12-Bit Low Power Sigma-Delta ADC AD7170 FUNCTIONAL BLOCK DIAGRAM Output data rate: 125 Hz Pin-programmable power-down and reset Status function Internal clock oscillator Current: 135 μA Power supply: 2.7 V to 5.25 V –40°C to +105°C temperature range Package: 10-lead 3 mm x 3 mm LFCSP INTERFACE 2-wire serial (read-only device) SPI compatible Schmitt trigger on SCLK APPLICATIONS GND VDD AIN(+) REFIN(+) REFIN(–) DOUT/RDY 12-BIT Σ-Δ ADC AIN(–) AD7170 SCLK INTERNAL CLOCK PDRST 08416-001 FEATURES Figure 1. Table 1. VREF = VDD 5V 3V RMS Noise 11.5 μV 6.9 μV P-P Noise 76 μV 45 μV P-P Resolution 12 bits 12 bits ENOB 12 bits 12 bits Pressure measurement Industrial process control Portable instrumentation GENERAL DESCRIPTION The AD7170 is a very low power 12-bit analog-to-digital converter (ADC). It contains a precision 12-bit sigma-delta (Σ-Δ) ADC and an on-chip oscillator. Consuming only 135 μA, the AD7170 is particularly suitable for portable or battery operated products where very low power is a requirement. The AD7170 also has a power-down mode in which the device consumes 5 μA, thus increasing the battery life of the product. The output data rate of the AD7170 is 125 Hz, whereas the settling time is 24 ms. The AD7170 has one differential input and a gain of 1. This is useful in applications where the user needs to use an external amplifier to implement system-specific filtering or gain requirements. For ease-of-use, all the features of the AD7170 are controlled by dedicated pins. Each time a data read occurs, eight status bits are appended to the 12-bit conversion. These status bits contain a pattern sequence that can be used to confirm the validity of the serial transfer. The AD7171 is a 16-bit version of the AD7170. It has the same feature set as the AD7170 and is pin-for-pin compatible. The AD7170 operates with a power supply from 2.7 V to 5.25 V. It is available in a 10-lead LFCSP package. Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2009 Analog Devices, Inc. All rights reserved. AD7170 TABLE OF CONTENTS Features .............................................................................................. 1 Overview ..................................................................................... 10 Interface ............................................................................................. 1 Filter, Data Rate, and Settling Time ......................................... 10 Applications ....................................................................................... 1 Gain .............................................................................................. 10 Functional Block Diagram .............................................................. 1 Power-Down/Reset(PDRST) .................................................... 10 General Description ......................................................................... 1 Analog Input Channel ............................................................... 10 Revision History ............................................................................... 2 Bipolar Configuration................................................................ 10 Specifications..................................................................................... 3 Data Output Coding .................................................................. 11 Timing Characteristics..................................................................... 5 Reference ..................................................................................... 11 Timing Diagrams.......................................................................... 5 Digital Interface .......................................................................... 11 Absolute Maximum Ratings............................................................ 6 Grounding and Layout .............................................................. 