ADC08031/ADC08032/ADC08034/ADC08038 8-Bit High-Speed Serial I/O A/D Converters with Multiplexer Options, Voltage Reference, and Track/Hold Function General Description The ADC08031/ADC08032/ADC08034/ADC08038 are 8-bit successive approximation A/D converters with serial I/O and configurable input multiplexers with up to 8 channels. The serial I/O is configured to comply with the NSC MICROWIRE™ serial data exchange standard for easy interface to the COPS™ family of controllers, and can easily interface with standard shift registers or microprocessors. The ADC08034 and ADC08038 provide a 2.6V band-gap derived reference. For devices offering guaranteed voltage reference performance over temperature see ADC08131, ADC08134 and ADC08138. A track/hold function allows the analog voltage at the positive input to vary during the actual A/D conversion. The analog inputs can be configured to operate in various combinations of single-ended, differential, or pseudo-differential modes. In addition, input voltage spans as small as 1V can be accommodated. Applications n n n n Digitizing automotive sensors Process control monitoring Remote sensing in noisy environments Instrumentation n Test systems n Embedded diagnostics Features n Serial digital data link requires few I/O pins n Analog input track/hold function n 2-, 4-, or 8-channel input multiplexer options with address logic n 0V to 5V analog input range with single 5V power supply n No zero or full scale adjustment required n TTL/CMOS input/output compatible n On chip 2.6V band-gap reference n 0.3" standard width 8-, 14-, or 20-pin DIP package n 14-, 20-pin small-outline packages Key Specifications n n n n n n Resolution: 8 bits Conversion time (fC = 1 MHz): 8µs (max) Power dissipation: 20mW (max) Single supply: 5VDC ( ± 5%) Total unadjusted error: ± 1⁄2 LSB and ± 1LSB No missing codes over temperature Ordering Information Industrial (−40˚C ≤ TA ≤ +85˚C) Package ADC08031CIN* N08E ADC08038CIN* N20A ADC08031CIWM, ADC08032CIWM, M14B ADC08034CIWM ADC08038CIWM M20B *Not recomended for new designs. COPS™ microcontrollers and MICROWIRE™ are trademarks of National Semiconductor Corporation. © 2000 National Semiconductor Corporation DS010555 www.national.com ADC08031/ADC08032/ADC08034/ADC08038 8-Bit High-Speed Serial I/O A/D Converters with Multiplexer Options, Voltage Reference, and Track/Hold Function June 2000 ADC08031/ADC08032/ADC08034/ADC08038 Connection Diagrams ADC08038 ADC08034 DS010555-3 DS010555-2 ADC08031 Dual-In-Line Package ADC08032 Small Outline Package DS010555-5 DS010555-30 ADC08031 Small Outline Package DS010555-31 www.national.com 2 Storage Temperature If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Operating Ratings (Notes 2, 3) Supply Voltage (VCC) Voltage at Inputs and Outputs Input Current at Any Pin (Note 4) Package Input Current (Note 4) Power Dissipation at TA = 25˚C (Note 5) ESD Susceptibility (Note 6) Soldering Information N Package (10 sec.) SO Package: Vapor Phase (60 sec.) Infrared (15 sec.) (Note 7) −65˚C to +150˚C Temperature Range ADC08031BIN, ADC08031CIN, ADC08032BIN, ADC08032CIN, ADC08034BIN, ADC08034CIN, ADC08038BIN, ADC08038CIN, ADC08031BIWM, ADC08032BIWM, ADC08034BIWM, ADC08038BIWM ADC08031CIWM, ADC08032CIWM, ADC08034CIWM, ADC08038CIWM Supply Voltage (VCC) 6.5V −0.3V to VCC + 0.3V ± 5 mA ± 20 mA 800 mW 1500V 235˚C TMIN ≤ TA ≤ TMAX −40˚C ≤ TA ≤ +85˚C 4.5 VDC to 6.3 VDC 215˚C 220˚C Electrical Characteristics The following specifications apply for VCC = VREF = +5 VDC, and fCLK = 1 MHz unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. Symbol Parameter Conditions Typical Limits Units (Note 8) (Note 9) (Limits) ± 1⁄2 ±1 LSB (max) 8 Bits (min) 1.3 kΩ (min) 6.0 kΩ (max) (VCC + 0.05) V (max) CONVERTER AND MULTIPLEXER CHARACTERISTICS Total Unadjusted Error (Note 10) BIN, BIWM CIN, CIWM Differential LSB (max) Linearity RREF VIN Reference Input Resistance Analog Input Voltage (Note 11) 3.5 (Note 12) DC Common-Mode Error Power Supply Sensitivity VCC = 5V ± 5%, kΩ (GND − 0.05) V (min) ± 1⁄4 ± 1⁄4 LSB (max) 