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| ADCV0831 8 Bit Serial I/O Low Voltage Low Power ADC with Auto Shutdown in a SOT Package August 1998 ADCV0831 8 Bit Serial I/O Low Voltage Low Power ADC with Auto Shutdown in a SOT Package General Description The ADCV0831 is a low voltage 8-bit successive approximation A/D converter with serial I/O. The I/O is a 3-wire serial interface compatible with NSC's MICROWIRE TM & Motorola's SPI standards. It easily interfaces with standard shift registers or microprocessors. Low voltage and auto shutdown features make the ADCV0831 ideal for portable battery operated electronic devices. The main benefits are most apparent in small portable electronic devices. The tiny A/D converter can be placed anywhere on the board. Features Tiny 6-pin SOT 23 package Serial digital data link requires few I/O pins Auto Shutdown 0V to 3V analog input range with single 3V power supply n TTL/CMOS input/output compatible n n n n Key Specifications (For 3V supply, typical, unless otherwise noted.) n Resolution: 8 bits n Conversion time (fC = 700 kHz): 16s n Low power dissipation: 720W n Single supply: 2.7V to 5VDC n Linearity error: 1.5LSB over temperature n No missing codes over temperature n Shutdown supply current 10nA Applications n n n n n n Digitizing automotive sensors Process control monitoring Remote sensing in noisy environments Instrumentation Test systems Embedded diagnostics Ordering Information Temperature Range (0C Tj +70C) ADCV0831M6X ADCV0831M6 Package MA06A MA06A Supplied As 3k Units Tape and Reel 250 Units Tape and Reel Connection Diagram ADCV0831 DS100104-1 TRI-STATE (R) is a registered trademark of National Semiconductor Corporation. COPSTM microcontrollers and MICROWIRETM are trademarks of National Semiconductor Corporation. (c) 1998 National Semiconductor Corporation DS100104 www.national.com Absolute Maximum Ratings (Notes 1, 3) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (VCC) Voltage at Inputs and Outputs Input Current at Any Pin (Note 4) Package Input Current (Note 4) Power Dissipation at TA = 25C (Note 5) ESD Susceptibility (Note 6) 5.5V -0.3V to VCC + 0.3V 5 mA 20 mA 470 mW 2000V Soldering Temperature (Note 7) Convection Infrared (15 sec.) Wave Soldering (4 sec.) (Note 7) Storage Temperature Thermal Resistance ( JA) 215C 260C -65C to +150C 265C/W Operating Ratings (Notes 2, 3) Temperature Range Supply Voltage (VCC) 0C Tj 70C 2.7VDC to 5V Electrical Characteristics The following specifications apply for VCC = 3VDC, and fCLK = 500 kHz unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to T MAX; all other limits TA = T J = 25C. Symbol Parameter Integral Linearity Error Offset Error Full Scale Error Resolution VIN VIN(1) VIN(0) IIN(1) IIN(0) VOUT(1) VOUT(0) IOUT ISOURCE ISINK ICC Analog Input Voltage Logical "1" Input Voltage Logical "0" Input Voltage Logical "1" Input Current Logical "0" Input Current Logical "1" Output Voltage Logical "0" Output Voltage TRI-STATE (R) Output Current Output Source Current Output Sink Current Supply Current VCC = 3V VCC = 3V VIN = 3V VIN = 0V Iout = -360A Iout = 1.6 mA VOUT = 0V VOUT = 0V VOUT = 3V CS = HIGH CS = LOW Conditions Typical (Note 8) Limits (Note 9) Units LSB (max) LSB (max) LSB (max) Bits (min) V (max) V (min) V (min) V (max) A (max) A (max) V (min) V (max) A (max) mA (min) mA (min) A (max) A (max) 0.6 0.1 0.3 1.5 1.5 1.5 8 (VCC + 0.05) (GND - 0.05) 2.0 0.8 0.01 0.01 2.8 0.24 0.01 2.6 7.4 0.01 200 1 -1 2.4 0.4 3.0 1.0 3.0 30 400 AC Electrical Characteristics The following specifications apply for VCC = +3 VDC, and tr = t f = 20 ns unless otherwise specified. Boldface limits apply for TA = TJ = T MIN to TMAX; all other limits TA = TJ = 25C. Symbol fCLK tSET-UP Clock Frequency 10 CS failing edge to CLK rising edge Clock Duty Cycle TC tpd t1H, t 0H Conversion Time CLK Falling Edge to Data Valid Low to High High to Low CS Rising Edge to Data Output TRI-STATE (see TRI-STATE Test Circuits) CL = 100 pF, RL = 2 k CL = 100 pF, RL = 10 k CL = 100 pF 142 70 75 50 25 40 60 11 250 200 250 ns (max) Parameter Conditions Typical (Note 8) Limits (Note 9) 700 kHz (max) kHz (min) ns % (min) % (max) Clock Periods ns (max) Units www.national.com 2 AC Electrical Characteristics Symbol CIN COUT Parameter Capacitance of Logic Inputs Capacitance of Logic Outputs (Continued) The following specifications apply for VCC = +3 VDC, and tr = t f = 20 ns unless