EVALUATION KIT AVAILABLE MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs General Description Features The MAX187/MAX189 serial 12-bit analog-to-digital converters (ADCs) operate from a single +5V supply and accept a 0 to 5V analog input. Both parts feature an 8.5Fs successive-approximation ADC, a fast track/hold (1.5Fs), an on-chip clock, and a high-speed 3-wire serial interface. S 12-Bit Resolution 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, QSPIK, and MICROWIREM. S Low Power: 2A Shutdown Current 1.5mA Operating Current 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 PDIP and 16-pin SO packages. Power consumption is 7.5mW and reduces to only 10FW 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. S 1/2 LSB Integral Nonlinearity (MAX187A/MAX189A) S Internal Track/Hold, 75kHz Sampling Rate S Single +5V Operation S Internal 4.096V Buffered Reference (MAX187) S 3-Wire Serial Interface, Compatible with SPI, QSPI, and MICROWIRE S Small-Footprint 8-Pin PDIP and 16-Pin SO Applications Portable Data Logging Remote Digital Signal Processing Isolated Data Acquisition High-Accuracy Process Control Ordering Information appears at end of data sheet. For related parts and recommended products to use with this part, refer to www.maximintegrated.com/MAX187.related. Functional Diagram GND 5 REF10kI +2.5V DAC AV = 1.638 (4.096V) 6 DOUT 8 SCLK REF+ BANDGAP REFERENCE 12-BIT SAR (MAX187 ONLY) REF 4 AIN 2 OUTPUT SHIFT REGISTER T/H MAX187 MAX189 COMPARATOR BUFFER ENABLE/DISABLE VDD 1 CONTROL AND TIMING 7 CS 3 SHDN NOTE: PIN NUMBERS SHOWN ARE FOR 8-PIN DIPs ONLY QSPI is a trademark of Motorola. MICROWIRE is a registered trademark of National Semiconductor Corp. For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maximintegrated.com. 19-0196; Rev 1; 3/12 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)............................. .......20s DOUT Current..................................................................Q20mA Continuous Power Dissipation (TA = +70NC) 8-Pin PDIP (derate 9.1mW/NC above +70NC)..............727mW 16-Pin Wide SO (derate 14.5mW/NC above 70NC).....1157mW Operating Temperature Ranges MAX187_C_ _/MAX189_C_ _..............................0NC to +70NC MAX187_E_ _/MAX189_E_ _...........................-40NC to +85NC Storage Temperature Range.............................-60NC to +150NC Lead Temperature (soldering, 10s) .................................+300NC Soldering Temperature (reflow) .......................................+260NC 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%; VGND = 0V; unipolar input mode; 75ksps, fCLK = 4.0MHz, external clock (50% duty cycle); MAX187--internal reference: VREF = 4.096V, 4.7F capacitor at REF pin, or MAX189--external reference: VREF = 4.096V applied to REF pin, 4.7F 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 Relative Accuracy (Note 2) Differential Nonlinearity DNL MAX18_A Q1/2 MAX18_B Q1 MAX18_C Q2 No missing codes over temperature Q1 MAX18_A Offset Error Gain Error (Note 3) Q11/2 MAX18_B/C Q3 MAX187 Q3 MAX189A Q1 MAX189B/C Gain Temperature Coefficient LSB LSB LSB LSB Q3 External reference, 4.096V ppm/NC Q0.8 DYNAMIC SPECIFICATIONS (10kHz Sine Wave Input, 0 to 4.096VP-P, 75ksps) Signal-to-Noise Plus Distortion Ratio 70 SINAD Total Harmonic Distortion (Up to the 5th Harmonic) THD Spurious-Free Dynamic Range SFDR Small-Signal Bandwidth dB -80 80 Rolloff -3dB Full-Power Bandwidth dB dB 4.5 MHz 0.8 MHz CONVERSION RATE Conversion Time tCONV Track/Hold Acquisition Time tACQ Throughput Rate Maxim Integrated 5.5 8.5 Fs 75 ksps 1.5 External clock, 4MHz, 13 clocks Fs 2 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs ELECTRICAL CHARACTERISTICS (continued) (VDD = +5V 5%; VGND = 0V; unipolar input mode; 75ksps, fCLK = 4.0MHz, external clock (50% duty cycle); MAX187--internal reference: VREF = 4.096V, 4.7F capacitor at REF pin, or MAX189--external reference: VREF = 4.096V applied to REF pin, 4.7F capacitor at REF pin; TA = TMIN to TMAX; unless otherwise noted.) PARAMETER SYMBOL Aperture Delay CONDITIONS MIN tAPR Aperture Jitter TYP MAX UNITS 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) 4.076 TA = +25NC REF Output Voltage VREF TA = TMIN to TMAX 4.096 4.116 MAX187_C 4.060 4.132 MAX187_E 4.050 4.140 REF Short-Circuit Current Q30 REF Tempco Load Regulation (Note 5) MAX187AC/BC Q30 Q50 MAX187AE/BE Q30 Q60 MAX187C Q30 0 to 6mA output load 1 V mA ppm/NC mV EXTERNAL REFERENCE AT REF (Buffer Disabled, VREF = 4.096V) Input Voltage Range 2.50 Input Current VDD + 50mV 200 Input Resistance 12 Shutdown REF Input Current 350 20 1.5 V A kI 10 A DIGITAL INPUTS (SCLK, CS, SHDN) SCLK, CS Input High Voltage SCKL, CS Input Low Voltage SCLK, CS Input Hysteresis VINH 2.4 V VINL 0.8 VHYST 0.15 V V SCLK, CS Input Leakage IIN VIN = 0V or VDD 1 A SCLK, CS Input Capacitance CIN (Note 4) 15 pF 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 Maxim Integrated VDD - 50mV VSHDN = VDD or 0V 1.5 0.5 V 4.0 A VDD - 1.5 2.75 SHDN = Open SHDN = Open V -100 V V 100 nA 3 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs ELECTRICAL CHARACTERISTICS (continued) (VDD = +5V 5%; VGND = 0V; unipolar input mode; 75ksps, fCLK = 4.0MHz, external clock (50% duty cycle); MAX187--internal reference: VREF = 4.096V, 4.7F capacitor at REF pin, or MAX189--external reference: VREF = 4.096V applied to REF pin, 4.7F capacitor at REF pin; TA = TMIN to TMAX; unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DIGITAL OUTPUT (DOUT) Output Voltage Low VOL Output Voltage High VOH Three-State Leakage Current Three-State Output Capacitance IL COUT ISINK = 5mA 0.4 ISINK = 16mA 0.3 ISOURCE = 1mA 4 V V VCS = 5V VCS = 5V (Note 4) Q10 FA 15 pF 5.25 V POWER REQUIREMENTS Supply Voltage Supply Current VDD IDD 4.75 Operating mode MAX187 1.5 2.5 MAX189 1.0 2.0 2 10 FA Q0.06 Q0.5 mV Power-down mode Power-Supply Rejection PSR VDD = +5V Q5%; external reference, 4.096V; full-scale input (Note 6) mA TIMING CHARACTERISTICS (VDD = +5V 5%, TA = TMIN to TMAX; unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX tACQ CS = high (Note7) SCLK Fall to Output Data Valid tDQ CLOAD = 100pF CS Fall to Output Enable tDV CLOAD = 100pF 100 tTR CLOAD = 100pF 100 ns 5 MHz CS Rise to Output Disable 1.5 UNITS Track/Hold Acquisition Time s MAX18_ _C/E 20 150 MAX18_ _M 20 200 ns ns SCLK Clock Frequency tSCLK SCLK Pulse Width High tCH 100 ns SCLK Pulse Width Low SCLK Low to CS Fall Setup Time CS Pulse Width tCL 100 ns tCSO 50 ns tCS 500 ns 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 minimumtime needed for the signal to be acquired. Maxim Integrated 4 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Typical Operating Characteristics POWER-SUPPLY REJECTION vs. TEMPERATURE VREF vs. TEMPERATURE 0.12 0.10 0.08 0.06 0.04 0.02 4.089 4.088 4.087 4.086 4.085 4.084 4.083 4.082 4.081 0 4.080 -20 20 60 100 140 -60 -20 20 60 100 TEMPERATURE (C) TEMPERATURE (C) SUPPLY vs. TEMPERATURE SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE 1.8 MAX187 1.4 MAX189 1.0 0.6 140 MAX187 toc04 2.2 7 SHUTDOWN SUPPLY CURRENT (A) MAX187 toc03 -60 SUPPLY CURRENT (mA) MAX187 toc02 0.14 4.090 INTERNAL REFERENCE VOLTAGE (V) MAX187 toc01 POWER-SUPPLY REJECTION (mV) 0.16 6 5 4 3 2 1 0.2 0 -60 -20 20 60 TEMPERATURE (C) Maxim Integrated 100 140 -60 -20 20 60 100 140 TEMPERATURE (C) 5 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Pin Configurations TOP VIEW 1 + VDD 2 AIN 3 SHDN 4 REF MAX187 MAX189 SCLK 8 CS 7 DOUT 6 GND 5 PDIP + VDD 1 16 SCLK N.C. 2 15 CS AIN 3 MAX187 MAX189 N.C. 4 14 N.C. 13 N.C. N.C. 5 12 DOUT SHDN 6 11 DGND N.C. 7 10 AGND REF 8 9 N.C. Wide SO Pin Description PIN NAME FUNCTION PDIP WIDE SO 1 1 VDD Supply Voltage. +5V, Q5% 2 3 AIN Sampling Analog Input. 