0.2 µA (max) LSB (max) VREF = 4.75V On Channel Leakage Current (Note 13) Off Channel Leakage Current (Note 13) On Channel = 5V, Off Channel = 0V 1 On Channel = 0V, −0.2 Off Channel = 5V −1 On Channel = 5V, −0.2 Off Channel = 0V −1 On Channel = 0V, 0.2 Off Channel = 5V 1 µA (max) µA (max) µA (max) DIGITAL AND DC CHARACTERISTICS VIN(1) Logical “1” Input Voltage VCC = 5.25V 2.0 V (min) VIN(0) Logical “0” Input Voltage VCC = 4.75V 0.8 V (max) IIN(1) Logical “1” Input Current VIN = 5.0V 1 µA (max) IIN(0) Logical “0” Input Current VIN = 0V −1 µA (max) VOUT(1) Logical “1” Output Voltage VCC = 4.75V: 2.4 V (min) IOUT = −360 µA VOUT(0) Logical “0” Output Voltage IOUT = −10 µA 4.5 V (min) VCC = 4.75V 0.4 V (max) IOUT = 1.6 mA 3 www.national.com ADC08031/ADC08032/ADC08034/ADC08038 Absolute Maximum Ratings (Notes 1, 3) ADC08031/ADC08032/ADC08034/ADC08038 Electrical Characteristics (Continued) The following specifications apply for VCC = VREF = +5 VDC, and fCLK = 1 MHz unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. Symbol Parameter Conditions Typical Limits Units (Note 8) (Note 9) (Limits) DIGITAL AND DC CHARACTERISTICS IOUT TRI-STATE ® Output Current VOUT = 0V −3.0 µA (max) VOUT = 5V 3.0 µA (max) ISOURCE Output Source Current VOUT = 0V −6.5 mA (min) ISINK Output Sink Current VOUT = VCC 8.0 mA (min) ICC Supply Current CS = HIGH 3.0 mA (max) 7.0 mA (max) ADC08031, ADC08034, and ADC08038 ADC08032 (Note 16) REFERENCE CHARACTERISTICS VREFOUT Nominal Reference Output VREFOUT Option Available Only on 2.6 V ADC08034 and ADC08038 Electrical Characteristics The following specifications apply for VCC = VREF = +5 VDC, and tr = tf = 20 ns unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. Symbol fCLK Parameter Conditions Clock Frequency Typical Limits (Note 8) (Note 9) 10 (Limits) kHz (min) 1 TC Units MHz (max) Clock Duty Cycle 40 % (min) (Note 14) 60 % (max) 8 1/fCLK (max) 8 µs (max) 12 ⁄ 1/fCLK(max) 25 ns (min) 20 ns (min) Conversion Time (Not Including fCLK = 1 MHz MUX Addressing Time) tCA Acquisition Time tSELECT CLK High while CS is High tSET-UP CS Falling Edge or Data Input tHOLD Data Input Valid after CLK 50 ns Valid to CLK Rising Edge Rising Edge tpd1, tpd0 CLK Falling Edge to Output Data Valid (Note 15) t1H, t0H CL = 100 pF: Data MSB First 250 ns (max) Data LSB First 200 ns (max) TRI-STATE Delay from Rising Edge CL = 10 pF, RL = 10 kΩ of CS to Data Output and SARS Hi-Z (see TRI-STATE Test Circuits) 50 CL = 100 pF, RL = 2 kΩ ns 180 ns (max) CIN Capacitance of Logic Inputs 5 pF COUT Capacitance of Logic Outputs 5 pF 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 AGND = DGND = 0 VDC, unless otherwise specified. Note 4: When the input voltage VIN at any pin exceeds the power supplies (VIN < (AGND or DGND) or VIN > VCC) the current at that pin should be limited to 5 mA. The 20 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 5 mA to four pins. Note 5: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA and the ambient temperature, TA. The maximum allowable power dissipation at any temperature is PD = (TJMAX − TA)/θJA or the number given in the Absolute Maximum Ratings, whichever is lower. For these de- www.national.com 4 (Continued) vices, TJMAX = 125˚C. The typical thermal resistances (θJA) of these parts when board mounted follow: ADC08031 and ADC08032 with BIN and CIN suffixes 120˚C/W, ADC08038 with CIN suffix 80˚C/W. ADC08031 with CIWM suffix 140˚C/W, ADC08032 140˚C/W, ADC08034 140˚C/W, ADC08038 with CIWM suffix 91˚C/W. Note 6: Human body model, 100 pF capacitor discharged through a 1.5 kΩ resistor. Note 7: See AN450 “Surface Mounting Methods and Their Effect on Product Reliability” or Linear Data Book section “Surface Mount” for other methods of soldering surface mount devices. Note 8: Typicals are at TJ = 25˚C and represent the most likely parametric norm. Note 9: Guaranteed to National’s AOQL (Average Outgoing Quality Level). Note 10: Total unadjusted error includes offset, full-scale, linearity, multiplexer. Note 11: Cannot be tested for the ADC08032. Note 