19-0196; Rev 0; 10/93 NUAL KIT MA ATION SHEET A EVALU T A D WS FOLLO +5V, Low-Power, 12-Bit Serial ADCs ________________________________Features ♦ ♦ ♦ ♦ ♦ ___________________________Applications Portable Data Logging 12-Bit Resolution ±1⁄2 LSB Integral Nonlinearity (MAX187A/MAX189A) Internal Track/Hold, 75kHz Sampling Rate Single +5V Operation Low Power: 2µA Shutdown Current 1.5mA Operating Current ♦ Internal 4.096V Buffered Reference (MAX187) ♦ 3-Wire Serial Interface, Compatible with SPI, QSPI, and Microwire ♦ Small-Footprint 8-Pin DIP and 16-Pin SO _________________Ordering Information TEMP. RANGE PIN-PACKAGE ERROR (LSB) PART MAX187ACPA 0°C to +70°C 8 Plastic DIP ±1⁄2 MAX187BCPA 0°C to +70°C 8 Plastic DIP ±1 MAX187CCPA 0°C to +70°C 8 Plastic DIP ±2 MAX187ACWE 0°C to +70°C 16 Wide SO ±1⁄2 MAX187BCWE 0°C to +70°C 16 Wide SO ±1 MAX187CCWE 0°C to +70°C 16 Wide SO ±2 MAX187BC/D 0°C to +70°C Dice* ±1 Ordering Information continued on last page. * Dice are specified at TA = +25°C, DC parameters only. ** Contact factory for availability and processing to MIL-STD-883. Remote Digital Signal Processing Isolated Data Acquisition High-Accuracy Process Control ________________Functional Diagram GND 5 REFDAC AV = 1.638 REF AIN 4 2 +2.5V BANDGAP REFERENCE (MAX187 ONLY) 10k (4.096V) OUTPUT SHIFT REGISTER 6 DOUT 8 SCLK REF+ 12-BIT SAR _________________Pin Configurations TOP VIEW V DD 1 8 SCLK AIN 2 7 CS 6 DOUT 5 GND SHDN 3 MAX187 MAX189 REF 4 T/H COMPARATOR MAX187 MAX189 VDD 1 7 BUFFER ENABLE/DISABLE CONTROL AND TIMING NOTE: PIN NUMBERS SHOWN ARE FOR 8-PIN DIPs ONLY. 3 DIP CS SHDN Pin Configurations continued on last page. ™ SPI and QSPI are trademarks of Motorola. Microwire is a trademark of National Semiconductor. ________________________________________________________________ Maxim Integrated Products Call toll free 1-800-998-8800 for free samples or literature. 1 MAX187/MAX189 __________________General Description The MAX187/MAX189 serial 12-bit analog-to-digital converters (ADCs) operate from a single +5V supply and accept a 0V to 5V analog input. Both parts feature an 8.5µs successive-approximation ADC, a fast track/hold (1.5µs), an on-chip clock, and a high-speed 3-wire serial interface. The MAX187/MAX189 digitize signals at a 75ksps throughput rate. An external clock accesses data from the interface, which communicates without external hardware to most digital signal processors and microcontrollers. The interface is compatible with SPI™, QSPI™, and Microwire™. The MAX187 has an on-chip buffered reference, and the MAX189 requires an external reference. Both the MAX187 and MAX189 save space with 8-pin DIP and 16-pin SO packages. Power consumption is 7.5mW and reduces to only 10µW in shutdown. Excellent AC characteristics and very low power consumption combined with ease of use and small package size make these converters ideal for remote DSP and sensor applications, or for circuits where power consumption and space are crucial. MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs ABSOLUTE MAXIMUM RATINGS VDD to GND .............................................................-0.3V to +6V AIN to GND................................................-0.3V to (VDD + 0.3V) REF to GND ...............................................-0.3V to (VDD + 0.3V) Digital Inputs to GND.................................-0.3V to (VDD + 0.3V) Digital Outputs to GND..............................-0.3V to (VDD + 0.3V) SHDN to GND.............................................-0.3V to (VDD + 0.3V) REF Load Current (MAX187) .........................4.0mA Continuous REF Short-Circuit Duration (MAX187)................................20sec DOUT Current ..................................................................±20mA Continuous Power Dissipation (TA = +70°C) 8-Pin Plastic DIP (derate 9.09mW/°C above +70°C) ..500mW 16-Pin Wide SO (derate 8.70mW/°C above +70°C) ...478mW 8-Pin CERDIP (derate 8.00mW/°C above +70°C) ......440mW Operating Temperature Ranges: MAX187_C_ _/MAX189_C_ _.............................0°C to +70°C MAX187_E_ _/MAX189_E_ _ ..........................-40°C to +85°C MAX187_MJA/MAX189_MJA .......................-55°C to +125°C Storage Temperature Range............................-60°C to +150°C Lead Temperature (soldering, 10sec) ............................