19-5225; Rev 0; 4/10 KIT ATION EVALU E L B AVAILA 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs Features o High-Speed I2C-Compatible Serial Interface o o o o o o o o 400kHz Fast Mode 1.7MHz High-Speed Mode Single-Supply 2.7V to 3.6V (MAX11645) 4.5V to 5.5V (MAX11644) Internal Reference 2.048V (MAX11645) 4.096V (MAX11644) External Reference: 1V to VDD Internal Clock 2-Channel Single-Ended or 1-Channel Fully Differential Internal FIFO with Channel-Scan Mode Low Power 670µA at 94.4ksps 230µA at 40ksps 60µA at 10ksps 6µA at 1ksps 0.5µA in Power-Down Mode Software-Configurable Unipolar/Bipolar Small, 8-Pin µMAX Package Applications Handheld Portable Applications Received-Signal-Strength Indicators Medical Instruments System Supervision Battery-Powered Test Equipment Power-Supply Monitoring Solar-Powered Remote Systems Ordering Information I2C SLAVE ADDRESS PART TEMP RANGE PINPACKAGE MAX11644EUA+ -40°C to +85°C 8 µMAX 0110110 MAX11645EUA+ -40°C to +85°C 8 µMAX 0110110 +Denotes a lead(Pb)-free/RoHs-compliant package. Typical Operating Circuit and Selector Guide appear at end of data sheet. AutoShutdown is a trademark and µMAX is a registered trademark of Maxim Integrated Products, Inc. ________________________________________________________________ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX11644/MAX11645 General Description The MAX11644/MAX11645 low-power, 12-bit, 1-/2channel analog-to-digital converters (ADCs) feature internal track/hold (T/H), voltage reference, clock, and an I2C-compatible 2-wire serial interface. These devices operate from a single supply of 2.7V to 3.6V (MAX11645) or 4.5V to 5.5V (MAX11644) and require only 670µA at the maximum sampling rate of 94.4ksps. Supply current falls below 230µA for sampling rates under 40ksps. AutoShutdown™ powers down the devices between conversions, reducing supply current to less than 1µA at low throughput rates. The MAX11644/MAX11645 each measure two single-ended or one differential input. The fully differential analog inputs are software configurable for unipolar or bipolar, and single-ended or differential operation. The full-scale analog input range is determined by the internal reference or by an externally applied reference voltage ranging from 1V to VDD. The MAX11645 features a 2.048V internal reference and the MAX11644 features a 4.096V internal reference. The MAX11644/MAX11645 are available in an 8-pin µMAX® package. The MAX11644/MAX11645 are guaranteed over the extended temperature range (-40°C to +85°C). For pin-compatible 10-bit parts, refer to the MAX11646/MAX11647 data sheet. MAX11644/MAX11645 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 4-/12-Channel, 2-Wire Serial, 12-Bit ADCs ABSOLUTE MAXIMUM RATINGS Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-60°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Soldering Temperature (reflow) .......................................+260°C VDD to GND ..............................................................-0.3V to +6V AIN0, AIN1, REF to GND ..............................-0.3V to the lower of (VDD + 0.3V) and 6V SDA, SCL to GND.....................................................-0.3V to +6V Maximum Current into Any Pin .........................................±50mA Continuous Power Dissipation (TA = +70°C) 8-Pin µMAX (derate 4.5mW/°C above +70°C) ..............362mW 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 = 2.7V to 3.6V (MAX11645), VDD = 4.5V to 5.5V (MAX11644), VREF = 2.048V (MAX11645), VREF = 4.096V (MAX11644), fSCL = 1.7MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C, see Tables 1–5 for programming notation.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC ACCURACY (Note 1) Resolution 12 Bits Relative Accuracy INL (Note 2) ±1 LSB Differential Nonlinearity DNL No missing codes over temperature ±1 LSB ±4 LSB Offset Error Offset-Error Temperature Coefficient Relative to FSR Gain Error (Note 3) Gain-Temperature Coefficient Relative to FSR 0.3 ppm/°C ±4 LSB 0.3 ppm/°C Channel-to-Channel Offset Matching ±0.1 LSB Channel-to-Channel Gain Matching ±0.1 LSB 70 dB DYNAMIC PERFORMANCE (fIN(SINE-WAVE) = 10kHz, VIN(P-P) = VREF, fSAMPLE = 94.4ksps) Signal-to-Noise Plus Distortion SINAD Total Harmonic Distortion THD Spurious-Free Dynamic Range SFDR Up to the 5th harmonic -78 dB 78 dB Full-Power Bandwidth SINAD > 68dB 3 MHz Full-Linear Bandwidth -3dB point 5 MHz CONVERSION RATE Conversion Time (Note 4) Throughput Rate tCONV fSAMPLE Internal clock External clock 51 External clock 94.4 800 Internal Clock Frequency 2 10.6 Internal clock, SCAN[1:0] = 01 Track/Hold Acquisition Time Aperture Delay (Note 5) 7.5 ksps ns 2.8 tAD µs External clock, fast mode 60 External clock, high-speed mode 30 _______________________________________________________________________________________ MHz ns 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs (VDD = 2.7V to 3.6V (MAX11645), VDD = 4.5V to 5.5V (MAX11644), VREF = 2.048V (MAX11645), VREF = 4.096V (MAX11644), fSCL = 1.7MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C, see Tables 1–5 for programming notation.