12 Thermal Resistance ...................................................................... 6 Applications Information .............................................................. 13 ESD Caution .................................................................................. 6 Temperature System ................................................................... 13 Pin Configuration and Function Descriptions ............................. 7 Signal Conditioning Circuit ........................................................ 13 Typical Performance Characteristics ............................................. 8 Outline Dimensions ....................................................................... 14 Output Noise and Resolution Specifications ................................ 9 Ordering Guide .......................................................................... 14 ADC Circuit Information .............................................................. 10 REVISION HISTORY 10/09—Revision 0: Initial Version Rev. 0 | Page 2 of 16 AD7170 SPECIFICATIONS VDD = 2.7 V to 5.25 V, VREF = VDD, GND = 0 V, all specifications TMIN to TMAX, unless otherwise noted. Table 1. Parameter ADC CHANNEL Output Data Rate (fADC) No Missing Codes 2 Noise Free Resolution Resolution Peak-to-Peak (p-p) Effective Resolution (ENOB) RMS Noise Integral Nonlinearity Offset Error Offset Error Drift vs. Temperature Full-Scale Error Gain Drift vs. Temperature Power Supply Rejection ANALOG INPUTS Differential Input Voltage Range Absolute AINx Voltage Limits2 Average Input Current2 Average Input Current Drift DC Common-Mode Rejection REFERENCE External REFIN Voltage Reference Voltage Range2 Absolute REFIN Voltage Limits2 Average Reference Input Current Average Reference Input Current Drift DC Common-Mode Rejection INTERNAL CLOCK Frequency2 LOGIC INPUTS Min AD7170B 1 Typ 125 12 12 12 12 See Table 6 ±0.1 ±200 ±250 ±0.015 ±0.07 85 ±VREF SCLK (Schmitt-Triggered Input)2 Hysteresis Input Currents Input Capacitance Unit Test Conditions/Comments Hz Bits Bits Bits Bits μV LSB μV nV/°C % of FS LSB/°C dB Settling time = 3/fADC ±400 V V nA/V ±60 90 pA/V/°C dB GND − 0.03 VDD + 0.03 VDD 400 ±0.15 V V V nA/V nA/V/°C 110 dB 0.5 GND − 0.03 VDD VDD + 0.03 64 − 5% SCLK, PDRST2 Input Low Voltage, VINL Input High Voltage, VINH Max VINx = 0 V, VREF = VDD VINx = 0 V, VREF = VDD VINx = 0 V, VREF = VDD VINx = 0 V, VREF = VDD VINx = 1 V VREF = REFIN(+) − REFIN(−) Input current varies with input voltage VINx = 1 V REFIN = REFIN(+) − REFIN(−) 64 + 5% kHz 0.4 0.8 V V V V VDD = 3 V VDD = 5 V VDD = 3 V VDD = 5 V mV mV μA pF VDD = 3 V VDD = 5 V VIN = VDD or GND All digital inputs 1.8 2.4 100 140 ±2 5 Rev. 0 | Page 3 of 16 AD7170 Parameter LOGIC OUTPUT (DOUT/RDY) Output High Voltage, VOH2 Min AD7170B 1 Typ IDD (Power-Down/Reset Mode) Unit Test Conditions/Comments 0.4 0.4 V V V V μA pF VDD = 3 V, ISOURCE = 100 μA VDD = 5 V, ISOURCE = 200 μA VDD = 3 V, ISINK = 100 μA VDD = 5 V, ISINK = 1.6 mA 5.25 V 130 150 μA μA μA VDD − 0.6 4 Output Low Voltage, VOL2 Floating-State Leakage Current Floating-State Output Capacitance Data Output Coding POWER REQUIREMENTS 3 Power Supply Voltage VDD – GND Power Supply Currents IDD Current Max ±2 5 Offset binary 2.7 110 135 5 1 Temperature range is –40°C to +105°C. Specification is not production tested but is supported by characterization data at initial product release. 3 Digital inputs equal to VDD or GND. 2 Rev. 0 | Page 4 of 16 VDD = 3 V VDD = 5 V AD7170 TIMING CHARACTERISTICS VDD = 2.7 V to 5.25 V,, GND = 0 V, Input Logic 0 = 0 V, Input Logic 1 = VDD, unless otherwise noted. Table 2. Parameter 1, 2 READ t1 t2 t3 3 Limit at TMIN, TMAX Unit Conditions/Comments t4 100 100 0 60 80 10 ns min ns min ns min ns max ns max ns min SCLK high pulse width SCLK low pulse width SCLK active edge to data valid delay 4 VDD = 4.75 V to 5.25 V VDD = 2.7 V to 3.6 V SCLK inactive edge to DOUT/RDY high RESET t5 t6 100 25 ns min ms typ PDRST low pulse width PDRST high to data valid delay 1 Sample tested during initial release to ensure compliance. All input signals are specified with tR = tF = 5 ns (10% to 90% of VDD) and timed from a voltage level of 1.6 V. See Figure 3. 