12: For VIN(−) ≥ VIN(+) the digital code will be 0000 0000. Two on-chip diodes are tied to each analog input (see Block Diagram) which will forward-conduct for analog input voltages one diode drop below ground or one diode drop greater than VCC supply. During testing at low VCC levels (e.g., 4.5V), high level analog inputs (e.g., 5V) can cause an input diode to conduct, especially at elevated temperatures, which will cause errors for analog inputs near full-scale. The spec allows 50 mV forward bias of either diode; this means that as long as the analog VIN does not exceed the supply voltage by more than 50 mV, the output code will be correct. Exceeding this range on an unselected channel will corrupt the reading of a selected channel. Achievement of an absolute 0 VDC to 5 VDC input voltage range will therefore require a minimum supply voltage of 4.950 VDC over temperature variations, initial tolerance and loading. Note 13: Channel leakage current is measured after a single-ended channel is selected and the clock is turned off. For off channel leakage current the following two cases are considered: one, with the selected channel tied high (5 VDC) and the remaining seven off channels tied low (0 VDC), total current flow through the off channels is measured; two, with the selected channel tied low and the off channels tied high, total current flow through the off channels is again measured. The two cases considered for determining on channel leakage current are the same except total current flow through the selected channel is measured. Note 14: A 40% to 60% duty cycle range insures proper operation at all clock frequencies. In the case that an available clock has a duty cycle outside of these limits the minimum time the clock is high or low must be at least 450 ns. The maximum time the clock can be high or low is 100 µs. Note 15: Since data, MSB first, is the output of the comparator used in the successive approximation loop, an additional delay is built in (see Block Diagram) to allow for comparator response time. Note 16: For the ADC08032 VREFIN is internally tied to VCC, therefore, for the ADC08032 reference current is included in the supply current. Typical Performance Characteristics Linearity Error vs Reference Voltage Linearity Error vs Temperature Linearity Error vs Clock Frequency DS010555-32 Power Supply Current vs Temperature (ADC08038, ADC08034, ADC08031) DS010555-34 DS010555-33 Output Current vs Temperature Power Supply Current vs Clock Frequency DS010555-36 DS010555-37 DS010555-35 Note: For ADC08032 add IREF 5 www.national.com ADC08031/ADC08032/ADC08034/ADC08038 Electrical Characteristics ADC08031/ADC08032/ADC08034/ADC08038 Leakage Current Test Circuit DS010555-7 TRI-STATE Test Circuits and Waveforms t1H DS010555-38 DS010555-39 t0H DS010555-41 DS010555-40 Timing Diagrams Data Input Timing DS010555-10 *To reset these devices, CLK and CS must be simultaneously high for a period of tSELECT or greater. Otherwise these devices are compatible with industry standards ADC0831/2/4/8. www.national.com 6 ADC08031/ADC08032/ADC08034/ADC08038 Timing Diagrams (Continued) Data Output Timing DS010555-11 ADC08031 Start Conversion Timing DS010555-12 ADC08031 Timing DS010555-13 *LSB first output not available on ADC08031. LSB information is maintained for remainder of clock periods until CS goes high. ADC08032 Timing DS010555-14 7 www.national.com ADC08031/ADC08032/ADC08034/ADC08038 Timing Diagrams (Continued) ADC08034 Timing DS010555-15 www.national.com 8 *Make sure clock edge #18 clocks in the LSB before SE is taken low DS010555-16 (Continued) 9 ADC08031/ADC08032/ADC08034/ADC08038 ADC08038 Timing Timing Diagrams www.national.com DS010555-17 *Some of these functions/pins are not available with other options. For the ADC08034, the “SEL 1” Flip-Flop is bypassed, for the ADC08032, both “SEL 0” and “SEL 1” Flip-Flops are bypassed. ADC08031/ADC08032/ADC08034/ADC08038 ADC08038 Functional Block Diagram Functional Description A unique input multiplexing scheme has been utilized