MAX1241BMJA

19-1155; Rev 2; 11/98 KIT ATION EVALU ABLE AVAIL +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO ________________________________Features o Single-Supply Operation: +2.7V to +3.6V (MAX1240) +2.7V to +5.25V (MAX1241) o o o o 12-Bit Resolution Internal 2.5V Reference (MAX1240) Small Footprint: 8-Pin DIP/SO Packages Low Power: 3.7µW (73ksps, MAX1240) 3mW (73ksps, MAX1241) 66µW (1ksps, MAX1241) 5µW (power-down mode) __________________General Description The MAX1240/MAX1241 are low-power, 12-bit analogto-digital converters (ADCs) available in 8-pin packages. The MAX1240 operates with a single +2.7V to +3.6V supply, and the MAX1241 operates with a single +2.7V to +5.25V supply. Both devices feature a 7.5µs successive-approximation ADC, a fast track/hold (1.5µs), an on-chip clock, and a high-speed, 3-wire serial interface. Power consumption is only 37mW (VDD = 3V) at the 73ksps maximum sampling speed. A 2µA shutdown mode reduces power at slower throughput rates. The MAX1240 has an internal 2.5V reference, while the MAX1241 requires an external reference. The MAX1241 accepts signals from 0V to VREF, and the reference input range includes the positive supply rail. An external clock accesses data from the 3-wire interface, which connects directly to standard microcontroller I/O ports. The interface is compatible with SPI™, QSPI™, and MICROWIRE™. Excellent AC characteristics and very low power combined with ease of use and small package size make these converters ideal for remote-sensor and dataacquisition applications, or for other circuits with demanding power consumption and space requirements. The MAX1240/MAX1241 are available in 8-pin DIP and SO packages. MAX1240/MAX1241 o Internal Track/Hold o SPI/QSPI/MICROWIRE 3-Wire Serial Interface o Internal Clock Ordering Information PART MAX1240ACPA MAX1240BCPA MAX1240CCPA MAX1240ACSA MAX1240BCSA MAX1240CCSA MAX1240BC/D TEMP. RANGE 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C PINPACKAGE 8 Plastic DIP 8 Plastic DIP 8 Plastic DIP 8 SO 8 SO 8 SO Dice* INL (LSB) ±1/2 ±1 ±1 ±1/2 ±1 ±1 ±1 Applications Battery-Powered Systems Portable Data Logging Isolated Data Acquisition Process Control Instrumentation Ordering Information continued at end of data sheet. *Dice are specified at TA = +25°C, DC parameters only. Functional Diagram VDD 1 CS 7 8 3 CONTROL LOGIC INT CLOCK Pin Configuration TOP VIEW VDD AIN 1 2 8 7 SCLK CS DOUT GND SCLK SHDN OUTPUT SHIFT REGISTER 6 DOUT SHDN 3 REF 4 MAX1240 MAX1241 AIN 2 T/H 2.5V REFERENCE (MAX1240 ONLY) 12-BIT SAR 6 5 REF 4 MAX1240 MAX1241 5 GND DIP/SO SPI and QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor Corp. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO MAX1240/MAX1241 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 +6V DOUT to GND............................................-0.3V to (VDD + 0.3V) DOUT Current ..................................................................±25mA Continuous Power Dissipation (TA = +70°C) Plastic DIP (derate 9.09mW/°C above +70°C) ...........727mW SO (derate 5.88mW/°C above +70°C)........................471mW CERDIP (derate 8.00mW/°C above +70°C)................640mW Operating Temperature Ranges MAX1240_C_A/MAX1241_C_A .........................0°C to +70°C MAX1240_E_ A/MAX1241_E_ A .....................