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VDD = +5V ±5%; GND = 0V; unipolar input mode; 75ksps, fCLK = 4.0MHz, external clock (50% duty cycle); MAX187—internal reference: VREF = 4.096V, 4.7µF capacitor at REF pin, or MAX189—external reference: VREF = 4.096V applied to REF pin, 4.7µF capacitor at REF pin; TA = TMIN to TMAX; unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 12 Bits DC ACCURACY (Note 1) Resolution ±1⁄2 MAX18_A Relative Accuracy (Note 2) Differential Nonlinearity DNL MAX18_B ±1 MAX18_C ±2 No missing codes over temperature ±1 ±1 MAX18_B/C Gain Error (Note 3) Gain Temperature Coefficient LSB 1 MAX18_A Offset Error ⁄2 LSB LSB ±3 MAX187 ±3 MAX189A ±1 MAX189B/C ±3 External reference, 4.096V ±0.8 LSB ppm/°C DYNAMIC SPECIFICATIONS (10kHz sine wave input, 0V to 4.096Vp-p, 75ksps) Signal-to-Noise plus Distortion Ratio SINAD Total Harmonic Distortion (up to the 5th harmonic) THD Spurious-Free Dynamic Range SFDR Small-Signal Bandwidth Full-Power Bandwidth 2 70 dB -80 80 Rolloff -3dB dB dB 4.5 MHz 0.8 MHz _______________________________________________________________________________________ +5V, Low-Power, 12-Bit Serial ADCs (VDD = +5V ±5%; GND = 0V; unipolar input mode; 75ksps, fCLK = 4.0MHz, external clock (50% duty cycle); MAX187—internal reference: VREF = 4.096V, 4.7µF capacitor at REF pin, or MAX189—external reference: VREF = 4.096V applied to REF pin, 4.7µF capacitor at REF pin; TA = TMIN to TMAX; unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS CONVERSION RATE Conversion Time tCONV Track/Hold Acquisition Time tACQ Throughput Rate 5.5 µs 75 ksps 1.5 µs External clock, 4MHz, 13 clocks Aperture Delay 8.5 tAPR Aperture Jitter 10 ns <50 ps ANALOG INPUT Input Voltage Range 0 to VREF Input Capacitance (Note 4) 16 V pF INTERNAL REFERENCE (MAX187 only, reference buffer enabled) TA = +25°C REF Output Voltage VREF TA = TMIN to TMAX 4.076 4.096 4.060 4.132 MAX187_E 4.050 4.140 MAX187_M 4.040 4.150 REF Short-Circuit Current 30 MAX187AC/BC REF Tempco Load Regulation (Note 5) 4.116 MAX187_C ±30 mA ±50 MAX187AE/BE ±30 ±60 MAX187AM/BM ±30 ±80 MAX187C ±30 0mA to 0.6mA output load V 1 ppm/°C mV EXTERNAL REFERENCE AT REF (Buffer disabled, VREF = 4.096V) Input Voltage Range 2.50 Input Current 200 Input Resistance 12 Shutdown REF Input Current VDD + 50mV V 350 µA 20 1.5 kΩ 10 µA _______________________________________________________________________________________ 3 MAX187/MAX189 ELECTRICAL CHARACTERISTICS (continued) MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs ELECTRICAL CHARACTERISTICS (continued) (VDD = +5V ±5%; GND = 0V; unipolar input mode; 75ksps, fCLK = 4.0MHz, external clock (50% duty cycle); MAX187—internal reference: VREF = 4.096V, 4.7µF capacitor at REF pin, or MAX189—external reference: VREF = 4.096V applied to REF pin, 4.7µF capacitor at REF pin; TA = TMIN to TMAX; unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DIGITAL INPUTS (SCLK, CS, SHDN) SCLK, CS Input High Voltage VINH SCLK, CS Input Low Voltage VINL SCLK, CS Input Hysteresis 2.4 VHYST V 0.8 V 0.15 V SCLK, CS Input Leakage IIN VIN = 0V or VDD ±1 µA SCLK, CS Input Capacitance CIN (Note 4) 15 pF 0.5 V ±4.0 µA VDD -1.5 V SHDN Input High Voltage VINSH SHDN Input Low Voltage VINSL SHDN Input Current IINS SHDN Input Mid Voltage VIM SHDN Voltage, Floating VFLT SHDN Maximum Allowed Leakage, Mid Input VDD - 0.5 V SHDN = VDD or 0V 1.5 SHDN = open 2.75 SHDN = open -100 V 100 nA DIGITAL OUTPUT (DOUT) Output Voltage Low Output Voltage High Three-State Leakage Current Three-State Output Capacitance VOL VOH IL COUT ISINK = 5mA 0.4 ISINK = 16mA V 0.3 ISOURCE = 1mA 4 V CS = 5V CS = 5V (Note 4) ±10 µA 15 pF 5.25 V POWER REQUIREMENTS Supply Voltage VDD 4.75 Operating mode Supply Current IDD MAX187 1.5 2.5 MAX189 1.0 2.0 2 10 µA ±0.06 ±0.5 mV Power-down mode Power-Supply Rejection 4 PSR VDD = +5V, ±5%; external reference, 4.096V; full-scale input (Note 6) _______________________________________________________________________________________ mA +5V, Low-Power, 12-Bit Serial ADCs (VDD = +5.0V ±5%, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL Track/Hold Acquisition Time tACQ SCLK Fall to Output Data Valid CONDITIONS CS = high (Note 7) MIN TYP MAX 1.5 UNITS µs MAX18_ _C/E 20 150 MAX18_ _M 20 200 tDO CLOAD = 100pF ns CS Fall to Output Enable tDV CLOAD = 100pF 100 CS Rise to Output Disable tTR CLOAD = 100pF 100 ns 5 MHz ns SCLK Clock Frequency fSCLK SCLK Pulse Width High tCH 100 ns SCLK Pulse Width Low tCL 100 ns tCSO 50 ns tCS 500 ns SCLK Low to CS Fall Setup Time CS Pulse Width Note 1: Tested at VDD = +5V. Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after the full-scale range has been calibrated. Note 3: MAX187—internal reference, offset nulled; MAX189–external +4.096V reference, offset nulled. Excludes reference errors. Note 4: Guaranteed by design. Not subject to production testing. Note 5: External load should not change during conversion for specified ADC accuracy. Note 6: DC test, measured at 4.75V and 5.25V only. Note 7: To guarantee acquisition time, tACQ is the maximum time the device takes to acquire the signal, and is also the minimum time needed for the signal to be acquired. _______________________________________________________________________________________ 5 MAX187/MAX189 TIMING CHARACTERISTICS ________________________________________________Typical Operating Characteristics POWER-SUPPLY REJECTION vs. TEMPERATURE VREF vs. TEMPERATURE 4.090 0.16 0.14 INTERNAL REFERENCE VOLTAGE (V) POWER-SUPPLY REJECTION (mV) 4.089 0.12 0.10 0.08 0.06 0.04 0.02 4.088 4.087 4.086 4.085 4.084 4.083 4.082 4.081 4.080 0 -60 -20 20 60 100 -60 140 -20 20 60 100 140 TEMPERATURE (°C) TEMPERATURE (°C) SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE SUPPLY CURRENT vs. TEMPERATURE 7 SHUTDOWN SUPPLY CURRENT (µA) 2.2 SUPPLY CURRENT (mA) MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs 1.8 MAX187 1.4 MAX189 1.0 0.6 6 5 4 3 2 1 0.2 0 -60 -20 20 60 TEMPERATURE (°C) 6 100 140 -60 -20 20 60 100 TEMPERATURE (°C) _______________________________________________________________________________________ 140 +5V, Low-Power, 12-Bit Serial ADCs PIN NAME DIP WIDE SO 1 1 VDD 2 3 AIN 3 6 SHDN FUNCTION Supply voltage, +5V ±5% Sampling analog input, 0V to VREF range Three-level shutdown input. Pulling SHDN low shuts the MAX187/MAX189 down to 10µA (max) supply current. Both MAX187 and MAX189 are fully operational with either SHDN high or floating. For the MAX187, pulling SHDN high enables the internal reference, and letting SHDN float disables the internal reference and allows for the use of an external reference. 4 8 REF Reference voltage—sets analog voltage range and functions as a 4.096V output for the MAX187 with enabled internal reference. REF also serves as a +2.5V to VDD input for a precision reference for both MAX187 (disabled internal reference) and MAX189. Bypass with 4.7µF if internal reference is used, and with 0.1µF if an external reference is applied. 5 — GND Analog and digital ground — 10 AGND Analog ground — 11 DGND Digital ground 6 12 DOUT Serial data output. Data changes state at SCLK’s falling edge. Active-low chip select initiates conversions on the falling edge. When CS is high, DOUT is high impedance. 15 CS 8 16 SCLK Serial clock input. Clocks data out with rates up to 5MHz. — 2,4,5,7,9,13,14 N.C. Not internally connected. Connect to AGND for best noise performance. 7 _______________Detailed Description Converter Operation The MAX187/MAX189 use input track/hold (T/H) and successive approximation register (SAR) circuitry to convert an analog input signal to a digital 12-bit output. No external hold capacitor is needed for the T/H. Figures 3a and 3b show the MAX187/MAX189 in their simplest configuration. The MAX187/MAX189 convert input signals in the 0V to VREF range in 10µs, including T/H acquisition time. The MAX187’s internal reference is trimmed to 4.096V, while the MAX189 requires an external reference. Both devices accept external reference voltages from +2.5V to VDD. The serial interface requires only three digital lines, SCLK, CS, and DOUT, and provides easy interface to microprocessors (µPs). Both converters have two modes: normal and shutdown. Pulling SHDN low shuts the device down and reduces supply current to below 10µA, while pulling SHDN high or leaving it floating puts the device into the operational mode. A conversion is initiated by CS falling. The conversion result is available at DOUT in unipolar serial format. A high bit, signaling the end of conversion (EOC), followed by the data bits (MSB first), make up the serial data stream. The MAX187 operates in one of two states: (1) internal reference and (2) external reference. Select internal reference operation by forcing SHDN high, and external reference operation by floating SHDN. Analog Input Figure 4 illustrates the sampling architecture of the ADC’s analog comparator. The full-scale input voltage depends on the voltage at REF. ZERO SCALE FULL SCALE Internal Reference (MAX187 only) 0V +4.096V External Reference 0V VREF REFERENCE For specified accuracy, the external reference voltage range spans from +2.5V to VDD. _______________________________________________________________________________________ 7 MAX187/MAX189 _______________________________________________________________________Pin Description MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs +5V 3k DOUT DOUT 3k CLOAD = 100pF CLOAD = 100pF DGND DGND a. High-Z to VOH and VOL to VOH b. High-Z to VOL and VOH to VOL Figure 1. Load Circuits for DOUT Enable Time +5V 3k DOUT DOUT 3k CLOAD = 100pF DGND a. VOH to High-Z CLOAD = 100pF DGND b. VOLto High-Z Figure 2. Load Circuits for DOUT Disable Time 8 _______________________________________________________________________________________ +5V, Low-Power, 12-Bit Serial ADCs 2 ANALOG INPUT 0V TO +5V SHUTDOWN INPUT 1 3 4.7µF 0.1µF 0.1µF SCLK VDD AIN MAX187 CS DOUT SHDN 8 +5V 7 SERIAL INTERFACE 6 4 OFF GND REF OFF