3 These numbers are measured with the load circuit shown in Figure 2 and defined as the time required for the output to cross the VOL or VOH limits. 4 SCLK active edge is the falling edge of SCLK. 2 ISINK (1.6mA WITH VDD = 5V, 100µA WITH VDD = 3V) TO OUTPUT PIN 1.6V ISOURCE (200µA WITH VDD = 5V, 100µA WITH VDD = 3V) 08416-002 50pF Figure 2. Load Circuit for Timing Characterization TIMING DIAGRAMS MSB DOUT/RDY (O) LSB t4 t3 t1 SCLK (I) 08416-003 t2 I = INPUT, O = OUTPUT Figure 3. Read Cycle Timing Diagram PDRST (I) t5 t6 I = INPUT, O = OUTPUT Figure 4. Resetting the AD7170 Rev. 0 | Page 5 of 16 08416-004 DOUT/RDY (O) AD7170 ABSOLUTE MAXIMUM RATINGS TA = 25°C, unless otherwise noted. THERMAL RESISTANCE Table 3. θJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. Parameter VDD to GND Analog Input Voltage to GND Reference Input Voltage to GND Digital Input Voltage to GND Digital Output Voltage to GND VINx/Digital Input Current Operating Temperature Range Storage Temperature Range Maximum Junction Temperature Lead Temperature, Soldering Reflow Rating −0.3 V to +7 V −0.3 V to VDD + 0.3 V −0.3 V to VDD + 0.3 V −0.3 V to VDD + 0.3 V −0.3 V to VDD + 0.3 V 10 mA −40°C to +105°C −65°C to +150°C 150°C Table 4. Package Type LFCSP ESD CAUTION 260°C Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Rev. 0 | Page 6 of 16 θJA 48.7 θJC 2.96 Unit °C/W AD7170 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SCLK 1 DOUT/RDY 2 AD7170 9 AIN(+) 3 8 VDD AIN(–) 4 TOP VIEW (Not to Scale) 7 GND REFIN(+) 5 6 REFIN(–) 10 NC NOTES 1. NC = NO CONNECT. 2. CONNECT EXPOSED PAD TO GROUND. 08416-005 PDRST Figure 5. Pin Configuration Table 5. Pin Function Descriptions Pin No. 1 Mnemonic SCLK 2 DOUT/RDY 3 4 5 AIN(+) AIN(−) REFIN(+) 6 7 8 9 REFIN(−) GND VDD PDRST 10 NC EPAD Description Serial Clock Input. This serial clock input is for data transfers from the ADC. The SCLK has a Schmitt-triggered input. The serial clock can be continuous with all data transmitted in a constant train of pulses. Alternatively, it can be a noncontinuous clock with the information being transmitted from the ADC in smaller batches of data. Serial Data Output/Data Ready Output. DOUT/RDY serves a dual purpose. DOUT/RDY operates as a data ready pin, going low to indicate the completion of a conversion. In addition, it functions as a serial data output pin to access the data register of the ADC. Eight status bits accompany each data read. See Figure 13 for further details. The DOUT/RDY falling edge can be used as an interrupt to a processor, indicating that new data is available. If the data is not read after the conversion, the pin goes high before the next update occurs. Analog Input. AIN(+) is the positive terminal of the differential analog input pair AIN(+)/AIN(−). Analog Input. AIN(−) is the negative terminal of the differential analog input pair AIN(+)/AIN(−). Positive Reference Input. An external reference can be applied between REFIN(+) and REFIN(–). The nominal reference voltage (REFIN(+) – REFIN(−)) is 5 V, but the part can function with a reference of 0.5 V to VDD. Negative Reference Input. Ground Reference Point. Supply Voltage, 2.7 V to 5.25 V. Power-Down/Reset. When this pin is low, the ADC is placed in power-down mode. All the logic on the chip is reset, and the DOUT/RDY pin is tristated. When PDRST is high, the ADC is taken out of power-down mode. The on-chip clock powers up and settles, and the ADC continuously converts. The internal clock requires 1 ms approximately to power up. This pin should be connected to GND for correct operation. Connect the exposed pad to ground. Rev. 0 | Page 7 of 16 