-40°C to +85°C MAX1240_MJA/MAX1241_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 = +2.7V to +3.6V (MAX1240); VDD = +2.7V to +5.25V (MAX1241); 73ksps, fSCLK = 2.1MHz (50% duty cycle); MAX1240—4.7µF capacitor at REF pin, MAX1241—external reference; VREF = 2.500V applied to REF pin; TA = TMIN to TMAX; unless otherwise noted.) PARAMETER DC ACCURACY (Note 1) Resolution Relative Accuracy (Note 2) Differential Nonlinearity Offset Error Gain Error (Note 3) Gain Temperature Coefficient DYNAMIC SPECIFICATIONS (10kHz sine-wave input, 0V to 2.500Vp-p, 73ksps, fSCLK = 2.1MHz) Signal-to-Noise Plus Distortion Ratio Total Harmonic Distortion Spurious-Free Dynamic Range Small-Signal Bandwidth Full-Power Bandwidth CONVERSION RATE Conversion Time Track/Hold Acquisition Time Throughput Rate Aperture Delay Aperture Jitter ANALOG INPUT Input Voltage Range Input Capacitance 2 0 16 VREF V pF tAPR tCONV tACQ fSCLK = 2.1MHz Figure 8 30 3.6V (MAX1241) 2.0 3.0 0.8 V V V µA pF V V µA V V nA SHDN = 0V 0.1 18 1.00 100 25 ±0.01 10 VDD + 50mV 150 V µA kΩ µA µF 0mA to 0.2mA output load 4.7 ±30 ±30 ±30 ±30 0.35 µF SYMBOL TA = +25°C CONDITIONS MIN 2.480 TYP 2.500 MAX 2.520 30 ±50 ±60 ±80 ppm/°C ppm/°C UNITS V mA MAX1240/MAX1241 INTERNAL REFERENCE (MAX1240 only) _______________________________________________________________________________________ 3 +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO MAX1240/MAX1241 ELECTRICAL CHARACTERISTICS (continued) (VDD = +2.7V to +3.6V (MAX1240); VDD = +2.7V to +5.25V (MAX1241); 73ksps, fSCLK = 2.1MHz (50% duty cycle); MAX1240—4.7µF capacitor at REF pin, MAX1241—external reference; VREF = 2.500V applied to REF pin; TA = TMIN to TMAX; unless otherwise noted.) PARAMETERS POWER REQUIREMENTS Supply Voltage VDD MAX1240 MAX1241 MAX1240A/B MAX1240C Operating mode Supply Current IDD MAX1241C Power-down, digital inputs at 0V or VDD Supply Rejection PSR (Note 5) MAX1241A/B VDD = 3.6V VDD = 3.6V VDD = 3.6V VDD = 5.25V VDD = 3.6V VDD = 5.25V VDD = 3.6V VDD = 5.25V 2.7 2.7 1.4 1.4 0.9 1.6 0.9 1.6 1.9 3.5 ±0.3 3.6 5.25 2.0 3.5 1.5 2.5 2.8 3.8 10 15 µA mV mA V SYMBOL CONDITIONS MIN TYP MAX UNITS TIMING CHARACTERISTICS (Figure 8) (VDD = +2.7V to +3.6V (MAX1240); VDD = +2.7V to +5.25V (MAX1241); TA = TMIN to TMAX, unless otherwise noted.) PARAMETERS Acquisition Time SCLK Fall to Output Data Valid CS Fall to Output Enable CS Rise to Output Disable SCLK Clock Frequency SCLK Pulse Width High SCLK Pulse Width Low SCLK Low to CS Fall Setup Time DOUT Rise to SCLK Rise (Note 5) CS Pulse Width SYMBOL tACQ tDO tDV tTR fSCLK tCH tCL tCS0 tSTR tCS Figure 1, CLOAD = 50pF Figure 1, CLOAD = 50pF Figure 2, CLOAD = 50pF 0 200 200 50 0 240 CONDITIONS CS = VDD (Note 6) MAX124_ _C/E MAX124_ _M MIN 1.5 20 20 200 240 240 240 2.1 TYP MAX UNITS µs ns ns ns MHz ns ns ns ns ns Note 1: Tested at VDD = +2.7V. Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after the full-scale range and offset have been calibrated. Note 3: MAX1240—internal reference, offset nulled; MAX1241—external reference (VREF = +2.500V), offset nulled. Note 4: External load should not change during conversion for specified accuracy. Note 5: Guaranteed by design. Not subject to production testing. Note 6: Measured as [VFS(2.7V) - VFS(VDD(MAX)]. 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. 4 _______________________________________________________________________________________ +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO MAX1240/MAX1241 +2.7V 6k DOUT 6k DGND a) High-Z to VOH and VOL to VOH b) High-Z to VOL and VOH to VOL CLOAD = 50pF DOUT CLOAD = 50pF DGND Figure 1. Load Circuits for DOUT Enable Time +2.7V 6k DOUT 6k DGND a) VOH to High-Z b) VOLto High-Z CLOAD = 50pF DOUT CLOAD = 50pF DGND Figure 2. Load Circuits for DOUT Disable Time __________________________________________Typical Operating Characteristics (VDD = 3.0V, VREF = 2.5V, fSCLK = 2.1MHz, CL = 20pF, TA = +25°C, unless otherwise noted.) OPERATING SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX1241-D