19-1155; Rev 2; 11/98 EALUATION KIT AAILABLE +2.7, Low-Power, General Description The are low-power, 12-bit analogto-digital converters (ADCs) available in 8-pin packages. The operates with a single +2.7 to +3.6 supply, and the operates with a single +2.7 to +5.25 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 ( DD = 3) at the 73ksps maximum sampling speed. A 2µA shutdown mode reduces power at slower throughput rates. The has an internal 2.5 reference, while the requires an external reference. The accepts signals from to REF, 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 are available in 8-pin DIP and SO packages. Battery-Powered Systems Portable Data Logging Isolated Data Acquisition Process Control Instrumentation TOP IEW DD AIN SHDN REF 1 2 3 4 DIP/SO Applications Pin Configuration 8 7 6 5 GND Features Single-Supply Operation: +2.7 to +3.6 () +2.7 to +5.25 () 12-Bit Resolution Internal 2.5 Reference () Small Footprint: 8-Pin DIP/SO Packages Low Power: 3.7µW (73ksps, ) 3mW (73ksps, ) 66µW (1ksps, ) 5µW (power-down mode) Internal Track/Hold SPI/QSPI/MICROWIRE 3-Wire Serial Interface Internal Clock PART Ordering Information TEMP. RANGE PIN- PACKAGE 8 Plastic DIP 8 Plastic DIP Ordering Information continued at end of data sheet. *Dice are specified at T A = +25 C, DC parameters only. INL (LSB) ± 1 /2 ±1 ACPA BCPA C to +7 C C to +7 C CCPA C to +7 C 8 Plastic DIP ±1 AA C to +7 C 8 SO ± 1 /2 BA C to +7 C 8 SO ±1 CA C to +7 C 8 SO ±1 BC/D C to +7 C Dice* ±1 SHDN AIN REF 7 8 3 2 4 CONTROL LOGIC T/H 2.5 REFERENCE ( ONLY) Functional Diagram DD 1 INT CLOCK 12-BIT SAR 5 GND OUTPUT SHIFT REGISTER 6 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 1-8-998-88. For small orders, phone 1-8-835-8769.
ABSOLUTE MAXIMUM RATINGS DD to GND...-.3 to +6 AIN to GND...-.3 to ( DD +.3) REF to GND...-.3 to ( DD +.3) Digital Inputs to GND...-.3 to +6 to GND...-.3 to ( DD +.3) Current...±25mA Continuous Power Dissipation (T A = +7 C) Plastic DIP (derate 9.9mW/ C above +7 C)...727mW SO (derate 5.88mW/ C above +7 C)...471mW CERDIP (derate 8.mW/ C above +7 C)...64mW ELECTRICAL CHARACTERISTI Operating Temperature Ranges _C_A/_C_A... C to +7 C _E_ A/_E_ A...-4 C to +85 C _MJA/_MJA...-55 C to +125 C Storage Temperature Range...-6 C to +15 C Lead Temperature (soldering, 1sec)...+3 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. ( DD = +2.7 to +3.6 (); DD = +2.7 to +5.25 (); 73ksps, f = 2.1MHz (5% duty cycle); 4.7µF capacitor at REF pin, external reference; REF = 2.5 applied to REF pin; T A = T MIN to T MAX ; unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC ACCURACY (Note 1) Resolution 12 Bits Relative Accuracy (Note 2) INL MAX124_A ±.5 MAX124_B/C ±1. LSB Differential Nonlinearity DNL No missing codes over temperature ±1 LSB Offset Error MAX124_A ±.5 ±3. MAX124_B/C ±.5 ±4. LSB Gain Error (Note 3) ±.5 ±4. LSB Gain Temperature Coefficient ±.25 ppm/ C DYNAMIC SPECIFICATIONS (1kHz sine-wave input, to 2.5p-p, 73ksps, f = 2.1MHz) Signal-to-Noise Plus MAX124_A/B 7 SINAD Distortion Ratio MAX124_C 71.5 db Total Harmonic Distortion THD Up to the 5th harmonic MAX124_A/B -8 MAX124_C -88 db Spurious-Free Dynamic Range SFDR MAX124_A/B 8 MAX124_C 88 db Small-Signal Bandwidth -3dB rolloff 2.25 MHz Full-Power Bandwidth 1. MHz CONERSION RATE Conversion Time t CON 5.5 7.5 µs Track/Hold Acquisition Time t ACQ 1.5 µs Throughput Rate f = 2.1MHz 73 ksps Aperture Delay t APR Figure 8 3 ns Aperture Jitter <5 ps ANALOG INPUT Input oltage Range REF Input Capacitance 16 pf 2