REFERENCE INPUT 5 4.7µF 2 ANALOG INPUT 0V TO +5V SHUTDOWN INPUT ON 1 3 VDD SCLK AIN MAX189 CS SHDN DOUT MAX187/MAX189 +5V 4.7µF 8 7 SERIAL INTERFACE 6 ON 4 REF GND 5 0.1µF Figure 3b. MAX189 Operational Diagram Figure 3a. MAX187 Operational Diagram 12-BIT CAPACITIVE DAC REF AIN HOLD CPACKAGE COMPARATOR TRACK INPUT CHOLD ZERO - + 16pF CSWITCH 5k RIN HOLD TRACK AT THE SAMPLING INSTANT, THE INPUT SWITCHES FROM AIN TO GND. GND Figure 4. Equivalent Input Circuit Track/Hold In track mode, the analog signal is acquired and stored in the internal hold capacitor. In hold mode, the T/H switch opens and maintains a constant input to the ADC’s SAR section. During acquisition, the analog input AIN charges capacitor CHOLD. Bringing CS low ends the acquisition interval. At this instant, the T/H switches the input side of CHOLD to GND. The retained charge on CHOLD represents a sample of the input, unbalancing the node ZERO at the comparator’s input. In hold mode, the capacitive DAC adjusts during the remainder of the conversion cycle to restore node ZERO to 0V within the limits of a 12-bit resolution. This action is equivalent to transferring a charge from CHOLD to the binary-weighted capacitive DAC, which in turn forms a digital representation of the analog input signal. At the conversion’s end, the input side of CHOLD switches back to AIN, and CHOLD charges to the input signal again. The time required for the T/H to acquire an input signal is a function of how quickly its input capacitance is charged. If the input signal’s source impedance is high, the acquisition time lengthens and more time must be allowed between conversions. Acquisition time is calculated by: tACQ = 9 (RS + RIN) 16pF, where RIN = 5kΩ, RS = the source impedance of the input signal, and tACQ is never less than 1.5µs. Source impedances below 5kΩ do not significantly affect the AC performance of the ADC. _______________________________________________________________________________________ 9 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Input Bandwidth The ADCs’ input tracking circuitry has a 4.5MHz smallsignal bandwidth, and an 8V/µs slew rate. It is possible to digitize high-speed transient events and measure periodic signals with bandwidths exceeding the ADC's sampling rate by using undersampling techniques. To avoid aliasing of unwanted high-frequency signals into the frequency band of interest, an anti-alias filter is recommended. See the MAX274/MAX275 continuous-time filters data sheet. ed by the 75ksps sample rate of the MAX187/MAX189. Therefore, the maximum sinusoidal input frequency allowed is 37.5kHz. Higher-frequency signals cause aliasing problems unless undersampling techniques are used. Reference The MAX187 can be used with an internal or external reference, while the MAX189 requires an external reference. Input Protection Internal protection diodes that clamp the analog input allow the input to swing from GND - 0.3V to VDD + 0.3V without damage. However, for accurate conversions near full scale, the input must not exceed VDD by more than 50mV, or be lower than GND by 50mV. If the analog input exceeds the supplies by more than 50mV beyond the supplies, limit the input current to 2mA, since larger currents degrade conversion accuracy. Internal Reference The MAX187 has an on-chip reference with a buffered temperature-compensated bandgap diode, lasertrimmed to +4.096V ±0.5%. Its output is connected to REF and also drives the internal DAC. The output can be used as a reference voltage source for other components and can source up to 0.6mA. Decouple REF with a 4.7µF capacitor. The internal reference is enabled by pulling the SHDN pin high. Letting SHDN float disables the internal reference, which allows the use of an external reference, as described in the External Reference section. Driving the Analog Input The input lines to AIN and GND should be kept as short as possible to minimize noise pickup. Shield longer leads. Also see the Input Protection section. Because the MAX187/MAX189 incorporate a T/H, the drive requirements of the op amp driving AIN are less stringent than those for a successive-approximation ADC without a T/H. The typical input capacitance is 16pF. The amplifier bandwidth should be sufficient to handle the frequency of the input signal. The MAX400 and OP07 work well at lower frequencies. For higherfrequency operation, the MAX427 and OP27 are practical choices. The allowed input frequency range is limit- External Reference The MAX189 operates with an external reference at the REF pin. To use the MAX187 with an external reference, disable the internal reference by letting SHDN float. Stay within the voltage range +2.5V to VDD to achieve specified accuracy. The minimum input impedance is 12kΩ for DC currents. During conversion, the external reference must be able to deliver up to 350µA DC load current and have an output impedance of 10Ω or less. The recommended minimum value for the bypass capacitor is 0.1µF. If the reference has higher output impedance or is noisy, bypass it close to the REF pin with a 4.7µF capacitor. COMPLETE CONVERSION SEQUENCE CS tWAKE SHDN DOUT CONVERSION 0 POWERED UP CONVERSION 1 POWERED DOWN POWERED UP Figure 5. MAX187/MAX189 Shutdown Sequence 10 ______________________________________________________________________________________ +5V, Low-Power, 12-Bit Serial ADCs MAX187/MAX189 10000 3.0 2.5 2.0 MAX187 tWAKE (ms) SUPPLY CURRENT (µA) 1000 100 MAX189* 1.5 1.0 10 0.5 *REF CONNECTED TO VDD 1 0.1 1 10 100 1000 10000 100000 CONVERSIONS PER SECOND Figure 6. Average Supply Current vs. Conversion Rate ____________________Serial Interface Initialization After Power-Up and Starting a Conversion When power is first applied, it takes the fully discharged 4.7µF reference bypass capacitor up to 20ms to provide adequate charge for specified accuracy. With SHDN not pulled low, the MAX187/MAX189 are now ready to convert. To start a conversion, pull CS low. At CS’s falling edge, the T/H enters its hold mode and a conversion is initiated. After an internally timed 8.5µs conversion period, the end of conversion is signaled by DOUT pulling high. Data can then be shifted out serially with the external clock. Using SHDN to Reduce Supply Current Power consumption can be reduced significantly by shutting down the MAX187/MAX189 between conversions. This is shown in Figure 6, a plot of average supply current vs. conversion rate. Because the MAX189 uses an external reference voltage (assumed to be present continuously), it "wakes up" from shutdown more quickly, and therefore provides lower average supply currents. The wakeup-time, tWAKE, is the time from SHDN deasserted to the time when a conversion may be initiated. For the MAX187, this time is 2µs. For the MAX189, this time depends on the time in shutdown (see Figure 7) because the external 4.7µF reference bypass capacitor loses charge slowly during shutdown (see the specifications for shutdown, REF Input Current = 10µA max). 0 0.0001 0.001 0.01 0.1 1 10 TIME IN SHUTDOWN (sec) Figure 7. tWAKE vs. Time in Shutdown (MAX187 only) External Clock The actual conversion does not require the external clock. This frees the µP from the burden of running the SAR conversion clock, and allows the conversion result to be read back at the µP’s convenience at any clock rate from 0MHz to 5MHz. The clock duty cycle is unrestricted if each clock phase is at least 100ns. Do not run the clock while a conversion is in progress. Timing and Control Conversion-start and data-read operations are controlled by the CS and SCLK digital inputs. The timing diagrams of Figures 8 and 9 outline the operation of the serial interface. A CS falling edge initiates a conversion sequence: The T/H stage holds input voltage, the ADC begins to convert, and DOUT changes from high impedance to logic low. SCLK must be kept inactive during the conversion. An internal register stores the data when the conversion is in progress. End of conversion (EOC) is signaled by DOUT going high. DOUT’s rising edge can be used as a framing signal. SCLK shifts the data out of this register any time after the conversion is complete. DOUT transitions on SCLK’s falling edge. The next falling clock edge produces the MSB of the conversion at DOUT, followed by the remaining bits. Since there are 12 data bits and one leading high bit, at least 13 falling clock edges are needed to shift out these bits. Extra clock pulses occurring after the conversion result has been clocked out, and prior to a rising edge of CS, produce trailing 0s at DOUT and have no effect on converter operation. ______________________________________________________________________________________ 11 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs CS 1 4 8 12 SCLK B11 B10 B9 DOUT CONVERSION IN PROGRESS INTERFACE IDLE A/D STATE EOC EOC B8 B7 B6 8.5µs (tCONV) MINIMUM CYCLE TIME B4 B3 B2 B1 B0 TRAILING ZEROS CLOCK OUTPUT DATA CONVERSION 0 TRACK B5 IDLE TRACK 0µs CONV. 1 12 × 0.250µs = 3.25µs 0.5µs (tCS) 0µs TOTAL = 12.25µs Figure 8. MAX187/MAX189 Interface Timing Sequence tCS CS … tCS0 tCH … SCLK tDO tDV tCL tTR tCONV … DOUT B2 B1 B0 tAPR INTERNAL T/H (TRACK) (HOLD) … (TRACK) Figure 9. MAX187/MAX189 Detailed Serial-Interface Timing 12 ______________________________________________________________________________________ +5V, Low-Power, 12-Bit Serial ADCs MAX187/MAX189 20 OUTPUT CODE 11…111 fS = 75ksps fT = 10kHz TA = +25°C 0 FULL-SCALE TRANSITION -20 11…110 FS = +4.096V 1LSB = FS 4096 AMPLITUDE (dB) 11…101 -40 -60 -80 00…011 -100 00…010 00…001 -120 00…000 0 1 2 FS 3 INPUT VOLTAGE (LSBs) FS - 3/2LSB -140 0 18.75 37.5 FREQUENCY (kHz) Figure 10. MAX187/MAX189 Unipolar Transfer Function, 4.096V = Full Scale Figure 11. MAX187/MAX189 FFT plot Minimum cycle time is accomplished by using DOUT’s rising edge as the EOC signal. Clock out the data with 13 clock cycles at full speed. Raise CS after the conversion’s LSB has been read. After the specified minimum time, tACQ, CS can be pulled low again to initiate the next conversion. input frequency. ADCs have traditionally been evaluated by specifications such as Zero and Full-Scale Error, Integral Nonlinearity (INL), and Differential Nonlinearity (DNL). Such parameters are widely accepted for specifying performance with DC and slowly varying signals, but are less useful in signal-processing applications, where the ADC’s impact on the system transfer function is the main concern. The significance of various DC errors does not translate well to the dynamic case, so different tests are required. Output Coding and Transfer Function The data output from the MAX187/MAX189 is binary, and Figure 10 depicts the nominal transfer function. Code transitions occur halfway between successive integer LSB values. If V REF = +4.096V, then 1 LSB = 1.00mV or 4.096V/4096. _____________Dynamic Performance High-speed sampling capability and a 75ksps throughput make the MAX187/MAX189 ideal for wideband signal processing. To support these and other related applications, Fast Fourier Transform (FFT) test techniques are used to guarantee the ADC’s dynamic frequency response, distortion, and noise at the rated throughput. Specifically, this involves applying a lowdistortion sine wave to the ADC input and recording the digital conversion results for a specified time. The data is then analyzed using an FFT algorithm that determines its spectral content. Conversion errors are then seen as spectral elements outside of the fundamental Signal-to-Noise Ratio and Effective Number of Bits Signal-to-noise plus distortion (SINAD) is the ratio of the fundamental input frequency’s RMS amplitude to the RMS amplitude of all other ADC output signals. The input bandwidth is limited to frequencies above DC and below one-half the ADC sample (conversion) rate. The theoretical minimum ADC noise is caused by quantization error and is a direct result of the ADC’s resolution: SINAD = (6.02N + 1.76)dB, where N is the number of bits of resolution. An ideal 12-bit ADC can, therefore, do no better than 74dB. An FFT plot of the output shows the output level in various spectral bands. Figure 11 shows the result of sampling a pure 10kHz sine wave at a 75ksps rate with the MAX187/MAX189. ______________________________________________________________________________________ 13 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs 12.2 12.0 I/O 11.8 11.6 SCK 11.4 EFFECTIVE BITS CS SCLK MISO 11.2 DOUT +5V 11.0 MAX187 MAX189 10.8 10.6 SS 10.4 (UNDERSAMPLED) 10.2 a. SPI 1 10 100 1000 INPUT FREQUENCY (kHz) CS CS SCK Figure 12. Effective Bits vs. Input Frequency SCLK MISO DOUT +5V The effective resolution (effective number of bits) the ADC provides can be determined by transposing the above equation and substituting in the measured SINAD: N = (SINAD - 1.76)/6.02. Figure 12 shows the effective number of bits as a function of the input frequency for the MAX187/MAX189. MAX187 MAX189 SS b. QSPI Total Harmonic Distortion If a pure sine wave is sampled by an ADC at greater than the Nyquist frequency, the nonlinearities in the ADC’s transfer function create harmonics of the input frequency present in the sampled output data. Total Harmonic Distortion (THD) is the ratio of the RMS sum of all the harmonics (in the frequency band above DC and below one-half the sample rate, but not including the DC component) to the RMS amplitude of the fundamental frequency. This is expressed as follows: THD = 20log √ V22 + V32 + V42 + … VN2 V1 where V1 is the fundamental RMS amplitude, and V2 through VN are the amplitudes of the 2nd through Nth harmonics. The THD specification in the Electrical Characteristics includes the 2nd through 5th harmonics. 