otherwise specified. Boldface limits apply for TA = TJ = T MIN to TMAX; all other limits TA = TJ = 25C. Conditions Typical (Note 8) 5 5 Limits (Note 9) pF pF Units Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Note 2: Operating Ratings indicate conditions for which the device is functional. These ratings do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 3: All voltages are measured with respect to GND = 0 VDC, unless otherwise specified. Note 4: When the input voltage VIN at any pin exceeds the power supplies (VIN Typical Performance Characteristics The following specifications apply for VCC = 3V, unless otherwise specified Integral Linearity Error vs Supply Voltage Linearity Error vs Temperature Linearity Error vs Clock Frequency DS100104-62 DS100104-56 DS100104-55 Power Supply Current vs Temperature Output Current vs Temperature Power Supply Current vs Clock Frequency DS100104-57 DS100104-58 DS100104-61 3 www.national.com TRI-STATE Test Circuits and Waveforms DS100104-8 Timing Diagrams Data Output Timing DS100104-10 Start Conversion Timing DS100104-11 www.national.com 4 Timing Diagrams (Continued) Timing DS100104-12 5 www.national.com Functional Description The design of this converter utilizes a comparator structure with built-in sample-and-hold which provides for VIN to be converted by a successive approximation routine. The analog input voltage can range from 50mV below ground to 50mV above VCC without degrading conversion accuracy. The ADCV0831 is intended to work with a CPU which strobes data on the clock's rising edge. The ADCV0831 strobes data on the clock's falling edge so that the data output is stable when the CPU reads it in. When the Chip Select pin is high, the output is TRI-STATE and the ADCV0831 is in shutdown mode and draws less than 30 A of current. During shutdown the digital logic draws no current at CMOS logic levels, and the analog circuitry is turned off. When the Chip Select pin goes low, all the analog circuitry turns on, and the conversion process begins. 1.0 THE DIGITAL INTERFACE The most important characteristic of this converter is the serial data link with the controlling processor. Using a serial communication format offers three very significant system improvements. It allows many functions to be included in a small package, it can eliminate the transmission of low level analog signals by locating the converter right at the analog sensor, and can transmit highly noise immune digital data back to the host processor. To understand the operation of this converter it is best to refer to the Timing Diagrams and to follow a complete conversion sequence. 1. A conversion is initiated by pulling the CS (chip select) line low. This line must be held low for the entire conversion. 2. During the conversion the output of the SAR comparator indicates whether the analog input is greater than (high) or less than (low) a series of successive voltages in a resistor ladder (last 8 bits). After each comparison the comparator's output is shifted to the DO line on the falling edge of CLK. This data is the result of the conversion being shifted out (with the MSB first) and can be read by the processor immediately. 3. After 11 clock periods the conversion is completed. 4. All internal registers are cleared when the CS line is high. See Data Input Timing under Timing Diagrams. If another conversion is desired CS must make a high to low transition. 2.0 REFERENCE CONSIDERATIONS In a ratiometric system, the analog input voltage is proportional to the voltage used for the A/D reference. This voltage is the system power supply. This technique relaxes the stability requirements of the system reference as the analog input and A/D reference move together maintaining the same output code for a given input condition. Since there is no separate reference and analog supply pins, the analog side is very sensitive. The PC layout of the ADCV0831 is very critical. The ADCV0831 should be used with an analog ground plane and single-point grounding techniques. The Gnd pin should be tied directly to the ground plane. One supply bypass capacitor (0.1 F) is recommended to decouple all the digital signals on the supplies. The lead length of the capacitor should be as short as possible. 