19-1532; Rev 0; 9/99 KIT ATION EVALU E L B AVAILA 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface Excellent dynamic performance and low power combined with ease of use and small package size make these converters ideal for battery-powered and dataacquisition applications or for other circuits with demanding power consumption and space requirements. The MAX1291 is available in a 28-pin QSOP package, while the MAX1293 is available in a 24-pin QSOP. For pin-compatible +5V, 12-bit versions, refer to the MAX1290/MAX1292 data sheet. Applications Features ♦ 12-Bit Resolution, ±0.5LSB Linearity ♦ +3V Single Operation ♦ User-Adjustable Logic Level (+1.8V to +3.6V) ♦ Internal +2.5V Reference ♦ Software-Configurable, Analog Input Multiplexer 8-Channel Single-Ended/ 4-Channel Pseudo-Differential (MAX1291) 4-Channel Single-Ended/ 2-Channel Pseudo-Differential (MAX1293) ♦ Software-Configurable, Unipolar/Bipolar Inputs ♦ Low Power: 1.7mA (250ksps) 1.0mA (100ksps) 400µA (10ksps) 2µA (Shutdown) ♦ Internal 3MHz Full-Power Bandwidth Track/Hold ♦ Byte-Wide Parallel (8+4) Interface ♦ Small Footprint: 28-Pin QSOP (MAX1291) 24-Pin QSOP (MAX1293) Pin Configurations TOP VIEW 28 VLOGIC HBEN 1 D7 2 27 VDD D6 3 26 REF D5 4 25 REFADJ D4 5 24 GND MAX1291 Industrial Control Systems Data Logging D3/D11 6 Energy Management Patient Monitoring D2/D10 7 22 CH0 Data-Acquisition Systems Touch Screens D1/D9 8 21 CH1 D0/D8 9 20 CH2 INT 10 19 CH3 Ordering Information PART TEMP. RANGE PIN-PACKAGE INL (LSB) MAX1291ACEI 0°C to +70°C 28 QSOP ±0.5 MAX1291BCEI 0°C to +70°C 28 QSOP ±1 MAX1291AEEI -40°C to +85°C 28 QSOP ±0.5 MAX1291BEEI -40°C to +85°C 28 QSOP ±1 Ordering Information continued at end of data sheet. 23 COM RD 11 18 CH4 WR 12 17 CH5 CLK 13 16 CH6 CS 14 15 CH7 QSOP Pin Configurations continued at end of data sheet. Typical Operating Circuits appear at end of data sheet. ________________________________________________________________ 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. MAX1291/MAX1293 General Description The MAX1291/MAX1293 low-power, 12-bit analog-todigital converters (ADCs) feature a successive-approximation ADC, automatic power-down, fast wake-up (2µs), an on-chip clock, +2.5V internal reference, and a high-speed, byte-wide parallel interface. They operate with a single +3V analog supply and feature a VLOGIC pin that allows them to interface directly with a +1.8V to +5.5V digital supply. Power consumption is only 5.7mW (VDD = VLOGIC) at the maximum sampling rate of 250ksps. Two softwareselectable power-down modes enable the MAX1291/ MAX1293 to be shut down between conversions; accessing the parallel interface returns them to normal operation. Powering down between conversions can cut supply current to under 10µA at reduced sampling rates. Both devices offer software-configurable analog inputs for unipolar/bipolar and single-ended/pseudo-differential operation. In single-ended mode, the MAX1291 has 8 input channels and the MAX1293 has 4 input channels (4 and 2 input channels, respectively, when in pseudo-differential mode). MAX1291/MAX1293 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface ABSOLUTE MAXIMUM RATINGS VDD to GND ..............................................................-0.3V to +6V VLOGIC to GND.........................................................-0.3V to +6V CH0–CH7, COM to GND ............................-0.3V to (VDD + 0.3V) REF, REFADJ to GND ................................-0.3V to (VDD + 0.3V) Digital Inputs to GND ...............................................-0.3V to +6V Digital Outputs (D0–D11, INT) to GND...-0.3V to (VLOGIC + 0.3V) Continuous Power Dissipation (TA = +70°C) 24-Pin QSOP (derate 9.5mW/°C above +70°C) ...........762mW 28-Pin QSOP (derate 8.00mW/°C above +70°C) .........667mW Operating Temperature Ranges MAX1291_C_ _/MAX1293_C_ _ ..............................0°C to +70°C MAX1291_E_ _/MAX1293_E_ _ ...........................-40°C to +85°C Storage Temperature Range .............................-65°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 = VLOGIC = +2.7V to +3.6V, COM = GND, REFADJ = VDD, VREF = +2.5V, 4.7µF capacitor at REF pin, fCLK = 4.8MHz (50% duty cycle); TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC ACCURACY (Note 1) Resolution RES Relative Accuracy (Note 2) INL Differential Nonlinearity DNL 12 Bits MAX129_A ±0.5 MAX129_B ±1 No missing codes over temperature ±1 LSB Offset Error ±4 LSB Gain Error (Note 3) ±4 LSB LSB Gain Temperature Coefficient ±2.0 ppm/°C Channel-to-Channel Offset Matching ±0.2 LSB DYNAMIC SPECIFICATIONS (fIN(sine wave) = 50kHz, VIN = 2.5Vp-p, 250ksps, external fCLK = 4.8MHz, bipolar input mode) Signal-to-Noise Plus Distortion SINAD Total Harmonic Distortion (including 5th-order harmonic) THD Spurious-Free Dynamic Range SFDR 67 70 dB -78 80 dB dB fIN1 = 49kHz, fIN2 = 52kHz 76 dB Channel-to-Channel Crosstalk fIN = 125kHz, VIN = 2.5Vp-p (Note 4) -78 dB Full-Linear Bandwidth SINAD > 68dB 250 kHz Full-Power Bandwidth -3dB rolloff 3 MHz Intermodulation Distortion IMD CONVERSION