ADC128S102QML

ADC128S102QML 8-Channel, 50 kSPS to 1 MSPS, 12-Bit A/D Converter May 17, 2010 ADC128S102QML 8-Channel, 50 kSPS to 1 MSPS, 12-Bit A/D Converter General Description The ADC128S102 is a low-power, eight-channel CMOS 12bit analog-to-digital converter specified for conversion throughput rates of 50 kSPS to 1 MSPS. The converter is based on a successive-approximation register architecture with an internal track-and-hold circuit. It can be configured to accept up to eight input signals at inputs IN0 through IN7. The output serial data is straight binary and is compatible with several standards, such as SPI™, QSPI™, MICROWIRE™, and many common DSP serial interfaces. The ADC128S102 may be operated with independent analog and digital supplies. The analog supply (VA) can range from +2.7V to +5.25V, and the digital supply (VD) can range from +2.7V to VA. Normal power consumption using a +3V or +5V supply is 2.3 mW and 10.7 mW, respectively. The powerdown feature reduces the power consumption to 0.06 µW using a +3V supply and 0.25 µW using a +5V supply. Features ■ ■ ■ ■ ■ ■ ■ Total Ionizing Dose 100 krad(Si) Single Event Latch-up 120 MeV-cm2/mg Eight input channels Variable power management Independent analog and digital supplies SPI/QSPI/MICROWIRE/DSP compatible Packaged in 16-lead Ceramic SOIC Key Specifications ■ ■ ■ ■ Conversion Rate DNL (VA = VD = 5.0 V) INL (VA = VD = 5.0 V) Power Consumption — 3V Supply — 5V Supply 50 kSPS to 1 MSPS +1.5 / −0.9 LSB (max) +1.4 / −1.25 LSB (max) 2.3 mW (typ) 10.7 mW (typ) Applications ■ ■ ■ ■ ■ Automotive Navigation Portable Systems Medical Instruments Mobile Communications Instrumentation and Control Systems Ordering Information NS Part Number ADC128S102WGRQV Flight Part ADC128S102WGMPR Pre-Flight Prototype ADC128S102CVAL Ceramic Evaluation Board SMD Part Number 5962R0722701VZA 100 krad(Si) NS Package Number WG16A WG16A Package Description 16LD Ceramic SOIC 16LD Ceramic SOIC 16LD Ceramic SOIC on Evaluation Board Connection Diagram 30018105 SPI™ is a trademark of Motorola, Inc. © 2010 National Semiconductor Corporation 300181 www.national.com ADC128S102QML Block Diagram 30018107 Pin Descriptions and Equivalent Circuits Pin No. ANALOG I/O 4 - 11 DIGITAL I/O 16 SCLK Digital clock input. The guaranteed performance range of frequencies for this input is 0.8 MHz to 16 MHz. This clock directly controls the conversion and readout processes. Digital data output. The output samples are clocked out of this pin on the falling edges of the SCLK pin. Digital data input. The ADC128S102QML's Control Register is loaded through this pin on rising edges of the SCLK pin. Chip select. On the falling edge of CS, a conversion process begins. Conversions continue as long as CS is held low. Positive analog supply pin. This voltage is also used as the reference voltage. This pin should be connected to a quiet +2.7V to +5.25V source and bypassed to GND with 1 µF and 0.1 µF monolithic ceramic capacitors located within 1 cm of the power pin. Positive digital supply pin. This pin should be connected to a +2.7V to VA supply, and bypassed to GND with a 0.1 µF monolithic ceramic capacitor located within 1 cm of the power pin. The ground return for the analog supply and signals. The ground return for the digital supply and signals. IN0 to IN7 Analog inputs. These signals can range from 0V to VREF. Symbol Equivalent Circuit Description 15 14 1 POWER SUPPLY DOUT DIN CS 2 VA 13 3 12 VD AGND DGND www.national.com 2 ADC128S102QML Absolute Maximum Ratings (Note 1) Analog