP2A ∆Σ Modulator Digital Filter Input 2 IN2 CAP2B CAP2B DVALID DXMIT DOUT DIN Digital Input/Output RANGE2 RANGE1 RANGE0 Control Dual Switched Integrator TEST CONV CLK FIGURE 1. Block Diagram. IN1, Integrator A Integrate Integrate IN1, Integrator B Integrate IN2, Integrator A Integrate Integrate Integrate IN2, Integrator B Conversion in Progress Integrate IN1B IN2B IN1A IN2A Integrate IN1B IN2B IN1A IN2A DVALID FIGURE 2. Basic Integration and Conversion Timing for the DDC112 (continuous mode). 8 DDC112 www.ti.com SBAS085B DEVICE OPERATION Basic Integration Cycle The fundamental topology of the front end of the DDC112 is a classical analog integrator, as shown in Figure 3. In this diagram, only Input 1 is shown. This representation of the input stage consists of an operational amplifier, a selectable feedback capacitor network (CF), and several switches that implement the integration cycle. The timing relationships of all of the switches shown in Figure 3 are illustrated in Figure 4. Figure 4 is used to conceptualize the operation of the integrator input stage of the DDC112 and should not be used as an exact timing tool for design. Block diagrams of the reset, integrate, converter, and wait states of the integrator section of the DDC112 are shown in Figure 5. This internal switching network is controlled externally with the convert command (CONV), range selection pins (RANGE0RANGE2), and the system clock (CLK). For the best noise performance, CONV must be synchronized with the rising edge of CLK. It is recommended CONV toggle within ±10ns of the rising edge of CLK. CF (pF, typ) INPUT RANGE (pC, typ) 0 External 12.5 to 250 Up to 1000 0 1 12.5 –0.2 to 50 1 0 25 –0.4 to 100 0 1 1 37.5 –0.6 to 150 1 0 0 50 –0.8 to 200 1 0 1 62.5 –0.1 to 250 1 1 0 75 –1.2 to 300 1 1 1 87.5 –1.4 to 350 RANGE2 RANGE1 RANGE0 0 0 0 0 TABLE I. Range Selection of the DDC112. SRESET (see Figures 4 and 5a). This is done during the reset time. In this manner, the selected capacitor is charged to the reference voltage, VREF. Once the integration capacitor is charged, SREF1, and SRESET are switched so that VREF is no longer connected to the amplifier circuit while it waits to begin integrating (see Figure 5b). With the rising edge on CONV, SINTA closes which begins the integration of Channel A. This puts the integrator stage into its integrate mode (see Figure 5c). The noninverting inputs of the integrators are internally referenced to ground. Consequently, the DDC112 analog ground should be as clean as possible. The range switches, along with the internal and external capacitors (CF) are shown in parallel between the inverting input and output of the operational amplifier. Table I shows the value of the integration capacitor (CF) for each range. At the beginning of a conversion, the switches SA/D, SINTA, SINTB, SREF1, SREF2, and SRESET are set (see Figure 4). Charge from the input signal is collected on the integration capacitor causing the voltage output of the amplifier to decrease. A falling edge CONV stops the integration by switching the input signal from side A to side B (SINTA and SINTB). Prior to the falling edge of CONV, the signal on side B was converted by the A/D converter and reset during the time that side A was integrating. With the falling edge of CONV, side B starts integrating the input signal. Now the output voltage of side A’s operational amplifier is presented to the input of the ∆Σ A/D converter (see Figure 5d). At the completion of an A/D conversion, the charge on the integration capacitor (C F ) is reset with S REF1 and CAP1A CAP1A SREF1 VREF 50pF RANGE2 25pF RANGE1 12.5pF RANGE0 SREF2 SINTA Input Current Photodiode IN1 ESD Protection Diode SA/D1A SRESET To Converter Integrator A SINTB Integrator B (same as A) FIGURE 3. Basic Integrator Configuration for Input 1 Shown with a 250pC (CF = 62.5pF) Input Range. DDC112 SBAS085B www.ti.com 9 CONV CLK SINTA SINTB SREF1 SREF2 SRESET Integrate Convert Wait Wait Wait Reset Convert Wait Configuration of Integrator A Reset SA/D1A VREF Integrator A Voltage Output FIGURE 4. Basic Integrator Timing Diagram as Illustrated in Figure 3. SREF1 CF VREF SINT SREF2 CF IN SREF1 VREF To Converter SRESET SA/D SINT SREF2 IN To Converter SRESET SA/D a) Reset Configuration CF SREF1 b) Wait Configuration VREF SINT SREF2 CF IN SRESET SREF1 VREF To Converter SA/D SINT SREF2 IN SRESET c) Integrate Configuration To Converter SA/D d) Convert Configuration FIGURE 5. Diagrams for the Four Configurations of the Front End Integrators of the DDC112. 10 DDC112 www.ti.com SBAS085B Determining the Integration Capacitor (CF) Value EXTERNAL CAPACITOR PINS DDC112U, UK The value of the integrator’s feedback capacitor, the integration period, and the reference voltage determine the positive full-scale (+FS) value of the DDC112. The approximate positive full-scale value of the DDC112 is given by the following equations: 5 3 23 25 QFS = (0.96) VREF × CF 1 31 23 25 and and and and 2 32 24 26 Channel Side 1 1 2 2 A B A B Since the range accuracy depends on the characteristics of the integration capacitor, they must be carefully selected. An external integration capacitor should have low-voltage coefficient, temperature coefficient, memory, and leakage current. The optimum selection depends on the requirements of the specific application. Suitable types include chip-on-glass (COG) ceramic, polycarbonate, polystyrene, and silver mica. (0.96) VREF × CF TINT or CF = DDC112Y, YK 6 4 24 26 TABLE II. External Capacitor Connections with Range Configuration of RANGE2-RANGE0 = 000. QIN = IIN × TINT IFS = and and and and INTEGRATOR