SUPPLY CURRENT vs. TEMPERATURE MAX1241-A/NEW OFFSET ERROR vs. SUPPLY VOLTAGE 0.9 0.8 OFFSET ERROR (LSB) 0.7 0.6 0.5 0.4 0.3 0.2 MAX1241-03 2.0 OPERATING SUPPLY CURRENT (mA) 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 2 RL = ∞ CODE = 101010100000 MAX1240 1.3 MAX1240 1.0 1.2 SUPPLY CURRENT (mA) 1.1 MAX1241 1.0 MAX1241 0.9 RLOAD = ∞ CODE = 10101010000 -60 -20 20 60 100 140 0.1 0 2.25 2.75 3.25 3.75 4.25 4.75 5.25 SUPPLY VOLTAGE (V) 0.8 3 4 SUPPLY VOLTAGE (V) 5 6 TEMPERATURE (°C) _______________________________________________________________________________________ 5 +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO MAX1240/MAX1241 ____________________________Typical Operating Characteristics (continued) (VDD = 3.0V, VREF = 2.5V, fSCLK = 2.1MHz, CL = 20pF, TA = +25°C, unless otherwise noted.) SHUTDOWN SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX1241-C/NEW SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE MAX1241-B OFFSET ERROR vs. TEMPERATURE VDD = 2.7V 0.7 OFFSET ERROR (LSB) 0.6 0.5 0.4 0.3 0.2 0.1 0 MAX1241-06 4.0 SHUTDOWN SUPPLY CURRENT (µA) 5.0 SHUTDOWN SUPPLY CURRENT (µA) 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0.8 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 2.25 2.75 3.25 3.75 4.25 4.75 5.25 -60 -20 20 60 100 140 -55 -30 -5 20 45 70 95 120 145 SUPPLY VOLTAGE (V) TEMPERATURE (°C) TEMPERATURE (°C) GAIN ERROR vs. SUPPLY VOLTAGE MAX1241-07 GAIN ERROR vs. TEMPERATURE MAX1241-08 MAX1240 INTERNAL REFERENCE VOLTAGE vs. SUPPLY VOLTAGE MAX1241-0X 0.8 0.7 0.6 GAIN ERROR (LSB) 0.8 VDD = 2.7V 0.7 0.6 GAIN ERROR (LSB) 2.5020 2.5015 2.5010 VREF (V) 0.5 0.4 0.3 0.2 0.1 0 2.25 2.75 3.25 3.75 4.25 4.75 5.25 SUPPLY VOLTAGE (V) 0.5 0.4 0.3 0.2 2.5005 2.5000 2.4995 0.1 0 -55 -30 -5 20 45 70 95 120 145 TEMPERATURE (°C) 2.4990 2.25 2.75 3.25 3.75 VDD (V) 4.25 4.75 5.25 MAX1240 INTERNAL REFERENCE VOLTAGE vs. TEMPERATURE MAX1241-0Y INTEGRAL NONLINEARITY vs. SUPPLY VOLTAGE MAX1241-09/NEW INTEGRAL NONLINEARITY vs. TEMPERATURE VDD = 2.7V 1.0 0.8 INL (LSB) 0.6 0.4 MAX1240 0.2 MAX1241 0 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (°C) MAX1241-10/NEW 2.501 2.500 2.499 2.498 2.497 2.496 2.495 2.494 -60 -20 20 60 100 VDD = 3.6V VDD = 2.7V VREF (V) 1.2 1.0 0.8 INL (LSB) 0.6 0.4 0.2 0 MAX1240 1.2 MAX1241 2.25 2.75 3.25 3.75 4.25 4.75 5.25 140 TEMPERATURE (°C) SUPPLY VOLTAGE (V) 6 _______________________________________________________________________________________ +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO ____________________________Typical Operating Characteristics (continued) (VDD = 3.0V, REF = 2.5V, fSCLK = 2.1MHz, CL = 20pF, TA = +25°C, unless otherwise noted.) INTEGRAL NONLINEARITY vs. CODE MAX1241-11A/NEW MAX1240/MAX1241 FFT PLOT MAX1241-TOC12A 0.6 0.4 0.2 INL (LSB) 0 -0.2 -0.4 -0.6 0 1024 2048 CODE 3072 20 0 -20 AMPLITUDE (dB) -40 -60 -80 -100 -120 -140 0 fAIN = 10kHz, 2.5Vp-p fSAMPLE = 73ksps 4096 18.75 FREQUENCY (kHz) 37.50 _______________________________________________________________________Pin Description PIN 1 2 NAME VDD AIN FUNCTION Positive Supply Voltage: 2.7V to 3.6V, (MAX1240); 2.7 to 5.25V (MAX1241) Sampling Analog Input, 0V to VREF range Three-Level Shutdown Input. Pulling SHDN low shuts the MAX1240/MAX1241 down to 15µA (max) supply current. Both the MAX1240 and MAX1241 are fully operational with either SHDN high or floating. For the MAX1240, pulling SHDN high enables the internal reference, and letting SHDN float disables the internal reference and allows for the use of an external reference. Reference Voltage for Analog-to-Digital Conversion. Internal 2.5V reference output for