RATE Conversion Time (Note 5) Track/Hold Acquisition Time tCONV External clock mode 3.3 External acquisition/internal clock mode 2.5 3.0 3.5 Internal acquisition/internal clock mode 3.2 3.6 4.1 tACQ 625 µs ns Aperture Delay External acquisition or external clock mode 50 ns Aperture Jitter External acquisition or external clock mode Internal acquisition/internal clock mode <50 <200 ps External Clock Frequency Duty Cycle 2 fCLK 0.1 4.8 MHz 30 70 % _______________________________________________________________________________________ 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface (VDD = VLOGIC = +2.7V to +3.6V, COM = GND, REFADJ = VDD, VREF = +2.5V, 4.7µF capacitor at REF pin, fCLK = 4.8MHz (50% duty cycle); TA = TMIN to TMAX unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS ANALOG INPUTS Analog Input Voltage Range Single-Ended and Differential (Note 6) VIN Unipolar, VCOM = 0 Bipolar, VCOM = VREF/2 Multiplexer Leakage Current 0 VREF -VREF/2 +VREF/2 ±0.01 On/off-leakage current, VIN = 0 or VDD Input Capacitance ±1 12 CIN V µA pF INTERNAL REFERENCE 2.49 REF Output Voltage REF Short-Circuit Current REF Temperature Coefficient TCREF TA = 0°C to +70°C REFADJ Input Range For small adjustments REFADJ High Threshold To power down the internal reference Load Regulation (Note 7) 0 to 0.5mA output load 2.51 V 15 mA ±20 ppm/°C ±100 mV VDD - 1.0 V 0.2 0.5 mV/mA 0.01 1 µF 4.7 10 µF 1.0 VDD + 50mV V Capacitive Bypass at REFADJ Capacitive Bypass at REF 2.5 EXTERNAL REFERENCE AT REF REF Input Voltage Range VREF REF Input Current IREF 200 VREF = 2.5V, fSAMPLE = 250ksps 300 2 Shutdown mode µA DIGITAL INPUTS AND OUTPUTS Input High Voltage VIH Input Low Voltage VIL Input Hysteresis VLOGIC = 2.7V 2.0 VLOGIC = 1.8V 1.5 VLOGIC = 2.7V 0.8 VLOGIC = 1.8V 0.5 200 VHYS Input Leakage Current IIN Input Capacitance CIN Output Low Voltage VOL ISINK = 1.6mA VOH ISOURCE = 1mA Output High Voltage Three-State Leakage Current Three-State Output Capacitance V VIN = 0 or VDD ±0.1 mV ±1 15 CS = VDD ±0.1 COUT CS = VDD 15 µA pF 0.4 V ±1 µA VLOGIC - 0.5 ILEAKAGE V V pF _______________________________________________________________________________________ 3 MAX1291/MAX1293 ELECTRICAL CHARACTERISTICS (continued) MAX1291/MAX1293 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface ELECTRICAL CHARACTERISTICS (continued) (VDD = VLOGIC = +2.7V to +3.6V, COM = GND, REFADJ = VDD, VREF = +2.5V, 4.7µF capacitor at REF pin, fCLK = 4.8MHz (50% duty cycle); TA = TMIN to TMAX unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 2.7 3.6 V 1.8 VDD + 0.3 V POWER REQUIREMENTS Analog Supply Voltage VDD Digital Supply Voltage VLOGIC Operating mode, fSAMPLE = 250ksps Positive Supply Current IDD Standby mode 2.3 1.9 0.9 0.5 2 Internal reference External reference Internal reference External reference Shutdown mode VLOGIC Current Power-Supply Rejection ILOGIC PSR CL = 20pF 2.6 2.3 1.2 0.8 10 fSAMPLE = 250ksps 150 Not converting 10 ±0.4 VDD = 3V ±10%, full-scale input ±0.7 mA µA µA mV TIMING CHARACTERISTICS (VDD = VLOGIC = +2.7V to +3.6V, COM = GND, REFADJ = VDD, VREF = +2.5V, 4.7µF capacitor at REF pin, fCLK = 4.8MHz (50% duty cycle); TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS CLK Period tCP 208 ns CLK Pulse Width High tCH 40 ns CLK Pulse Width Low tCL 40 ns Data Valid to WR Rise Time tDS 40 ns WR Rise to Data Valid Hold Time tDH 0 ns WR to CLK Fall Setup Time tCWS 40 ns CLK Fall to WR Hold Time tCWH 40 ns CS to CLK or WR Setup Time tCSWS 60 ns CLK or WR to CS Hold Time tCSWH 0 ns CS Pulse Width tCS 100 ns WR Pulse Width (Note 8) tWR CS Rise to Output Disable tTC 4 60 CLOAD = 20pF, Figure 1 20 _______________________________________________________________________________________ ns 100 ns 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface (VDD = VLOGIC = +2.7V to +3.6V, COM = GND, REFADJ = VDD, VREF = +2.5V, 4.7µF capacitor at REF pin, fCLK = 4.8MHz (50% duty cycle); TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL RD Rise to Output Disable CONDITIONS MIN MAX UNITS 70 ns 20 70 ns 20 110 ns CLOAD = 20pF, Figure 1 100 ns CLOAD = 20pF, Figure 1 110 ns tTR CLOAD = 20pF, Figure 1 20 RD Fall to Output Data Valid tDO CLOAD = 20pF, Figure 1 HBEN to Output Data Valid tDO1 CLOAD = 20pF, Figure 1 RD Fall to INT High Delay tINT1 CS Fall to Output Data Valid tDO2 TYP Note 1: Tested at VDD = +3V, COM = GND, unipolar single-ended input mode. Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after offset and gain errors have been removed. Note 3: Offset nulled. Note 4: On channel is grounded; sine wave applied to off channels. Note 5: Conversion time is defined as the number of clock cycles times the clock period; clock has 50% duty cycle. Note 6: Input voltage range referenced to negative input. The absolute range for the analog inputs is from GND to VDD. Note 7: External load should not change during conversion for specified accuracy. Note 8: When bit 5 is set low for internal acquisition, WR must not return low until after the first falling clock edge of the conversion. VLOGIC 3k DOUT CLOAD 20pF 3k DOUT CLOAD 20pF GND GND a) HIGH-Z TO VOH AND VOL TO VOH b) HIGH-Z TO VOL AND VOH TO VOL Figure 1. Load Circuits for Enable/Disable Times _______________________________________________________________________________________ 5 MAX1291/MAX1293 TIMING CHARACTERISTICS (continued) Typical Operating Characteristics (VDD = VLOGIC = +3V, VREF = +2.500V, fCLK = 4.8MHz, CL = 20pF, TA = +25°C, unless otherwise noted.) 