IFS × TINT (0.96) VREF Voltage Reference The 0.96 factor allows the front end integrators to reach fullscale without having to completely swing to ground. The negative full-scale (–FS) range is approximately 0.4% of the positive full-scale range. For example, Range 5 has a nominal +FS range of 250pC. The –FS range is then approximately –1pC. This relationship holds for external capacitors as well and is independent of VREF (for VREF within the allowable range, see the Electrical Characteristics table). The external voltage reference is used to reset the integration capacitors before an integration cycle begins. It is also used by the ∆Σ converter while the converter is measuring the voltage stored on the integrators after an integration cycle ends. During this sampling, the external reference must supply charge needed by the ∆Σ converter. For an integration time of 500µs, this charge translates to an average VREF current of approximately 150µA. The amount of charge needed by the ∆Σ converter is independent of the integration time; therefore, increasing the integration time lowers the average current. For example, an integration time of 1000µs lowers to average VREF current to 75µA. Integration Capacitors There are seven different capacitors available on-chip for each side of each channel in the DDC112. These internal capacitors are trimmed in production to achieve the specified performance for range error of the DDC112. The range control pins (RANGE0-RANGE2) change the capacitor value for all four integrators. Consequently, both inputs and both sides of each input will always have the same full-scale range unless external capacitors are used. It is critical that VREF be stable during the different modes of operation in Figure 5. The ∆Σ converter measures the voltage on the integrator with respect to VREF. Since the integrator’s capacitors are initially reset to VREF, any droop in VREF from the time the capacitors are reset to the time when the converter measures the integrator’s output will introduce an offset. It is also important that VREF be stable over longer periods of time as changes in VREF correspond directly to changes in the full-scale range. Finally, VREF should introduce as little additional noise as possible. External integration capacitors may be used instead of the internal capacitors values by setting [RANGE2-RANGE0 = 000]. The external capacitor pin connections are summarized in Table II. Usually, all four external capacitors are equal in value; however, it is possible to have differing pairs of external capacitors between Input 1 and Input 2 of the DDC112. Regardless of the selected value of the capacitor, it is strongly recommended that the capacitors for sides A and B be the same. For reasons mentioned above, it is strongly recommended that the external reference source be buffered with an operational amplifier, as shown in Figure 6. In this circuit, the voltage reference is generated by a 4.096V reference. +5V 0.10µF +5V 7 0.47µF 2 1 REF3040 2 3 OPA350 + + 3 To VREF Pin 22 of the DDC112 6 10kΩ 10µF 0.10µF 10µF 0.1µF 4 FIGURE 6. Recommended External Voltage Reference Circuit for Best Low-Noise Operation with the DDC112. DDC112 SBAS085B www.ti.com 11 A low-pass filter to reduce noise connects it to an operational amplifier configured as a buffer. This amplifier should have a unity-gain bandwidth greater than 4MHz, low noise, and input/output common-mode ranges that support VREF. Following the buffer are capacitors placed close to the DDC112 VREF pin. Even though the circuit in Figure 6 might appear to be unstable due to the large output capacitors, it works well for most operational amplifiers. It is NOT recommended that series resistance be placed in the output lead to improve stability since this can cause droop in VREF which produces large offsets. 0 Gain (dB) –10 –20 –30 –40 –50 The frequency response of the DDC112 is set by the front end integrators and is that of a traditional continuous time integrator, as shown in Figure 7. By adjusting TINT, the user can change the 3dB bandwidth and the location of the notches in the response. The frequency response of the ∆Σ converter that follows the front end integrator is of no consequence because the converter samples a held signal from the integrators. That is, the input to the ∆Σ converter is always a DC signal. Since the output of the front end integrators are sampled, aliasing can occur. Whenever the frequency of the input signal exceeds one-half of the sampling rate, the signal will fold back down to lower frequencies. Test Mode Disabled Integrate A integration capacitors of both Input 1 and Input 2. This fixed charge can be transferred to the integration capacitors either once during an integration cycle or multiple times. In the case where multiple packets are transferred during one integration period, the 13pC charge is additive. This mode can be used in both the continuous and noncontinuous mode timing. The timing diagrams for test mode are shown in Figure 8. The top three lines in Figure 8 define the timing when one packet of 13pC is sent to the integration capacitors. The bottom three lines define the timing when multiple packets are sent to the integration capacitors. Test Mode Enabled 13pC into B 100 TINT FIGURE 7. Frequency Response of the DDC112. When TEST is used, pins IN1 and IN2 are grounded and packets of approximately 13pC charge are transferred to the Action 10 TINT Frequency Test Mode Integrate B 1 TINT 0.1 TINT DDC112 Frequency Response 13pC into A Test Mode Disabled 13pC into B 13pC into A Integrate B Integrate A