Supply Voltage VA Digital Supply Voltage VD Voltage on Any Pin to GND Input Current at Any Pin (Note 3) Power Dissipation (Note 4) Package Input Current (Note 3) ESD Susceptibility (Note 5) Human Body Model Soldering Temperature 10 seconds Junction Temperature Storage Temperature −0.3V to 6.5V −0.3V to VA + 0.3V, max 6.5V −0.3V to VA +0.3V ±10 mA TA = 25°C ±20 mA   (Class 3A) 8000V 260°C +175°C −65°C to +150°C Operating Ratings Operating Temperature TMIN TMAX VA Supply Voltage VD Supply Voltage Digital Input Voltage Analog Input Voltage Clock Frequency (Note 1, Note 2) −55°C +125°C +2.7V to +5.25V +2.7V to VA 0V to VA 0V to VA 0.8 MHz to 16 MHz Package Thermal Resistance Package 16-lead Cerpack Gullwing θJA 127°C/W θJC 11.2°C/ W Quality Conformance Inspection MIL-STD-883, Method 5005 - Group A Subgroup 1 2 3 4 5 6 7 8A 8B 9 10 11 12 13 14 Description Static tests at Static tests at Static tests at Dynamic tests at Dynamic tests at Dynamic tests at Functional tests at Functional tests at Functional tests at Switching tests at Switching tests at Switching tests at Setting time at Setting time at Setting time at Temp (°C) +25 +125 -55 +25 +125 -55 +25 +125 -55 +25 +125 -55 +25 +125 -55 3 www.national.com ADC128S102QML ADC128S102QML Converter Electrical Characteristics The following specifications apply for AGND = DGND = 0V, fSCLK = 0.8 MHz to 16 MHz, fSAMPLE = 50 kSPS to 1 MSPS, CL = 50pF, unless otherwise noted. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25°C. Symbol Parameter Conditions Notes Typical (Note 6) Min Max Units Subgroups STATIC CONVERTER CHARACTERISTICS Resolution with No Missing Codes INL Integral Non-Linearity (End Point Method) VA = VD = +3.0V VA = VD = +5.0V VA = VD = +3.0V DNL Differential Non-Linearity VA = VD = +5.0V VOFF OEM FSE FSEM Offset Error Offset Error Match Full Scale Error Full Scale Error Match VA = VD = +3.0V VA = VD = +5.0V VA = VD = +3.0V VA = VD = +5.0V VA = VD = +3.0V VA = VD = +5.0V VA = VD = +3.0V VA = VD = +5.0V VA = VD = +3.0V VA = VD = +5.0V VA = VD = +3.0V, fIN = 40.2 kHz, −0.02 dBFS VA = VD = +5.0V, fIN = 40.2 kHz, −0.02 dBFS VA = VD = +3.0V, fIN = 40.2 kHz, −0.02 dBFS VA = VD = +5.0V, fIN = 40.2 kHz, −0.02 dBFS VA = VD = +3.0V, fIN = 40.2 kHz, −0.02 dBFS VA = VD = +5.0V, fIN = 40.2 kHz, −0.02 dBFS VA = VD = +3.0V, fIN = 40.2 kHz, −0.02 dBFS VA = VD = +5.0V, fIN = 40.2 kHz, −0.02 dBFS VA = VD = +3.0V, fIN = 40.2 kHz VA = VD = +5.0V, fIN = 40.2 kHz, −0.02 dBFS VA = VD = +3.0V, fIN = 20 kHz VA = VD = +5.0V, fIN = 20 kHz, −0.02 dBFS ±0.6 ±0.9 +0.5 −0.3 +0.9 −0.5 +0.8 +1.1 ±0.1 ±0.3 +0.8 +0.3 ±0.1 ±0.3 6.8 10 72 72 72 72 −86 −87 91 90 11.6 11.6 84 85 75 75 11.1 11.1 68 68 69 68.5 −74 −74 −0.9 −2.3 −2.3 −1.5 −1.5 −2.0 −2.0 −1.5 −1.5 +2.3 +2.3 +1.5 +1.5 +2.0 +2.0 +1.5 +1.5 −0.7 +1.5 −1.0 −1.25 12 +1.1 +1.4 +0.9 Bits LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB LSB MHz MHz dB dB dB dB dB dB dB dB Bits Bits dB dB 4, 5, 6 4, 5, 6 4, 5, 6 4, 5, 6 4, 5, 6 4, 5, 6 4, 5, 6 4, 5, 6 4, 5, 6 4, 5, 6 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 DYNAMIC CONVERTER CHARACTERISTICS FPBW Full Power Bandwidth (−3dB) Signal-to-Noise Plus Distortion Ratio SINAD SNR Signal-to-Noise Ratio THD Total Harmonic Distortion SFDR Spurious-Free Dynamic Range ENOB Effective Number of Bits ISO Channel-to-Channel Isolation www.national.com 4 ADC128S102QML Symbol Parameter Conditions VA = VD = +3.0V, fa = 19.5 kHz, fb = 20.5 kHz VA = VD = +5.0V, fa = 19.5 kHz, fb = 20.5 kHz VA = VD = +3.0V, fa = 19.5 kHz, fb = 20.5 kHz VA = VD = +5.0V, fa = 19.5 