ELECTRICAL CHARACTERISTI (continued) ( DD = +2.7 to +3.6 (); DD = +2.7 to +5.25 (); 73ksps, f = 2.1MHz (5% duty cycle); 4.7µF capacitor at REF pin, external reference; REF = 2.5 applied to REF pin; T A = T MIN to T MAX ; unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX INTERNAL REFERENCE ( only) REF Output oltage T A = +25 C 2.48 2.5 2.52 REF Short-Circuit Current 3 AC/BC ±3 ±5 REF Temperature Coefficient AE/BE ±3 ±6 AM/BM ±3 ±8 C ±3 Load Regulation (Note 4) ma to.2ma output load.35 Capacitive Bypass at REF 4.7 EXTERNAL REFERENCE ( REF = 2.5) Input oltage Range 1. DD + 5m UNITS ma ppm/ C ppm/ C µf Input Current Input Resistance REF Input Current in Shutdown Capacitive Bypass at REF DIGITAL INPUTS:,, SHDN, Input High oltage IH, Input Low oltage IL, Input Hysteresis HYST, Input Leakage I IN, Input Capacitance C IN SHDN Input High oltage SH SHDN Input Low oltage SL SHDN Input Current SHDN Input Mid oltage SM SHDN oltage, Floating FLT 18 25 1 15 SHDN = ±.1 1 µa DD 3.6 2. DD > 3.6 () 3..8.2 IN = or DD ±.1 ±1 µa (Note 5) 15 pf DD -.4.4 SHDN = or DD ±4. µa 1.1 DD - 1.1 SHDN = float DD /2.1 µa kω µf SHDN Max Allowed Leakage, Mid Input SHDN = float ±1 na DIGITAL OUTPUT: Output oltage Low Output oltage High Three-State Leakage Current Three-State Output Capacitance OL OH I L C OUT I SINK = 5mA.4 I SINK = 16mA.8 I SOURCE =.5mA DD -.5 = DD ±.1 ±1 µa = DD (Note 5) 15 pf 3
ELECTRICAL CHARACTERISTI (continued) ( DD = +2.7 to +3.6 (); DD = +2.7 to +5.25 (); 73ksps, f = 2.1MHz (5% duty cycle); 4.7µF capacitor at REF pin, external reference; REF = 2.5 applied to REF pin; T A = T MIN to T MAX ; unless otherwise noted.) PARAMETERS SYMBOL CONDITIONS MIN TYP MAX UNITS POWER REQUIREMENTS Supply oltage Supply Current Supply Rejection DD I DD PSR 2.7 3.6 2.7 5.25 A/B DD 3.6 1.4 2. DD = 3.6 C 1.4 3.5 Operating DD = 3.6.9 1.5 A/B mode DD = 5.25 1.6 2.5 C DD = 3.6.9 2.8 DD = 5.25 1.6 3.8 Power-down, digital inputs DD = 3.6 1.9 1 at or DD DD = 5.25 3.5 15 (Note 5) ±.3 ma µa m TIMING CHARACTERISTI (Figure 8) ( DD = +2.7 to +3.6 (); DD = +2.7 to +5.25 (); T A = T MIN to T MAX, unless otherwise noted.) PARAMETERS SYMBOL CONDITIONS MIN TYP MAX UNITS Acquisition Time t ACQ = DD (Note 6) 1.5 µs Fall to Output Data alid t DO Figure 1, MAX124 C/E 2 2 C LOAD = 5pF MAX124 M 2 24 ns Fall to Output Enable t D Figure 1, C LOAD = 5pF 24 ns Rise to Output Disable t TR Figure 2, C LOAD = 5pF 24 ns Clock Frequency f 2.1 MHz Pulse Width High t CH 2 ns Pulse Width Low t CL 2 ns Low to Fall Setup Time t 5 ns Rise to Rise (Note 5) t STR ns Pulse Width t 24 ns Note 1: Tested at DD = +2.7. 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: internal reference, offset nulled; external reference ( REF = +2.5), 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 [ FS (2.7) - FS ( DD(MAX )]. Note 7: To guarantee acquisition time, t ACQ 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
6k DGND a) High-Z to OH and OL to OH Figure 1. Load Circuits for Enable Time C LOAD = 5pF +2.7 6k C LOAD = 5pF DGND b) High-Z to OL and OH to OL +2.7 6k 6k C LOAD = 5pF C LOAD = 5pF DGND DGND a) OH to High-Z b) OL to High-Z Figure 2. Load Circuits for Disable Time Typical Operating Characteristics ( DD = 3., REF = 2.5, f = 2.1MHz, C L = 2pF, T A = +25 C, unless otherwise noted.) OPERATING SUPPLY CURRENT (ma) 2. 1.8 1.6 1.4 1.2 1..8.6.4.2 OPERATING SUPPLY CURRENT vs. SUPPLY OLTAGE R L = CODE = 1111 2 3 4 5 6 SUPPLY OLTAGE () -D SUPPLY CURRENT (ma) 1.3 1.2 1.1 1..9 SUPPLY CURRENT vs. TEMPERATURE R LOAD = CODE = 1111.8-6 -2 2 6 1 14 TEMPERATURE ( C) -A/NEW OFFSET ERROR (LSB) 1..9.8.7.6.5.4.3.2.1 OFFSET ERROR vs. SUPPLY OLTAGE 2.25 2.75 3.25 3.75 4.25 4.75 5.25 SUPPLY OLTAGE () -3 5
Typical Operating Characteristics (continued) ( DD = 3., REF = 2.5, f = 2.1MHz, C L = 2pF, T A = +25 C, unless otherwise noted.) SHUTDOWN SUPPLY CURRENT (µa) 4. 3.5 3. 2.5 2. 1.5 1..5 2.25 2.75 SHUTDOWN SUPPLY CURRENT vs. SUPPLY OLTAGE 3.25 3.75 4.25 4.75 5.25 SUPPLY OLTAGE () -C/NEW SHUTDOWN SUPPLY CURRENT (µa) 5. 4.5 4. 3.5 3. 2.5 2. 1.5 1..5 SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE -6-2 2 6 1 14 TEMPERATURE ( C) -B OFFSET ERROR (LSB).8.7.6.5.4.3.2.1 OFFSET ERROR vs. TEMPERATURE DD = 2.7-55 -3-5 2 45 7 95 12 145 TEMPERATURE ( C) -6.8.7 GAIN ERROR vs. SUPPLY OLTAGE -7.8.7 DD = 2.7 GAIN ERROR vs. TEMPERATURE -8 2.52 2.515 INTERNAL REFERENCE OLTAGE vs. SUPPLY OLTAGE -X GAIN ERROR (LSB).6.5.4.3 GAIN ERROR (LSB).6.5.4.3 REF () 2.51 2.55 2.5.2.1.2.1 2.4995 2.25 2.75 3.25 3.75 4.25 4.75 5.25 SUPPLY OLTAGE () -55-3 -5 2 45 7 95 12 145 TEMPERATURE ( C) 2.499 2.25 2.75 3.25 3.75 4.25 4.75 5.25 DD () 2.51 2.5 INTERNAL REFERENCE OLTAGE vs. TEMPERATURE DD = 3.6 -Y 1.2 1. INTEGRAL NONLINEARITY vs. SUPPLY OLTAGE -9/NEW 1.2 1. DD = 2.7 INTEGRAL NONLINEARITY vs. TEMPERATURE -1/NEW REF () 2.499 2.498 2.497 2.496 2.495 DD = 2.7 2.494-6 -2 2 6 1 14 TEMPERATURE ( C) INL (LSB).8.6.4.2 2.25 2.75 3.25 3.75 4.25 4.75 5.25 SUPPLY OLTAGE () INL (LSB).8.6.4.2-6 -4-2 2 4 6 8 1 12 14 TEMPERATURE ( C) 6
Typical Operating Characteristics (continued) ( DD = 3., REF = 2.5, f = 2.1MHz, C L = 2pF, T A = +25 C, unless otherwise noted.) INL (LSB).6.4.2 -.2 -.4 -.6 INTEGRAL NONLINEARITY vs. CODE 124 248 372 496 CODE -11A/NEW AMPLITUDE (db) 2-2 -4-6 -8-1 -12-14 FFT PLOT 18.75 37.5 FREQUENCY (khz) f AIN = 1kHz, 2.5p-p f SAMPLE = 73ksps -TOC12A Pin Description PIN NAME FUNCTION 1 DD Positive Supply oltage: 2.7 to 3.6, (); 2.7 to 5.25 () 2 AIN Sampling Analog Input, to REF range 3 SHDN 4 REF Three-Level Shutdown Input. Pulling SHDN low shuts the down to 15µA (max) supply current. Both the and are fully operational with either SHDN high or floating. For the, 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 oltage for Analog-to-Digital Conversion. Internal 2.5 reference output for ; bypass with 4.7µF capacitor. External reference voltage input for, or for with the internal reference disabled. Bypass REF with a minimum of.1µf when using an external reference. 5 GND Analog and Digital Ground 6 7 8 Serial Data Output. Data changes state at s falling edge. is high impedance when is high. Active-Low Chip Select initiates conversions on the falling edge. When is high, is high impedance. Serial Clock Input. clocks data out at rates up to 2.1MHz. 7