AD7170 TYPICAL PERFORMANCE CHARACTERISTICS 10 0.025 VREF = VDD = 5V 0.023 8 GAIN ERROR (%) 6 4 2 0.019 0.017 –10 20 50 80 110 TEMPERATURE (°C) 0.015 –40 08416-015 0 –40 0.021 –10 20 50 80 110 80 110 TEMPERATURE (°C) 08416-008 RMS NOISE (µV) VREF = VDD = 3V Figure 9. Gain Error vs. Temperature Figure 6. AD7170 RMS Noise vs. Temperature 140 0.020 0.015 132 VREF = VDD = 5V 0.005 IDD (µA) INL (LSB) 0.010 0 124 116 –0.005 VREF = VDD = 3V 108 –2 –1 0 1 2 3 VIN (V) 100 –40 08416-006 –0.015 –3 –10 20 50 TEMPERATURE (°C) Figure 7. Integral Nonlinearity (VREF = VDD) 08416-016 –0.010 Figure 10. Power Supply Current vs. Temperature 180 4.5 4.0 3.5 160 IDD (µA) OFFSET (µV) 3.0 140 VREF = VDD = 5V 2.5 2.0 1.5 1.0 –10 20 50 TEMPERATURE (°C) 80 110 08416-007 120 –40 Figure 8. Offset vs. Temperature 0 –40 –10 20 50 80 TEMPERATURE (°C) Figure 11. Power-Down Current vs. Temperature Rev. 0 | Page 8 of 16 110 08416-017 VREF = VDD = 3V 0.5 AD7170 OUTPUT NOISE AND RESOLUTION SPECIFICATIONS Table 6 shows the rms noise of the AD7170. The numbers given are for a 5 V and a 3 V reference. These numbers are typical and are generated with a differential input voltage of 0 V. The corresponding p-p resolution is also listed, along with the effective resolution (ENOB). It is important to note that the effective resolution is calculated using the rms noise, whereas the p-p resolution is based on the p-p noise. The p-p resolution represents the resolution for which there is no code flicker. These numbers are typical. The noise-free bits, or p-p resolution, are defined as Noise-Free Bits = ln (FSR/Peak-to-Peak Noise)/ln(2) where FSR is the full-scale range and is equal to 2 × VREF/gain. Table 6. RMS Noise and Resolution of the AD7170 VREF = VDD 5V 3V The effective number of bits (ENOB) is defined as ENOB = ln (FSR/RMS noise)/ln(2) Rev. 0 | Page 9 of 16 RMS Noise 11.5 μV 6.9 μV P-P Noise 76 μV 45 μV P-P Resolution 12 bits 12 bits ENOB 12 bits 12 bits AD7170 ADC CIRCUIT INFORMATION OVERVIEW POWER-DOWN/RESET(PDRST) The AD7170 is a low power ADC that incorporates a precision 12-bit Σ-Δ modulator and an on-chip digital filter intended for measuring wide dynamic range, low frequency signals. The device has an internal clock and one differential input. It operates with an output data rate of 125 Hz and has a gain of 1. A 2-wire interface simplifies data retrieval from the AD7170. The PDRST pin functions as a power-down pin and a reset pin. When PDRST is taken low, the AD7170 is powered down. The entire ADC is powered down (including the on-chip clock), and the DOUT/RDY pin is tristated. The circuitry and serial interface are also reset. This resets the logic, the digital filter, and the analog modulator. PDRST must be held low for 100 ns minimum to initiate the reset function (see Figure 4). FILTER, DATA RATE, AND SETTLING TIME The AD7170 uses a sinc3 filter. The output data rate is set to 125 Hz; thus, valid conversions are available every 1/125 = 8 ms. If a reset occurs, then the user must allow the complete settling time for the first conversion after the reset. The settling time is equal to 24 ms. Subsequent conversions are available at 125 Hz. When a step change occurs on the analog input, the AD7170 requires several conversion cycles to generate a valid conversion. If the step change occurs synchronous to the conversion period, then the settling time of the AD7170 must be allowed to generate a valid conversion. If the step change occurs asynchronous to the end of a conversion, then an extra conversion must be allowed to generate a valid conversion. The data register is updated with all the conversions but, for an accurate result, the user must allow the required time. Figure 12 shows the filter response of the filter. The only external filtering required on the analog inputs is a simple R-C filter to provide rejection at multiples of the master clock. A 1 KΩ resistor in series with each analog input, a 0.01 μF capacitor from each input to GND, and a 0.1 μF capacitor from AIN(+) to AIN(−) are recommended. 