CONV TEST t1 t2 Test Mode Enabled Test Mode Disabled Test Mode Disabled Action Integrate B Integrate A 13pC into B 26pC into A 39pC into B 52pC into A Integrate B Integrate A CONV t4 t5 t2 TEST t1 t4 t3 FIGURE 8. Timing Diagram of the Test Mode of the DDC112. CLK = 10MHz SYMBOL DESCRIPTION MIN TYP CLK = 15MHz MAX MIN TYP MAX UNITS t1 Setup Time for Test Mode Enable 100 100 ns t2 Setup Time for Test Mode Disable 100 100 ns t3 Hold Time for Test Mode Enable 100 100 ns t4 From Rising Edge of TEST to the Edge of CONV while Test Mode Enabled 5.4 3.6 µs t5 Rising Edge to Rising Edge of TEST 5.4 3.6 µs TABLE III. Timing for the DDC112 in the Test Mode. 12 DDC112 www.ti.com SBAS085B TEST and CONV work together to implement this feature. The test mode is entered when TEST is HIGH prior to a CONV edge. At that point, a CONV edge triggers the grounding of the analog inputs and the switching of 13pC packets of charge onto the integration capacitors. If TEST is kept HIGH through at least two conversions (that is, a rise and fall of CONV), all four integrators will be charged with a 13pC packet. At the end of each conversion, the voltage at the output of the integrators is digitized as discussed in the Continuous and Non-Continuous Operational Modes section of this data sheet. The test mode is exited when TEST is LOW and a CONV edge occurs. Continuous and Non-Continuous Operational Modes The state diagram of the DDC112 is shown in Figure 9. In all, there are 8 states. Table IV provides a brief explanation of each of the states. mbsy 1 Ncont Once the test mode is entered as described above, TEST can cycle as many times as desired. When this is done, additional 13pC packets are added on the rising edge of TEST to the existing charge on the integrator capacitors. Multiple charge packets can be added in this way as long as the TEST pin is not LOW when CONV toggles. Ncont CONV 3 Int A Cont CONV • mbsy CONV 4 The digital interface of the DDC112 provides the digital results via a synchronous serial interface consisting of a data clock (DCLK), a transmit enable pin (DXMIT), a valid data pin (DVALID), a serial data output pin (DOUT), and a serial data input pin (DIN). The DDC112 contains only one A/D converter, so the conversion process is interleaved between the two inputs (see Figure 2). The integration and conversion process is fundamentally independent of the data retrieval process. Consequently, the CLK frequency and DCLK frequencies need not be the same. DIN is used when multiple converters are cascaded. Cascading or daisy-chaining greatly simplifies the interconnection and routing of the digital outputs in cases where a large number of converters are needed. Refer to the Cascading Multiple Converters section of this data sheet for more detail. The conversion rate of the DDC112 is set by a combination of the integration time (determined by the user) and the speed of the A/D conversion process. The A/D conversion time is primarily a function of the system clock (CLK) speed. One A/D conversion cycle encompasses the conversion of two signals (one from each input of the DDC112) and reset time for each of the integrators involved in the two conversions. In most situations, the A/D conversion time is shorter than the integration time. If this condition exists, the DDC112 will operate in the continuous mode. When the DDC112 is in the continuous mode, the sensor output is continuously integrated by one of the two sides of each input. In the event that the A/D conversion takes longer than the integration time, the DDC112 will switch into a noncontinuous mode. In noncontinuous mode, the A/D converter is not able to keep pace with the speed of the integration process. Consequently, the integration process is periodically halted until the digitizing process catches up. These two basic modes of operation for the DDC112—continuous and noncontinuous modes—are described in the Continuous and Noncontinuous Operational Modes section of this data sheet. 5 CONV • mbsy Int B/Meas A Cont DIGITAL ISSUES Int A/Meas B Cont CONV • mbsy 6 CONV CONV • mbsy Int B Cont CONV 7 Ncont 8 Ncont CONV • mbsy mbsy FIGURE 9. State Diagram. STATE MODE DESCRIPTION 1 Ncont Complete m/r/az of side A, then side B (if previous state is state 4). Initial power-up state when CONV is initially held HIGH. 2 Ncont Prepare side A for integration. 3 Cont Integrate on side A. 4 Cont Integrate on side B; m/r/az on side A. 5 Cont Integrate on side A; m/r/az on side B. 6 Cont Integrate on side B. 7 Ncont Prepare side B for integration. 8 Ncont Complete m/r/az of side B, then side A (if previous state is state 5). Initial power-up state when CONV is initially held LOW. TABLE IV. State Descriptions. Four signals are used to control progression around the state diagram: CONV and mbsy and their complements. The state machine uses the level as opposed to the edges of CONV to control the progression. mbsy is an internally-generated signal not available to the user. It is active whenever a measurement/reset/auto-zero (m/r/az) cycle is in progress. DDC112 SBAS085B 2 CONV • mbsy www.ti.com 13 Table V can be easily found for a given CLK. For example, if CLK = 10MHz, then a CLK period = 0.1µs. t6 in Table V would then be 479.4µs. During the cont mode, mbsy is not active when CONV toggles. The non-integrating side is always ready to begin integrating when the other side finishes its integration. Consequently, keeping track of the current status of CONV is all that is needed to know the current state. Cont mode operation corresponds to states 3-6. Two of the states, 3 and 6, only perform an integration (no m/r/az cycle). SYMBOL mbsy becomes important when operating in the ncont mode; states 1, 2, 7, and 8. Whenever CONV is toggled while mbsy is active, the DDC112 will enter or remain in either ncont state 1 (or 8). After mbsy goes inactive, state 2 (or 7) is entered. This state prepares the appropriate side for integration. As mentioned above, in the ncont states, the inputs to the DDC112 are grounded. DESCRIPTION VALUE (CLK periods) t6 Cont mode m/r/az cycle. 