+2.7 to +3.6* * DD,MAX = +5.25 () ** 4.7µF ().1µF () 4.7µF ANALOG INPUT TO REF SHUTDOWN INPUT REFERENCE INPUT ( ONLY).1µF 1 2 3 4 C** DD AIN SHDN REF Figure 3. Operational Diagram Detailed Description Converter Operation The 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 in its simplest configuration. The convert input signals in the to REF range in 9µs, including T/H acquisition time. The s internal reference is trimmed to 2.5, while the requires an external reference. Both devices accept voltages from 1. to DD. The serial interface requires only three digital lines (,, and ) and provides an easy interface to microprocessors (µps). The have two modes: normal and shutdown. Pulling SHDN low shuts the device down and reduces supply current below 1µA ( DD 3.6), while pulling SHDN high or leaving it open puts the device into operational mode. Pulling low initiates a conversion. The conversion result is available at 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). 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 GND 8 7 6 5 SERIAL INTERFACE AIN GND REF TRACK INPUT HOLD 12-BIT CAPACITIE DAC C HOLD - + 16pF C SWITCH TRACK 9k R IN Figure 4. Equivalent Input Circuit ZERO HOLD COMPARATOR AT THE SAMPLING INSTANT, THE INPUT SWITCHES FROM AIN TO GND. switch opens and maintains a constant input to the ADC s SAR section. During acquisition, the analog input (AIN) charges capacitor C HOLD. Bringing low ends the acquisition interval. At this instant, the T/H switches the input side of C HOLD to GND. The retained charge on C HOLD 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 within the limits of 12- bit resolution. This action is equivalent to transferring a charge from C HOLD 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 (t ACQ ) 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: t ACQ = 9(R S + R IN ) x 16pF where R IN = 9kΩ, R S = the input signal s source impedance, and t ACQ is never less than 1.5µs. Source impedances below 1kΩ do not significantly affect the ADC s AC performance. 8
Higher source impedances can be used if a.1µf 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. 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 DD and GND, allow the input to swing from GND -.3 to DD +.3 without damage. However, for accurate conversions near full scale, the input must not exceed DD by more than 5m, or be lower than GND by 5m. If the analog input exceeds 5m beyond the supplies, limit the input current to 2mA. Internal Reference () The has an on-chip voltage reference trimmed to 2.5. 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 4µA. Bypass REF with a 4.7µF capacitor. Larger capacitors increase wake-up time when exiting shutdown (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 operate with an external reference at the REF pin. To use the with an external reference, disable the internal reference by letting SHDN float. Stay within the +1. to DD 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 25µA of DC load current and have an output impedance of 1Ω or less. The recommended minimum value for the bypass capacitor is.1µf. If the reference has higher output impedance or is noisy, bypass it close to the REF pin with a 4.7µF capacitor. 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 2ms to provide adequate charge for specified accuracy. With an external reference, the internal reset time is 1µs after the power supplies have stabilized. No conversions should be performed during these times. To start a conversion, pull low. At s falling edge, the T/H enters its hold mode and a conversion is initiat- COMPLETE CONERSION SEQUENCE SHDN t WAKE CONERSION CONERSION 1 POWERED UP POWERED DOWN POWERED UP Figure 5. Shutdown Sequence 9