kHz, fb = 20.5 kHz Notes Typical (Note 6) −93 −93 −91 −91 Min Max −78 −78 −70 −70 Units dB dB dB dB Subgroups 4, 5, 6 4, 5, 6 4, 5, 6 4, 5, 6 Intermodulation Distortion, Second Order Terms IMD Intermodulation Distortion, Third Order Terms ANALOG INPUT CHARACTERISTICS VIN IDCL Input Range DC Leakage Current 0 to VA ±0.01 Track Mode (Note 7) (Note 7) 38 4.5 ±1.0 V µA pF pF 1, 2, 3 CINA Input Capacitance Hold Mode DIGITAL INPUT CHARACTERISTICS VIH VIL IIN CIND Input High Voltage Input Low Voltage Input Current Digital Input Capacitance VA = VD = +2.7V to +3.6V VA = VD = +4.75V to +5.25V VA = VD = +2.7V to +5.25V VIN = 0V or VD (Note 7) ISOURCE = 200 µA, VA = VD = +2.7V to +5.25V ISINK = 200 µA to 1.0 mA, VA = VD = +2.7V to +5.25V VA = VD = +2.7V to +5.25V (Note 7) ±0.01 3.5 Straight (Natural) Binary ±1.0 3.5 2.1 2.4 0.8 ±1.0 V V V µA pF (max) 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 DIGITAL OUTPUT CHARACTERISTICS VOH VOL IOZH, IOZL COUT Output High Voltage Output Low Voltage Hi-Impedance Output Leakage Current Hi-Impedance Output Capacitance Output Coding VD −0.5 0.4 ±1.0 V V µA pF (max) 1, 2, 3 1, 2, 3 1, 2, 3 5 www.national.com ADC128S102QML Symbol Parameter Conditions Notes Typical (Note 6) Min Max Units Subgroups 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 POWER SUPPLY CHARACTERISTICS (CL = 10 pF) VA, VD Analog and Digital Supply Voltages Total Supply Current Normal Mode ( CS low) IA + ID Total Supply Current Shutdown Mode (CS high) VA ≥ VD VA = VD = +2.7V to +3.6V, fSAMPLE = 1 MSPS, fIN = 40 kHz VA = VD = +4.75V to +5.25V, fSAMPLE = 1 MSPS, fIN = 40 kHz VA = VD = +2.7V to +3.6V, fSCLK = 0 kSPS VA = VD = +4.75V to +5.25V, fSCLK = 0 kSPS VA = VD = +3.0V fSAMPLE = 1 MSPS, fIN = 40 kHz VA = VD = +5.0V fSAMPLE = 1 MSPS, fIN = 40 kHz VA = VD = +3.0V fSCLK = 0 kSPS VA = VD = +5.0V fSCLK = 0 kSPS VA = VD = +2.7V to +5.25V VA = VD = +2.7V to +5.25V VA = VD = +2.7V to +5.25V VA = VD = +2.7V to +5.25V VA = VD = +2.7V to +5.25V VA = VD = +2.7V to +5.25V Acquisition Time + Conversion Time VA = VD = +2.7V to +5.25V VA = VD = +2.7V to +5.25V 4 40 60 3 50 1 13 0.9 2.2 0.11 0.12 2.7 11.0 0.33 0.6 2.7 5.25 1.5 3.1 1.0 1.4 4.5 15.5 3.0 7.0 V V mA mA μA μA mW mW µW µW Power Consumption Normal Mode ( CS low) PC Power Consumption Shutdown Mode (CS high) AC ELECTRICAL CHARACTERISTICS fSCLKMIN fSCLK fS tCONVERT DC tACQ Minimum Clock Frequency Maximum Clock Frequency Sample Rate Continuous Mode Conversion (Hold) Time SCLK Duty Cycle Acquisition (Track) Time 0.8 16 MHz MHz kSPS MSPS SCLK cycles % % SCLK cycles SCLK cycles ns 9, 10, 11 9, 10, 11 9, 10, 11 9, 10, 11 9, 10, 11 9, 10, 11 Throughput Time tAD Aperture Delay 16 9, 10, 11 www.national.com 6 ADC128S102QML Timing Specifications The following specifications apply for VA = VD = +2.7V to +5.25V, AGND = DGND = 0V, fSCLK = 0.8 MHz to 16 MHz, fSAMPLE = 50 kSPS to 1 MSPS, and CL = 50pF. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25°C. Symbol tCSH tCSS tEN tDACC tDHLD tDS tDH tCH tCL tDIS Parameter CS Hold Time after SCLK Rising Edge CS Setup Time prior to SCLK Rising Edge CS Falling Edge to DOUT enabled DOUT Access Time after SCLK Falling Edge DOUT Hold Time after SCLK Falling Edge DIN Setup Time prior to SCLK Rising Edge DIN Hold Time after SCLK Rising Edge SCLK High Time SCLK Low Time CS Rising Edge to DOUT High-Impedance DOUT falling DOUT rising Conditions Notes (Note 8) (Note 8) Typical (Note 6) 0 4.5 5 17 4 3 3 0.4 X tSCLK 0.4 X tSCLK 2.4 0.9 20 20 11 10 10 Min 10 10 30 27 Max Units ns ns ns ns ns ns ns ns (min) ns (min) ns ns 9, 10, 11 9, 10, 11 Subgroups 9, 10, 11 9, 10, 11 9, 10, 11 9, 10, 11 9, 10, 11 9, 10, 11 9, 10, 11 Radiation Electrical Characteristics (Note 9) The following specifications apply for VA = VD = +2.7V to +5.25V, AGND = DGND = 0V, fSCLK = 0.8 MHz to 16 MHz, fSAMPLE = 50 kSPS to 1 MSPS, and CL = 50pF, TA = 25°C. Parameter Conditions VA = VD = +2.7V to +3.6V, fSCLK = 0 kSPS VA = VD = +4.75V to +5.25V, fSCLK = 0 kSPS VA = VD = +2.7V to +5.25V Notes Typical Min Max 30 100 ±10 Units µA µA µA Subgroups 1 1 1 Symbol IA + ID Total Supply Current Shutdown Mode (CS high) Hi-Impedance Output Leakage Current IOZH, IOZL 7 www.national.com ADC128S102QML Burn In Delta Parameters (Note 10) The following specifications apply for VA = VD = +2.7V to +5.25V, AGND = DGND = 0V, fSCLK = 0.8 MHz to 16 MHz, fSAMPLE = 50 kSPS to 1 MSPS, and CL = 50pF, TA = 25°C. Parameter Integral Non-LInearity Intermodulation Distortion, Second Order Terms Intermodulation Distortion, Third Order Terms Conditions VA = VD = 3.0V VA = VD = +5.0V VA = VD = 3.0V VA = VD = 5.0V VA = VD = 3.0V VA = VD = 5.0V Notes Typical .106 .016 1.35 1.67 .47 .90 Mim −0.5 −0.35 −14 −17 −10 −10 Max +0.5 +0.35 +14 +17 +10 +10 Units LSB LSB dB dB dB dB Subgroups TA @ 25°C Symbol INL IMD IMD Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 2: All voltages are measured with respect to GND = 0V, unless otherwise specified. Note 3: When the input voltage at any pin exceeds the power supplies (that is, VIN < AGND or VIN > VA or VD), the current at that pin should be limited to 10 mA. The 20 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 10 mA to two. Note 4: The absolute maximum junction temperature (TJmax) for this device is 175°C. The maximum allowable power dissipation is dictated by TJmax, the junction-to-ambient thermal resistance (θJA), and the ambient temperature (TA), and can be calculated using the formula PDMAX = (TJmax − TA)/θJA. The values for maximum power dissipation listed above will be reached only when the ADC128S102QML is operated in a severe fault condition (e.g. when input or output pins are driven beyond the power supply voltages, or the power supply polarity is reversed). Obviously, such conditions should always be avoided. Note 5: Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through ZERO ohms Note 6: Typical figures are at TJ = 25°C, and represent most likely parametric norms. Note 7: This parameter is guaranteed by design and/or characterization and is not tested in production. Note 8: Clock may be in any state (high or low) when CS goes high. Setup and hold time restrictions apply only to CS going low. Note 9: Pre and post irradiation limits are identical to those listed in the “DC Parameters” and “AC and Timing Characteristics” tables, except as listed in the “Radiation Electrical Characteristics” table. When performing post irradiation electrical measurements for any RHA level, TA = +25°C. Note 10: This is worse case drift, Deltas are performed at room temperature post operational life. All other parameters, no deltas are required. www.national.com 8 ADC128S102QML Timing Diagrams 30018151 FIGURE 1. ADC128S102 Operational Timing Diagram 30018106 FIGURE 2. ADC128S102 Serial Timing Diagram 30018150 FIGURE 3. SCLK and CS Timing Parameters 9 www.national.com ADC128S102QML Specification Definitions ACQUISITION TIME is the time required for the ADC to acquire the input voltage. During this time, the hold capacitor is charged by the input voltage. APERTURE DELAY is the time between the fourth falling