MAX1240; bypass with 4.7µF capacitor. External reference voltage input for MAX1241, or for MAX1240 with the internal reference disabled. Bypass REF with a minimum of 0.1µF when using an external reference. Analog and Digital Ground Serial Data Output. Data changes state at SCLK’s falling edge. DOUT is high impedance when CS is high. Active-Low Chip Select initiates conversions on the falling edge. When CS is high, DOUT is high impedance. Serial Clock Input. SCLK clocks data out at rates up to 2.1MHz. 3 SHDN 4 5 6 7 8 REF GND DOUT CS SCLK _______________________________________________________________________________________ 7 +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO MAX1240/MAX1241 +2.7V to +3.6V* * VDD,MAX = +5.25V (MAX1241) ** 4.7µF (MAX1240) 0.1µF (MAX1241) 4.7µF 0.1µF 1 2 3 4 C** VDD SCLK 8 7 6 5 GND SERIAL INTERFACE AIN 12-BIT CAPACITIVE DAC REF TRACK INPUT CHOLD -+ 16pF CSWITCH TRACK 9k RIN HOLD AT THE SAMPLING INSTANT, THE INPUT SWITCHES FROM AIN TO GND. COMPARATOR ZERO ANALOG INPUT 0V TO VREF SHUTDOWN INPUT REFERENCE INPUT (MAX1241 ONLY) AIN MAX1240 CS MAX1241 SHDN REF DOUT GND HOLD Figure 3. Operational Diagram Figure 4. Equivalent Input Circuit _______________Detailed Description Converter Operation The MAX1240/MAX1241 use an 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. Figure 3 shows the MAX1240/MAX1241 in its simplest configuration. The MAX1240/MAX1241 convert input signals in the 0V to VREF range in 9µs, including T/H acquisition time. The MAX1240’s internal reference is trimmed to 2.5V, while the MAX1241 requires an external reference. Both devices accept voltages from 1.0V to VDD. The serial interface requires only three digital lines (SCLK, CS, and DOUT) and provides an easy interface to microprocessors (µPs). The MAX1240/MAX1241 have two modes: normal and shutdown. Pulling SHDN low shuts the device down and reduces supply current below 10µA (VDD ≤ 3.6V), while pulling SHDN high or leaving it open puts the device into operational mode. Pulling CS low initiates a conversion. The conversion result is available at DOUT in unipolar serial format. The serial data stream consists of a high bit, signaling the end of conversion (EOC), followed by the data bits (MSB first). 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 node ZERO at the comparator’s input. In hold mode, the capacitive digital-to-analog converter (DAC) adjusts during the remainder of the conversion cycle to restore node ZERO to 0V within the limits of 12bit 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 C HOLD switches back to AIN, and C HOLD 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. The 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. Acquisition time is calculated by: tACQ = 9(RS + RIN) x 16pF where RIN = 9kΩ, RS = the input signal’s source impedance, and tACQ is never less than 1.5µs. Source impedances below 1kΩ do not significantly affect the ADC’s AC performance. Analog Input Figure 4 illustrates the sampling architecture of the analog-to-digital converter’s (ADC’s) comparator. The fullscale input voltage is set by the voltage at REF. Track/Hold In track mode, the analog signal is acquired and stored in the internal hold capacitor. In hold mode, the T/H 8 _______________________________________________________________________________________ +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO Higher source impedances can be used if a 0.01µF capacitor is connected to the analog input. Note that the input capacitor forms an RC filter with the input source impedance, limiting the ADC’s input signal bandwidth. down (see the section Using SHDN to Reduce Supply Current). 