14 I/O CS SK SCLK SI DOUT MAX187 MAX189 c. MICROWIRE Figure 13. Common Serial-Interface Connections to the MAX187/MAX189 ______________________________________________________________________________________ +5V, Low-Power, 12-Bit Serial ADCs SCLK’s falling edge and is available in MSB-first format. Observe the SCLK to DOUT valid timing characteristic. Data can be clocked into the µP on SCLK’s rising edge. 4. Pull CS high at or after the 13th falling clock edge. If CS remains low, trailing zeros are clocked out after the LSB. 5. With CS = high, wait the minimum specified time, tCS, before launching a new conversion by pulling CS low. If a conversion is aborted by pulling CS high before the conversions end, wait for the minimum acquisition time, t ACQ , before starting a new conversion. Connection to Standard Interfaces The MAX187/MAX189 serial interface is fully compatible with SPI, QSPI, and Microwire standard serial interfaces. If a serial interface is available, set the CPU’s serial interface in master mode so the CPU generates the serial clock. Choose a clock frequency up to 2.5MHz. 1. Use a general-purpose I/O line on the CPU to pull CS low. Keep SCLK low. 2. Wait the for the maximum conversion time specified before activating SCLK. Alternatively, look for a DOUT rising edge to determine the end of conversion. 3. Activate SCLK for a minimum of 13 clock cycles. The first falling clock edge will produce the MSB of the DOUT conversion. DOUT output data transitions on Data can be output in 1-byte chunks or continuously, as shown in Figure 8. The bytes will contain the result of the conversion padded with one leading 1, and trailing 0s if SCLK is still active with CS kept low. 1ST BYTE READ 2ND BYTE READ SCLK CS HI-Z DOUT tCONV HI-Z MSB D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 LSB EOC Figure 14. SPI/Microwire Serial Interface Timing (CPOL = CPHA = 0) SCLK CS HI-Z DOUT tCONV HI-Z MSB D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 LSB EOC Figure 15. QSPI Serial Interface Timing (CPOL = CPHA = 0) ______________________________________________________________________________________ 15 MAX187/MAX189 ____________Applications Information MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs SPI and Microwire When using SPI or QSPI, set CPOL = 0 and CPHA = 0. Conversion begins with a CS falling edge. DOUT goes low, indicating a conversion in progress. Wait until DOUT goes high or the maximum specified 8.5µs conversion time. Two consecutive 1-byte reads are required to get the full 12 bits from the ADC. DOUT output data transitions on SCLK’s falling edge and is clocked into the µP on SCLK’s rising edge. The first byte contains a leading 1 and 7 bits of conversion result. The second byte contains the remaining 5 bits and 3 trailing 0s. See Figure 13 for connections and Figure 14 for timing. QSPI Set CPOL = CPHA = 0. Unlike SPI, which requires two 1-byte reads to acquire the 12 bits of data from the ADC, QSPI allows the minimum number of clock cycles necessary to clock in the data. The MAX187/MAX189 require 13 clock cycles from the µP to clock out the 12 bits of data with no trailing 0s (Figure 15). The maximum clock frequency to ensure compatibility with QSPI is 2.77MHz. Opto-Isolated Interface, Serial-to-Parallel Conversion Many industrial applications require electrical isolation to separate the control electronics from hazardous electrical conditions, provide noise immunity, or prevent excessive current flow where ground disparities exist between the ADC and the rest of the system. Isolation amplifiers typically used to accomplish these tasks are expensive. In cases where the signal is eventually converted to a digital form, it is cost effective to isolate the input using opto-couplers in a serial link. The MAX187 is ideal in this application because it includes both T/H amplifier and voltage reference, operates from a single supply, and consumes very little power (Figure 16). CS/START +5V ON THIS SIDE OF BARRIER MUST BE ISOLATED POWER 6N136 +5V 3k 10µF 8 1 7 2 6 3 5 4 MAX187 0.1µF 1 2 4 ANALOG INPUT 4.7µF 5 VDD AIN REF GND 200Ω CS SCLK DOUT 8 1 7 2 8 6 3 6 5 4 3 7 3k 200Ω 74HC04 SER 13 470Ω 8 2 7 3 6 4 5 D11 (MSB) D10 D9 D8 +5V 8 9 QH′ 1 7 6 5 4 3 2 1 15 16 0.1µF 6N136 SIGNAL GROUND QH QG 74HC595 QF 11 QE SCK QD 12 QC RCK QB 10 QA SCLR 14 74HC04 6N136 SHDN SCLK/INPUT CLOCK +5V QH QG 74HC595 QF 11 QE SCK QD 12 QC RCK QB 10 QA +5V SCLR 14 SER 8.2k 13 7 6 5 4 3 2 1 15 16 D7 D6 D5 D4 D3 D2 D1 D0(LSB) +5V 8 0.1µF Figure 16. 12-Bit Isolated ADC 16 ______________________________________________________________________________________ +5V, Low-Power, 12-Bit Serial ADCs +5V Layout, Grounding, Bypassing VDD For best performance, use printed circuit boards. Wirewrap boards are not recommended. Board layout should ensure that digital and analog signal lines are separated from each other. Do not run analog and digital (especially clock) lines parallel to one another, or digital lines underneath the ADC package. Figure 17 shows the recommended system ground connections. A single-point analog ground (“star” ground point) should be established at GND, separate from the logic ground. All other analog grounds should be connected to this ground. The 16-pin versions also have a dedicated DGND pin available. Connect DGND to this star ground point for