4794 t7 Cont mode data ready. 4212 (tINT > 4794) 4212 ±3 (tINT = 4794) t8 1st ncont mode data ready. 4212 ±3 t9 2nd ncont mode data ready. 4548 t10 Ncont mode m/r/az cycle. 9108 TABLE V. Timing Specifications Generalized in CLK Periods. Figure 10 shows a few integration cycles beginning with initial power-up for a cont mode example. The top signal is CONV and is supplied by the user. The next line indicates the current state in the state diagram. The following two traces show when integrations and measurement cycles are underway. The internal signal mbsy is shown next. Finally, DVALID is given. As described in the data sheet, DVALID goes active LOW when data is ready to be retrieved from the DDC112. It stays LOW until DXMIT is taken LOW by the user. In Figure 10 and the following timing diagrams, it is assumed that DXMIT it taken LOW soon after DVALID goes LOW. The text below the DVALID pulse indicates the side of the data and arrows help match the data to the corresponding integration. The signals shown in Figures 10 through 19 are drawn at approximately the same scale. One interesting observation from the state diagram is that the integrations always alternate between sides A and B. This relationship holds for any CONV pattern and is independent of the mode. States 2 and 7 insure this relationship during the ncont mode. When power is first applied to the DDC112, the beginning state is either 1 or 8, depending on the initial level of CONV. For CONV held HIGH at power-up, the beginning state is 1. Conversely, for CONV held LOW at power-up, the beginning state is 8. In general, there is a symmetry in the state diagram between states 1-8, 2-7, 3-6, and 4-5. Inverting CONV results in the states progressing through their symmetrical match. In Figure 10, the first state is ncont state 1. The DDC112 always powers up in the ncont mode. In this case, the first state is 1 because CONV is initially HIGH. After the first two states, cont mode operation is reached and the states begin toggling between 4 and 5. From now on, the input is being continuously integrated, either by side A or side B. The time needed for the m/r/az cycle, t6, is the same time that TIMING EXAMPLES Cont Mode A few timing diagrams will now be discussed to help illustrate the operation of the state machine. These are shown in Figures 10 through 19. Table V gives generalized timing specifications in units of CLK periods. Values in µs for CONV State 1 2 Integration Status 3 4 5 4 Integrate A Integrate B Integrate A Integrate B m/r/az Status m/r/az A m/r/az B m/r/az A t6 mbsy DVALID t7 t=0 Power-Up SYMBOL Side A Data Side B Data Side A Data DESCRIPTION VALUE (CLK = 10MHz) VALUE (CLK = 15MHz) t6 Cont mode m/r/az cycle. 479.4µs 319.6µs t7 Cont mode data ready. 421.2µs 421.2 ±0.3µs (TINT > 479.4µs) (TINT = 479.4µs) 280.8µs 280.8 ±0.2µs (TINT > 319.6µs) (TINT = 319.6µs) FIGURE 10. Continuous Mode Timing (CONV HIGH at power-up). 14 DDC112 www.ti.com SBAS085B Figure 11 shows the result of inverting the logic level of CONV. The only difference is in the first three states. Afterwards, the states toggle between 4 and 5 just as in the previous example. Figure 12 shows the timing diagram of the internal operations occurring during continuous mode operation. determines the boundary between the cont and ncont modes described earlier in the Overview section. DVALID goes LOW after CONV toggles in time t7, indicating that data is ready to be retrieved. As shown in Figure 10, there are two values for t7, depending on TINT. The reason for this will be discussed in the Special Considerations section. CONV State 8 7 Integration Status 6 5 4 5 Integrate B Integrate A Integrate B Integrate A m/r/az Status m/r/az B m/r/az A m/r/az B t6 mbsy DVALID t7 t=0 Power-Up Side B Data Side A Data Side B Data FIGURE 11. Continuous Mode Timing (CONV LOW at power-up). End Integration Side B Start Integration Side A End Integration Side A Start Integration Side B TINT CONV TINT Side B Side A A/D Conversion Input 1 (Internal) End Integration Side A Start Integration Side B Side A t12 Side A A/D Conversion Input 2 (Internal) Side B t12 t13 t14 DVALID Side B Data Ready Side A Data Ready FIGURE 12. Timing Diagram of the Internal Operation in Continuous Mode of the DDC112. CLK = 10MHz SYMBOL TYP CLK = 15MHz DESCRIPTION MIN MAX MIN 1,000,000 333 TYP MAX UNITS TINT Integration Period (continuous mode) 500 t12 A/D Conversion Time (internally controlled) 202.2 134.8 1,000,000 µs µs t13 A/D Conversion Reset Time (internally controlled) 13.2 8.8 µs t14 Integrator and A/D Conversion Reset Time (internally controlled) 61.8 41.2 µs TABLE VI. Timing for the Internal Operation in the Continuous Mode. DDC112 SBAS085B www.ti.com 15 Ncont Mode same time as in the cont mode. The second data will be ready in time t9 after the first data is ready. One result of the naming convention used in this application bulletin is that when the DDC112 is operating in the ncont mode, it passes through both ncont mode states and cont mode states. For example, in Figure 13, the state pattern is 3, 4, 1, 2, 3, 4, 1, 2, 3, 4...where 3 and 4 are cont mode