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 MAX1240/MAX1241 operate with an external reference at the REF pin. To use the MAX1240 with an external reference, disable the internal reference by letting SHDN float. Stay within the +1.0V to VDD voltage range to achieve specified accuracy. The minimum input impedance is 18kΩ for DC currents. During conversion, the external reference must be able to deliver up to 250µA of 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. MAX1240/MAX1241 Input Bandwidth The ADCs’ input tracking circuitry has a 2.25MHz smallsignal bandwidth, so it is possible to digitize highspeed 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, anti-alias filtering is recommended. Analog Input Protection Internal protection diodes, which clamp the analog input to VDD and GND, 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 50mV beyond the supplies, limit the input current to 2mA. ____________________Serial Interface Initialization after Power-Up and Starting a Conversion When power is first applied, and if SHDN is not pulled low, it takes the fully discharged 4.7µF reference bypass capacitor up to 20ms to provide adequate charge for specified accuracy. With an external reference, the internal reset time is 10µs after the power supplies have stabilized. No conversions should be performed during these times. To start a conversion, pull CS low. At CS’s falling edge, the T/H enters its hold mode and a conversion is initiat- Internal Reference (MAX1240) The MAX1240 has an on-chip voltage reference trimmed to 2.5V. The internal reference output is connected to REF and also drives the internal capacitive DAC. The output can be used as a reference voltage source for other components and can source up to 400µA. Bypass REF with a 4.7µF capacitor. Larger capacitors increase wake-up time when exiting shut- COMPLETE CONVERSION SEQUENCE CS tWAKE SHDN DOUT CONVERSION 0 POWERED UP POWERED DOWN CONVERSION 1 POWERED UP Figure 5. Shutdown Sequence _______________________________________________________________________________________ 9 +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO MAX1240/MAX1241 VDD = VREF = 3.0V RLOAD = ∞, CLOAD = 50pF SUPPLY CURRNET (mA) 1 CODE = 010101010000 MAX1241 FIG. 06a ed. After an internally timed conversion period, the end of conversion is signaled by DOUT pulling high. Data can then be shifted out serially with the external clock. 10 Using SHDN to Reduce Supply Current Power consumption can be reduced significantly by shutting down the MAX1240/MAX1241 between conversions. Figure 6 shows a plot of average supply current versus conversion rate. Because the MAX1241 uses an external reference voltage (assumed to be present continuously), it “wakes up” from shutdown more quickly (in 4µs) and therefore provides lower average supply currents. The wake-up time (tWAKE) is the time from when SHDN is deasserted to the time when a conversion may be initiated (Figure 5). For the MAX1240, this time depends on the time in shutdown (Figure 7) because the external 4.7µF reference bypass capacitor loses charge slowly during shutdown. 0.1 MAX1240 0.01 MAX1241 0.001 0.1 1 10 100 1k 10k 100k CONVERSION RATE (Hz) Figure 6. Average Supply Current vs. Conversion Rate External Clock The actual conversion does not require the external clock. This allows the conversion result to be read back at the µP’s convenience at any clock rate from up to 2.1MHz. The clock duty cycle is unrestricted if each clock phase is at least 200ns. Do not run the clock while a conversion is in progress. MAX1240/41-07a 1.0 0.8 POWER-UP DELAY (ms) 0.6 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 serial-interface operation. A CS falling edge initiates a conversion sequence: the T/H stage holds the input voltage, the ADC begins to convert, and DOUT changes from high impedance to logic low. SCLK must be kept low during the conversion. An internal register stores the data when the conversion is in progress. 