ed. After an internally timed conversion period, the end of conversion is signaled by 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 between conversions. Figure 6 shows a plot of average supply current versus conversion rate. Because the 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 (t WAKE ) is the time from when SHDN is deasserted to the time when a conversion may be initiated (Figure 5). For the, this time depends on the time in shutdown (Figure 7) because the external 4.7µF reference bypass capacitor loses charge slowly during shutdown. 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 2ns. Do not run the clock while a conversion is in progress. Timing and Control Conversion-start and data-read operations are controlled by the and digital inputs. The timing diagrams of Figures 8 and 9 outline serial-interface operation. A falling edge initiates a conversion sequence: the T/H stage holds the input voltage, the ADC begins to convert, and changes from high impedance to logic low. must be kept low during the conversion. An internal register stores the data when the conversion is in progress. SUPPLY CURRNET (ma) 1 1.1.1 DD = REF = 3. R LOAD =, C LOAD = 5pF CODE = 1111.1.1 1 1 1 1k 1k 1k CONERSION RATE (Hz) Figure 6. Average Supply Current vs. Conversion Rate POWER-UP DELAY (ms) 1..8.6.4.2..1.1.1 1 1 TIME IN SHUTDOWN (sec) Figure 7. Typical Reference Power-Up Delay vs. Time in Shutdown /41-7a FIG. 6a 1 4 8 12 16 B11 B1 B9 B8 B7 B6 B5 B4 B3 B2 B1 B EOC INTERFACE IDLE CONERSION IN PROGRESS EOC CLOCK OUT SERIAL DATA TRAILING ZEROS TRACK/HOLD STATE TRACK HOLD TRACK HOLD.24µs 7.5µs (t CON ) µs 12.5.476µs = 5.95µs µs (t ) CYCLE TIME TOTAL = 13.7µs IDLE Figure 8. Interface Timing Sequence 1
INTERNAL T/H OUTPUT CODE 11 111 11 11 11 11 (TRACK/ACQUIRE) t t D t APR FULL-SCALE TRANSITION t CON (HOLD) Figure 9. Detailed Serial-Interface Timing 11 1 1 1 2 3 FS INPUT OLTAGE (LSBs) FS - 3/2LSB FS = REF - 1LSB 1LSB = REF 496 Figure 1. Unipolar Transfer Function, Full Scale (FS) = REF - 1LSB, Zero Scale (ZS) = GND t STR t CH t DO t CL t TR B2 B1 B (TRACK/ACQUIRE) End of conversion (EOC) is signaled by going high. s rising edge can be used as a framing signal. shifts the data out of this register any time after the conversion is complete. transitions on s falling edge. The next falling clock edge produces the MSB of the conversion at, 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, produce trailing zeros at and have no effect on converter operation. Minimum cycle time is accomplished by using s rising edge as the EOC signal. Clock out the data with 12.5 clock cycles at full speed. Pull high after reading the conversion s LSB. After the specified minimum time (t ), can be pulled low again to initiate the next conversion. Output Coding and Transfer Function The data output from the is binary, and Figure 1 depicts the nominal transfer function. Code transitions occur halfway between successiveinteger LSB values. If REF = +2.5, then 1 LSB = 61µ or 2.5/496. Applications Information Connection to Standard Interfaces The 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 low. Keep low. 2) Wait the for the maximum conversion time specified before activating. Alternatively, look for a rising edge to determine the end of conversion. 3) Activate for a minimum of 13 clock cycles. The first falling clock edge produces the MSB of the conversion. output data transitions on s falling edge and is available in MSB-first format. Observe the to valid timing characteristic. Data can be clocked into the µp on s rising edge. 4) Pull high at or after the 13th falling clock edge. If remains low, trailing zeros are clocked out after the LSB. t 11