edge of SCLK and the time when the input signal is internally acquired or held for conversion. CONVERSION TIME is the time required, after the input voltage is acquired, for the ADC to convert the input voltage to a digital word. CHANNEL-TO-CHANNEL ISOLATION is resistance to coupling of energy from one channel into another channel. CROSSTALK is the coupling of energy from one channel into another channel. This is similar to Channel-to-Channel Isolation, except for the sign of the data. DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1 LSB. DUTY CYCLE is the ratio of the time that a repetitive digital waveform is high to the total time of one period. The specification here refers to the SCLK. EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE BITS) is another method of specifying Signal-to-Noise and Distortion or SINAD. ENOB is defined as (SINAD - 1.76) / 6.02 and says that the converter is equivalent to a perfect ADC of this (ENOB) number of bits. FULL POWER BANDWIDTH is a measure of the frequency at which the reconstructed output fundamental drops 3 dB below its low frequency value for a full scale input. GAIN ERROR is the deviation of the last code transition (111...110) to (111...111) from the ideal (VREF - 1.5 LSB), after adjusting for offset error. INTEGRAL NON-LINEARITY (INL) is a measure of the deviation of each individual code from a line drawn from negative full scale (½ LSB below the first code transition) through positive full scale (½ LSB above the last code transition). The deviation of any given code from this straight line is measured from the center of that code value. INTERMODULATION DISTORTION (IMD) is the creation of additional spectral components as a result of two sinusoidal frequencies being applied to an individual ADC input at the same time. It is defined as the ratio of the power in either the second or the third order intermodulation products to the sum of the power in both of the original frequencies. Second order products are fa ± fb, where fa and fb are the two sine wave input frequencies. Third order products are (2fa ± fb ) and (fa ± 2fb). IMD is usually expressed in dB. MISSING CODES are those output codes that will never appear at the ADC outputs. The ADC128S102 is guaranteed not to have any missing codes. OFFSET ERROR is the deviation of the first code transition (000...000) to (000...001) from the ideal (i.e. GND + 0.5 LSB). SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in dB, of the rms value of the input signal to the rms value of the sum of all other spectral components below one-half the sampling frequency, not including harmonics or d.c. SIGNAL TO NOISE PLUS DISTORTION (S/N+D or SINAD) Is the ratio, expressed in dB, of the rms value of the input signal to the rms value of all of the other spectral components below half the clock frequency, including harmonics but excluding d.c. SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the desired signal amplitude to the amplitude of the peak spurious spectral component, where a spurious spectral component is any signal present in the output spectrum that is not present at the input and may or may not be a harmonic. TOTAL HARMONIC DISTORTION (THD) is the ratio, expressed in dBc, of the rms total of the first five harmonic components at the output to the rms level of the input signal frequency as seen at the output. THD is calculated as where Af1 is the RMS power of the input frequency at the output and Af2 through Af10 are the RMS power in the first 9 harmonic