0.4 0.2 0.0 0.001 0.01 0.1 1 10 TIME IN SHUTDOWN (sec) Figure 7. Typical Reference Power-Up Delay vs. Time in Shutdown CS 1 SCLK DOUT EOC INTERFACE IDLE TRACK/HOLD TRACK STATE CONVERSION IN PROGRESS HOLD 7.5µs (tCONV) CYCLE TIME 0µs EOC CLOCK OUT SERIAL DATA TRACK 12.5 × 0.476µs = 5.95µs TOTAL = 13.7µs 0µs 0.24µs (tCS) TRAILING ZEROS IDLE HOLD B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 4 8 12 16 Figure 8. Interface Timing Sequence 10 ______________________________________________________________________________________ +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO MAX1240/MAX1241 CS tCS0 tCS … … tCH tDO SCLK tDV DOUT tAPR tSTR (HOLD) tCONV tCL B2 B1 B0 tTR … … INTERNAL T/H (TRACK/ACQUIRE) (TRACK/ACQUIRE) Figure 9. Detailed Serial-Interface Timing 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 zeros at DOUT and have no effect on converter operation. Minimum cycle time is accomplished by using DOUT’s rising edge as the EOC signal. Clock out the data with 12.5 clock cycles at full speed. Pull CS high after readOUTPUT CODE 11…111 11…110 11…101 ing the conversion’s LSB. After the specified minimum time (tCS), CS can be pulled low again to initiate the next conversion. Output Coding and Transfer Function The data output from the MAX1240/MAX1241 is binary, and Figure 10 depicts the nominal transfer function. Code transitions occur halfway between successiveinteger LSB values. If VREF = +2.500V, then 1 LSB = 610µV or 2.500V/4096. ____________Applications Information Connection to Standard Interfaces The MAX1240/MAX1241 serial interface is fully compatible with SPI/QSPI and MICROWIRE standard serial interfaces (Figure 11). 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 2.1MHz. 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 produces 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 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. FULL-SCALE TRANSITION FS = VREF - 1LSB 1LSB = VREF 4096 00…011 00…010 00…001 00…000 0 1 2 3 INPUT VOLTAGE (LSBs) FS FS - 3/2LSB Figure 10. Unipolar Transfer Function, Full Scale (FS) = VREF 1LSB, Zero Scale (ZS) = GND ______________________________________________________________________________________ 11 +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO MAX1240/MAX1241 5) With CS = high, wait the minimum specified time, tCS, before initiating a new conversion by pulling CS low. If a conversion is aborted by pulling CS high before the conversion’s end, wait for the minimum acquisition time, tACQ, before starting a new conversion. CS must be held low until all data bits are clocked out. Data can be output in two bytes or continuously, as shown in Figure 8. The bytes contain the result of the conversion padded with one leading 1, and trailing 0s. a) SPI I/O SCK MISO +3V CS SCLK DOUT MAX1240 MAX1241 SS SPI and MICROWIRE When using SPI or MICROWIRE, 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 until the maximum specified 7.5µs conversion time elapses. 