0V to VREF range 3 6 4 8 SHDN Three-Level Shutdown Input. Pulling SHDN low shuts the MAX187/MAX189 down to 10FA (max) supply current. Both MAX187 and MAX189 are fully operational with either SHDN high or unconnected. For the MAX187, pulling SHDN high enables the internal reference, and letting SHDN unconnected disables the internal reference and allows for the use of an external reference. 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 4.7FF if internal reference is used, and with 0.1FF if an external reference is applied. Analog and Digital Ground 5 -- GND -- 10 AGND Analog Ground -- 11 DGND Digital Ground 6 12 DOUT Serial Data Output. Data changes state at SCLK's falling edge. 7 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. No Connection. Not internally connected. Connect to AGND for best noise performance. Maxim Integrated Active-Low Chip Select. Initiates conversions on the falling edge. When CS is high, DOUT is high impedance. 6 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs 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 10s, 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 (Ps). Both converters have two modes: normal and shutdown. Pulling SHDN low shuts the device down and reduces supply current to below 10A, 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) REFERENCE 0V +4.096V External Reference 0V VREF For specified accuracy, the external reference voltage range spans from +2.5V to VDD. +5V 3kI DOUT DOUT CLOAD = 100pF 3kI 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 3kI DOUT DOUT CLOAD = 100pF 3kI DGND A. VOH TO HIGH-Z CLOAD = 100pF DGND B. VOL TO HIGH-Z Figure 2. Load Circuits for DOUT Disable Time Maxim Integrated 7 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs 4.7F 4.7F 0.1F 0.1F 1 +5V ANALOG INPUT 0 TO +5V 2 SHUTDOWN INPUT 3 ON AIN MAX187 SHDN 4 OFF SCLK VDD CS DOUT GND REF 8 +5V 7 SERIAL INTERFACE OFF REFERENCE INPUT 5 4.7F Figure 3a. MAX187 Operational Diagram 12-BIT CAPACITIVE DAC TRACK INPUT CHOLD 16pF - CPACKAGE CSWITCH COMPARATOR ZERO + RIN 5kI HOLD TRACK GND 3 SCLK VDD AIN MAX189 SHDN CS DOUT 8 7 SERIAL INTERFACE 6 ON 4 REF GND 5 0.1F Figure 3b. MAX189 Operational Diagram REF AIN 2 ANALOG INPUT 0 TO +5V SHUTDOWN INPUT 6 1 HOLD AT THE SAMPLING INSTANT, THE INPUT SWITCHES FROM AIN TO GND. 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 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 Maxim Integrated where RIN = 5kI, RS = the source impedance of the input signal, and tACQ is never less than 1.5Fs. Source impedances below 5kI do not significantly affect the AC performance of the ADC. Input Bandwidth The ADCs' input tracking circuitry has a 4.5MHz smallsignal bandwidth, and an 8V/Fs 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. 8 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs 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. 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 higher-frequency operation, the MAX427 and OP27 are practical choices. The allowed input frequency range is limited 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. Internal Reference The MAX187 has an on-chip reference with a buffered temperature-compensated bandgap diode, lasertrimmed to +4.096V Q0.5%. 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 4.7FF 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. 