to provide multiple analog channels with software-configurable single-ended, differential, or pseudo-differential (which will convert the difference between the voltage at any analog input and a common terminal) operation. The analog signal conditioning required in transducer-based data acquisition systems is significantly simplified with this type of input flexibility. One converter package can now handle ground referenced inputs and true differential inputs as well as signals with some arbitrary reference voltage. A particular input configuration is assigned during the MUX addressing sequence, prior to the start of a conversion. The MUX address selects which of the analog inputs are to be 1.0 MULTIPLEXER ADDRESSING The design of these converters utilizes a comparator structure with built-in sample-and-hold which provides for a differential analog input to be converted by a successiveapproximation routine. The actual voltage converted is always the difference between an assigned “+” input terminal and a “−” input terminal. The polarity of each input terminal of the pair indicates which line the converter expects to be the most positive. If the assigned “+” input voltage is less than the “−” input voltage the converter responds with an all zeros output code. www.national.com 10 channels. This voltage does not have to be analog ground; it can be any reference potential which is common to all of the inputs. This feature is most useful in single-supply applications where the analog circuity may be biased up to a potential other than ground and the output signals are all referred to this potential. (Continued) enabled and whether this input is single-ended or differential. Differential inputs are restricted to adjacent channel pairs. For example, channel 0 and channel 1 may be selected as a differential pair but channel 0 or 1 cannot act differentially with any other channel. In addition to selecting differential mode the polarity may also be selected. Channel 0 may be selected as the positive input and channel 1 as the negative input or vice versa. This programmability is best illustrated by the MUX addressing codes shown in the following tables for the various product options. The MUX address is shifted into the converter via the DI line. Because the ADC08031 contains only one differential input channel with a fixed polarity assignment, it does not require addressing. The common input line (COM) on the ADC08038 can be used as a pseudo-differential input. In this mode the voltage on this pin is treated as the “−” input for any of the other input TABLE 1. Multiplexer/Package Options Part Number Number of Analog Channels Single-Ended Differential Number of Package Pins ADC08031 1 1 8 ADC08032 2 1 8 ADC08034 4 2 14 ADC08038 8 4 20 TABLE 2. MUX Addressing: ADC08038 Single-Ended MUX Mode Analog Single-Ended Channel # MUX Address START SGL/ ODD/ SELECT DIF SIGN 1 0 1 1 0 0 0 1 1 0 0 1 1 1 0 1 0 1 1 0 1 1 1 1 1 0 0 1 1 1 0 1 1 1 1 1 0 1 1 1 1 1 0 1 2 3 4 5 6 7 COM + − + − + − + − + − + − + − + − TABLE 3. MUX Addressing: ADC08038 Differential MUX Mode Analog Differential Channel-Pair # MUX Address START SGL/ ODD/ DIF SIGN 1 SELECT 0 0 0 1 1 0 0 0 0 + − 1 0 0 0 1 1 0 0 1 0 1 0 0 1 1 1 0 1 0 0 1 0 1 0 1 1 0 1 1 0 1 0 1 1 1 − 1 2 2 3 + − 3 4 5 + − 6 7 + − − + + − + − 11 + www.national.com ADC08031/ADC08032/ADC08034/ADC08038 Functional Description ADC08031/ADC08032/ADC08034/ADC08038 Functional Description (Continued) TABLE 4. MUX Addressing: ADC08034 Single-Ended MUX Mode Channel # MUX Address START SGL/ ODD/ SELECT DIF SIGN 1 1 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1 0 1 2 3 + + + + COM is internally tied to AGND MUX Addressing: ADC08032 Single-Ended MUX Mode Channel # MUX Address START SGL/ ODD/ DIF SIGN 1 1 0 1 1 1 0 1 + + COM is internally tied to AGND Differential MUX Mode Channel # MUX Address START SGL/ ODD/ SELECT DIF SIGN 1 1 0 0 0 1 0 0 1 1 0 1 0 1 0 1 1 0 1 + − − + 2 3 + − − + Differential MUX Mode Channel # MUX Address START SGL/ ODD/ 1 DIF SIGN 1 0 0 + − 1 