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS ANALOG INPUT (AIN0/AIN1) Input Voltage Range, SingleEnded and Differential (Note 6) Input Multiplexer Leakage Current Input Capacitance Unipolar 0 VREF Bipolar 0 ±VREF/2 ±0.01 On/off leakage current, VAIN_ = 0 or VDD CIN ±1 22 V µA pF INTERNAL REFERENCE (Note 7) Reference Voltage VREF Reference-Voltage Temperature Coefficient TA = +25°C MAX11645 1.968 2.048 2.128 MAX11644 3.936 4.096 4.256 TCVREF 25 REF Short-Circuit Current ppm/°C 2 REF Source Impedance V 1.5 mA kΩ EXTERNAL REFERENCE REF Input Voltage Range VREF (Note 8) REF Input Current IREF fSAMPLE = 94.4ksps 1 VDD V 40 µA DIGITAL INPUTS/OUTPUTS (SCL, SDA) Input-High Voltage VIH Input-Low Voltage VIL Input Hysteresis 0.7 x VDD VHYST Input Current IIN Input Capacitance CIN Output Low Voltage VOL V 0.3 x VDD 0.1 x VDD V V ±10 VIN = 0 to VDD 15 ISINK = 3mA µA pF 0.4 V POWER REQUIREMENTS Supply Voltage VDD MAX11645 2.7 3.6 MAX11644 4.5 5.5 Internal reference 900 1150 External reference 670 900 Internal reference 530 External reference 230 fSAMPLE = 10ksps internal clock Internal reference 380 External reference 60 fSAMPLE =1ksps internal clock Internal reference 330 External reference 6 fSAMPLE = 94.4ksps external clock fSAMPLE = 40ksps internal clock Supply Current IDD Power-Supply Rejection Ratio PSRR V µA Shutdown (internal REF off) 0.5 10 Full-scale input (Note 9) ±0.5 ±2.0 LSB/V _______________________________________________________________________________________ 3 MAX11644/MAX11645 ELECTRICAL CHARACTERISTICS (continued) MAX11644/MAX11645 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs TIMING CHARACTERISTICS (Figure 1) (VDD = 2.7V to 3.6V (MAX11645), VDD = 4.5V to 5.5V (MAX11644), VREF = 2.048V (MAX11645), VREF = 4.096V (MAX11644), fSCL = 1.7MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C, see Tables 1–5 for programming notation.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 400 kHz TIMING CHARACTERISTICS FOR FAST MODE Serial-Clock Frequency fSCL Bus Free Time Between a STOP (P) and a START (S) Condition tBUF 1.3 µs Hold Time for START Condition tHD,STA 0.6 µs Low Period of the SCL Clock tLOW 1.3 µs High Period of the SCL Clock tHIGH 0.6 µs Setup Time for a Repeated START (Sr) Condition tSU,STA 0.6 µs Data Hold Time tHD,DAT Data Setup Time tSU,DAT (Note 10) 0 900 100 ns ns Rise Time of Both SDA and SCL Signals, Receiving tR Measured from 0.3VDD - 0.7VDD 20 + 0.1CB 300 ns Fall Time of SDA Transmitting tF Measured from 0.3VDD - 0.7VDD (Note 11) 20 + 0.1CB 300 ns Setup Time for STOP Condition tSU,STO 0.6 µs Capacitive Load for Each Bus Line CB 400 pF Pulse Width of Spike Suppressed tSP 50 ns 1.7 MHz TIMING CHARACTERISTICS FOR HIGH-SPEED MODE (CB = 400pF, Note 12) Serial-Clock Frequency Hold Time, Repeated START Condition fSCLH (Note 13) tHD,STA 160 ns Low Period of the SCL Clock tLOW 320 ns High Period of the SCL Clock tHIGH 120 ns Setup Time for a Repeated START Condition tSU,STA 160 ns Data Hold Time tHD,DAT Data Setup Time tSU,DAT 10 tRCL 20 Rise Time of SCL Signal (Current Source Enabled) 4 (Note 10) 0 _______________________________________________________________________________________ 150 ns ns 80 ns 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs (VDD = 2.7V to 3.6V (MAX11645), VDD = 4.5V to 5.5V (MAX11644), VREF = 2.048V (MAX11645), VREF = 4.096V (MAX11644), fSCL = 1.7MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C, see Tables 1–5 for programming notation.) PARAMETER Rise Time of SCL Signal After Acknowledge Bit SYMBOL CONDITIONS MIN TYP MAX UNITS 160 ns tRCL1 Measured from 0.3VDD - 0.7VDD 20 Fall Time of SCL Signal tFCL Measured from 0.3VDD - 0.7VDD 20 80 ns Rise Time of SDA Signal tRDA Measured from 0.3VDD - 0.7VDD 20 160 ns Fall Time of SDA Signal tFDA Measured from 0.3VDD - 0.7VDD (Note 11) 20 160 ns 400 pF 10 ns Setup Time for STOP Condition tSU, STO Capacitive Load for Each Bus Line CB Pulse Width of Spike Suppressed tSP 160 (Notes 10 and 13) 0 ns Note 1: For DC accuracy, the MAX11644 is tested at VDD = 5V and the MAX11645 is tested at VDD = 3V with an external reference for both ADCs. All devices are configured for unipolar, single-ended inputs. Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after the full-scale range and offsets have been calibrated. Note 3: Offset nulled. Note 4: Conversion time is defined as the number of clock cycles needed for conversion multiplied by the clock period. Conversion time does not include acquisition time. SCL is the conversion clock in the external clock mode. Note 5: A filter on the SDA and SCL inputs suppresses noise spikes and delays the sampling instant. Note 6: The absolute input voltage range for the analog inputs (AIN0/AIN1) is from GND to VDD. Note 7: When the internal reference is configured to be available at REF (SEL[2:1] = 11), decouple REF to GND with a 0.1µF capacitor and a 2kΩ series resistor (see the Typical Operating Circuit). Note 8: ADC performance is limited by the converter’s noise floor, typically 300µVP-P. Note 9: Measured for the MAX11645 as: ⎡ 2N ⎤ ⎥ ⎢⎡⎣VFS (3.6V) − VFS (2.7V)⎤⎦ × VREF ⎥⎦ ⎢⎣ (3.6V − 2.7V) and for the MAX11644, where N is the number of bits: ⎡ 2N ⎤ ⎥ ⎢⎡⎣VFS (5.5V) − VFS (4.5V)⎤⎦ × VREF ⎥⎦ ⎢⎣ (5.5V − 4.5V) Note 10: A master device must provide a data hold time for SDA (referred to VIL of SCL) to bridge the undefined region of SCL’s falling edge (see Figure 1). Note 11: The minimum value is specified at TA = +25°C. Note 12: CB = total capacitance of one bus line in pF. Note 13: fSCL must meet the minimum clock low time plus the rise/fall times. _______________________________________________________________________________________ 5 MAX11644/MAX11645 TIMING CHARACTERISTICS (Figure 1) (continued) Typical Operating Characteristics (VDD = 3.3V (MAX11645), VDD = 5V (MAX11644), fSCL = 1.7MHz, 50% duty cycle, fSAMPLE = 94.4ksps, single-ended, unipolar, TA = +25°C, unless otherwise noted.) INTEGRAL NONLINEARITY vs. DIGITAL CODE 0.8 0.6 0.4 0.1 0.2 INL (LSB) 0.2 0 -0.1 0 -0.2 -0.2 -0.4 -0.3 -0.6 -0.4 -0.8 -0.5 500 1000 1500 2000 2500 3000 3500 4000 0 DIGITAL OUTPUT CODE 0 30k 40k MAX11644 toc05 MAX11644 toc04 0.6 SDA = SCL = VDD 0.5 0.4 600 INTERNAL REFERENCE MAX11645 0.3 500 0.2 EXTERNAL REFERENCE MAX11644 350 0.1 EXTERNAL REFERENCE MAX11645 0 300 -40 -25 -10 5 20 35 50 65 3.7 4.2 4.7 5.2 SUPPLY VOLTAGE (V) SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE ANALOG SUPPLY CURRENT vs. CONVERSION RATE (EXTERNAL