further noise reduction. No other digital system ground should be connected to this single-point analog ground. The ground return to the power supply for this ground should be low impedance and as short as possible for noise-free operation. High-frequency noise in the V DD power supply may affect the ADC’s high-speed comparator. Bypass this supply to the single-point analog ground with 0.01µF and 4.7µF bypass capacitors. Minimize capacitor lead lengths for best supply-noise rejection. If the +5V power supply is very noisy, a 10Ω resistor can be connected as a lowpass filter to attenuate supply noise (Figure 17). MAX187/MAX189 The ADC results are transmitted across a 1500V isolation barrier provided by three 6N136 opto-isolators. Isolated power must be supplied to the converter and the isolated side of the opto-couplers. 74HC595 threestate shift registers are used to construct a 12-bit parallel data output. The timing sequence is identical to the timing shown in Figure 8. Conversion speed is limited by the delay through the opto-isolators. With a 140kHz clock, conversion time is 100µs. The universal 12-bit parallel data output can also be used without the isolation stage when a parallel interface is required. Clock frequencies up to 2.9MHz are possible without violating the 20ns shift-register setup time. Delay or invert the clock signal to the shift registers beyond 2.9MHz. SUPPLIES GND R* = 10Ω 4.7µF 0.01µF AGND DGND MAX187 MAX189 +5V DGND DIGITAL CIRCUITRY *OPTIONAL Figure 17. Power-Supply Grounding Condition ______________________________________________________________________________________ 17 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs __Ordering Information (continued) PART ____Pin Configurations (continued) TEMP. RANGE PIN-PACKAGE ERROR (LSB) MAX187AEPA -40°C to +85°C 8 Plastic DIP ±1⁄2 MAX187BEPA -40°C to +85°C 8 Plastic DIP ±1 V DD 1 16 SCLK MAX187CEPA -40°C to +85°C 8 Plastic DIP ±2 N.C. 2 -40°C to +85°C 16 Wide SO ±1⁄2 15 CS MAX187AEWE AIN 3 MAX187BEWE -40°C to +85°C 16 Wide SO ±1 MAX187CEWE -40°C to +85°C 16 Wide SO ±2 MAX187AMJA -55°C to +125°C 8 CERDIP** ±1⁄2 MAX187BMJA -55°C to +125°C 8 CERDIP** ±1 MAX189ACPA 0°C to +70°C 8 Plastic DIP ±1⁄2 MAX189BCPA 0°C to +70°C 8 Plastic DIP ±1 MAX189CCPA 0°C to +70°C 8 Plastic DIP ±2 MAX189ACWE 0°C to +70°C 16 Wide SO ±1⁄2 MAX189BCWE 0°C to +70°C 16 Wide SO ±1 MAX189CCWE 0°C to +70°C 16 Wide SO ±2 MAX189BC/D 0°C to +70°C Dice* ±1 MAX189AEPA -40°C to +85°C 8 Plastic DIP ±1⁄2 MAX189BEPA -40°C to +85°C 8 Plastic DIP ±1 MAX189CEPA -40°C to +85°C 8 Plastic DIP ±2 MAX189AEWE -40°C to +85°C 16 Wide SO ±1⁄2 MAX189BEWE -40°C to +85°C 16 Wide SO ±1 MAX189CEWE -40°C to +85°C 16 Wide SO ±2 MAX189AMJA -55°C to +125°C 8 CERDIP** ±1⁄2 MAX189BMJA -55°C to +125°C 8 CERDIP** ±1 N.C. 4 N.C. 5 14 N.C. MAX187 MAX189 13 N.C. 12 DOUT SHDN 6 11 DGND N.C. 7 10 AGND REF 8 9 Wide SO * Dice are specified at TA = +25°C, DC parameters only. **Contact factory for availability and processing to MIL-STD-883. 18 ______________________________________________________________________________________ N.C. +5V, Low-Power, 12-Bit Serial ADCs MAX187/MAX189 ___________________Chip Topography MAX187/MAX189 V DD SCLK CS AIN 0.151" (3.84mm) DOUT DGND SHDN REF 0.117" (2.97mm) AGND AGND TRANSISTOR COUNT: 2278; SUBSTRATE CONNECTED TO VDD. ______________________________________________________________________________________ 19 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs ________________________________________________________________Package Information DIM E A2 A3 D A E1 0°-15° A1 C e L eA B1 eB B D1 P PACKAGE PLASTIC DUAL-IN-LINE A A1 A2 A3 B B1 C D1 E E1 e eA eB L DIM PINS D D D DIM D 0°- 8° A e B 0.101mm 0.005in. A1 C L INCHES MAX MIN 0.200 – – 0.015 0.175 0.125 0.080 0.055 0.020 0.016 0.065 0.045 0.012 0.008 0.090 0.050 0.625 0.600 0.575 0.525 – 0.100 – 0.600 0.700 – 0.150 0.120 A A1 B C E e H L 24 28 40 INCHES MAX MIN 0.104 0.093 0.012 0.004 0.019 0.014 0.013 0.009 0.299 0.291 0.050 0.419 0.394 0.050 0.016 DIM PINS E W PACKAGE SMALL OUTLINE H D D D D D INCHES MIN MAX 1.230 1.270 1.430 1.470 2.025 2.075 16 18 20 24 28 INCHES MIN MAX 0.398 0.413 0.447 0.463 0.496 0.512 0.598 0.614 0.697 0.713 MILLIMETERS MIN MAX – 5.08 0.38 – 3.18 4.45 1.40 2.03 0.41 0.51 1.14 1.65 0.20 0.30 1.27 2.29 15.24 15.88 13.34 14.61 2.54 – 15.24 – – 17.78 3.05 3.81 MILLIMETERS MIN MAX 31.24 32.26 36.32 37.34 51.44 52.71 MILLIMETERS MIN MAX 2.35 2.65 0.10 0.30 0.35 0.49 0.23 0.32 7.40 7.60 1.27 10.00 10.65 0.40 1.27 MILLIMETERS MIN MAX 10.10 10.50 11.35 11.75 12.60 13.00 15.20 15.60 17.70 18.10 21-0042A Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 20 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 © 1993 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.