MAX1178CEUP

19-2755; Rev 1; 8/03 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range General Description The MAX1178/MAX1188 16-bit, low-power, successiveapproximation analog-to-digital converters (ADCs) feature automatic power-down, a factory-trimmed internal clock, and a byte-wide parallel interface. The devices operate from a single +4.75V to +5.25V analog supply and feature a separate digital supply input for direct interface with a +2.7V to +5.25V digital logic. The MAX1188 accepts a bipolar analog input voltage range of ±10V, while the MAX1178 accepts a bipolar analog input voltage range of ±5V. All devices consume no more than 26.5mW at a sampling rate of 135ksps when using an external reference, and 31mW when using the internal +4.096V reference. AutoShutdown™ reduces supply current to 0.4mA at 10ksps. The MAX1178/MAX1188 are ideal for high-performance, battery-powered, data-acquisition applications. Excellent AC performance (THD = -100dB) and DC accuracy (±2 LSB INL) make the MAX1178/MAX1188 ideal for industrial process control, instrumentation, and medical applications. The MAX1178/MAX1188 are available in a 20-pin TSSOP package and are fully specified over the -40°C to +85°C extended temperature range and the 0°C to +70°C commercial temperature range. o Byte-Wide Parallel Interface o Analog Input Voltage Range: ±10V, ±5V o Single +4.75V to +5.25V Analog Supply Voltage o Interface with +2.7V to +5.25V Digital Logic o ±2 LSB INL o ±1 LSB DNL o Low Supply Current (max) 2.9mA (External Reference) 3.8mA (Internal Reference) 5µA AutoShutdown Mode o Small Footprint o 20-Pin TSSOP Package Features MAX1178/MAX1188 Ordering Information PART MAX1178ACUP MAX1178BCUP MAX1178CCUP MAX1178AEUP MAX1178BEUP MAX1178CEUP TEMP RANGE 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 INPUT PINVOLTAGE PACKAGE RANGE (V) 20 TSSOP 20 TSSOP 20 TSSOP 20 TSSOP 20 TSSOP 20 TSSOP ±5 ±5 ±5 ±5 ±5 ±5 Ordering Information continued at end of data sheet. Applications Temperature Sensing and Monitoring Industrial Process Control I/O Modules Data-Acquisition Systems Precision Instrumentation ANALOG INPUT Typical Operating Circuit +5V ANALOG +5V DIGITAL 0.1µF AVDD AIN DVDD 0.1µF µP DATA D0–D7 BUS OR D8–D15 EOC REF REFADJ AGND DGND 0.1µF 10µF MAX1178 MAX1188 R/C CS HBEN Pin Configuration and Functional Diagram appear at end of data sheet. AutoShutdown is a trademark of Maxim Integrated Products, Inc. HIGH BYTE LOW BYTE ________________________________________________________________ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range MAX1178/MAX1188 ABSOLUTE MAXIMUM RATINGS AVDD to AGND .........................................................-0.3V to +6V DVDD to DGND.........................................................-0.3V to +6V AGND to DGND.....................................................-0.3V to +0.3V AIN to AGND .....................................................-16.5V to +16.5V REF, REFADJ to AGND............................-0.3V to (AVDD + 0.3V) CS, R/C, HBEN to DGND .........................................-0.3V to +6V D_, EOC to DGND ...................................-0.3V to (DVDD + 0.3V) Maximum Continuous Current into Any Pin ........................50mA Continuous Power Dissipation (TA = +70°C) TSSOP (derate 10.9mW/°C above +70°C) ..................879mW Operating Temperature Ranges MAX11_ _ _CUP..................................................0°C to +70°C MAX11_ _ _EUP ...............................................-40°C to +85°C Storage Temperature Range .............................-65°C to +150°C Junction Temperature ......................................................