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 12kI for DC currents. During conversion, the external reference must be able to deliver up to 350FA DC load current and have an output impedance of 10I or less. The recommended minimum value for the bypass capacitor is 0.1FF. If the reference has higher output impedance or is noisy, bypass it close to the REF pin with a 4.7FF capacitor. COMPLETE CONVERSION SEQUENCE CS tWAKE SHDN DOUT CONVERSION 1 POWERED UP CONVERSION 1 POWERED DOWN POWERED UP Figure 5. MAX187/MAX189 Shutdown Sequence Maxim Integrated 9 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Serial Interface Initialization After Power-Up and Starting a Conversion When power is first applied, it takes the fully discharged 4.7FF 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 8.5Fs 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 2Fs. For the MAX189, this time depends on the time in shutdown (see Figure 7) because the external 4.7FF reference bypass capacitor loses charge slowly during shutdown (see the specifications for shutdown, REF Input Current = 10FA max). External Clock The actual conversion does not require the external clock. This frees the FP from the burden of running the SAR conversion clock, and allows the conversion result to be read back at the FP's convenience at any clock rate from 0 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. 3.0 10,000 2.0 tWAKE (ms) SUPPLY CURRENT (A) 2.5 1000 MAX187 100 1.0 MAX189* 10 1.5 0.5 *REF CONNECTED TO VDD 1 0.1 1 10 100 1k 10k 100k CONVERSIONS PER SECOND Figure 6. Average Supply Current vs. Conversion Rate Maxim Integrated 0 0.0001 0.001 0.01 0.1 1 10 TIME IN SHUTDOWN (s) Figure 7. tWAKE vs. Time in Shutdown (MAX187 Only) 10 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs CS 1 SCLK 4 B11 B10 B9 DOUT 8 B8 B7 B6 B5 12 B4 B3 B2 B1 B0 EOC INTERFACE IDLE A/D STATE TRACK CONVERSION IN PROGRESS EOC CONVERSION 0 8.5s (tCONV) TRAILING ZEROS CLOCK OUTPUT DATA IDLE TRACK 0s MINIMUM CYCLE TIME CONV. 1 0s 12 x 0.250s = 3.25s 0.5s (tCS) TOTAL = 12.25s Figure 8. MAX187/MAX189 Interface Timing Sequence tCS CS tCS0 tCH SCLK tDO tDV tCL tCONV DOUT B2 tTR B1 B0 tAPR INTERNAL T/H (TRACK) (HOLD) (TRACK) Figure 9. MAX187/MAX189 Detailed Serial-Interface Timing Maxim Integrated 11 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs 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. 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 VREF = +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 low-distortion 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 input frequency. ADCs have traditionally been evaluated by specifications such as Zero and FullScale 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. 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. 20 OUTPUT CODE FULL-SCALE TRANSITION 11...111 fS = 75ksps fT = 10kHz TA = +25C 0 11...110 -20 FS = +4.096V 1 LSB = FS 4096 AMPLITUDE (dB) 11...101 -40 -60 -80 00...011 -100 00...010 00...01 -120 00...000 0 1 2 FS 3 INPUT VOLTAGE (LSBs) FS - 3/2 LSB -140 0 18.75 37.5 FREQUENCY (kHz) Figure 10. MAX187/MAX189 UnipolarTransfer Function, 4.096V = Full Scale Maxim Integrated Figure 11. MAX187/MAX189 FFT plot 12 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs 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. 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 V2 2 + V3 2 + V4 2 + ... VN 2 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. 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 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 FP 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, tACQ, before starting a new conversion. 12.2 12.0 11.8 11.6 EFFECTIVE BITS Applications Information 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. 11.4 11.2 11.0 10.8 SPI and MICROWIRE 10.6 10.4 (UNDERSAMPLED) 10.2 1 10 100 INPUT FREQUENCY (kHz) Figure 12. Effective Bits vs. Input Frequency 1000 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 8.5Fs 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 FP 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. Maxim Integrated 13 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs QSPI I/O 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 FP 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. CS SCK SCLK MISO DOUT +5V MAX187 MAX189 Opto-Isolated Interface, Serial-to-Parallel Conversion SS 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). 