CLOCK) 1000 MAX11644 toc06 0.45 MAX11644 900 0.30 0.25 MAX11645 INTERNAL REFERENCE ALWAYS ON 800 AVERAGE IDD (µA) 0.35 0.20 3.2 TEMPERATURE (°C) 0.50 0.40 2.7 80 MAX11644 toc07 450 400 SUPPLY CURRENT (µA) 20k FREQUENCY (Hz) IDD (µA) SUPPLY CURRENT (µA) SETUP BYTE EXT REF: 10111011 INT REF: 11011011 650 10k SHUTDOWN SUPPLY CURRENT vs. SUPPLY VOLTAGE INTERNAL REFERENCE MAX11644 700 700 600 500 400 0.15 300 0.10 200 0.05 100 EXTERNAL REFERENCE 0 0 -40 -25 -10 5 20 35 50 TEMPERATURE (°C) 6 -100 DIGITAL OUTPUT CODE 800 550 -80 -140 500 1000 1500 2000 2500 3000 3500 4000 SUPPLY CURRENT vs. TEMPERATURE 750 -60 -120 -1.0 0 fSAMPLE = 94.4ksps fIN = 10kHz -40 AMPLITUDE (dBc) 0.3 -20 MAX11644 toc02 0.4 FFT PLOT 1.0 MAX11644 toc01 0.5 65 80 MAX11644 toc03 DIFFERENTIAL NONLINEARITY vs. DIGITAL CODE DNL (LSB) MAX11644/MAX11645 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs 0 20 40 60 CONVERSION RATE (ksps) _______________________________________________________________________________________ 80 100 50k 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs NORMALIZED REFERENCE VOLTAGE vs. SUPPLY VOLTAGE INTERNAL REFERENCE VOLTAGE vs. TEMPERATURE NORMALIZED TO VALUE AT TA = +25°C MAX11644 1.00006 1.0004 1.00004 1.0002 1.00002 1.0000 0.9994 1.00000 0.99998 0.9998 0.9996 MAX11644 NORMALIZED TO REFERENCE VALUE AT VDD = 5V 1.00008 VREF (V) VREF NORMALIZED 1.0006 1.00010 0.99996 MAX11645 MAX11645 NORMALIZED TO REFERENCE VALUE AT VDD = 3.3V 0.99994 0.99992 0.9992 0.99990 0.9990 -40 -25 -10 5 20 35 50 65 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4 80 VDD (V) TEMPERATURE (°C) OFFSET ERROR vs. TEMPERATURE 1.6 1.2 OFFSET ERROR (LSB) -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 MAX11644 toc12 -0.1 OFFSET ERROR (LSB) OFFSET ERROR vs. SUPPLY VOLTAGE 2.0 MAX11644 toc11 0 0.8 0.4 0 -0.4 -0.8 -0.8 -1.2 -0.9 -1.6 -1.0 -2.0 -40 -25 -10 5 20 35 50 65 80 2.7 3.2 3.7 TEMPERATURE (°C) 1.6 1.6 1.2 GAIN ERROR (LSB) 1.4 1.2 1.0 0.8 0.8 0.4 0 -0.4 0.6 -0.8 0.4 -1.2 0.2 -1.6 0 -2.0 5 20 35 50 TEMPERATURE (°C) 5.2 5.5 65 80 MAX11644 toc14 2.0 MAX11644 toc13 1.8 -10 4.7 GAIN ERROR vs. SUPPLY VOLTAGE GAIN ERROR vs. TEMPERATURE -40 -25 4.2 VDD (V) 2.0 GAIN ERROR (LSB) MAX11644 toc10 1.0008 MAX11644 toc09 1.0010 2.7 3.2 3.7 4.2 4.7 5.2 5.5 VDD (V) _______________________________________________________________________________________ 7 MAX11644/MAX11645 Typical Operating Characteristics (continued) (VDD = 3.3V (MAX11645), VDD = 5V (MAX11644), fSCL = 1.7MHz, 50% duty cycle, fSAMPLE = 94.4ksps, single-ended, unipolar, TA = +25°C, unless otherwise noted.) 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs MAX11644/MAX11645 Pin Configuration TOP VIEW + AIN0 1 AIN1 2 N.C. MAX11644 MAX11645 3 REF 4 8 VDD 7 GND 6 SDA 5 SCL µMAX Pin Description PIN NAME 1, 2 AIN0, AIN1 FUNCTION 3 N.C. 4 REF Reference Input/Output. Selected in the setup register (see Tables 1 and 6). 5 SCL Clock Input Analog Inputs No Connection. Not internally connected. 6 SDA Data Input/Output 7 GND Ground 8 VDD Positive Supply. Bypass to GND with a 0.1µF capacitor. A) F/S-MODE 2-WIRE SERIAL-INTERFACE TIMING tR tF t SDA tSU,DAT tHD,DAT tLOW tHD,STA tBUF tSU,STA tSU,STO SCL tHD,STA tHIGH tR tF S A Sr P B) HS-MODE 2-WIRE SERIAL-INTERFACE TIMING S tRDA tFDA SDA tSU,DAT tHD,DAT tLOW tBUF tHD,STA tSU,STO tSU,STA SCL tHD,STA tHIGH tRCL tFCL tRCL1 S Sr HS MODE A S P F/S MODE Figure 1. 2-Wire Serial-Interface Timing 8 _______________________________________________________________________________________ 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs MAX11644/MAX11645 SDA SCL INPUT SHIFT REGISTER VDD SETUP REGISTER GND CONTROL LOGIC INTERNAL OSCILLATOR CONFIGURATION REGISTER AIN0 AIN1 T/H ANALOG INPUT MUX 12-BIT ADC OUTPUT SHIFT REGISTER AND RAM REF REFERENCE 4.096V (MAX11644) 2.048V (MAX11645) MAX11644 MAX11645 REF Figure 2. Simplified Functional Diagram serial interface supporting data rates up to 1.7MHz. Figure 2 shows the simplified internal structure for the MAX11644/MAX11645. VDD IOL Power Supply VOUT SDA 400pF IOH The MAX11644/MAX11645 operate from a single supply and consume 670µA (typ) at sampling rates up to 94.4ksps. The MAX11645 feature a 2.048V internal reference and the MAX11644 feature a 4.096V internal reference. All devices can be configured for use with an external reference from 1V to VDD. Analog Input and Track/Hold Figure 3. Load Circuit Detailed Description The MAX11644/MAX11645 analog-to-digital converters (ADCs) use successive-approximation conversion techniques and fully differential input track/hold (T/H) circuitry to capture and convert an analog signal to a serial 12-bit digital output. The MAX11644/MAX11645 measure either two single-ended or one differential input(s). These devices feature a high-speed, 2-wire The MAX11644/MAX11645 analog-input architecture contains an analog-input multiplexer (mux), a fully differential track-and-hold (T/H) capacitor, T/H switches, a comparator, and a fully differential switched capacitive digital-to-analog converter (DAC) (Figure 4). In single-ended mode, the analog input multiplexer connects CT/H between the analog input selected by CS[0] (see the Configuration/Setup Bytes (Write Cycle) section) and GND (Table 3). In differential mode, the analog-input multiplexer connects CT/H to the + and analog inputs selected by CS[0] (Table 4). _______________________________________________________________________________________ 9 During the acquisition interval, the T/H switches are in the track position and CT/H charges to the analog input signal. At the end of the acquisition interval, the T/H switches move to the hold position retaining the charge on CT/H as a stable sample of the input signal. During the conversion interval, the switched capacitive DAC adjusts to restore