+150°C Lead Temperature (soldering, 10s) .................................+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 (AVDD = DVDD = +5V ±5%, external reference = +4.096V, CREF = 10µF, CREFADJ = 0.1µF, VREFADJ = AVDD, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER DC ACCURACY Resolution Differential Nonlinearity RES MAX11_ _A DNL No missing codes over temperature MAX11_ _A Integral Nonlinearity INL MAX11_ _B MAX11_ _C Transition Noise Offset Error Gain Error Offset Drift Gain Drift AC ACCURACY (fIN = 1kHz, VAIN = full range, 135ksps) Signal-to-Noise Plus Distortion Signal-to-Noise Ratio Total Harmonic Distortion Spurious-Free Dynamic Range ANALOG INPUT Input Range VAIN MAX1178 MAX1188 MAX1178 Input Resistance RAIN MAX1188 Normal operation Shutdown mode Normal operation Shutdown mode -5 -10 5.3 3.0 7.8 6.0 10 13.0 6.9 +5 +10 9.2 kΩ V SINAD SNR THD SFDR 92 86 87 90 91 -100 103 -92 dB dB dB dB RMS noise, external reference Internal reference -10 MAX11_ _B MAX11_ _C 16 -1 -1.0 -1 -2 -2 -4 0.6 0.75 0 0 16 ±1 +10 ±0.2 +1 +1.5 +2 +2 +2 +4 LSBRMS mV %FSR µV/°C ppm/°C LSB LSB Bits SYMBOL CONDITIONS MIN TYP MAX UNITS 2 _______________________________________________________________________________________ 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range ELECTRICAL CHARACTERISTICS (continued) (AVDD = DVDD = +5V ±5%, external reference = +4.096V, CREF = 10µF, CREFADJ = 0.1µF, VREFADJ = AVDD, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MAX1178, -5V ≤ VAIN ≤ +5V MAX1188, -10V ≤ VAIN ≤ +10V Normal operation Shutdown mode Normal operation Shutdown mode MIN -1.8 -1.8 -1.8 -1.8 1 0.5 10 4.056 4.096 ±35 IREF-SC ±10 4.136 TYP MAX +0.4 +1.8 +1.2 +1.8 1.4 mA MAX1188, VAIN = +10V, shutdown mode to operating mode 0.7 pF V ppm/°C mA mA UNITS MAX1178/MAX1188 Input Current IAIN MAX1178, VAIN = +5V, shutdown mode to operating mode Input Current Step at Power-Up IPU Input Capacitance INTERNAL REFERENCE REF Output Voltage REF Output Tempco REF Short-Circuit Current EXTERNAL REFERENCE REF and REFADJ Input-Voltage Range REFADJ Buffer-Disable Threshold REF Input Current REFADJ Input Current DIGITAL INPUTS/OUTPUTS Output High Voltage Output Low Voltage Input High Voltage Input Low Voltage Input Leakage Current Input Hysteresis Input Capacitance Tri-State Output Leakage Tri-State Output Capacitance CIN VREF 3.8 AVDD 0.4 IREF IREFADJ Normal mode, fSAMPLE = 135ksps Shutdown mode (Note 1) REFADJ = AVDD ISOURCE = 0.5mA, DVDD = +2.7V to +5.25V, AVDD = +5.25V ISINK = 1.6mA, DVDD = +2.7V to +5.25V, AVDD = +5.25V 0.7 × DVDD DVDD 0.4 60 ±0.1 16 4.2 AVDD 0.1 100 ±10 V V µA µA VOH VOL VIH VIL V 0.4 V V 0.3 × DVDD V µA V pF ±10 15 µA pF Digital input = DVDD or 0V VHYST CIN IOZ COZ -1 0.2 15 +1 _______________________________________________________________________________________ 3 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range MAX1178/MAX1188 ELECTRICAL CHARACTERISTICS (continued) (AVDD = DVDD = +5V ±5%, external reference = +4.096V, CREF = 10µF, CREFADJ = 0.1µF, VREFADJ = AVDD, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER POWER SUPPLIES Analog Supply Voltage Digital Supply Voltage Analog Supply Current AVDD DVDD IAVDD External reference, 135ksps Internal reference, 135ksps Shutdown mode (Note 1), digital input = DVDD or 0V Standby mode Digital Supply Current Power-Supply Rejection IDVDD AVDD = DVDD = 4.75V to 5.25V 3.5 4.75 2.70 4 5.2 0.5 3.7 0.75 5.25 5.25 5.3 6.2 5 V V mA µA mA mA LSB SYMBOL CONDITIONS MIN TYP MAX UNITS Shutdown Supply Current ISHDN TIMING CHARACTERISTICS (Figures 1 and 2) (AVDD = +4.75V to +5.25V, DVDD = +2.7V to