5) With = high, wait the minimum specified time, t, before initiating a new conversion by pulling low. If a conversion is aborted by pulling high before the conversion s end, wait for the minimum acquisition time, t ACQ, before starting a new conversion. 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 s. SPI and MICROWIRE When using SPI or MICROWIRE, set CPOL = and CPHA =. Conversion begins with a falling edge. goes low, indicating a conversion in progress. Wait until 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. output data transitions on s falling edge and is clocked into the µp on 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. QSPI Set CPOL = CPHA =. 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 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 2.97MHz. 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 DD power supply may affect a) SPI b) QSPI c) MICROWIRE I/O SCK MISO SS SCK MISO SS I/O SK SI +3 +3 Figure 11. Common Serial-Interface Connections to the the ADC s high-speed comparator. Bypass this supply to the single-point analog ground with.1µf and 4.7µF bypass capacitors. Minimize capacitor lead lengths for best supply-noise rejection. If the power supply is very noisy, a 1Ω resistor can be connected as a lowpass filter to attenuate supply noise (Figure 14). 12
* t CON EOC *WHEN IS HIGH, = HIGH -Z 1ST BYTE READ 2ND BYTE READ D11 D1 D9 D8 D7 D6 D5 D4 D3 D2 D1 D MSB Figure 12. SPI/MICROWIRE Serial Interface Timing (CPOL = CPHA = ) * t CON D11 D1 D9 D8 D7 D6 D5 D4 D3 D2 D1 D MSB LSB LSB HIGH-Z HIGH-Z EOC *WHEN IS HIGH, = HIGH -Z Figure 13. QSPI Serial Interface Timing (CPOL = CPHA = ) SUPPLIES +3 +3 GND R* = 1Ω 4.7µF.1µF DD GND +3 DGND DIGITAL CIRCUITRY *OPTIONAL Figure 14. Power-Supply Grounding Condition 13
Ordering Information (continued) PART TEMP. RANGE PIN- PACKAGE 8 Plastic DIP INL (LSB) AEPA BEPA -4 C to +85 C -4 C to +85 C 8 Plastic DIP ± 1 /2 ±1 CEPA -4 C to +85 C 8 Plastic DIP ±1 AESA -4 C to +85 C 8 SO ± 1 /2 BESA CESA -4 C to +85 C -4 C to +85 C 8 SO 8 SO ±1 ±1 AMJA -55 C to +125 C 8 CERDIP** ± 1 /2 BMJA -55 C to +125 C 8 CERDIP** ±1 CMJA -55 C to +125 C 8 CERDIP** ±1 ACPA C to +7 C 8 Plastic DIP ± 1 /2 BCPA C to +7 C 8 Plastic DIP ±1 CCPA C to +7 C 8 Plastic DIP ±1 AA C to +7 C 8 SO ± 1 /2 BA C to +7 C 8 SO ±1 CA C to +7 C 8 SO ±1 BC/D C to +7 C Dice* ±1 AEPA -4 C to +85 C 8 Plastic DIP ± 1 /2 BEPA -4 C to +85 C 8 Plastic DIP ±1 CEPA -4 C to +85 C 8 Plastic DIP ±1 AESA -4 C to +85 C 8 SO ± 1 /2 BESA -4 C to +85 C 8 SO ±1 CESA -4 C to +85 C 8 SO ±1 AMJA -55 C to +125 C 8 CERDIP** ± 1 /2 BMJA -55 C to +125 C 8 CERDIP** ±1 CMJA -55 C to +125 C 8 CERDIP** ±1 * Dice are specified at T A = +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
SOICN.EPS +2.7, Low-Power, Package Information PDIPN.EPS 15
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, 12 San Gabriel Drive, Sunnyvale, CA 9486 48-737-76 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.