0 1 − + Since the input configuration is under software control, it can be modified as required before each conversion. A channel can be treated as a single-ended, ground referenced input for one conversion; then it can be reconfigured as part of a differential channel for another conversion. Figure 1 illustrates the input flexibility which can be achieved. The analog input voltages for each channel can range from 50mV below ground to 50mV above VCC (typically 5V) without degrading conversion accuracy. level analog signals by locating the converter right at the analog sensor; transmitting highly noise immune digital data back to the host processor. To understand the operation of these converters it is best to refer to the Timing Diagrams and Functional Block Diagram and to follow a complete conversion sequence. For clarity a separate timing diagram is shown for each device. 1. A conversion is initiated by pulling the CS (chip select) line low. This line must be held low for the entire conversion. The converter is now waiting for a start bit and its MUX assignment word. 2. On each rising edge of the clock the status of the data in (DI) line is clocked into the MUX address shift register. The start bit is the first logic “1” that appears on this line (all leading zeros are ignored). Following the start bit the converter expects the next 2 to 4 bits to be the MUX assignment word. 2.0 THE DIGITAL INTERFACE A most important characteristic of these converters is their serial data link with the controlling processor. Using a serial communication format offers two very significant system improvements; it allows many functions to be included in a small package and it can eliminate the transmission of low www.national.com 0 12 7. The stored data in the successive approximation register is loaded into an internal shift register. If the programmer prefers the data can be provided in an LSB first format [this makes use of the shift enable (SE) control line]. On the ADC08038 the SE line is brought out and if held high the value of the LSB remains valid on the DO line. When SE is forced low the data is clocked out LSB first. On devices which do not include the SE control line, the data, LSB first, is automatically shifted out the DO line after the MSB first data stream. The DO line then goes low and stays low until CS is returned high. The ADC08031 is an exception in that its data is only output in MSB first format. 8. All internal registers are cleared when the CS line is high and the tSELECT requirement is met. See Data Input Timing under Timing Diagrams. If another conversion is desired CS must make a high to low transition followed by address information. The DI and DO lines can be tied together and controlled through a bidirectional processor I/O bit with one wire. This is possible because the DI input is only “looked-at” during the MUX addressing interval while the DO line is still in a high impedance state. (Continued) 3. When the start bit has been shifted into the start location of the MUX register, the input channel has been assigned and a conversion is about to begin. An interval of 1⁄2 clock period (where nothing happens) is automatically inserted to allow the selected MUX channel to settle. The SARS line goes high at this time to signal that a conversion is now in progress and the DI line is disabled (it no longer accepts data). 4. The data out (DO) line now comes out of TRI-STATE and provides a leading zero for this one clock period of MUX settling time. 5. 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 generated internally from a ratioed capacitor array (first 5 bits) and a resistor ladder (last 3 bits). After each comparison the comparator’s output is shipped 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. 6. After 8 clock periods the conversion is completed. The SARS line returns low to indicate this 1⁄2 clock cycle later. 