AVDD, external reference = +4.096V, CREF = 10µF, CREFADJ = 0.1µF, VREFADJ = AVDD, CLOAD = 20pF, TA = TMIN to TMAX.) PARAMETER Maximum Sampling Rate Acquisition Time Conversion Time CS Pulse-Width High CS Pulse-Width Low (Note 2) R/C to CS Fall Setup Time R/C to CS Fall Hold Time CS to Output Data Valid EOC Fall to CS Fall CS Rise to EOC Rise Bus Relinquish Time HBEN Transition to Output Data Valid SYMBOL fSAMPLE-MAX tACQ tCONV tCSH tCSL tDS tDH tDO tDV tEOC tBR tDO1 DVDD = 4.75V to 5.25V DVDD = 2.7V to 5.25V DVDD = 4.75V to 5.25V DVDD = 2.7V to 5.25V DVDD = 4.75V to 5.25V DVDD = 2.7V to 5.25V DVDD = 4.75V to 5.25V DVDD = 2.7V to 5.25V DVDD = 4.75V to 5.25V DVDD = 2.7V to 5.25V 0 40 80 40 80 40 80 (Note 2) DVDD = 4.75V to 5.25V DVDD = 2.7V to 5.25V 40 40 60 0 40 60 40 80 2 4.7 CONDITIONS MIN TYP MAX 135 UNITS ksps µs µs ns ns ns ns ns ns ns ns ns Note 1: Maximum specification is limited by automated test equipment. Note 2: To ensure best performance, finish reading the data and wait tBR before starting a new acquisition. 4 _______________________________________________________________________________________ 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range Typical Operating Characteristics (Typical Operating Circuit, AVDD = DVDD = +5V, external reference = +4.096V, CREF = 10µF, CREFADJ = 0.1µF, VREFADJ = AVDD, CLOAD = 20pF. Typical values are at TA = +25°C, unless otherwise noted.) INL vs. CODE 2.5 2.0 1.5 1.0 DNL (LSB) INL (LSB) 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 0 10,000 20,000 30,000 40,000 50,000 60,000 CODE MAX1178/88 toc01 MAX1178/MAX1188 DNL vs. CODE 2.5 2.0 1.5 SUPPLY CURRENT (mA) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 0 10,000 20,000 30,000 40,000 50,000 60,000 CODE 4.70 4.65 4.60 4.55 MAX1178/88 toc02 SUPPLY CURRENT (AVDD + DVDD) vs. TEMPERATURE 4.75 5.0V 5.25V MAX1178/88 toc03 4.80 4.75V 4.50 4.45 4.40 -40 -20 0 20 40 60 80 TEMPERATURE (°C) fSAMPLE = 135ksps SHUTDOWN MODE BETWEEN CONVERSIONS SUPPLY CURRENT (AVDD + DVDD) vs. SAMPLE RATE MAX1178/88 toc04 SHUTDOWN CURRENT (AVDD + DVDD) vs. TEMPERATURE NO CONVERSIONS MAX1178/88 toc05 OFFSET ERROR vs. TEMPERATURE 8 6 OFFSET ERROR (mV) 4 2 0 -2 -4 -6 -8 -10 MAX1178 MAX1188 MAX1178/88 toc06 10 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 -40 -20 0 20 10 1 SUPPLY CURRENT (mA) STANDBY MODE 0.1 SHUTDOWN MODE 0.01 0.001 VAIN = 0V 0.0001 0.01 0.1 1 10 100 1000 SAMPLE RATE (ksps) 40 60 80 -40 -20 0 20 40 60 80 TEMPERATURE (°C) TEMPERATURE (°C) GAIN ERROR vs. TEMPERATURE MAX1178/88 toc07 INTERNAL REFERENCE vs. TEMPERATURE MAX1178/88 toc08 FFT AT 1kHz -20 -40 MAGNITUDE (dB) -60 -80 -100 -120 -140 -160 -180 fSAMPLE = 131ksps MAX1178/88 toc09 0.20 0.15 GAIN ERROR (%FSR) 0.10 0.05 0 -0.05 -0.10 -0.15 -0.20 -40 -20 0 20 40 60 80 TEMPERATURE (°C) 4.136 4.126 INTERNAL REFERENCE (V) 4.116 4.106 4.096 4.086 4.076 4.066 4.056 -40 -20 0 20 40 60 80 TEMPERATURE (°C) 0 0 10 20 30 40 50 60 FREQUENCY (kHz) _______________________________________________________________________________________ 5 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range MAX1178/MAX1188 Typical Operating Characteristics (continued) (Typical Operating Circuit, AVDD = DVDD = +5V, external reference = +4.096V, CREF = 10µF, CREFADJ = 0.1µF, VREFADJ = AVDD, CLOAD = 20pF. Typical values are at TA = +25°C, unless otherwise noted.) SINAD vs. FREQUENCY MAX1178/88 toc10 SFDR vs. FREQUENCY MAX1178/88 toc11 THD vs. FREQUENCY -10 -20 -30 -40 -50 -60 -70 -80 -90 MAX1178/88 toc12 100 90 80 70 SINAD (dB) 60 50 40 30 20 10 0 1 10 FREQUENCY (kHz) fSAMPLE = 131ksps 120 100 80 SFDR (dB) 60 40 20 fSAMPLE = 131ksps 0 1 10 FREQUENCY (kHz) 0 THD (dB) -100 -110 100 1 10 fSAMPLE = 131ksps 100 100 FREQUENCY (kHz) Pin Description PIN 1 2 3 4 NAME D4/D12 D5/D13 D6/D14 D7/D15 Tri-State Digital-Data Output Tri-State Digital-Data Output Tri-State Digital-Data Output Tri-State Digital-Data Output. D15 is the MSB. Read/Convert Input. Power up and put the MAX1178/MAX1188 in acquisition mode by holding R/C low during the first falling edge of CS. During the second falling edge of CS, the level on R/C determines whether the reference and reference buffer power down or remain on after conversion. Set R/C high during the second falling edge of CS to power down the reference and buffer, or set R/C low to leave the reference and buffer powered up. Set R/C high during the third falling edge of CS to put valid data on the bus. End of Conversion. EOC drives low when conversion is complete. Analog Supply Input. Bypass with a 0.1µF capacitor to AGND. Analog Ground. Primary analog ground (star ground). Analog Input Analog Ground. Connect pin 10 to pin 8. Reference Buffer Output. Bypass REFADJ with a 0.1µF capacitor to AGND for internal reference mode. Connect REFADJ to AVDD to select external reference mode. Reference Input/Output. Bypass REF with a 10µF capacitor to AGND for internal reference mode. External reference input when in external reference mode. FUNCTION 5 R/C 6 7 8 9 10 11 12 EOC AVDD AGND AIN AGND REFADJ REF 6 _______________________________________________________________________________________ 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range Pin Description (continued) PIN 13 NAME HBEN FUNCTION High-Byte Enable Input. Used to multiplex the 16-bit conversion result. 1: MSB available on the data bus. 0: LSB available on the data bus. Convert Start. The first falling edge of CS powers up the device and enables acquire mode when R/C is low. The second falling edge of CS starts conversion. The third falling edge of CS loads the result onto the bus when R/C is high. Digital Ground Digital Supply Voltage. Bypass with a 0.1µF capacitor to DGND. Tri-State Digital-Data Output. D0 is the LSB. Tri-State Digital-Data Output Tri-State Digital-Data Output Tri-State Digital-Data Output MAX1178/MAX1188 14 15 16 17 18 19 20 CS DGND DVDD D0/D8 D1/D9 D2/D10 D3/D11 DVDD 1mA DO–D15 DO–D15 CLOAD = 20pF DGND a) HIGH-Z TO VOH, VOL TO VOH, AND VOH TO HIGH-Z b) HIGH-Z TO VOL, VOH TO VOL, AND VOL TO HIGH-Z CLOAD = 20pF DGND Analog Input Input Scaler The MAX1178/MAX1188 have an input scaler, which allows conversion of true bipolar input voltages and input voltages greater than the power supply, while operating from a single +5V analog supply. The input scaler attenuates and shifts the analog input to match the input range of the internal digital-to-analog converter (DAC). The MAX1178 input voltage range is ±5V, while the MAX1188 input voltage range is ±10V. Figure 4 shows the equivalent input circuit of the MAX1178/ MAX1188. This circuit limits the current going into or out of AIN to less than 1.8mA. Track and Hold (T/H) In track mode, the internal hold capacitor acquires the analog signal (Figure 4). In hold mode, the T/H switches open and the capacitive DAC samples the analog input. During the acquisition, the analog input (AIN) charges capacitor CHOLD. The acquisition ends on the second falling edge of C S . At this instant, the T/H switches open. The retained charge on CHOLD represents a sample of the input. In hold mode, the capacitive DAC adjusts during the remainder of the conversion time to restore node T/H OUT to zero within the limits of 16-bit resolution. Force CS low to put valid data on the bus after conversion is complete. 