0.4 0.3 0.2 0.1 0.1 DNL (LSB) 0.2 0 -0.1 0 -0.2 -0.3 -0.3 -0.4 -0.4 3000 4000 5000 1000 2000 3000 4000 0.1 5000 10 RL = ∞ CODE = 101010100000 2.1 1.95 1.9 1.90 1.8 1.85 1.7 1.80 3.6 100k 920 910 900 880 -40 -15 10 35 60 2.7 85 3.0 3.3 3.6 VDD (V) TEMPERATURE (°C) VDD (V) STANDBY CURRENT vs. TEMPERATURE POWER-DOWN CURRENT vs. SUPPLY VOLTAGE POWER-DOWN CURRENT vs. TEMPERATURE 910 900 1.00 880 -15 10 35 TEMPERATURE (°C) 60 85 1.0 0.8 0.50 -40 1.1 0.9 0.75 890 MAX1291/3 toc09 1.25 POWER-DOWN IDD (µA) POWER-DOWN IDD (µA) 920 1.2 MAX1291/3 toc08 1.50 MAX1291/3 toc07 930 1M 890 1.6 3.3 10k STANDBY CURRENT vs. SUPPLY VOLTAGE 2.0 IDD (mA) 2.00 1k 930 STANDBY IDD (µA) 2.05 100 fSAMPLE (Hz) SUPPLY CURRENT vs. TEMPERATURE 2.2 MAX1291/93 toc04 RL = ∞ CODE = 101010100000 3.0 1 DIGITAL OUTPUT CODE SUPPLY CURRENT vs. SUPPLY VOLTAGE 2.7 WITH EXTERNAL REFERENCE 1 0 DIGITAL OUTPUT CODE 2.10 100 MAX1291/3 toc06 2000 MAX1291/3 toc05 1000 WITH INTERNAL REFERENCE 10 -0.5 0 IDD (mA) 1000 -0.1 -0.2 -0.5 10,000 IDD (µA) 0.3 MAX1291/93 toc02 0.4 INL (LSB) 0.5 MAX1291/93 toc01 0.5 6 SUPPLY CURRENT vs. SAMPLE FREQUENCY DIFFERENTIAL NONLINEARITY vs. DIGITAL OUTPUT CODE MAX1291/93 toc03 INTEGRAL NONLINEARITY vs. DIGITAL OUTPUT CODE STANDBY IDD (µA) MAX1291/MAX1293 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface 2.7 3.0 3.3 VDD (V) 3.6 -40 -15 10 35 TEMPERATURE (°C) _______________________________________________________________________________________ 60 85 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface INTERNAL REFERENCE VOLTAGE vs. TEMPERATURE 2.51 2.50 2.49 2.49 3.0 3.3 -2.5 -40 3.6 -15 35 60 85 2.7 OFFSET ERROR vs. TEMPERATURE GAIN ERROR vs. SUPPLY VOLTAGE GAIN ERROR vs. TEMPERATURE 0.0 -1.0 -1.5 GAIN ERROR (LSB) GAIN ERROR (LSB) 0 -0.5 -1 -2 35 60 2.7 3.0 3.3 VDD (V) LOGIC SUPPLY CURRENT vs. SUPPLY VOLTAGE LOGIC SUPPLY CURRENT vs. TEMPERATURE 35 60 85 FFT PLOT max1291/3 toc17 VDD = 3V fIN = 50kHz fSAMPLE = 250ksps 0 AMPLITUDE (dB) -20 150 100 100 10 20 200 ILOGIC (µA) 150 -15 TEMPERATURE (°C) 250 MAX1291/3 toc16 200 -40 3.6 TEMPERATURE (°C) 250 ILOGIC (µA) 85 -1.0 -2.0 -3 10 -0.5 -1.5 -2.0 -2.5 3.6 0.5 MAX1291/3 toc14 0.0 -15 3.3 VDD (V) 1 MAX1291/3 toc13 0.5 -40 3.0 TEMPERATURE (°C) VDD (V) OFFSET ERROR (LSB) 10 MAX1291/3 toc15 2.7 -1.5 -2.0 2.48 2.48 -1.0 MAX1291/93 toc18 2.50 -0.5 OFFSET ERROR (LSB) 2.52 VREF (V) 2.51 OFFSET ERROR vs. SUPPLY VOLTAGE 0.0 MAX1291/3 toc11 2.52 VREF (V) 2.53 MAX1291/3 toc10 2.53 MAX1291/3 toc12 INTERNAL REFERENCE VOLTAGE vs. SUPPLY VOLTAGE -40 -60 -80 -100 -120 50 50 2.7 3.0 3.3 VDD (V) 3.6 -140 -40 -15 10 35 TEMPERATURE (°C) 60 85 0 200 400 600 800 1000 1200 FREQUENCY (kHz) _______________________________________________________________________________________ 7 MAX1291/MAX1293 Typical Operating Characteristics (continued) (VDD = VLOGIC = +3V, VREF = +2.500V, fCLK = 4.8MHz, CL = 20pF, TA = +25°C, unless otherwise noted.) 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface MAX1291/MAX1293 Pin Description PIN 8 NAME FUNCTION MAX1291 MAX1293 1 1 HBEN 2 2 D7 Three-State Digital I/O Line (D7) 3 3 D6 Three-State Digital I/O Line (D6) 4 4 D5 Three-State Digital I/O Line (D5) 5 5 D4 Three-State Digital I/O Line (D4) 6 6 D3/D11 Three-State Digital I/O Line (D3, HBEN = 0; D11, HBEN = 1) 7 7 D2/D10 Three-State Digital I/O Line (D2, HBEN = 0; D10, HBEN = 1) 8 8 D1/D9 Three-State Digital I/O Line (D1, HBEN = 0; D9, HBEN = 1) 9 9 D0/D8 Three-State Digital I/O Line (D0, HBEN = 0; D8, HBEN = 1 10 10 INT INT goes low when the conversion is complete and the output data is ready. 11 11 RD Active-Low Read Select. If CS is low, a falling edge on RD will enable the read operation on the data bus. High Byte Enable. Used to multiplex the 12-bit conversion result. 1: Four MSBs are multiplexed on the data bus. 0: Eight LSBs are available on the data bus. 12 12 WR Active-Low Write Select. When CS is low in internal acquisition mode, a rising edge on WR latches in configuration data and starts an acquisition plus a conversion cycle. When CS is low in external acquisition mode, the first rising edge on WR ends acquisition and starts a conversion. 13 13 CLK Clock Input. In external clock mode, drive CLK with a TTL/CMOS-compatible clock. In internal clock mode, connect this pin to either VDD or GND. 14 14 CS Active-Low Chip Select. When CS is high, digital outputs (INT, D7–D0) are high impedance. 15 — CH7 Analog Input Channel 7 16 — CH6 Analog Input Channel 6 17 — CH5 Analog Input Channel 5 18 — CH4 Analog Input Channel 4 19 15 CH3 Analog Input Channel 3 20 16 CH2 Analog Input Channel 2 21 17 CH1 Analog Input Channel 1 22 18 CH0 Analog Input Channel 0 23 19 COM Ground Reference for Analog Inputs. Sets zero-code voltage in single-ended mode and must be stable to ±0.5LSB during conversion. 