states. Ncont mode by definition means that for some portion of the time, neither side A nor B is integrating. States that perform an integration are labeled cont mode states while those that do not are called ncont mode states. Since integrations are performed in the ncont mode, just not continuously, some cont mode states must be used in an ncont mode state pattern. Figure 13 illustrates operation in the ncont mode. The integrations come in pairs (that is, sides A/B or sides B/A) followed by a time during which no integrations occur. During that time, the previous integrations are being measured, reset and auto-zeroed. Before the DDC112 can advance to states 3 or 6, both sides A and B must be finished with the m/r/az cycle which takes time t10. When the m/r/az cycles are completed, time t11 is needed to prepare the next side for integration. This time is required for the ncont mode because the m/r/az cycle of the ncont mode is slightly different from that of the cont mode. After the first integration ends, DVALID goes LOW in time t8. This is the CONV State 3 4 1 2 3 4 1 2 t11 Integration Status Int A m/r/az Status Int B Int A m/r/az A Int B m/r/az A m/r/az B m/r/az B t10 mbsy t9 DVALID t8 Side A Data SYMBOL Side B Data Side A Data DESCRIPTION VALUE (CLK = 10MHz) t8 1st ncont mode data ready. 421.2 ±0.3µs 280.8 ±0.2µs t9 2nd ncont mode data ready. 454.8µs 303.2µs t10 Ncont mode m/r/az cycle. 910.8µs 607.2µs t11 Prepare side for integration. ≥ 24.0µs ≥ 24.0µs Side B Data VALUE (CLK = 15MHz) FIGURE 13. Non-Continuous Mode Timing. 16 DDC112 www.ti.com SBAS085B Start Integration Side A Start Integration Side A End Integration Side A Start Integration Side B End Integration Side B Release State Wait State TINT t17 CONV TINT t16 A/D Conversion Input 1 t12 A/D Conversion Input 2 t12 t13 t15 DVALID Side A Data Ready Side B Data Ready FIGURE 14. Conversion Detail for the Internal Operation of the Non-Continuous Mode with Side A Integrated First. CLK = 10MHz SYMBOL DESCRIPTION MIN TINT Integration Time (noncontinuous mode) 50 t12 A/D Conversion Time (internally controlled) 202.2 134.8 t13 A/D Conversion Reset Time (internally controlled) 13.2 8.8 µs t15 Integrator and A/D Conversion Reset Time (internally controlled) Total A/D Conversion and Rest Time (internally controlled) Release Time 37.8 25.2 µs 910.8 607.2 µs t16 t17 TYP CLK = 15MHz MAX MIN 1,000,000 50 24 TYP MAX UNITS 1,000,000 µs µs µs 24 TABLE VII. Internal Timing for the DDC112 in the Non-Continuous Mode. Start Integration Side B Start Integration Side B End Integration Side B Start Integration Side A End Integration Side A Release State Wait State CONV TINT TINT t17 t16 A/D Conversion Input 1 t12 A/D Conversion Input 2 t12 t13 t15 DVALID Side B Data Ready Side A Data Ready FIGURE 15. Internal Operation Timing Diagram of the Non-Continuous Mode with Side B Integrated First. DDC112 SBAS085B www.ti.com 17 a 50% duty cycle CONV signal with TINT = 1620 CLK periods. Care must be exercised when using a square wave to generate CONV. There are certain integration times that must be avoided since they produce very short intervals for state 2 (or state 7 if CONV is inverted). As seen in the state diagram, the state progresses from 2 to 3 as soon as CONV is HIGH. The state machine does not insure that the duration of state 2 is long enough to properly prepare the next side for integration (t11). This must be done by the user with proper timing of CONV. For example, if CONV is a square wave with TINT = 3042 CLK periods, state 2 will only be 18 CLK periods long, therefore, t11 will not be met. Looking at the state diagram, one can see that the CONV pattern needed to generate a given state progression is not unique. Upon entering states 1 or 8, the DDC112 remains in those states until mbsy goes LOW, independent of CONV. As long as the m/r/az cycle is underway, the state machine ignores CONV (see Figure 9). The top two signals are different CONV patterns that produce the same state. This feature can be a little confusing at first, but it does allow flexibility in generating ncont mode CONV patterns. For example, the DDC112 Evaluation Fixture operates in the ncont mode by generating a square wave with pulse width < t6. Figure 17 illustrates operation in the ncont mode using CONV1 CONV2 mbsy State 3 4 1 2 3 4 1 2 FIGURE 16. Equivalent CONV Signals in Non-Continuous Mode. CONV State Integration Status 3 4 Int A Int B 1 2 3 4 Int A Int B 1 mbsy DVALID Side A Data Side B Data Side A Data FIGURE 17. Non-Continuous Mode Timing with a 50% Duty Cycle CONV Signal. 18 DDC112 www.ti.com SBAS085B Changing Between Modes Changing from the ncont to cont mode occurs when TINT is increased so that TINT is always ≥ t6 (see Figure 14). With a longer TINT, the m/r/az cycle has enough time to finish before the next integration begins and continuous integration of the input signal is possible. For the special case of the very first integration when changing to the cont mode, TINT can be < t6. This is allowed because there is no simultaneous m/r/az cycle on the side B during state 3—there is no need to wait for it to finish before ending the integration on side A. Changing from the cont to ncont mode occurs whenever TINT < t6. Figure 18 shows an example of this transition. In this figure, the cont mode is entered when the integration on side A is completed before the m/r/az cycle on side B is complete. The DDC112 completes the measurement on sides B and A during states 8 and 7 with the input signal shorted to ground. Ncont integration begins with state 6. CONV State 5 4 5 8 Continuous Integration