frequencies. THROUGHPUT TIME is the minimum time required between the start of two successive conversions. It is the acquisition time plus the conversion time. www.national.com 10 ADC128S102QML Typical Performance Characteristics unless otherwise stated. DNL TA = +25°C, fSAMPLE = 1 MSPS, fSCLK = 16 MHz, fIN = 40.2 kHz DNL 30018140 30018141 INL INL 30018142 30018143 DNL vs. Supply INL vs. Supply 30018121 30018120 11 www.national.com ADC128S102QML SNR vs. Supply THD vs. Supply 30018122 30018132 ENOB vs. Supply DNL vs. SCLK Duty Cycle 30018133 30018155 INL vs. SCLK Duty Cycle SNR vs. SCLK Duty Cycle 30018158 30018161 www.national.com 12 ADC128S102QML THD vs. SCLK Duty Cycle ENOB vs. SCLK Duty Cycle 30018164 30018152 DNL vs. SCLK INL vs. SCLK 30018156 30018159 DNL vs. SCLK INL vs. SCLK 30018130 30018131 13 www.national.com ADC128S102QML SNR vs. SCLK SNR vs. SCLK 30018162 30018123 THD vs. SCLK THD vs SCLK 30018165 30018124 ENOB vs. SCLK ENOB vs. SCLK 30018153 30018145 www.national.com 14 ADC128S102QML ENOB vs. Temperature DNL vs. Temperature 30018154 30018157 INL vs. Temperature SNR vs. Temperature 30018160 30018163 THD vs. Temperature Power Consumption vs. SCLK 30018166 30018144 15 www.national.com ADC128S102QML 1.0 Functional Description The ADC128S102 is a successive-approximation analog-todigital converter designed around a charge-redistribution digital-to-analog converter. 1.1 ADC128S102 OPERATION Simplified schematics of the ADC128S102 in both track and hold operation are shown in Figure 4 and Figure 5 respectively. In Figure 4, the ADC128S102 is in track mode: switch SW1 connects the sampling capacitor to one of eight analog input channels through the multiplexer, and SW2 balances the comparator inputs. The ADC128S102 is in this state for the first three SCLK cycles after CS is brought low. Figure 5 shows the ADC128S102 in hold mode: switch SW1 connects the sampling capacitor to ground, maintaining the sampled voltage, and switch SW2 unbalances the comparator. The control logic then instructs the charge-redistribution DAC to add or subtract fixed amounts of charge to or from the sampling capacitor until the comparator is balanced. When the comparator is balanced, the digital word supplied to the DAC is the digital representation of the analog input voltage. The ADC128S102 is in this state for the last thirteen SCLK cycles after CS is brought low. 30018109 FIGURE 4. ADC128S102 in Track Mode 30018110 FIGURE 5. ADC128S102 in Hold Mode 1.2 SERIAL INTERFACE An operational timing diagram and a serial interface timing diagram for the ADC128S102 are shown in The Timing Diagrams section. CS, chip select, initiates conversions and frames the serial data transfers. SCLK (serial clock) controls both the conversion process and the timing of serial data. DOUT is the serial data output pin, where a conversion result is sent as a serial data stream, MSB first. Data to be written to the ADC128S102's Control Register is placed on DIN, the serial data input pin. New data is written to DIN with each conversion. A serial frame is initiated on the falling edge of CS and ends on the rising edge of CS. Each frame must contain an integer multiple of 16 rising SCLK edges. The ADC's DOUT pin is in a high impedance state when CS is high and is active when CS is low. Thus, CS acts as an output enable. Similarly, SCLK is internally gated off when CS is brought high. During the first 3 cycles of SCLK, the ADC is in the track mode, acquiring the input voltage. For the next 13 SCLK cycles the conversion is accomplished