the comparator input voltage to 0V within the limits of a 12-bit resolution. This action requires 12 conversion clock cycles and is equivalent to transferring a charge of 11pF x (VIN+ - VIN-) from CT/H to the binary weighted capacitive DAC, forming a digital representation of the analog input signal. MAX11645 hold SCL low. With external clock mode, the T/H circuitry enters track mode after a valid address on the rising edge of the clock during the read (R/W = 1) bit. Hold mode is then entered on the rising edge of the second clock pulse during the shifting out of the first byte of the result. The conversion is performed during the next 12 clock cycles. The time required for the T/H circuitry to acquire an input signal is a function of the input sample capacitance. If the analog-input source impedance is high, the acquisition time constant lengthens and more time must be allowed between conversions. The acquisition time (tACQ) is the minimum time needed for the signal to be acquired. It is calculated by: tACQ ≥ 95 (RSOURCE + RIN) x CIN Sufficiently low source impedance is required to ensure an accurate sample. A source impedance of up to 1.5kΩ does not significantly degrade sampling accuracy. To minimize sampling errors with higher source impedances, connect a 100pF capacitor from the analog input to GND. This input capacitor forms an RC filter with the source impedance limiting the analog-input bandwidth. For larger source impedances, use a buffer amplifier to maintain analog-input signal integrity and bandwidth. When operating in internal clock mode, the T/H circuitry enters its tracking mode on the eighth rising clock edge of the address byte. See the Slave Address section. The T/H circuitry enters hold mode on the falling clock edge of the acknowledge bit of the address byte (the ninth clock pulse). A conversion or a series of conversions is then internally clocked and the MAX11644/ where RSOURCE is the analog-input source impedance, RIN = 2.5kΩ, and CIN = 22pF. tACQ is 1.5/fSCL for internal clock mode and tACQ = 2/fSCL for external clock mode. Analog Input Bandwidth The MAX11644/MAX11645 feature input-tracking circuitry with a 5MHz small-signal bandwidth. The 5MHz input bandwidth makes it possible to digitize highspeed transient events and measure periodic signals with bandwidths exceeding the ADC’s sampling rate by using under sampling techniques. To avoid high-frequency signals being aliased into the frequency band of interest, anti-alias filtering is recommended. REF HOLD ANALOG INPUT MUX CT/H CAPACITIVE DAC HOLD TRACK HOLD TRACK TRACK VDD/2 HOLD AIN1 TRACK AIN0 TRACK MAX11644/MAX11645 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs CAPACITIVE DAC GND CT/H HOLD REF MAX11644 MAX11645 Figure 4. Equivalent Input Circuit 10 ______________________________________________________________________________________ 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs Single-Ended/Differential Input The SGL/DIF of the configuration byte configures the MAX11644/MAX11645 analog-input circuitry for singleended or differential inputs (Table 2). In single-ended mode (SGL/DIF = 1), the digital conversion results are the difference between the analog input selected by CS[0] and GND (Table 3). In differential mode (SGL/ DIF = 0), the digital conversion results are the difference between the + and the - analog inputs selected by CS[0] (Table 4). Unipolar/Bipolar When operating in differential mode, the BIP/UNI bit of the set-up byte (Table 1) selects unipolar or bipolar operation. Unipolar mode sets the differential input range from 0 to VREF. A negative differential analog input in unipolar mode causes the digital output code to be zero. Selecting bipolar mode sets the differential input range to ±VREF/2. The digital output code is binary in unipolar mode and two’s complement in bipolar mode. See the Transfer Functions section. In single-ended mode, the MAX11644/MAX11645 always operate in unipolar mode irrespective of BIP/UNI. The analog inputs are internally referenced to GND with a full-scale input range from 0 to VREF. 2-Wire Digital Interface The MAX11644/MAX11645 feature a 2-wire interface consisting of a serial-data line (SDA) and serial-clock line (SCL). SDA and SCL facilitate bidirectional communication between the MAX11644/MAX11645 and the master at rates up to 1.7MHz. The MAX11644/ MAX11645 are slaves that transfer and receive data. The master (typically a microcontroller) initiates data transfer on the bus and generates the SCL signal to permit that transfer. SDA and SCL must be pulled high. This is typically done with pullup resistors (750Ω or greater) (see the Typical Operating Circuit). Series resistors (RS) are optional. They protect the input architecture of the MAX11644/ MAX11645 from high voltage spikes on the bus lines and minimize crosstalk and undershoot of the bus signals. The data on SDA must remain stable during the high period of the SCL clock pulse. Changes in SDA while SCL is stable are considered control signals (see the START and STOP Conditions section). Both SDA and SCL remain high when the bus is not busy. START and STOP Conditions The master initiates a transmission with a START (S) condition, a high-to-low transition on SDA while SCL is high. The master terminates a transmission with a STOP (P) condition, a low-to-high transition on SDA while SCL is high (Figure 5). A repeated START (Sr) condition can be used in place of a STOP condition to leave the bus active and the interface mode unchanged (see the HS Mode section). Acknowledge Bits Data transfers are acknowledged with an acknowledge bit (A) or a not-acknowledge bit (A). Both the master and the MAX11644/MAX11645 (slave) generate acknowledge bits. To generate an acknowledge, the receiving