Status m/r/az Status Integrate A Integrate B m/r/az B 7 5 Int B Int A Non-Continuous Int A m/r/az A 6 m/r/az B m/r/az A m/r/az B mbsy FIGURE 18. Changing from Continuous Mode to Non-Continuous Mode. CONV State 3 4 1 2 Non-Continuous Integration Status m/r/az Status Int A Int B m/r/az A 3 Continuous Integrate A m/r/az B 4 Integrate B m/r/az A mbsy FIGURE 19. Changing from Non-Continuous Mode to Continuous Mode. DDC112 SBAS085B www.ti.com 19 SPECIAL CONSIDERATIONS NCONT MODE INTEGRATION TIME The DDC112 uses a relatively fast clock. For CLK = 10MHz, this allows TINT to be adjusted in steps of 100ns since CONV should be synchronized to CLK. However, for the internal measurement, reset and auto-zero operations, a slower clock is more efficient. The DDC112 divides CLK by six and uses this slower clock with a period of 600ns to run the m/r/ az cycle and data ready logic. Because of the divider, it is possible for the integration time to be a non-integer number of slow clock periods. For example, if TINT = 5000 CLK periods (500µs for CLK = 10MHz), there will be 833 1/3 slow clocks in an integration period. This non-integer relationship between TINT and the slow clock period causes the number of rising and falling slow clock edges within an integration period to change from integration to integration. The digital coupling of these edges to the integrators will in turn change from integration to integration which produces noise. The change in the clock edges is not random, but will repeat every 3 integrations. The coupling noise on the integrators appears as a tone with a frequency equal to the rate at which the coupling repeats. To avoid this problem in cont mode, the internal slow clock is shut down after the m/r/az cycle is complete when it is no longer needed. It starts up again just after the next integration begins. Since the slow clock is always off when CONV toggles, the same number of slow clock edges fall within an integration period regardless of its length. Therefore, TINT ≥ 4794 CLK periods will not produce the coupling problem described above. For the ncont mode however, the slow clock must always be left running. The m/r/az cycle is not completed before an integration ends. It is then possible to have digital coupling to the integrators. The digital coupling noise depends heavily on the layout of the printed circuit board used for the DDC112. For solid grounds and power supplies with good bypassing, it is possible to greatly reduce the coupling. However, for ensuring the best performance in the ncont mode, the integration time should be chosen to be an integer multiple of 1/(2fSLOWCLOCK). For CLK = 10MHz, the integration time should be an integer multiple of 300ns—TINT = 100µs is not. A better choice would be TINT = 99µs. For TINT ≤ t6, the internal slow clock, is not allowed to shut down and the synchronization never occurs. Therefore, the time between CONV toggling and DVALID indicating data is ready has uncertainty due to the random phase relationship between CONV and the slow clock. This variation is ±1/(2fSLOWCLOCK) or ±3/fCLK. The timing to the second DVALID in the ncont mode will not have a variation since it is triggered off the first data ready (t9) and both are derived from the slow clock. Polling DVALID to determine when data is ready eliminates any concern about the variation in timing since the readback is automatically adjusted as needed. If the data readback is triggered off the toggling of CONV directly (instead of polling), then waiting the maximum value of t7 or t8 insures that data will always be ready before readback occurs. Data Retrieval In the continuous and noncontinuous modes of operation, the data from the last conversion is available for retrieval with the falling edge of DVALID (see Figure 22). The falling edge of DXMIT in combination with the data clock (DCLK) will initiate the serial transmission of the data from the DDC112. Typically, data is retrieved from the DDC112 as soon as DVALID falls and completed before the next CONV transition from HIGH to LOW or LOW to HIGH occurs. If this is not the case, care should be taken to stop activity on DCLK and consequently DOUT by at least 10µs around a CONV transition. If this caution is ignored it is possible that the integration that is being initiated by CONV will have additional noise introduced. The serial output data at DOUT is transmitted in Straight Binary Code per Table VIII. An output offset has been built into the DDC112 to allow for the measurement of input signals near and below zero. Board leakage up to ≈ –0.4% of the positive full-scale can be tolerated before the digital output clips to all zeroes. CODE INPUT SIGNAL 1111 1111 1111 1111 1111 FS 1111 1111 1111 1111 1110 FS – 1LSB 0000 0001 0000 0000 0001 +1LSB 0000 0001 0000 0000 0000 Zero 0000 0000 0000 0000 0000 –0.4% FS TABLE VIII. Straight Binary Code Table. DATA READY The DVALID signal which indicates that data is ready is generated using the internal slow clock. The phase relationship between this clock and CLK is set when power is first applied and is random. Since CONV is synchronized with CLK, it will have a random phase relationship with respect to the slow clock. When TINT > t6, the slow clock will temporarily shut down as described above. This shutdown process synchronizes the internal clock with CONV so that the time between when CONV toggles to when DVALID goes LOW (t7 and t8) is fixed. 