24 20 GND Analog and Digital Ground 25 21 REFADJ 26 22 REF Bandgap Reference Buffer Output/External Reference Input. Add a 4.7µF capacitor to GND when using the internal reference. 27 23 VDD Analog +5V Power Supply. Bypass with a 0.1µF capacitor to GND. 28 24 VLOGIC Bandgap Reference Output/Bandgap Reference Buffer Input. Bypass to GND with a 0.01µF capacitor. When using an external reference, connect REFADJ to VDD to disable the internal bandgap reference. Digital Power Supply. VLOGIC powers the digital outputs of the data converter and can range from +1.8V to VDD + 300mV. _______________________________________________________________________________________ 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface Converter Operation The MAX1291/MAX1293 ADCs use a successiveapproximation (SAR) conversion technique and an input track/hold (T/H) stage to convert an analog input signal to a 12-bit digital output. Their parallel 8+4 output format provides an easy interface to standard microprocessors (µPs). Figure 2 shows the simplified internal architecture of the MAX1291/MAX1293. Single-Ended and Pseudo-Differential Operation The sampling architecture of the ADC’s analog comparator is illustrated in the equivalent input circuit in Figure 3. In single-ended mode, IN+ is internally switched to channels CH0–CH7 for the MAX1291 (Figure 3a) and to CH0–CH3 for the MAX1293 (Figure 3b), while IN- is switched to COM (Table 3). In differential mode IN+ and IN- are selected from analog input pairs (Table 4) and are internally switched to either of the analog inputs. This configuration is pseudo-differential in that only the signal at IN+ is sampled. The return side (IN-) must remain stable within ±0.5LSB (±0.1LSB for best performance) with respect to GND during a conversion. To accomplish this, connect a 0.1µF capacitor from IN- (the selected input) to GND. During the acquisition interval, the channel selected as the positive input (IN+) charges capacitor CHOLD. At the end of the acquisition interval, the T/H switch opens, retaining charge on CHOLD as a sample of the signal at IN+. The conversion interval begins with the input multiplexer switching CHOLD from the positive input (IN+) to the negative input (IN-). This unbalances node ZERO at the comparator’s positive input. The capacitive digital-toanalog converter (DAC) adjusts during the remainder of the conversion cycle to restore node ZERO to 0V within the limits of 12-bit resolution. This action is equivalent to transferring a 12pF[(VIN+) - (VIN-)] charge from CHOLD to the binary-weighted capacitive DAC, which in turn forms a digital representation of the analog input signal. REF (CH7) (CH6) (CH5) (CH4) CH3 CH2 CH1 CH0 AV = 2.05 ANALOG INPUT MULTIPLEXER CS WR RD 17k 1.22V REFERENCE T/H CHARGE REDISTRIBUTION 12-BIT DAC COMP 12 COM CLK REFADJ SUCCESSIVEAPPROXIMATION REGISTER CLOCK CONTROL LOGIC & LATCHES 4 8 4 8 MUX INT 8 8 THREE-STATE, BIDIRECTIONAL I/O INTERFACE ( ) ARE FOR MAX1291 ONLY. MAX1291 MAX1293 HBEN VDD VLOGIC GND D0–D7 8-BIT DATA BUS Figure 2. Simplified Internal Architecture for 8-/4-Channel MAX1291/MAX1293 _______________________________________________________________________________________ 9 MAX1291/MAX1293 Detailed Description MAX1291/MAX1293 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface Track/Hold 12-BIT CAPACITIVE DAC REF COMPARATOR INPUT CHOLD MUX – + CH0 CH1 CH2 12pF CH3 CH4 CSWITCH ZERO RIN 800Ω HOLD TRACK CH5 CH6 CH7 AT THE SAMPLING INSTANT, THE MUX INPUT SWITCHES FROM THE SELECTED IN+ CHANNEL TO THE SELECTED IN- CHANNEL. T/H SWITCH COM SINGLE-ENDED MODE: IN+ = CH0–CH7, IN- = COM PSEUDO-DIFFERENTIAL MODE: IN+ AND IN- SELECTED FROM PAIRS OF CH0/CH1, CH2/CH3, CH4/CH5, AND CH6/CH7 Figure 3a. MAX1291 Simplified Input Structure 12-BIT CAPACITIVE DAC REF CH0 COMPARATOR INPUT CHOLD MUX – + ZERO 12pF RIN 800Ω CH1 CH2 CSWITCH TRACK CH3 COM T/H SWITCH HOLD AT THE SAMPLING INSTANT, THE MUX INPUT SWITCHES FROM THE SELECTED IN+ CHANNEL TO THE SELECTED IN- CHANNEL. SINGLE-ENDED MODE: IN+ = CH0–CH3, IN- = COM PSEUDO-DIFFERENTIAL MODE: IN+ AND IN- SELECTED FROM PAIRS OF CH0/CH1 AND CH2/CH3 Figure 3b. MAX1293 Simplified Input Structure Analog Input Protection Internal protection diodes, which clamp the analog input to VDD and GND, allow each input channel to swing within (GND - 300mV) to (VDD + 300mV) without damage. However, for accurate conversions near full scale, both inputs must not exceed (VDD + 50mV) or be less than (GND - 50mV). If an off-channel analog input voltage exceeds the supplies by more than 50mV, limit the forward-bias input current to 4mA. 10 The MAX1291/MAX1293 T/H stage enters its tracking mode on the rising edge of WR. In external acquisition mode, the part enters its hold mode on the next rising edge of WR. In internal acquisition mode, the part enters its hold mode on the fourth falling edge of clock after writing the control byte. Note