device must pull SDA low before the rising edge of the acknowledge-related clock pulse (ninth pulse) and keep it low during the high period of the clock pulse (Figure 6). To generate a not-acknowledge, the receiver allows SDA to be pulled high before the rising edge of the acknowledge-related clock pulse and leaves SDA high during the high period of the clock pulse. Monitoring the acknowledge bits allows for detection of unsuccessful data transfers. An unsuccessful data transfer happens if a receiving device is busy or if a system fault has occurred. In the event of an unsuccessful data transfer, the bus master should reattempt communication at a later time. Sr S P SDA SCL Figure 5. START and STOP Conditions S NOT-ACKNOWLEDGE SDA ACKNOWLEDGE Bit Transfer One data bit is transferred during each SCL clock cycle. A minimum of 18 clock cycles are required to transfer the data in or out of the MAX11644/MAX11645. SCL 1 2 8 9 Figure 6. Acknowledge Bits ______________________________________________________________________________________ 11 MAX11644/MAX11645 Analog Input Range and Protection Internal protection diodes clamp the analog input to VDD and GND. These diodes allow the analog inputs to swing from (GND - 0.3V) to (VDD + 0.3V) without causing damage to the device. For accurate conversions, the inputs must not go more than 50mV below GND or above VDD. MAX11644/MAX11645 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs Slave Address A bus master initiates communication with a slave device by issuing a START condition followed by a slave address. When idle, the MAX11644/MAX11645 continuously wait for a START condition followed by their slave address. When the MAX11644/MAX11645 recognize their slave address, they are ready to accept or send data. The slave address is factory programmed to 0110110. The least significant bit (LSB) of the address byte (R/W) determines whether the master is writing to or reading from the MAX11644/MAX11645 (R/W = 0 selects a write condition, R/W = 1 selects a read condition). After receiving the address, the MAX11644/MAX11645 (slave) issues an acknowledge by pulling SDA low for one clock cycle. operate in high-speed mode (HS mode) to achieve conversion rates up to 94.4ksps. Figure 1 shows the bus timing for the MAX11644/MAX11645’s 2-wire interface. HS Mode At power-up, the MAX11644/MAX11645 bus timing is set for F/S mode. The bus master selects HS mode by addressing all devices on the bus with the HS-mode master code 0000 1XXX (X = don’t care). After successfully receiving the HS-mode master code, the MAX11644/MAX11645 issue a not-acknowledge, allowing SDA to be pulled high for one clock cycle (Figure 8). After the not-acknowledge, the MAX11644/ MAX11645 are in HS mode. The bus master must then send a repeated START followed by a slave address to initiate HS mode communication. If the master generates a STOP condition, the MAX11644/MAX11645 return to F/S mode. Bus Timing At power-up, the MAX11644/MAX11645 bus timing is set for fast-mode (F/S mode), which allows conversion rates up to 22.2ksps. The MAX11644/MAX11645 must SLAVE ADDRESS MAX11644/MAX11645 S 0 1 1 0 1 1 0 R/W A SDA 1 SCL 2 3 4 5 6 7 8 9 SEE ORDERING INFORMATION FOR SLAVE ADDRESS OPTIONS AND DETAILS. Figure 7. MAX11644/MAX11645 Slave Address Byte HS-MODE MASTER CODE S 0 0 0 0 1 X X X A Sr SDA SCL F/S MODE HS MODE Figure 8. F/S-Mode to HS-Mode Transfer 12 ______________________________________________________________________________________ 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs can write either one or two bytes to the slave in any order (setup byte, then configuration byte; configuration byte, then setup byte; setup byte or configuration byte only; Figure 9). If the slave receives a byte successfully, it issues an acknowledge. The master ends the write cycle by issuing a STOP condition or a repeated START condition. When operating in HS mode, a STOP condition returns the bus into F/S mode (see the HS Mode section). MASTER TO SLAVE SLAVE TO MASTER A) ONE-BYTE WRITE CYCLE 1 7 1 1 S SLAVE ADDRESS W A 8 1 1 NUMBER OF BITS SETUP OR A P OR Sr CONFIGURATION BYTE MSB DETERMINES WHETHER SETUP OR CONFIGURATION BYTE B) TWO-BYTE WRITE CYCLE 1 S 7 1 1 SLAVE ADDRESS W A 8 SETUP OR CONFIGURATION BYTE 1 A 8 1 1 NUMBER OF BITS SETUP OR A P OR Sr CONFIGURATION BYTE MSB DETERMINES WHETHER SETUP OR CONFIGURATION BYTE Figure 9. Write Cycle Table 1. Setup Byte Format BIT 7 (MSB) BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 (LSB) REG SEL2 SEL1 SEL0 CLK BIP/UNI RST X BIT NAME 7 REG 6 SEL2 5 SEL1 4 SEL0 3 CLK 2 BIP/UNI 1 RST 0 X DESCRIPTION Register bit. 1 = setup byte, 0 = configuration byte (Table 2). Three bits select the reference voltage (Table 6). Default to 000 at power-up. 1 = external clock, 0 = internal clock. Defaults to 0 at power-up. 1 = bipolar, 0 = unipolar. Defaults to 0 at power-up (see the Unipolar/Bipolar section). 1 = no action, 0 = resets the configuration register to default. Setup register remains unchanged. Don’t-care bit. This bit can be set to 1 or 0. ______________________________________________________________________________________ 13 MAX11644/MAX11645 Configuration/Setup Bytes (Write Cycle) A write cycle begins with the bus master issuing a START condition followed by seven address bits (Figure 7) and a write bit (R/W = 0). If the address byte is successfully received, the MAX11644/MAX11645 (slave) issues an acknowledge. The master then writes to the slave. The slave recognizes the received byte as the set-up byte (Table 1) if the most significant bit (MSB) is 1. If the MSB is 0, the slave recognizes that byte as the configuration byte (Table 2). The master MAX11644/MAX11645 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs Table 2. Configuration