1mA Figure 1. Load Circuits Detailed Description Converter Operation The MAX1178/MAX1188 use a successive-approximation (SAR) conversion technique with an inherent trackand-hold (T/H) stage to convert an analog input into a 16-bit digital output. Parallel outputs provide a highspeed interface to microprocessors (µPs). The Functional Diagram shows a simplified internal architecture of the MAX1178/MAX1188. Figure 3 shows a typical operating circuit for the MAX1178/MAX1188. _______________________________________________________________________________________ 7 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range MAX1178/MAX1188 tCSL CS tACQ R/C tDH EOC tCONV tDO REF POWERDOWN CONTROL tDS tDV tEOC tCSH HBEN HIGH-Z D7/D15–D0/D8 tDO tDO1 HIGH/LOW BYTE VALID tBR HIGH-Z HIGH/LOW BYTE VALID Figure 2. MAX1178/MAX1188 Timing Diagram Power-Down Modes Select standby mode or shutdown mode with the R/C bit during the second falling edge of C S (see the Selecting Standby or Shutdown Mode section). The MAX1178/MAX1188 automatically enter either standby mode (reference and buffer on) or shutdown (reference and buffer off) after each conversion, depending on the status of R/C during the second falling edge of CS. +5V ANALOG +5V DIGITAL 0.1µF 0.1µF Internal Clock The MAX1178/MAX1188 generate an internal conversion clock to free the µP from the burden of running the SAR conversion clock. Total conversion time (tCONV) after entering hold mode (second falling edge of CS) to end-of-conversion (EOC) falling is 4.7µs (max). ANALOG INPUT AIN AVDD DVDD µP DATA D0–D7 BUS OR D8–D15 MAX1178 MAX1188 R/C CS HBEN HIGH BYTE LOW BYTE EOC REF REFADJ 0.1µF 10µF Applications Information Starting a Conversion CS and R/C control acquisition and conversion in the MAX1178/MAX1188 (Figure 2). The first falling edge of CS powers up the device and puts it in acquire mode if R/C is low. The convert start is ignored if R/C is high. The MAX1178/MAX1188 need at least 12ms for the internal reference to wake up and settle before starting the conversion (C REFADJ = 0.1µF, C REF = 10µF), if powering up from shutdown. 8 AGND DGND Figure 3. Typical Operating Circuit for the MAX1178/MAX1188 _______________________________________________________________________________________ 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range Selecting Standby or Shutdown Mode The MAX1178/MAX1188 have a selectable standby or low-power shutdown mode. In standby mode, the ADC’s internal reference and reference buffer do not power down between conversions, eliminating the need to wait for the reference to power up before performing the next conversion. Shutdown mode powers down the reference and reference buffer after completing a conversion. The reference and reference buffer require a minimum of 12ms to power up and settle from shutdown (CREFADJ = 0.1µF, CREF = 10µF). The state of R/ C at the second falling edge of C S selects which power-down mode the MAX1178/ MAX1188 enter upon conversion completion. Holding R/C low causes the MAX1178/MAX1188 to enter standby mode. The reference and buffer are left on after the conversion completes. R/ C high causes the MAX1178/MAX1188 to enter shutdown mode and power-down the reference and buffer after conversion (Figures 5 and 6). Set the voltage at R/C high during the second falling edge of CS to realize the lowest current operation. Standby Mode While in standby mode, the supply current is less than 3.7mA (typ). The next falling edge of CS with R/C low causes the MAX1178/MAX1188 to exit standby mode and begin acquisition. The reference and reference buffer remain active