that in internal clock mode this occurs approximately 1µs after writing the control byte. In single-ended operation, IN- is connected to COM and the converter samples the positive (“+”) input. In pseudo-differential operation, IN- connects to the negative input (“-”), and the difference of (IN+) - (IN-) is sampled. At the beginning of the next conversion, the positive input connects back to IN+ and C HOLD charges to the input signal. The time required for the T/H stage to acquire an input signal depends on 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 required for the signal to be acquired. Calculate this with the following equation: tACQ = 9 (RS + RIN) CIN where RS is the source impedance of the input signal, RIN (800Ω) is the input resistance, and CIN (12pF) is the ADC’s input capacitance. Source impedances below 3kΩ have no significant impact on the MAX1291/ MAX1293’s AC performance. Higher source impedances can be used if a 0.01µF capacitor is connected to the individual analog inputs. Together with the input impedance, this capacitor forms an RC filter, limiting the ADC’s signal bandwidth. Input Bandwidth The MAX1291/MAX1293 T/H stage offers a 250kHz fulllinear and a 3MHz full-power bandwidth, enabling these parts to use undersampling techniques to digitize high-speed transients and measure periodic signals with bandwidths exceeding the ADCs sampling rate. To avoid high-frequency signals being aliased into the frequency band of interest, anti-alias filtering is recommended. Starting a Conversion Initiate a conversion by writing a control byte that selects the multiplexer channel and configures the MAX1291/MAX1293 for either unipolar or bipolar operation. A write pulse (WR + CS) can either start an acquisition interval or initiate a combined acquisition plus ______________________________________________________________________________________ 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface Internal Acquisition Select internal acquisition by writing the control byte with the ACQMOD bit cleared (ACQMOD = 0). This causes the write pulse to initiate an acquisition interval whose duration is internally timed. Conversion starts when this acquisition interval ends (three external cycles or approximately 1µs in internal clock mode) (Figure 4). Note that when the internal acquisition is combined with the internal clock, the aperture jitter can be as high as 200ps. Internal clock users wishing to achieve the 50ps jitter specification should always use external acquisition mode. External Acquisition Use external acquisition mode for precise control of the sampling aperture and/or dependent control of acquisition and conversion times. The user controls acquisition and start-of-conversion with two separate write pulses. The first pulse, written with ACQMOD = 1, starts an acquisition interval of indeterminate length. The second write pulse, written with ACQMOD = 0, terminates acquisition and starts conversion on WR’s rising edge (Figure 5). The address bits for the input multiplexer must have the same values on the first and second write pulse. Power-down mode bits (PD0, PD1) can assume new values on the second write pulse (see the Power-Down Modes section). Changing other bits in the control byte will corrupt the conversion. Reading a Conversion A standard interrupt signal INT is provided to allow the MAX1291/MAX1293 to flag the microprocessor when the conversion has ended and a valid result is available. INT goes low when the conversion is complete and the output data is ready (Figures 4, 5). It returns high on the first read cycle or if a new control byte is written. Table 1. Control Byte Functional Description BIT NAME FUNCTION PD1 and PD0 select the various clock and power-down modes. D7, D6 PD1, PD0 0 0 Full Power-Down Mode. Clock mode is unaffected. 0 1 Standby Power-Down Mode. Clock mode is unaffected. 1 0 Normal Operation Mode. Internal clock mode selected. 1 1 Normal Operation Mode. External clock mode selected. D5 ACQMOD ACQMOD = 0: Internal Acquisition Mode ACQMOD = 1: External Acquisition Mode D4 SGL/DIF SGL/DIF = 0: Pseudo-Differential Analog Input Mode SGL/DIF = 1: Single-Ended Analog Input Mode In single-ended mode, input signals are referred to COM. In pseudo-differential mode, the voltage difference between two channels is measured (see Tables 2, 3). D3 UNI/BIP UNI/BIP = 0: Bipolar Mode UNI/BIP = 1: Unipolar Mode In unipolar mode, an analog input signal from 0 to VREF can be converted; in bipolar mode, the signal can range from -VREF/2 to +VREF/2. A2, A1, A0 Address bits A2–A0 select which of the 8/4 (MAX1291/MAX1293) channels are to be converted (see Tables 3, 4). D2, D1, D0 ______________________________________________________________________________________ 11 MAX1291/MAX1293 conversion. The sampling interval occurs at the end of the acquisition interval. The ACQMOD (acquisition mode) bit in the input control byte (Table 1) offers two options for acquiring the signal: an internal and an external acquisition. The conversion period