8 Single-Ended 8 Pseudo-Differential DS010555-48 DS010555-49 Mixed Mode 4 Differential DS010555-50 DS010555-51 FIGURE 1. Analog Input Multiplexer Options for the ADC08038 13 www.national.com ADC08031/ADC08032/ADC08034/ADC08038 Functional Description ADC08031/ADC08032/ADC08034/ADC08038 Functional Description For absolute accuracy, where the analog input varies between very specific voltage limits, the reference pin can be biased with a time and temperature stable voltage source. For the ADC08034 and the ADC08038 a band-gap derived reference voltage of 2.6V (Note 8) is tied to VREFOUT. This can be tied back to VREFIN. Bypassing VREFOUT with a 100µF capacitor is recommended. The LM385 and LM336 reference diodes are good low current devices to use with these converters. The maximum value of the reference is limited to the VCC supply voltage. The minimum value, however, can be quite small (see Typical Performance Characteristics) to allow direct conversions of transducer outputs providing less than a 5V output span. Particular care must be taken with regard to noise pickup, circuit layout and system error voltage sources when operating with a reduced span due to the increased sensitivity of the converter (1 LSB equals VREF/256). (Continued) 3.0 REFERENCE CONSIDERATIONS The voltage applied to the reference input on these converters, VREFIN, defines the voltage span of the analog input (the difference between VIN(MAX) and VIN(MIN) over which the 256 possible output codes apply. The devices can be used either in ratiometric applications or in systems requiring absolute accuracy. The reference pin must be connected to a voltage source capable of driving the reference input resistance which can be as low as 1.3kΩ. This pin is the top of a resistor divider string and capacitor array used for the successive approximation conversion. In a ratiometric system the analog input voltage is proportional to the voltage used for the A/D reference. This voltage is typically the system power supply, so the VREFIN pin can be tied to VCC (done internally on the ADC08032). 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. DS010555-52 a) Ratiometric DS010555-53 b) Absolute with a Reduced Span FIGURE 2. Reference Examples 4.0 THE ANALOG INPUTS VPEAK is its peak voltage value and fCLK is the A/D clock frequency. For a 60Hz common-mode signal to generate a 1⁄4 LSB error (≈5mV) with the converter running at 250kHz, its peak value would have to be 6.63V which would be larger than allowed as it exceeds the maximum analog input limits. 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 1kΩ. The worst-case leakage current of ± 1µA over temperature will create a 1mV input error with a 1kΩ 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. The most important feature of these converters is that they can be located right at the analog signal source and through just a few wires can communicate with a controlling processor with a highly noise immune serial bit stream. This in itself 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 differential input of these converters actually reduces the effects of common-mode input noise, a signal common to both selected “+” and “−” inputs for a conversion (60 Hz is most typical). The time interval between sampling the “+” input and then the “−” input is 1⁄2 of a clock period. The change in the common-mode voltage during this short time interval can cause conversion errors. For a sinusoidal common-mode signal this error is: 5.0 OPTIONAL ADJUSTMENTS 5.1 Zero Error The zero of the A/D does not require adjustment. If the minimum analog input voltage value, VIN(MIN), is not ground a zero offset can be done. The converter can be made to out- where fCM is the frequency of the common-mode signal, www.national.com 14 should be properly adjusted first. A VIN (+) voltage which equals this desired zero reference plus 1⁄2 LSB (where the LSB is calculated for the desired analog span, using 1 LSB = analog span/256) is applied to selected “+” input and the zero reference voltage at the corresponding “−” input should then be adjusted to just obtain the 00HEX to 01HEX code transition. (Continued) put 0000 