to allow quick turn-on time. Shutdown Mode In shutdown mode, the reference and reference buffer are shut down between conversions. Shutdown mode reduces supply current to 0.5µA (typ) immediately after the conversion. The next falling edge of CS with R/C low causes the reference and buffer to wake up and enter acquisition mode. To achieve 16-bit accuracy, allow 12ms for the internal reference to wake up (CREFADJ = 0.1µF, CREF = 10µF). REF MAX1178/MAX1188 R2 AIN R3 S3 POWERDOWN 161Ω R1 3.4kΩ TRACK S1 HOLD TRACK HOLD S2 MAX1178/MAX1188 CHOLD 30pF T/H OUT R2 = 7.85kΩ (MAX1188) OR 3.92kΩ (MAX1178) R3 = 5.45kΩ (MAX1188) OR 17.79kΩ (MAX1178) S1, S2 = T/H SWITCH S3 = POWER-DOWN Figure 4. Equivalent Input Circuit ACQUISITION CONVERSION DATA OUT CS R/C EOC REF AND BUFFER POWER Figure 5. Selecting Standby Mode ACQUISITION CONVERSION DATA OUT Internal and External Reference Internal Reference The internal reference of the MAX1178/MAX1188 is internally buffered to provide +4.096V output at REF. Bypass REF to AGND and REFADJ to AGND with 10µF and 0.1µF, respectively. Sink or source current at REFADJ to make fine adjustments to the internal reference. The input impedance of REFADJ is nominally 5kΩ. Use the circuit in Figure 7 to adjust the internal reference to ±1.5%. CS R/C EOC REF AND BUFFER POWER Figure 6. Selecting Shutdown Mode _______________________________________________________________________________________ 9 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range MAX1178/MAX1188 OUTPUT CODE MAX1178 INPUT RANGE = -5V TO +5V FULL-SCALE TRANSITION +5V 68kΩ 100kΩ 0.1µF MAX1178 MAX1188 11 1111 1111 1111 11 1111 1111 1110 11 1111 1111 1101 REFADJ 10 0000 0000 0001 10 0000 0000 0000 01 1111 1111 1111 00 0000 0000 0011 00 0000 0000 0010 FULL-SCALE RANGE (FSR) = +1V 1 LSB = FSR x VREF 65,536 x 4.096 150kΩ Figure 7. MAX1178/MAX1188 Reference-Adjust Circuit 00 0000 0000 0001 External Reference An external reference can be placed at either the input (REFADJ) or the output (REF) of the MAX1178/ MAX1188s’ internal buffer amplifier. Using the buffered REFADJ input makes buffering the external reference unnecessary. The input impedance of REFADJ is typically 5kΩ. The internal buffer output must be bypassed at REF with a 10µF capacitor. Connect REFADJ to AVDD to disable the internal buffer. Directly drive REF using an external 3.8V to 4.2V reference. During conversion, the external reference must be able to drive 100µA of DC load current and have an output impedance of 10Ω or less. For optimal performance, buffer the reference through an op amp and bypass REF with a 10µF capacitor. Consider the MAX1178/MAX1188s ’ e quivalent input noise (0.6 LSB) when choosing a reference. 00 0000 0000 0000 -32,768 -32,766 0 +32,766 +32,768 +1 -32,767 -32,765 -1 +32,767 INPUT VOLTAGE (LSB) Figure 8. MAX1178 Transfer Function OUTPUT CODE 1111 1111 1111 1111 1111 1111 1111 1110 1111 1111 1111 1101 1000 0000 0000 0001 1000 0000 0000 0000 0001 1111 1111 1111 0000 0000 0000 0011 0000 0000 0000 0010 0000 0000 0000 0001 MAX1188 INPUT RANGE = -10V TO +10V FULL-SCALE TRANSITION FULL-SCALE RANGE (FSR) = +20V 1 LSB = FSR x VREF 65,536 x 4.096 Reading the Conversion Result EOC is provided to flag the µP when a conversion is complete. The falling edge of EOC signals that the data is valid and ready to be output to the bus. D0–D15 are the parallel outputs of the MAX1178/MAX1188. These tri-state outputs allow for direct connection to a microcontroller I/O bus. The outputs remain high impedance during acquisition and conversion. Data is loaded onto the output bus with the third falling edge of CS with R/C high (after