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 three-state 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 100Fs. 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. A. SPI CS CS SCK SCLK MISO DOUT +5V MAX187 MAX189 SS B. QSPI I/O CS SK SCLK SI DOUT MAX187 MAX189 C. MICROWIRE Figure 13. Common Serial-Interface Connections to the MAX187/MAX189 1ST BYTE READ 2ND BYTE READ SCLK CS HI-Z DOUT tCONV MSB D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 LSB HI-Z EOC Figure 14. SPI/MICROWIRE Serial Interface Timing (CPOL = CPHA = 0) Maxim Integrated 14 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs SCLK CS tCONV HI-Z HI-Z DOUT MSB D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 LSB EOC Figure 15. QSPI Serial Interface Timing (CPOL = CPHA = 0) +5V ON THIS SIDE OF BARRIER MUST BE ISOLATED POWER +5V 3kI 6N136 +5V 1 8 2 7 CS/START SCLK/INPUT CLOCK 200I 3 6 4 74HC04 5 10F 6N136 MAX187 0.1F 1 2 4 ANALOG INPUT 5 4.7F 1 8 VDD SHDN AIN CS REF GND SCLK DOUT 3 7 3kI 8 7 2 6 3 13 4 6N136 1 8 2 7 3 6 6 5 4 3 2 1 15 16 8 9 QH' QH QG 14 SER 74HC595 QF 11 QE SCK QD 12 QC RCK QB 10 SCLR +5V QA 6 5 SIGNAL GROUND 7 D11 (MSB) D10 D9 D8 +5V 0.1F 200I 74HC04 470I QH 14 QG SER 74HC595 QF 11 QE SCK QD 12 QC RCK QB 10 QA SCLR 8.2kI 13 8 7 6 5 4 3 2 1 15 16 D7 D6 D5 D4 D3 D10 D1 D0 (LSB) +5V 0.1F 4 5 Figure 16. 12-Bit Isolated ADC Maxim Integrated 15 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Layout, Grounding, Bypassing 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 singlepoint 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 VDD power supply may affect the ADC's high-speed comparator. Bypass this supply to the single-point analog ground with 0.01FF and 4.7FF bypass capacitors. Minimize capacitor lead lengths for best supply-noise rejection. If the +5V power supply is very noisy, a 10I resistor can be connected as a lowpass filter to attenuate supply noise (Figure 17). Maxim Integrated SUPPLIES +5V GND R* = 10I 4.7F 0.01F VDD AGND DGND MAX187 MAX189 +5V DGND DIGITAL CIRCUITRY *OPTIONAL Figure 17. Power-Supply Grounding Condition 16 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Ordering Information PINPACKAGE ERROR (LSB) PART TEMP RANGE MAX187ACPA+ 0NC to +70NC 8 PDIP 1/2 MAX187BCPA+ 0NC to +70NC 8 PDIP 1 MAX187CCPA+ 0NC to +70NC 8 PDIP 2 MAX187ACWE+ 0NC to +70NC 16 Wide SO 1/2 MAX187BCWE+ 0NC to +70NC 16 Wide SO 1 MAX187CCWE+ 0NC to +70NC 16 Wide SO MAX187AEPA+ -40NC to +85NC 8 PDIP 1/2 MAX187BEPA+ -40NC to +85NC 8 PDIP 1 MAX187CEPA+ -40NC to +85NC 8 PDIP 2 MAX187AEWE+ -40NC to +85NC 16 Wide SO 1/2 MAX187BEWE+ -40NC to +85NC 16 Wide SO 1 MAX187CEWE+ -40NC to +85NC 16 Wide SO MAX189ACPA+ 0NC to +70NC 8 PDIP 1/2 MAX189BCPA+ 0NC to +70NC 8 PDIP 1 MAX189CCPA+ 0NC to +70NC 8 PDIP MAX189ACWE+ 0NC to +70NC 16 Wide SO 1/2 MAX189BCWE+ 0NC to +70NC 16 Wide SO 1 MAX189CCWE+ 0NC to +70NC 16 Wide SO MAX189AEPA+ -40NC to +85NC 8 PDIP 1/2 MAX189BEPA+ -40NC to +85NC 8 PDIP 1 MAX189CEPA+ -40NC to +85NC 8 PDIP MAX189AEWE+ -40NC to +85NC 16 Wide SO 1/2 MAX189BEWE+ -40NC to +85NC 16 Wide SO 1 MAX189CEWE+ -40NC to +85NC 16 Wide SO 2 2 2 Chip Information PROCESS: BiCMOS Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 8 PDIP P8+3 21-0043 -- 16 SO W16+3 21-0042 90-0107 2 2 2 *Denotes a lead(Pb)-free/RoHS-compliant package. Maxim Integrated 17 MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Revision History REVISION NUMBER REVISION DATE 0 10/93 Initial release 1 3/12 Updated the Electrical Characteristics and Ordering Information. DESCRIPTION PAGES CHANGED -- 1, 3, 18 Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 (c) 2012 Maxim Integrated Products, Inc. 18 The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.