0 –10 When PDRST is taken high, the AD7170 is taken out of powerdown mode. When the on-chip clock has powered up (1 ms, typically), the modulator then begins sampling the analog input. The DOUT/RDY pin becomes active, going high until a valid conversion is available. A reset is automatically performed on power-up. ANALOG INPUT CHANNEL The AD7170 has one differential analog input channel that is connected to the modulator; that is, the input is unbuffered. Note that this unbuffered input path provides a dynamic load to the driving source. Therefore, resistor/capacitor combinations on the input pins can cause dc gain errors, depending on the output impedance of the source that is driving the ADC input. Table 7 shows the allowable external resistance/capacitance values such that no gain error at the 12-bit level is introduced. Table 7. External R-C Combination for No Gain Error C (pF) 50 100 500 1000 5000 R (Ω) 9k 6k 1.5 k 900 200 –20 The absolute input voltage range is restricted to a range between GND − 30 mV and VDD + 30 mV. Care must be taken in setting up the common-mode voltage to avoid exceeding these limits. Otherwise, there is degradation in linearity and noise performance. FILTER GAIN (dB) –30 –40 –50 –60 BIPOLAR CONFIGURATION –70 The AD7170 accepts a bipolar input range. A bipolar input range does not imply that the part can tolerate negative voltages with respect to system GND. Signals on the AIN(+) input are referenced to the voltage on the AIN(−) input. For example, if AIN(−) is 2.5 V, the analog input range on the AIN(+) input is 0 V to 5 V when a 2.5 V reference is used. –80 0 125 250 375 500 INPUT SIGNAL FREQUENCY (Hz) 625 750 08416-011 –90 –100 Figure 12. Filter Response GAIN The AD7170 has a gain of 1. The acceptable analog input range is +VREF. Therefore, with VREF = 5 V, the input range is +5 V. Rev. 0 | Page 10 of 16 AD7170 DATA OUTPUT CODING The AD7170 uses offset binary coding. Therefore, a negative full-scale voltage results in a code of 000...000, a zero differential input voltage results in a code of 100...000, and a positive fullscale input voltage results in a code of 111...111. The output code for any analog input voltage can be represented as Code = 2N – 1 × [(VINx/VREF) + 1] DOUT/RDY pin is dual purpose: it functions as a data ready pin and as a data out pin. DOUT/RDY goes low when a new data-word is available in the output register. A 24-bit word is placed on the DOUT/RDY pin when sufficient SCLK pulses are applied. This consists of a 12-bit conversion result followed by four 0s to generate a 16-bit word. Following this, eight status bits are output. Table 8 shows the functions of the status bits. RDY: ready bit. This bit is set low to indicate that a conversion is available. where: VINx is the analog input voltage. N = 12 for the AD7170. 0: This bit is set to 0. REFERENCE The AD7170 has a fully differential input capability for the channel. The common-mode range for these differential inputs is GND to VDD. The reference input is unbuffered; therefore, excessive R-C source impedances introduce gain errors. The reference voltage REFIN (REFIN(+) − REFIN(−)) is VDD nominal, but the AD7170 is functional with reference voltages of 0.5 V to VDD. In applications where the excitation (voltage or current) for the transducer on the analog input also drives the reference voltage for the part, the effect of the low frequency noise in the excitation source is removed because the application is ratiometric. If the AD7170 is used in a nonratiometric application, a low noise reference should be used. Recommended 2.5 V reference voltage sources for the AD7170 include the ADR381 and ADR391, which are low noise, low power references. Also note that the reference inputs provide a high impedance, dynamic load. Because