tDO). Bringing CS high forces the output bus back to high impedance. The MAX1178/MAX1188 then wait for the next falling edge of CS to start the next conversion cycle (Figure 2). HBEN toggles the output between the high/low byte. The low byte is loaded onto the output bus when HBEN is low, and the high byte is on the bus when HBEN is high. 0000 0000 0000 0000 0 +32,766 +32,768 -32,68 -32,766 +1 -32,767 -32,765 -1 +32,767 INPUT VOLTAGE (LSB) Figure 9. MAX1188 Transfer Function Transfer Function Figures 8 and 9 show the MAX1178/MAX1188 output transfer functions. The MAX1178 and MAX1188 outputs are coded in offset binary. Input Buffer Most applications require an input buffer amplifier to achieve 16-bit accuracy and prevent loading the source. When the input signal is multiplexed, switch the channels immediately after acquisition, rather than near the end of, or after, a conversion. This allows more time for the input buffer amplifier to respond to a large step 10 ______________________________________________________________________________________ 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range MAX1178/MAX1188 MAX1178 ANALOG INPUT CURRENT vs. ANALOG INPUT VOLTAGE 1.5 ANALOG INPUT CURRENT (mA) 1.0 0.5 0 -0.5 -1.0 -1.5 -5.0 -2.5 0 2.5 5.0 ANALOG INPUT VOLTAGE (V) STANDBY MODE SHUTDOWN MODE MAX1178 MAX1188 REF AIN ANALOG INPUT MAX427 Figure 10. MAX1178/MAX1188 Fast-Settling Input Buffer Figure 11. MAX1178 Analog Input Current change in input signal. The input amplifier must have a high enough slew rate to complete the required output voltage change before the beginning of the acquisition time. Figure 10 shows an example of this circuit using the MAX427. Figures 11 and 12 show how the MAX1178/MAX1188 analog input current varies depending on whether the chip is operating or powered down. The part is fully powered down between conversions if the voltage at R/C is set high during the second falling edge of CS. The input current abruptly steps to the powered-up value at the start of acquisition. This step in the input current can disrupt the ADC input, depending on the driving circuit’s output impedance at high frequencies. If the driving circuit cannot fully settle by the end of acquisition, the accuracy of the system can be compromised. To avoid this situation, increase the acquisition time, use a driving circuit that can settle within tACQ, or leave the MAX1178/MAX1188 powered up by setting the voltage at R/C low during the second falling edge of CS. ANALOG INPUT CURRENT (mA) MAX1188 ANALOG INPUT CURRENT vs. ANALOG INPUT VOLTAGE 1.5 1.0 0.5 0 -0.5 -1.0 -1.5 -10 -5 0 5 10 ANALOG INPUT VOLTAGE (V) STANDBY MODE SHUTDOWN MODE Figure 12. MAX1188 Analog Input Current Layout, Grounding, and Bypassing For best performance, use printed circuit boards. Do not run analog and digital lines parallel to each other, and do not lay out digital signal paths underneath the ADC package. Use separate analog and digital ground planes with only one point connecting the two ground systems (analog and digital) as close to the device as possible. Route digital signals far away from sensitive analog and reference inputs. If digital lines must cross analog lines, do so at right angles to minimize coupling digital noise onto the analog lines. If the analog and digital sections share the same supply, isolate the digital and analog supply by connecting them with a low-value (10 Ω ) resistor or ferrite bead. The ADC is sensitive to high-frequency noise on the AV DD supply. Bypass AV DD to AGND with a 0.1µF capacitor in parallel with a 1µF to 10µF low-ESR capacitor with the smallest capacitor