lasts for 13 clock cycles in either the internal or external clock or acquisition mode. Writing a new control byte during a conversion cycle will abort the conversion and start a new acquisition interval. MAX1291/MAX1293 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface tCS CS tACQ tCSWS tCSWH tWR tCONV WR tDH tDS CONTROL BYTE D7–D0 ACQMOD ="0" tINT1 INT RD HBEN tD0 tTR tD01 HIGH-Z HIGH / LOW BYTE VALID DOUT HIGH / LOW BYTE VALID HIGH-Z Figure 4. Conversion Timing Using Internal Acquisition Mode tCS CS tCSWS tWR tACQ tCSHW tCONV WR tDH tDS CONTROL BYTE ACQMOD = "1" D7–D0 CONTROL BYTE ACQMOD = "0" tINT1 INT RD HBEN tD0 HIGH-Z DOUT tD01 HIGH / LOW BYTE VALID tTR HIGH / LOW BYTE VALID Figure 5. Conversion Timing Using External Acquisition Mode 12 ______________________________________________________________________________________ HIGH-Z 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface Internal Clock Mode Select internal clock mode to release the µP from the burden of running the SAR conversion clock. To select this mode, bits D6 and D7 of the control byte must be set to 1; the internal clock frequency is then selected, resulting in a conversion time of 3.6µs. When using the internal clock mode, tie the CLK pin either high or low to prevent the pin from floating. External Clock Mode To select the external clock mode, bits D6 and D7 of the control byte must be set to zero. Figure 6 shows the clock and WR timing relationship for internal (Figure 6a) and external (Figure 6b) acquisition modes with an external clock. For proper operation, a 100kHz to 4.8MHz clock frequency with 30% to 70% duty cycle is recommended. Operating the MAX1291/MAX1293 with clock frequencies lower than 100kHz is not recommended because it will cause a voltage droop across ACQUISITION STARTS tCP the hold capacitor in the T/H stage that will result in degraded performance. Digital Interface Input (control byte) and output data are multiplexed on a three-state parallel interface. This parallel interface (I/O) can easily be interfaced with standard µPs. The signals CS, WR, and RD control the write and read operations. CS represents the chip select signal, which enables a µP to address the MAX1291/MAX1293 as an I/O port. When high, CS disables the CLK WR and RD inputs and forces the interface into a high-impedance (high-Z) state. Input Format The control byte is latched into the device on pins D7–D0 during a write command. Table 2 shows the control byte format. Output Format The output format for both the MAX1291/MAX1293 is binary in unipolar mode and two’s complement in bipolar mode. When reading the output data, CS and RD must be low. When HBEN = 0, the lower 8 bits are read. With HBEN = 1, the upper 4 bits are available and the output data bits D7–D4 are set either low in unipolar mode or set to the value of the MSB in bipolar mode (Table 5). ACQUISITION ENDS CONVERSION STARTS CLK tCWS tCH WR tCL WR GOES HIGH WHEN CLK IS HIGH. ACQMOD = "0" tCWH ACQUISITION STARTS ACQUISITION ENDS CONVERSION STARTS CLK WR ACQMOD = "0" WR GOES HIGH WHEN CLK IS LOW. Figure 6a. External Clock and WR Timing (Internal Acquisition Mode) ______________________________________________________________________________________ 13 MAX1291/MAX1293 Selecting Clock Mode The MAX1291/MAX1293 operate with either an internal or an external clock. Control bits D6 and D7 select either internal or external clock mode. The parts retain the last requested clock mode if a power-down mode is selected in the current input word. For both internal and external clock mode, internal or external acquisition can be used. At power-up, the MAX1291/MAX1293 enter the default external clock mode. MAX1291/MAX1293 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface ACQUISITION STARTS ACQUISITION ENDS CONVERSION STARTS CLK tCWS tDH WR ACQMOD = "0" WR GOES HIGH WHEN CLK IS HIGH. ACQMOD = "1" ACQUISITION STARTS ACQUISITION ENDS CONVERSION STARTS CLK tCWH tDH WR ACQMOD = "1" WR GOES HIGH WHEN CLK IS LOW. ACQMOD = "0" Figure 6b. External Clock and WR Timing (External Acquisition Mode) Table 2. Control Byte Format D7 (MSB) D6 D5 D4 D3 D2 D1 D0 (LSB) PD1 PD0 ACQMOD SGL/DIF UNI/BIP A2 A1 A0 Table 3. Channel Selection for Single-Ended Operation (SGL/DIF = 1) A2 A1 A0 CH0 0 0 0 + 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1 CH1 CH2 CH3 CH4* CH5* CH6* COM - + + + + + + *Channels CH4–CH7 apply to MAX1291 only. 14 CH7* ______________________________________________________________________________________ + - 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface A2 A1 A0 CH0 CH1 CH2 CH3 0 0 0 + - 0 0 1 - + 0 1 0 1 CH4* CH5* CH6* CH7* 0 + - 1 1 - + 0 0 + - 1 0 1 - + 1 1 0 + - 1 1 1 - + *Channels CH4–CH7 apply to MAX1291 only. Internal and External Reference Internal Reference With the internal reference, the full-scale range is +2.5V with unipolar inputs and ±1.25V with bipolar inputs. The internal reference buffer allows for small adjustments (±100mV) in the reference voltage. See Figure 7. Note that the reference buffer must