20 Cascading Multiple Converters Multiple DDC112 units can be connected in serial or parallel configurations, as illustrated in Figures 20 and 21. DOUT can be used with DIN to daisy-chain several DDC112 devices together to minimize wiring. In this mode of operation, the serial data output is shifted through multiple DDC112s, as illustrated in Figure 20. RPULLUP prevents DIN from floating when DXMIT is HIGH. Care should be taken to keep the capacitive load on DOUT as low as possible when running CLK=15MHz. DDC112 www.ti.com SBAS085B Sensor “F” Sensor “E” Sensor “D” IN2 IN1 Sensor “C” IN2 IN1 DDC112 RP DOUT “F” “E” DCLK DVALID DXMIT DIN 40 Bits IN2 DDC112 DCLK DVALID DXMIT Sensor “A” IN1 DDC112 DCLK DIN Sensor “B” “D” “C” DVALID DXMIT RP DOUT DIN 40 Bits “B” “A” RP DOUT Data Retrieval Outputs 40 Bits Data Retrievel Inputs FIGURE 20. Daisy-Chained DDC112s. DDC112 DIN DOUT DXMIT DDC112 Data Output DOUT DXMIT DIN DDC112 DOUT DXMIT DIN Enable FIGURE 21. DDC112 in Parallel Operation. CLK t18 DVALID t19 DXMIT t20 DCLK(1) t22 t21 DOUT Output Disabled t23 Input 2 Bit 1 Input 2 Bit 20 Input 1 Bit 1 Input 1 Bit 20 MSB LSB MSB LSB Output Disabled Output Enabled NOTE: (1) Disable DCLK (preferably hold LOW) when DXMIT is HIGH. FIGURE 22. Digital Interface Timing Diagram for Data Retrieval From a Single DDC112. SYMBOL DESCRIPTION MIN t 18 t 19 t 20 t 21 t 22 t 23 Propagation Delay from Rising Edge of CLK to DVALID LOW Propagation Delay from DXMIT LOW to DVALID HIGH Setup Time from DCLK LOW TO DXMIT LOW Propagation Delay from DXMIT LOW to Valid DOUT Hold Time that DOUT is Valid After Falling Edge of DCLK Propagation Delay from DXMIT HIGH to DOUT Disabled Propagation Delay from Falling Edge of DCLK to Valid DOUT Propagation Delay from Falling Edge of DCLK to Valid DOUT 30 30 t22A(1) t22B(2) TYP MAX 20 30 5 30 25 30 UNITS ns ns ns ns ns ns ns ns NOTES: (1) Applies to DDC112UK, YK only, with a maximum load of one DDC112UK, YK DIN (4pF typical) with an additional load of (5pF 100kΩ). (2) Applies to DDC112U, Y only, with a maximum load of one DDC112U,Y DIN (4pF typical) with an additional load of (5pF 100kΩ). TABLE IX. Timing for the DDC112 Data Retrieval. DDC112 SBAS085B www.ti.com 21 CLK t18 t26 DVALID t14 DXMIT t20 DCLK(1) t22 t24 t25 DIN t22A, t22B t21 DOUT Output Disabled t23 Input A Bit 1 Input E Bit 20 Input F Bit 1 Input F Bit 20 MSB LSB MSB LSB Output Disabled Output Enabled NOTE: (1) Disable DCLK (preferably LOW) when DXMIT is HIGH. FIGURE 23. Timing Diagram When Using the DIN Function of the DDC112. CLK = 10MHz SYMBOL DESCRIPTION MIN TYP CLK = 15MHz MAX MIN TYP MAX UNITS t24 Set-Up Time From DIN to Rising Edge of DCLK 10 5 t25 Hold Time For DIN After Rising Edge of DCLK 10 10 ns ns t26 Hold Time for DXMIT HIGH Before Falling Edge of DVALID 2 1.33 µs TABLE X. Timing for the DDC112 Data Retrieval Using DIN. RETRIEVAL BEFORE CONV TOGGLES (CONTINUOUS MODE) RETRIEVAL AFTER CONV TOGGLES (CONTINUOUS MODE) This is the most straightforward method. Data retrieval begins soon after DVALID goes LOW and finishes before CONV toggles, see Figure 24. For best performance, data retrieval must stop t28 before CONV toggles. This method is the most appropriate for longer integration times. The maximum time available for readback is TINT – t27 – t28. For DCLK and CLK = 10MHz, the maximum number of DDC112s that can be daisy-chained together is: For shorter integration times, more time is available if data retrieval begins after CONV toggles and ends before the new data is ready. Data retrieval must wait t29 after CONV toggles before beginning. Figure 25 shows an example of this. The maximum time available for retrieval is t27 – t29 – t26 (421.2µs – 10µs – 2µs for CLK = 10MHz), regardless of TINT. The maximum number of DDC112s that can be daisychained together is: TINT – 431.2µs 40τ DCLK 409.2µs 40τ DCLK Where τDCLK is the period of the data clock. For example, if TINT = 1000µs and DCLK = 10MHz, the maximum number of DDC112s is: For DCLK = 10MHz, the maximum number of DDC112s is 102. 1000µs – 431.2µs = 142.2 → 142 DDC112s (40)(100ns) 22 DDC112 www.ti.com SBAS085B CONV TINT TINT DVALID t27 t28 DXMIT DCLK ••• DOUT ••• ••• ••• Side B Data Side A Data CLK = 10MHz SYMBOL DESCRIPTION MIN t27 Cont Mode Data Ready t28 Data Retrieval Shutdown Before Edge of CONV TYP CLK = 15MHz MAX MIN 421.2 TYP MAX µs 280.8 10 UNITS µs 10 FIGURE 24. Readback Before CONV Toggles. TINT CONV TINT TINT DVALID t27 t29 t26 DXMIT DCLK DOUT ••• ••• ••• ••• ••• ••• Side A Data Side B Data Side A Data CLK = 10MHz SYMBOL DESCRIPTION MIN t26 Hold Time for DXMIT HIGH Before Falling Edge of DVALID 2 t27 Cont Mode Data Ready t29 Data Retrieval Start-Up After Edge of CONV TYP CLK = 15MHz MAX MIN 280.8 10 MAX UNITS µs 1.33 421.2 10 TYP µs µs FIGURE 25. Readback After CONV Toggles. DDC112 SBAS085B www.ti.com 23 RETRIEVAL BEFORE AND AFTER CONV TOGGLES (CONTINUOUS MODE) (available for download at www.ti.com), DVALID goes LOW in time t30 after the first integration completes. If TINT is shorter than this time, all of t31 is available to retrieve data before the other side’s data is ready. For TINT > t30, the first integration’s data is ready before the second integration completes. Data retrieval must be delayed until the second integration completes leaving less time available for retrieval. The time available is t31 – (TINT – t30). The second integration’s data must be retrieved before the next round of integrations begin. This time is highly dependent on the pattern used to generate CONV. As with the continuous mode, data retrieval must halt before and after CONV toggles (t28 and t29) and be completed before new data is ready (t26). For the absolute maximum time for data retrieval, data can be retrieved before and after CONV toggles. Nearly all of TINT