closest to the device. Keep capacitor leads short to minimize stray inductance. ______________________________________________________________________________________ 11 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range MAX1178/MAX1188 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 end points of the transfer function, once offset and gain errors have been nullified. The static linearity parameters for the MAX1178/MAX1188 are measured using the end-point method. Signal-to-Noise Plus Distortion Signal-to-noise plus distortion (SINAD) is the ratio of the fundamental input frequency’s RMS amplitude to the RMS equivalent of all the other ADC output signals:   SignalRMS SINAD(dB) = 20 × log   (Noise + Distortion)RMS   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 error consists of quantization noise only. With an input range equal to the fullscale range of the ADC, calculate the ENOB as follows: ENOB = SINAD − 1.76 6.02 Differential Nonlinearity Differential nonlinearity (DNL) is the difference between an actual step width and the ideal value of 1 LSB. A DNL error specification of 1 LSB guarantees no missing codes and a monotonic transfer function. Signal-to-Noise Ratio For a waveform perfectly reconstructed from digital samples, signal-to-noise ratio (SNR) is the ratio of the full-scale analog input (RMS value) to the RMS quantization error (residual error). The ideal, theoretical minimum analog-to-digital noise is caused by quantization noise error only and results directly from the ADC’s resolution (N bits): SNR = (6.02 × N + 1.76)dB where N = 16 bits. In reality, there are other noise sources besides quantization noise: thermal noise, reference noise, clock jitter, etc. The SNR is computed by taking the ratio of the RMS signal to the RMS noise, which includes all spectral components minus the fundamental, the first five harmonics, and the DC offset. Total Harmonic Distortion 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:  V22 + V32 + V4 2 + V52 THD = 20 × log   V1        where V1 is the fundamental amplitude and V2 through V5 are the 2nd- through 5th-order harmonics. Spurious-Free Dynamic Range Spurious-free dynamic range (SFDR) is the ratio of the RMS amplitude of the fundamental (maximum signal component) to the RMS value of the next-largest frequency component. 12 ______________________________________________________________________________________ 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range Functional Diagram REFADJ 5kΩ REFERENCE 8 BITS 8 BITS D0–D7 OR D8–D15 HBEN AVDD AGND DVDD DGND MAX1178/MAX1188 OUTPUT REGISTERS REF AIN INPUT SCALER CAPACITIVE DAC MAX1178 MAX1188 AGND SUCCESSIVEAPPROXIMATION REGISTER AND CONTROL LOGIC CLOCK CS R/C EOC Pin Configuration TOP VIEW D4/D12 1 D5/D13 2 D6/D14 3 D7/D15 4 R/C 5 EOC 6 AVDD 7 AGND 8 AIN 9 AGND 10 20 D3/D11 19 D2/D10 18 D1/D9 17 D0/D8 Ordering Information (continued) PART MAX1188ACUP MAX1188BCUP MAX1188CCUP MAX1188AEUP MAX1188BEUP MAX1188CEUP TEMP RANGE 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 INPUT PINVOLTAGE PACKAGE RANGE (V) 20 TSSOP 20 TSSOP 20 TSSOP 20 TSSOP 20 TSSOP 20 TSSOP ±10 ±10 ±10 ±10 ±10 ±10 MAX1178 MAX1188 16 DVDD 15 DGND 14 CS 13 HBEN 12 REF 11 REFADJ Chip Information TRANSISTOR COUNT: 15,383 PROCESS: BiCMOS TSSOP ______________________________________________________________________________________ 13 16-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range MAX1178/MAX1188 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) TSSOP4.40mm.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. 14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.