Byte Format BIT 7 (MSB) BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 (LSB) REG SCAN1 SCAN0 X X X CS0 SGL/DIF BIT NAME 7 REG 6 SCAN1 5 SCAN0 4 X 3 X 2 X 1 CS0 0 SGL/DIF DESCRIPTION Register bit. 1 = setup byte (see Table 1), 0 = configuration byte. Scan select bits. Two bits select the scanning configuration (Table 5). Default to 00 at power-up. Channel select bit. CS0 selects which analog input channels are to be used for conversion (Tables 3 and 4). Default to 0000 at power-up. 1 = single-ended, 0 = differential (Tables 3 and 4). Defaults to 1 at power-up. See the SingleEnded/Differential Input section. X = Don’t care. Table 3. Channel Selection in Single-Ended Mode (SGL/DIF = 1) CS0 AIN0 0 + AIN1 GND + - - 1 Table 4. Channel Selection in Differential Mode (SGL/DIF = 0) 14 CS0 AIN0 AIN1 0 + - 1 - + ______________________________________________________________________________________ 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs clock. On the falling edge of the ninth clock, the analog signal is acquired and the conversion begins. While converting the analog input signal, the MAX11644/ MAX11645 hold SCL low (clock stretching). After the conversion completes, the results are stored in internal memory. If the scan mode is set for multiple conversions, they all happen in succession with each additional result stored in memory. The MAX11644/ MAX11645 contain two 12-bit blocks of memory. Once all conversions are complete, the MAX11644/ MAX11645 release SCL, allowing it to be pulled high. The master can now clock the results out of the memory in the same order the scan conversion has been done at a clock rate of up to 1.7MHz. SCL is stretched for a maximum of 8.3µs per channel (see Figure 10). The device memory contains all of the conversion results when the MAX11644/MAX11645 release SCL. The converted results are read back in a first-in-first-out (FIFO) sequence. The memory contents can be read continuously. If reading continues past the result stored in memory, the pointer wraps around and points to the first result. Note that only the current conversion results are read from memory. The device must be addressed with a read command to obtain new conversion results. The internal clock mode’s clock stretching quiets the SCL bus signal, reducing the system noise during conversion. Using the internal clock also frees the bus master (typically a microcontroller) from the burden of running the conversion clock, allowing it to perform other tasks that do not need to use the bus. Clock Modes The clock mode determines the conversion clock and the data acquisition and conversion time. The clock mode also affects the scan mode. The state of the setup byte’s CLK bit determines the clock mode (Table 1). At power-up, the MAX11644/MAX11645 are defaulted to internal clock mode (CLK = 0). Internal Clock When configured for internal clock mode (CLK = 0), the MAX11644/MAX11645 use their internal oscillator as the conversion clock. In internal clock mode, the MAX11644/MAX11645 begin tracking the analog input after a valid address on the eighth rising edge of the MASTER TO SLAVE SLAVE TO MASTER A) SINGLE CONVERSION WITH INTERNAL CLOCK 1 7 1 1 S SLAVE ADDRESS R A 8 CLOCK STRETCH RESULT 4 MSBs 8 A RESULT 8 LSBs 1 1 NUMBER OF BITS A P OR Sr tACQ tCONV B) SCAN MODE CONVERSIONS WITH INTERNAL CLOCK 1 7 1 1 S SLAVE ADDRESS R A 8 CLOCK STRETCH tACQ1 tCONV1 tACQ2 tCONV2 CLOCK STRETCH 1 8 1 RESULT 1 ( 4MSBs) A RESULT 1 (8 LSBs) A 8 1 8 1 1 NUMBER OF BITS RESULT N (4MSBs) A RESULT N (8LSBs) A P OR Sr tACQN tCONVN Figure 10. Internal Clock Mode Read Cycles ______________________________________________________________________________________ 15 MAX11644/MAX11645 Data Byte (Read Cycle) A read cycle must be initiated to obtain conversion results. Read cycles begin with the bus master issuing a START condition followed by seven address bits and a read bit (R/W = 1). If the address byte is successfully received, the MAX11644/MAX11645 (slave) issues an acknowledge. The master then reads from the slave. The result is transmitted in 2 bytes; first 4 bits of the first byte are high, then MSB through LSB are consecutively clocked out. After the master has received the byte(s), it can issue an acknowledge if it wants to continue reading or a not-acknowledge if it no longer wishes to read. If the MAX11644/MAX11645 receive a not-acknowledge, they release SDA, allowing the master to generate a STOP or a repeated START condition. See the Clock Modes and Scan Mode sections for detailed information on how data is obtained and converted. MAX11644/MAX11645 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs External Clock When configured for external clock mode (CLK = 1), the MAX11644/MAX11645 use the SCL as the conversion clock. In external clock mode, the MAX11644/ MAX11645 begin tracking the analog input on the ninth rising clock edge of a valid slave address byte. Two SCL clock cycles later, the analog signal is acquired and the conversion begins. Unlike the internal clock mode, converted data is available immediately after the first four empty high bits. The device continuously converts input channels dictated by the scan mode until given a not-acknowledge. There is no need to readdress the device with a read command to obtain new conversion results (see Figure 11). The conversion must complete in 1ms, or droop on the track-and-hold capacitor degrades conversion results. Use internal clock mode if the SCL clock period exceeds 60µs. The MAX11644/MAX11645 must operate in external clock mode for conversion rates from 40ksps to 94.4ksps. Below 40ksps, internal clock mode is recommended due to much smaller power consumption. Scan Mode SCAN0 and SCAN1 of the configuration byte set the scan mode configuration. Table 