0000 digital code for this minimum input voltage by biasing any VIN (−) input at this VIN(MIN) value. This utilizes the differential mode operation of the A/D. The zero error of the A/D converter relates to the location of the first riser of the transfer function and can be measured by grounding the VIN (−) input and applying a small magnitude positive voltage to the VIN (+) input. Zero error is the difference between the actual DC input voltage which is necessary to just cause an output digital code transition from 0000 0000 to 0000 0001 and the ideal 1⁄2 LSB value (1⁄2 LSB = 9.8mV for VREF = 5.000VDC). The full-scale adjustment should be made [with the proper VIN (−) voltage applied] by forcing a voltage to the VIN (+) input which is given by: 5.2 Full Scale The full-scale adjustment can be made by applying a differential input voltage which is 11⁄2 LSB down from the desired analog full-scale voltage range and then adjusting the magnitude of the VREFIN input (or VCC for the ADC08032) for a digital output code which is just changing from 1111 1110 to 1111 1111. where: VMAX = the high end of the analog input range and VMIN = the low end (the offset zero) of the analog range. (Both are ground referenced.) The VREFIN (or VCC) voltage is then adjusted to provide a code change from FEHEX to FFHEX. This completes the adjustment procedure. 5.3 Adjusting for an Arbitrary Analog Input Voltage Range If the analog zero voltage of the A/D is shifted away from ground (for example, to accommodate an analog input signal which does not go to ground), this new zero reference 15 www.national.com ADC08031/ADC08032/ADC08034/ADC08038 Functional Description ADC08031/ADC08032/ADC08034/ADC08038 Applications A “Stand-Alone” Hook-Up for ADC08038 Evaluation DS010555-44 *Pinouts shown for ADC08038. For all other products tie to pin functions as shown. Low-Cost Remote Temperature Sensor DS010555-45 www.national.com 16 ADC08031/ADC08032/ADC08034/ADC08038 Applications (Continued) Digitizing a Current Flow DS010555-22 Operating with Ratiometric Transducers DS010555-23 *VIN(−) = 0.15 VCC 15% of VCC ≤ VXDR ≤ 85% of VCC 17 www.national.com ADC08031/ADC08032/ADC08034/ADC08038 Applications (Continued) Span Adjust; 0V ≤ VIN ≤ 3V DS010555-46 Zero-Shift and Span Adjust: 2V ≤ VIN ≤ 5V DS010555-47 www.national.com 18 ADC08031/ADC08032/ADC08034/ADC08038 Applications (Continued) Protecting the Input High Accuracy Comparators DS010555-26 DS010555-25 DO = all 1s if +VIN DO = all 0s if +VIN > −VIN < −VIN Diodes are 1N914 Digital Load Cell DS010555-27 • • • • Uses one more wire than load cell itself Two mini-DIPs could be mounted inside load cell for digital output transducer Electronic offset and gain trims relax mechanical specs for gauge factor and offset Low level cell output is converted immediately for high noise immunity 19 www.national.com ADC08031/ADC08032/ADC08034/ADC08038 Applications (Continued) 4 mA-20 mA Current Loop Converter DS010555-28 • • All power supplied by loop 1500V isolation at output www.national.com 20 ADC08031/ADC08032/ADC08034/ADC08038 Applications (Continued) Isolated Data Converter DS010555-29 • • No power required remotely 1500V isolation 21 www.national.com ADC08031/ADC08032/ADC08034/ADC08038 Physical Dimensions inches (millimeters) unless otherwise noted Order Number ADC08031CIWM, ADC08032CIWM, or ADC08034CIWM NS Package Number M14B www.national.com 22 ADC08031/ADC08032/ADC08034/ADC08038 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) Order Number ADC08038CIWM NS Package Number M20B Order Number ADC08031CIN NS Package Number N08E 23 www.national.com ADC08031/ADC08032/ADC08034/ADC08038 8-Bit High-Speed Serial I/O A/D Converters with Multiplexer Options, Voltage Reference, and Track/Hold Function Physical Dimensions inches (millimeters) unless otherwise noted (Continued) Order Number ADC08038CIN NS Package Number N20A 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 AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. 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