the input impedance of each reference input is dynamic, resistor/capacitor combinations on these inputs can cause dc gain errors, depending on the output impedance of the source that is driving the reference inputs. Reference voltage sources such as those recommended above (the ADR391, for example) typically have low output impedances and are, therefore, tolerant to decoupling capacitors on REFIN(+) without introducing gain errors in the system. Deriving the reference input voltage across an external resistor means that the reference input sees a significant external source impedance. External decoupling on the REFIN(±) pins is not recommended in this type of circuit configuration. DIGITAL INTERFACE The serial interface of the AD7170 consists of two signals: SCLK and DOUT/RDY. SCLK is the serial clock input for the device, and data transfers occur with respect to the SCLK signal. The ERR: This bit is set to 1 if an error occurred during the conversion. An error occurs when the analog input is outside range. ID1, ID0: ID bits. These bits indicate the ID number for the AD7170. Bit ID1 is set to 1, and Bit ID0 is set to 0 for the AD7170. PAT2, PAT1, PAT0: status pattern bits. They are set to 101 by default. When the user reads the data from the AD7170, a pattern check can be performed. If the PAT2 to PAT0 bits are different from their default values, the serial transfer from the ADC was not performed correctly. Table 8. Status Bits RDY 0 ERR ID1 ID0 PAT2 PAT1 PAT0 DOUT/RDY is reset high when the conversion is read. If the conversion is not read, DOUT/RDY goes high prior to the data register update to indicate when not to read from the device. This ensures that a read operation is not attempted while the register is being updated. Each conversion can be read only once. The data register is updated for every conversion. So, when a conversion is complete, the serial interface is reset, and the new conversion is placed in the data register. Therefore, the user must ensure that the complete word is read before the next conversion is complete. When PDRST is low, the DOUT/RDY pin is tristated. When PDRST is taken high, the internal clock requires 1 ms, approximately, to power up. Following this, the ADC continuously converts. The first conversion requires the complete settling time (see Figure 4). DOUT/RDY goes high when PDRST is taken high and returns low only when a conversion is available. The ADC then converts continuously, subsequent conversions being available at 125 Hz. Figure 3 shows the timing for a read operation from the AD7170. Rev. 0 | Page 11 of 16 AD7170 GROUNDING AND LAYOUT Because the analog input and reference input of the ADC are differential, most of the voltages in the analog modulator are common-mode voltages. The excellent common-mode rejection of the part removes common-mode noise on these inputs. The digital filter provides rejection of broadband noise on the power supply, except at integer multiples of the modulator sampling frequency. The digital filter also removes noise from the analog and reference inputs provided that these noise sources do not saturate the analog modulator. As a result, the AD7170 is more immune to noise interference than conventional high resolution converters. However, because the noise levels from the AD7170 are so low, care must be taken with regard to grounding and layout. The printed circuit board that houses the AD7170 should be designed such that the analog and digital sections are separated and confined to certain areas of the board. A minimum etch technique is generally best for ground planes because it gives the best shielding. It is recommended that the GND pin of the AD7170 be tied to the analog ground (AGND) plane of the system. In any layout, it is important that the user pay attention to the flow of currents in the system and ensure that the return paths for all currents are as close