5 shows the scanning configurations. The scanned results are written to memory in the same order as the conversion. Read the results from memory in the order they were converted. Each result needs a 2-byte transmission; the first byte begins with 4 empty bits, during which SDA is left high. Each byte has to be acknowledged by the master or the memory transmission is terminated. It is not possible to read the memory independently of conversion. MASTER TO SLAVE SLAVE TO MASTER A) SINGLE CONVERSION WITH EXTERNAL CLOCK 1 7 1 1 8 1 8 S SLAVE ADDRESS R A RESULT (4 MSBs) A RESULT (8 LSBs) 1 1 A P OR Sr NUMBER OF BITS tACQ tCONV B) SCAN MODE CONVERSIONS WITH EXTERNAL CLOCK 1 7 1 1 S SLAVE ADDRESS R A 8 RESULT 1 (4 MSBs) 1 8 1 8 1 8 A RESULT 2 (8 LSBs) A RESULT N (4 MSBs) A RESULT N (8 LSBs) tACQ2 tACQN tACQ1 tCONV1 1 1 NUMBER OF BITS A P OR Sr tCONVN Figure 11. External Clock Mode Read Cycle Table 5. Scanning Configuration SCAN1 SCAN0 0 0 Scans up from AIN0 to the input selected by CS0. SCANNING CONFIGURATION 0 1 Converts the input selected by CS0 eight times (see Tables 3 and 4).* 1 0 Reserved. Do not use. 1 1 Converts the input selected by CS0.* *When operating in external clock mode, there is no difference between SCAN[1:0] = 01 and SCAN[1:0] = 11, and converting occurs perpetually until not-acknowledge occurs. 16 ______________________________________________________________________________________ 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs SEL2 SEL1 SEL0 REFERENCE VOLTAGE REF INTERNAL REFERENCE STATE 0 0 X VDD Not connected Always off 0 1 X External reference Reference input Always off 1 0 0 Internal reference Not connected* Always off 1 0 1 Internal reference Not connected* Always on 1 1 0 Internal reference Reference output Always off 1 1 1 Internal reference Reference output Always on X = Don’t care. *Preferred configuration for internal reference. Applications Information Power-On Reset The configuration and setup registers (Tables 1 and 2) default to a single-ended, unipolar, single-channel conversion on AIN0 using the internal clock with VDD as the reference. The memory contents are unknown after power-up. Automatic Shutdown Automatic shutdown occurs between conversions when the MAX11644/MAX11645 are idle. All analog circuits participate in automatic shutdown except the internal reference due to its prohibitively long wake-up time. When operating in external clock mode, a STOP, notacknowledge, or repeated START condition must be issued to place the devices in idle mode and benefit from automatic shutdown. A STOP condition is not necessary in internal clock mode to benefit from automatic shutdown because power-down occurs once all conversion results are written to memory (Figure 10). When using an external reference or VDD as a reference, all analog circuitry is inactive in shutdown and supply current is less than 0.5µA. The digital conversion results obtained in internal clock mode are maintained in memory during shutdown and are available for access through the serial interface at any time prior to a STOP or a repeated START condition. When idle, the MAX11644/MAX11645 continuously wait for a START condition followed by their slave address (see the Slave Address section). Upon reading a valid address byte, the MAX11644/MAX11645 power up. The internal reference requires 10ms to wake up, so when using the internal reference it should be powered up 10ms prior to conversion or powered continuously. Wake-up is invisible when using an external reference or VDD as the reference. Automatic shutdown results in dramatic power savings, particularly at slow conversion rates and with internal clock. For example, at a conversion rate of 10ksps, the average supply current for the MAX11645 is 60µA (typ) and drops to 6µA (typ) at 1ksps. At 0.1ksps the average supply current is just 1µA, or a minuscule 3µW of power consumption. See Average Supply Current vs. Conversion Rate (External Clock) in the Typical Operating Characteristics section). Reference Voltage SEL[2:0] of the setup byte (Table 1) control the reference configuration (Table 6). Internal Reference The internal reference is 4.096V for the MAX11644 and 2.048V for the MAX11645. When REF is configured to be an internal reference output (SEL[2:1] = 11), decouple REF to GND with a 0.1µF capacitor and a 2kΩ series resistor (see the Typical Operating Circuit). Once powered up, the reference always remains on until reconfigured. The internal reference requires 10ms to wake up and is accessed using SEL0 (Table 6). When in shutdown, the internal reference output is in a highimpedance state. The reference should not be used to supply current for external circuitry. The internal reference does not require an external bypass capacitor and works best when left unconnected (SEL1 = 0). External Reference The external reference can range from 1V to VDD. For maximum conversion accuracy, the reference must be able to deliver up to 40µA and have an output impedance of 500kΩ or less. If the reference has a higher output impedance or is noisy, bypass it to GND as close as possible to REF with a 0.1µF capacitor. ______________________________________________________________________________________ 17 MAX11644/MAX11645 Table 6. Reference Voltage and REF Format MAX11644/MAX11645 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs Transfer Functions Output data coding for the MAX11644/MAX11645 is binary in unipolar mode and two’s complement in bipolar mode with 1 LSB = (VREF/2N) where N is the number of bits (12). Code transitions occur halfway between successive-integer LSB values. Figures 12 and 13 show the input/output (I/O) transfer functions for unipolar and bipolar operations, respectively. Layout, Grounding, and Bypassing Only