3.0 THE ANALOG INPUT The most important feature of this converter is that it can be located right at the analog signal source through just a few wires. It can communicate with a processor with a highly noise immune serial bit stream. This greatly minimizes circuitry to maintain analog signal accuracy which otherwise is most susceptible to noise pickup. However, a few words are in order with regard to the analog inputs should the input be noisy to begin with or possibly riding on a large common-mode voltage. The input has a sample and hold, therefore a capacitor (0.01 F) is needed at the input pin in order to swamp out any feedthrough signal coming from the sample and hold circuitry. The input capacitor lead length is not as critical as the supply decoupling capacitor, as long as the capacitor is large enough to swamp out any sample and hold feedthrough. Source resistance limitation is important with regard to the DC leakage currents of the input multiplexer. Bypass capacitors should not be used if the source resistance is greater than 1k. The worst-case leakage current of 1A over temperature will create a 1mV input error with a 1k source resistance. An op-amp RC active low pass filter can provide both impedance buffering and noise filtering should a high impedance signal source be required. DS100104-59 Recommended Power Supply Bypassing www.national.com 6 Applications The ADCV0831 is ideal for applications operating with ratiometric transducers. The ADCV0831 can measure the signal produced by the transducer and produce a corresponding code to the microprocessor. The microprocessor can then control the system producing the signal. Operating with Ratiometric Transducers DS100104-63 The ADCV0831 can be used in low-cost remote temperature sensor system. For a temperature sensor, the LM60 is an excellent companion to the ADCV0831, since it can operate off 3V supply. The LM60 linear scale factor is 6.25mV/C. Therefore, the ADCV0831 can digitize a couple of degrees change in temperature and provide the output to the microprocessor, which in turn can adjust the system environment. For higher accuracy, a low-offset op-amp can be used to gain up the LM60 output. Low-Cost Remote Temperature Sensor DS100104-60 7 www.national.com Applications (Continued) When the input of the ADCV0831 is driven by an op-amp operating at a supply voltage greater than 5V, it is a good idea to protect the input of the ADCV0831 from exceeding the supply voltage. Two diodes can be added to the input one to supply and one to the ground pin. Protecting the input DS100104-64 Note: Diodes are IN914 This circuit utilizes the LM385 reference to detect the power supply voltage level. When the supply voltage is 3V, the LSB = 3/256 = 11.7mV. Since the LM385 reference sets the input to 1.2V. The output code is 102. As the supply voltage decreases, the LSB decreases and the output code increases. When the supply voltage reaches 2.7V, the LSB = 10.5 mV. The input voltage is still at 1.2V, and the output code is 114. If the supply voltage increases, the LSB increases and the output code decreases. When the supply voltage reaches 3.3V, the LSB = 12.9mV and the output code is 93. Power Supply Level Detection DS100104-65 www.national.com 8 9 ADCV0831 8 Bit Serial I/O Low Voltage Low Power ADC with Auto Shutdown in a SOT Package Physical Dimensions inches (millimeters) unless otherwise noted Order Number ADCV0831M6X, ADCV0831M6 NS Package Number MA06A LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 2. A critical component in any component of a life support 1. Life support devices or systems are devices or sysdevice or system whose failure to perform can be reatems which, (a) are intended for surgical implant into sonably expected to cause the failure of the life support the body, or (b) support or sustain life, and whose faildevice or system, or to affect its safety or effectiveness. ure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Corporation Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: support@nsc.com National Semiconductor Europe Fax: +49 (0) 1 80-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 1 80-530 85 85 English Tel: +49 (0) 1 80-532 78 32 Francais Tel: +49 (0) 1 80-532 93 58 Italiano Tel: +49 (0) 1 80-534 16 80 National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: sea.support@nsc.com National Semiconductor Japan Ltd. Tel: 81-3-5620-6175 Fax: 81-3-5620-6179 www.national.com National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. |
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