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 seven bits of conversion result. The second byte contains the remaining five bits and three trailing zeros. See Figure 11 for connections and Figure 12 for timing. CS SCK MISO +3V CS SCLK DOUT SS b) QSPI MAX1240 MAX1241 I/O SK SI CS SCLK DOUT 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 MAX1240/MAX1241 requires 13 clock cycles from the µP to clock out the 12 bits of data with no trailing zeros (Figure 13). The maximum clock frequency to ensure compatibility with QSPI is 2.097MHz. MAX1240 MAX1241 c) MICROWIRE Figure 11. Common Serial-Interface Connections to the MAX1241 Layout, Grounding, and 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 14 shows the recommended system ground connections. Establish a single-point analog ground (“star” ground point) at GND, separate from the logic ground. Connect all other analog grounds and 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 VDD power supply may affect the ADC’s high-speed comparator. Bypass this supply to the single-point analog ground with 0.1µF and 4.7µF bypass capacitors. Minimize capacitor lead lengths for best supply-noise rejection. If the power supply is very noisy, a 10Ω resistor can be connected as a lowpass filter to attenuate supply noise (Figure 14). 12 ______________________________________________________________________________________ +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO MAX1240/MAX1241 1ST BYTE READ SCLK CS tCONV DOUT* D11 MSB EOC *WHEN CS IS HIGH, DOUT = HIGH -Z D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 LSB HIGH-Z 2ND BYTE READ Figure 12. SPI/MICROWIRE Serial Interface Timing (CPOL = CPHA = 0) SCLK CS tCONV DOUT* D11 MSB D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 LSB HIGH-Z EOC *WHEN CS IS HIGH, DOUT = HIGH -Z Figure 13. QSPI Serial Interface Timing (CPOL = CPHA = 0) SUPPLIES +3V +3V GND R* = 10Ω 4.7µF 0.1µF VDD GND +3V DGND MAX1240 MAX1241 *OPTIONAL DIGITAL CIRCUITRY Figure 14. Power-Supply Grounding Condition ______________________________________________________________________________________ 13 +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO MAX1240/MAX1241 __Ordering Information (continued) PART MAX1240AEPA MAX1240BEPA MAX1240CEPA MAX1240AESA MAX1240BESA MAX1240CESA MAX1240AMJA MAX1240BMJA MAX1240CMJA MAX1241ACPA MAX1241BCPA MAX1241CCPA MAX1241ACSA MAX1241BCSA MAX1241CCSA MAX1241BC/D MAX1241AEPA MAX1241BEPA MAX1241CEPA MAX1241AESA MAX1241BESA MAX1241CESA MAX1241AMJA MAX1241BMJA MAX1241CMJA TEMP. RANGE -40°C to +85°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -55°C to +125°C -55°C to +125°C -55°C to +125°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -55°C to +125°C -55°C to +125°C -55°C to +125°C PINPACKAGE 8 Plastic DIP 8 Plastic DIP 8 Plastic DIP 8 SO 8 SO 8 SO 8 CERDIP** 8 CERDIP** 8 CERDIP** 8 Plastic DIP 8 Plastic DIP 8 Plastic DIP 8 SO 8 SO 8 SO Dice* 8 Plastic DIP 8 Plastic DIP 8 Plastic DIP 8 SO 8 SO 8 SO 8 CERDIP** 8 CERDIP** 8 CERDIP** INL (LSB) ±1/2 ±1 ±1 ±1/2 ±1 ±1 ±1/2 ±1 ±1 ±1/2 ±1 ±1 ±1/2 ±1 ±1 ±1 ±1/2 ±1 ±1 ±1/2 ±1 ±1 ±1/2 ±1 ±1 * Dice are specified at TA = +25°C, DC parameters only. ** Contact factory for availability and processing to MIL-STD-883. ___________________Chip Information TRANSISTOR COUNT: 2558 SUBSTRATE CONNECTED TO GND 14 ______________________________________________________________________________________ +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO ________________________________________________________Package Information PDIPN.EPS MAX1240/MAX1241 ______________________________________________________________________________________ SOICN.EPS 15 +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO MAX1240/MAX1241 ___________________________________________Package Information (continued) CDIPS.EPS 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. 16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.