be compensated with an external capacitor (4.7µF min) connected between REF and GND to reduce reference noise and switching spikes from the ADC. To further minimize noise on the reference, connect a 0.01µF capacitor between REFADJ and GND. The MAX1291/MAX1293 can be used with an internal or external reference voltage. An external reference can be connected directly to REF or REFADJ. An internal buffer is designed to provide +2.5V at REF for the both the MAX1291 and the MAX1293. The internally trimmed +1.22V reference is buffered with a +2.05V/V gain. External Reference With both the MAX1291 and MAX1293, an external reference can be placed at either the input (REFADJ) or the output (REF) of the internal reference buffer amplifier. Using the REFADJ input makes buffering the external reference unnecessary. The REFADJ input impedance is typically 17kΩ. __________Applications Information Power-On Reset When power is first applied, internal power-on reset circuitry activates the MAX1291/MAX1293 in external clock mode and sets INT high. After the power supplies stabilize, the internal reset time is 10µs, and no conversions should be attempted during this phase. When using the internal reference, 500µs is required for VREF to stabilize. Table 5. Data-Bus Output (8+4 Parallel Interface) PIN HBEN = 0 D0 B0 (LSB) B8 D1 B1 B9 +3V HBEN = 1 50k MAX1291 MAX1293 330k D2 B2 B10 D3 B3 B11 (MSB) 50k UNIPOLAR (UNI/BIP = 1) BIPOLAR (UNI/BIP = 0) D4 B4 B11 0 D5 B5 B11 0 D6 B6 B11 0 D7 B7 B11 0 REFADJ GND 4.7µF REF 0.01µF GND Figure 7. Reference Voltage Adjustment with External Potentiometer ______________________________________________________________________________________ 15 MAX1291/MAX1293 Table 4. Channel Selection for Pseudo-Differential Operation (SGL/DIF = 0) MAX1291/MAX1293 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface When applying an external reference to REF, disable the internal reference buffer by connecting REFADJ to V DD . The DC input resistance at REF is 25kΩ. Therefore, an external reference at REF must deliver up to 200µA DC load current during a conversion and have an output impedance less than 10Ω. If the reference has higher output impedance or is noisy, bypass it close to the REF pin with a 4.7µF capacitor. Power-Down Modes Save power by placing the converter in a low-current shutdown state between conversions. Select standby mode or shutdown mode via bits D6 and D7 of the control byte (Tables 1 and 2). In both software power-down modes, the parallel interface remains active, but the ADC does not convert. ed. A rising edge on WR causes the MAX1291/MAX1293 to exit shutdown mode and return to normal operation. To achieve full 12-bit accuracy with a 4.7µF reference bypass capacitor, 500µs is required after power-up. Waiting this 500µs in standby mode instead of in fullpower mode can reduce power consumption by a factor of 3 or more. When using an external reference, only 50µs is required after power-up. Enter standby mode by performing a dummy conversion with the control byte specifying standby mode. Note: Bypassing capacitors larger than 4.7µF between REF and GND will result in longer power-up delays. Transfer Function Table 6 shows the full-scale voltage ranges for unipolar and bipolar modes. Standby Mode While in standby mode, the supply current is 850µA (typ). The part will power up on the next rising edge on WR and is ready to perform conversions. This quick turn-on time allows the user to realize significantly reduced power consumption for conversion rates below 250ksps. Figure 8 depicts the nominal, unipolar input/output (I/O) transfer function and Figure 9 shows the bipolar I/O transfer function. Code transitions occur halfway between successive-integer LSB values. Output coding is binary, with 1LSB = (VREF/4096). Shutdown Mode Shutdown mode turns off all chip functions that draw quiescent current, reducing the typical supply current to 2µA immediately after the current conversion is complet- When running at the maximum clock frequency of 4.8MHz, the specified throughput of 250ksps is achieved by completing a conversion every 19 clock cycles: 1 write cycle, 3 acquisition cycles, 13 conver- OUTPUT CODE OUTPUT CODE FULL-SCALE TRANSITION 111 . . . 111 FS = REF + COM 111 . . . 110 ZS = COM 011 . . . 111 FS = REF + COM 2 011 . . . 110 ZS = COM 000 . . . 010 100 . . . 010 100 . . . 001 1LSB = 100 . . . 000 000 . . . 001 REF 4096 000 . . . 000 011 . . . 111 111 . . . 111 011 . . . 110 111 . . . 110 011 . . . 101 111 . . . 101 000 . . . 001 100 . . . 001 000 . . . 000 100 . . . 