use PCBs. Wire-wrap configurations are not recommended since the layout should ensure proper separation of analog and digital traces. Do not run analog and digital lines parallel to each other, and do not layout digital signal paths underneath the ADC package. Use separate analog and digital PCB ground sections with only one star point (Figure 14) connecting the two ground systems (analog and digital). For lowest noise operation, ensure the ground return to the star ground’s power supply is low impedance and as short as possible. Route digital signals far away from sensitive analog and reference inputs. High-frequency noise in the power supply (VDD) could influence the proper operation of the ADC’s fast comparator. Bypass VDD to the star ground with a network of two parallel capacitors, 0.1µF and 4.7µF, located as close as possible to the MAX11644/MAX11645 power-supply pin. Minimize capacitor lead length for best supply noise rejection, and add an attenuation resistor (5Ω) in series with the power supply if it is extremely noisy. Definitions Integral Nonlinearity Integral nonlinearity (INL) is the deviation of the values on an actual transfer function from a straight line. This straight line can be either a best straight-line fit or a line drawn between the endpoints of the transfer function, once offset and gain errors have been nullified. The MAX11644/MAX11645’s INL is measured using the endpoint. Differential Nonlinearity Differential nonlinearity (DNL) is the difference between an actual step width and the ideal value of 1 LSB. A DNL error specification of less than 1 LSB guarantees no missing codes and a monotonic transfer function. Aperture Jitter Aperture jitter (tAJ) is the sample-to-sample variation in the time between the samples. Aperture Delay Aperture delay (tAD) is the time between the falling edge of the sampling clock and the instant when an actual sample is taken. OUTPUT CODE OUTPUT CODE FULL-SCALE TRANSITION 11 . . . 111 MAX11644 MAX11645 11 . . . 110 011 . . . 111 V FS = REF 2 011 . . . 110 ZS = 0 11 . . . 101 000 . . . 010 000 . . . 001 FS = VREF 00 . . . 011 MAX11644 MAX11645 -VREF 2 VREF 1 LSB = 4096 -FS = 000 . . . 000 ZS = GND 111 . . . 111 V 1 LSB = REF 4096 111 . . . 110 111 . . . 101 00 . . . 010 100 . . . 001 00 . . . 001 100 . . . 000 00 . . . 000 0 1 2 3 FS 0 - FS INPUT VOLTAGE (LSB) Figure 12. Unipolar Transfer Function 18 FS - 3/2 LSB INPUT VOLTAGE (LSB) Figure 13. Bipolar Transfer Function ______________________________________________________________________________________ +FS - 1 LSB 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs SUPPLIES 3V OR 5V VLOGIC = 3V/5V GND 4.7µF R* = 5Ω Effective Number of Bits 0.1µF VDD ⎡ ⎤ SignalRMS SINAD(dB) = 20 × log ⎢ ⎥ Noise + THD RMS RMS ⎦ ⎣ GND 3V/5V DGND DIGITAL CIRCUITRY MAX11644 MAX11645 Effective number of bits (ENOB) indicates the global accuracy of an ADC at a specific input frequency and sampling rate. An ideal ADC’s error consists of quantization noise only. With an input range equal to the ADC’s full-scale range, calculate the ENOB as follows: ENOB = (SINAD - 1.76)/6.02 Total Harmonic Distortion *OPTIONAL Figure 14. Power-Supply Grounding Connection Signal-to-Noise Ratio For a waveform perfectly reconstructed from digital samples, the theoretical maximum SNR is the ratio of the full-scale analog input (RMS value) to the RMS quantization error (residual error). The ideal, theoretical minimum analog-to-digital noise is caused by quantization error only and results directly from the ADC’s resolution (N bits): SNRMAX[dB] = 6.02dB x N + 1.76dB In reality, there are other noise sources besides quantization noise: thermal noise, reference noise, clock jitter, etc. SNR is computed by taking the ratio of the RMS signal to the RMS noise, which includes all spectral components minus the fundamental, the first five harmonics, and the DC offset. Total harmonic distortion (THD) is the ratio of the RMS sum of the input signal’s first five harmonics to the fundamental itself. This is expressed as: ⎛ ⎛ 2 ⎞ V + V32 + V42 + V52 ⎞ THD = 20 × log ⎜ ⎜ 2 ⎟⎟ V1 ⎜ ⎝ ⎠ ⎟⎠ ⎝ where V1 is the fundamental amplitude, and V2 through V5 are the amplitudes of the 2nd- through 5th-order harmonics. Spurious-Free Dynamic Range Spurious-free dynamic range (SFDR) is the ratio of the RMS amplitude of the fundamental (maximum signal component) to the RMS value of the next largest distortion component. ______________________________________________________________________________________ 19 MAX11644/MAX11645 Signal-to-Noise Plus Distortion Signal-to-noise plus distortion (SINAD) is the ratio of the fundamental input frequency’s RMS amplitude to the RMS equivalent of all other ADC output signals. 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs MAX11644/MAX11645 Typical Operating Circuit Selector Guide 3.3V or 5V PART 0.1µF INTERNAL SUPPLY INPUT INL REFERENCE VOLTAGE CHANNELS (LSB) (V) (V) VDD ANALOG INPUTS RS* AIN0 AIN1 MAX11644 MAX11645 CREF 0.1µF 2 singleended/1 differential 4.096 4.5 to 5.5 ±1 MAX11645 2 singleended/1 differential 2.048 2.7 to 3.6 ±1 SDA SCL RS * RC NETWORK* 2kΩ REF MAX11644 GND 5V RP 5V RP µC SDA SCL *OPTIONAL Package Information Chip Information PROCESS: BiCMOS 20 For the latest package outline information and land patterns, go to www.maxim-ic.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 DOCUMENT NO. 8 µMAX U8CN+1 21-0036 ______________________________________________________________________________________ 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 12-Bit ADCs REVISION NUMBER REVISION DATE 0 4/10 DESCRIPTION Initial release PAGES CHANGED — 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 21 © 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX11644/MAX11645 Revision History