as possible to the paths the currents took to reach their destinations. Avoid forcing digital currents to flow through the AGND sections of the layout. The ground plane of the AD7170 should be allowed to run under the AD7170 to prevent noise coupling. The power supply lines to the AD7170 should use as wide a trace as possible to provide low impedance paths and reduce the effects of glitches on the power supply line. Fast switching signals such as clocks should be shielded with digital ground to avoid radiating noise to other sections of the board, and clock signals should never be run near the analog inputs. Avoid crossover of digital and analog signals. Traces on opposite sides of the board should run at right angles to each other. This reduces the effects of feedthrough through the board. A microstrip technique is by far the best, but it is not always possible with a double-sided board. In this technique, the component side of the board is dedicated to ground planes, while signals are placed on the solder side. Good decoupling is important when using high resolution ADCs. VDD should be decoupled with 10 μF tantalum capacitors in parallel with 0.1 μF capacitors to GND, with the system’s analog ground to digital ground (DGND) connection being close to the AD7170. To achieve the best results from these decoupling components, they should be placed as close as possible to the device, ideally right up against the device. All logic chips should be decoupled with 0.1 μF ceramic capacitors to DGND. Rev. 0 | Page 12 of 16 AD7170 APPLICATIONS INFORMATION TEMPERATURE SYSTEM Figure 13 shows the AD7170 used in a temperature measurement system. The thermistor is connected in series with a precision resistor, RREF, the precision resistor being used to generate the reference voltage. The value of RREF is equal to the maximum resistance produced by the thermistor. The complete dynamic range of the ADC is then used, resulting in optimum performance. SIGNAL CONDITIONING CIRCUIT Figure 14 shows the AD7170 used in a signal conditioning circuit for a single-ended analog input. In a low side shunt current monitor, a low resistance shunt resistor converts the current to voltage. The resulting voltage is amplified and applied to the AD7170. 32kΩ 1kΩ AIN(+) ANALOG INPUT AD8631 AD5041 VDD 1µF AIN(–) REFIN(+) REFIN(–) GND VDD 12-BIT Σ-Δ ADC GND VDD DOUT/RDY 12-BIT Σ-Δ ADC AIN(–) SCLK AD7170 INTERNAL CLOCK PDRST REFIN(–) 08416-013 REFIN(+) RREF Figure 13. Temperature System Using the AD7170 Rev. 0 | Page 13 of 16 SCLK INTERNAL CLOCK AD7170 Figure 14. Signal Conditioning Circuit AIN(+) DOUT/RDY 08416-018 The AD7170 provides a low cost, high resolution analog-todigital function. Because the analog-to-digital function is provided by a Σ-Δ architecture, the part is more immune to noisy environments, making it ideal for use in sensor measurement and industrial and process-control applications. AD7170 OUTLINE DIMENSIONS 0.30 0.23 0.18 3.00 BSC SQ 0.50 BSC 10 6 PIN 1 INDEX AREA 0.50 0.40 0.30 5 TOP VIEW SEATING PLANE 0.80 MAX 0.55 NOM 1 2.48 2.38 2.23 PIN 1 INDICATOR (R 0.20) 0.05 MAX 0.02 NOM 0.20 REF *FOR PROPER CONNECTION OF THE EXPOSED PAD PLEASE REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. 031208-B 0.80 0.75 0.70 1.74 1.64 1.49 *EXPOSED PAD (BOTTOM VIEW) Figure 15. 10-Lead Lead Frame Chip Scale Package [LFCSP_WD] 3 mm × 3 mm Body, Very Very Thin, Dual Lead (CP-10-9) Dimensions shown in millimeters ORDERING GUIDE Model AD7170BCPZ- REEL7 1 AD7170BCPZ-500RL71 1 Temperature Range –40°C to +105°C –40°C to +105°C Package Description 10-Lead Lead Frame Chip Scale Package [LFCSP_WD] 10-Lead Lead Frame Chip Scale Package [LFCSP_WD] Z = RoHS Compliant Part. Rev. 0 | Page 14 of 16 Package Option CP-10-9 CP-10-9 Branding C6F C6F AD7170 NOTES Rev. 0 | Page 15 of 16 AD7170 NOTES ©2009 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D08416-0-10/09(0) Rev. 0 | Page 16 of 16