000 0 1 (COM) 2 2048 INPUT VOLTAGE (LSB) Figure 8. Unipolar Transfer Function 16 Maximum Sampling Rate/ Achieving 300ksps COM* - FS FS FS - 3/2LBS -REF + COM 2 REF 1LSB = 4096 -FS = INPUT VOLTAGE (LSB) *COM ≥ VREF/2 Figure 9. Bipolar Transfer Function ______________________________________________________________________________________ +FS - 1LSB 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface UNIPOLAR MODE BIPOLAR MODE Full Scale VREF + COM Positive Full Scale Zero Scale COM Zero Scale COM — — Negative Full Scale -VREF/2 + COM sion cycles, and 2 read cycles. This assumes that the results of the last conversion are read before the next control byte is written. Throughputs up to 300ksps can be achieved by first writing a control word to begin the acquisition cycle of the next conversion, and then reading the results of the previous conversion from the bus (Figure 10). This technique allows a conversion to be completed every 16 clock cycles. Note that the switching of the data bus during acquisition or conversion can cause additional supply noise, which may make it difficult to achieve true 12-bit performance. Layout, Grounding, and Bypassing For best performance use printed circuit (PC) boards. 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 don’t lay out digital signal paths underneath the ADC package. Use separate analog and digital PC Board ground sections with only one starpoint (Figure 11) 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 MAX1291/MAX1293s’ power supply pin. Minimize capacitor lead length for best supply-noise rejection; add an attenuation resistor (5Ω) if the power supply is extremely noisy. VREF/2 + COM 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 static linearity parameters for the MAX1291/MAX1293 are measured using the endpoint method. Differential Nonlinearity Differential nonlinearity (DNL) is the difference between an actual step width and the ideal value of 1LSB. A DNL error specification of less than 1LSB guarantees no missing codes and a monotonic transfer function. Aperture Definitions Aperture jitter (tAJ) is the sample-to-sample variation in the time between the samples. Aperture delay (tAD) is the time between the rising edge of the sampling clock and the instant when an actual sample is taken. Signal-to-Noise Ratio For a waveform perfectly reconstructed from digital samples, signal-to-noise ratio (SNR) is the ratio of fullscale 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): SNR = (6.02 · N + 1.76)dB In reality, there are other noise sources besides quantization noise: thermal noise, reference noise, clock jitter, etc. Therefore, 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. Signal-to-Noise Plus Distortion Signal-to-noise plus distortion (SINAD) is the ratio of the fundamental input frequency’s RMS amplitude to RMS equivalent of all other ADC output signals. SINAD (dB) = 20 · log (SignalRMS / NoiseRMS) ______________________________________________________________________________________ 17 MAX1291/MAX1293 Table 6. Full-Scale and Zero-Scale for Unipolar and Bipolar Operation MAX1291/MAX1293 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 CLK WR RD HBEN D7–D0 CONTROL BYTE D7–D0 D11–D8 LOW BYTE STATE CONTROL BYTE HIGH BYTE D11–D8 LOW BYTE HIGH BYTE ACQUISITION CONVERSION ACQUISITION D7–D0 SAMPLING INSTANT Figure 10. Timing Diagram for Fastest Conversion Effective Number of Bits 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 fullscale range of the ADC, calculate the effective number of bits as follows: ENOB = (SINAD - 1.76) / 6.02 Total Harmonic Distortion SUPPLIES +3V R* = 5Ω Total harmonic distortion (THD) is the ratio of the RMS sum of the first five harmonics of the input signal to the fundamental itself. This is expressed as: THD = 20 ⋅log V22 + V32 + V4 2 + V52 / 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 RMS amplitude of the fundamental (maximum signal component) to the RMS value of the next largest distortion component. 18 VLOGIC = +2V/+3V GND 4.7µF 0.1µF VDD GND COM +2V/+3V DGND DIGITAL CIRCUITRY MAX1291 MAX1293 *OPTIONAL Figure 11. Power-Supply and Grounding Connections Chip Information TRANSISTOR COUNT: 5781 SUBSTRATE CONNECTED TO GND ______________________________________________________________________________________ 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface CLK +1.8V TO +3.6V VLOGIC CS REF WR REFADJ RD VLOGIC +3V MAX1291 VDD µP CONTROL INPUTS CLK 4.7µF +3V MAX1293 VDD +2.5V 0.1µF +1.8V TO +3.6V µP CONTROL INPUTS CS REF WR REFADJ RD HBEN +2.5V 4.7µF 0.1µF HBEN INT OUTPUT STATUS INT OUTPUT STATUS CH7 D7 CH6 D7 D6 CH5 D6 D5 CH4 D4 CH3 D3/D11 CH2 D2/D10 CH1 D1/D9 CH0 D0/D8 COM D5 ANALOG INPUTS GND D4 CH3 D3/D11 CH2 D2/D10 CH1 D1/D9 CH0 D0/D8 COM ANALOG INPUTS GND µP DATA BUS µP DATA BUS Pin Configurations (continued) Ordering Information (continued) PART TOP VIEW HBEN 1 D7 2 INL (LSB) MAX1293ACEG 0°C to +70°C 24 QSOP 23 VDD MAX1293BCEG 0°C to +70°C 24 QSOP ±1 MAX1293AEEG -40°C to +85°C 24 QSOP ±0.5 MAX1293BEEG -40°C to +85°C 24 QSOP ±1 22 REF D5 4 21 REFADJ D4 5 20 GND MAX1293 PIN-PACKAGE 24 VLOGIC D6 3 D3/D11 6 TEMP. RANGE ±0.5 19 COM D2/D10 7 18 CH0 D1/D9 8 17 CH1 D0/D8 9 16 CH2 INT 10 15 CH3 RD 11 14 CS WR 12 13 CLK QSOP ______________________________________________________________________________________ 19 MAX1291/MAX1293 Typical Operating Circuits MAX1291/MAX1293 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface QSOP.EPS Package Information Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.