is available for data retrieval. Figure 26 illustrates how this is done by combining the two previous methods. You must pause the retrieval during CONV toggling to prevent digital noise, as discussed previously, and finish before the next data is ready. The maximum number of DDC112s that can be daisy-chained together is: TINT – 20µs – 2µs 40τ DCLK For TINT = 500µs and DCLK = 10MHz, the maximum number of DDC112s is 119. POWER-UP SEQUENCING Prior to power-up, all digital and analog input pins must be LOW. At the time of power-up, these signal inputs can be biased to a voltage other than 0V, however, they should never exceed AVDD or DVDD. The level of CONV at powerup is used to determine which side (A or B) will be integrated first. Before integrations can begin though, CONV must toggle; see Figure 28. RETRIEVAL: NONCONTINUOUS MODE Retrieving in noncontinuous mode is slightly different as compared with the continuous mode. As shown in Figure 27 and described in detail in Application Bulletin SBAA024 CONV TINT TINT TINT t29 DVALID t26 t28 DXMIT DCLK ••• ••• ••• ••• ••• ••• DOUT ••• ••• ••• ••• ••• ••• Side B Data Side A Data CLK = 10MHz TYP CLK = 15MHz SYMBOL DESCRIPTION MIN t26 Hold Time for DXMIT HIGH Before Falling Edge of DVALID 2 MAX MIN t28 Data Retrieval Shutdown Before Edge of CONV 10 10 µs t29 Data Retrieval Start-Up After dge of CONV 10 10 µs 1.33 TYP MAX UNITS µs FIGURE 26. Readback Before and After CONV Toggles. 24 DDC112 www.ti.com SBAS085B CONV TINT TINT TINT TINT DVALID t30 t31 DXMIT ••• DCLK ••• ••• ••• Side A Data Side B Data DOUT CLK = 10MHz SYMBOL DESCRIPTION t30 t31 1st Ncont Mode Data Ready (see SBAA024) 2nd Ncont Mode Data Ready (see SBAA024) MIN TYP CLK = 15MHz MAX MIN 421.1 ±0.3 454.8 TYP MAX UNITS µs µs 280.8 303.2 FIGURE 27. Readback in Noncontinuous Mode. Release State Power-Up Initialization CONV (HIGH at power-up) t32 Start Integration t33 CONV (LOW at power-up) Integrate Side A Integrate Side B Power Supplies FIGURE 28. Timing Diagram at Power-Up of the DDC112. SYMBOL DESCRIPTION MIN t32 t33 Power-On Initialization Period From Release Edge to Integration Start 50 50 TYP MAX UNITS µs µs TABLE XI. Timing for the DDC112 Power-Up Sequence. LAYOUT Power Supplies and Grounding Both AVDD and DVDD should be as quiet as possible. It is particularly important to eliminate noise from AVDD that is non-synchronous with the DDC112 operation. Figure 29 illustrates two acceptable ways to supply power to the DDC112. The first case shows two separate +5V supplies for AVDD and DVDD. In this case, each +5V supply of the DDC112 should be bypassed with 10µF solid tantalum capacitors and 0.1µF ceramic capacitors. The second case shows the DVDD power supply derived from the AVDD supply with a < 10Ω isolation resistor. In both cases, the 0.1µF capacitors should be placed as close to the DDC112 package as possible. Shielding Analog Signal Paths As with any precision circuit, careful printed circuit layout will ensure the best performance. It is essential to make short, direct interconnections and avoid stray wiring capacitance— particularly at the analog input pins. Digital signals should be kept as far from the analog input signals as possible on the PC board. DDC112 SBAS085B www.ti.com 25 Input shielding practices should be taken into consideration when designing the circuit layout for the DDC112. The inputs to the DDC112 are high impedance and extremely sensitive to extraneous noise. Leakage currents between the PCB traces can exceed the input bias current of the DDC112 if shielding is not implemented. Figure 30 illustrates an acceptable approach to this problem. A PC ground plane is placed around the inputs of the DDC112. This shield helps minimize coupled noise into the input pins. Additionally, the pins that are used for the external integration capacitors should be guarded by a ground plane when the external capacitors are used. The approach above reduces leakage affects by surrounding these sensitive pins with a low impedance analog ground. Leakage currents from other portions of the circuit will flow harmlessly to the low impedance analog ground rather than into the analog input stage of the DDC112. IN1 IN2 Analog Ground V S+ AVDD 10µF Analog Ground 0.1µF DDC112 VDD+ DVDD 10µF 0.1µF Shield external caps when used Separate +5V Supplies Analog Power V S+ AVDD 10µF 0.1µF DDC112 < 10Ω DVDD 0.1µF 1 28 2 27 3 26 4 25 5 24 6 23 7 DDC112U Analog Ground Shield external caps when used 22 8 21 9 20 10 19 11 18 12 17 13 16 14 15 Analog Ground One +5V Supply Digital I/O and Digital Power FIGURE 29. Power Supply Connection Options. 26 Digital I/O and Digital Power FIGURE 30. Recommended Shield for DDC112U Layout Design. DDC112 www.ti.com SBAS085B PACKAGE OPTION ADDENDUM www.ti.com 20-Aug-2021 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) DDC112U ACTIVE SOIC DW 28 20 RoHS & Green NIPDAU Level-1-260C-UNLIM -40 to 85 DDC112U DDC112U/1K ACTIVE SOIC DW 28 1000 RoHS & Green NIPDAU Level-1-260C-UNLIM -40 to 85 DDC112U DDC112UG4 ACTIVE SOIC DW 28 20 RoHS & Green NIPDAU Level-1-260C-UNLIM -40 to 85 DDC112U DDC112UK ACTIVE SOIC DW 28 20 RoHS & Green NIPDAU Level-1-260C-UNLIM 0 to 70 DDC112Y/250 ACTIVE TQFP PJT 32 250 RoHS & Green NIPDAU Level-2-260C-1 YEAR -40 to 85 DDC112Y DDC112Y/2K ACTIVE TQFP PJT 32 2000 RoHS & Green NIPDAU Level-2-260C-1 YEAR -40 to 85 DDC112Y DDC112YK/250 ACTIVE TQFP PJT 32 250 RoHS & Green NIPDAU Level-2-260C-1 YEAR 0 to 70 DDC112YK DDC112YK/250G4 ACTIVE TQFP PJT 32 250 RoHS & Green NIPDAU Level-2-260C-1 YEAR 0 to 70 DDC112YK DDC112UK (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