and the data is clocked out. SCLK falling edges 1 through 4 clock out leading zeros while falling edges 5 through 16 clock out the conversion result, MSB first. If there is more than one conversion in a frame (continuous conversion mode), the ADC will re-enter the track mode on the falling edge of SCLK after the N*16th rising edge of SCLK and re-enter the hold/convert mode on the N*16+4th falling edge of SCLK. "N" is an integer value. The ADC128S102 enters track mode under three different conditions. In Figure 1, CS goes low with SCLK high and the ADC enters track mode on the first falling edge of SCLK. In the second condition, CS goes low with SCLK low. Under this www.national.com 16 ADC128S102QML condition, the ADC automatically enters track mode and the falling edge of CS is seen as the first falling edge of SCLK. In the third condition, CS and SCLK go low simultaneously and the ADC enters track mode. While there is no timing restriction with respect to the falling edges of CS and SCLK, see Figure 3 for setup and hold time requirements for the falling edge of CS with respect to the rising edge of SCLK. During each conversion, data is clocked into a control register through the DIN pin on the first 8 rising edges of SCLK after the fall of CS. The control register is loaded with data indicating the input channel to be converted on the subsequent conversion (see Tables 1, 2, 3). Although the ADC128S102 is able to acquire the input signal to full resolution in the first conversion immediately following power-up, the first conversion result after power-up will be that of a randomly selected channel. Therefore, the user needs to incorporate a dummy conversion to set the required channel that will be used on the subsequent conversion. TABLE 1. Control Register Bits Bit 7 (MSB) DONTC Bit 6 DONTC Bit 5 ADD2 Bit 4 ADD1 Bit 3 ADD0 Bit 2 DONTC Bit 1 DONTC Bit 0 DONTC TABLE 2. Control Register Bit Descriptions Bit #: 7, 6, 2, 1, 0 5 4 3 Symbol: DONTC ADD2 ADD1 ADD0 Description Don't care. The values of these bits do not affect the device. These three bits determine which input channel will be sampled and converted at the next conversion cycle. The mapping between codes and channels is shown in Table 3. 1.4 ANALOG INPUTS An equivalent circuit for one of the ADC128S102's input channels is shown in Figure 7. Diodes D1 and D2 provide ESD protection for the analog inputs. The operating range for the analog inputs is 0 V to VA. Going beyond this range will cause the ESD diodes to conduct and result in erratic operation. The capacitor C1 in Figure 7 has a typical value of 3 pF and is mainly the package pin capacitance. Resistor R1 is the on resistance of the multiplexer and track / hold switch and is typically 500 ohms. Capacitor C2 is the ADC128S102 sampling capacitor, and is typically 30 pF. The ADC128S102 will deliver best performance when driven by a low-impedance source (less than 100 ohms). This is especially important when using the ADC128S102 to sample dynamic signals. Also important when sampling dynamic signals is a band-pass or low-pass filter which reduces harmonics and noise in the input. These filters are often referred to as anti-aliasing filters. TABLE 3. Input Channel Selection ADD2 0 0 0 0 1 1 1 1 ADD1 0 0 1 1 0 0 1 1 ADD0 0 1 0 1 0 1 0 1 Input Channel IN0 IN1 IN2 IN3 IN4 IN5 IN6 IN7 1.3 ADC128S102 TRANSFER FUNCTION The output format of the ADC128S102 is straight binary. Code transitions occur midway between successive integer LSB values. The LSB width for the ADC128S102 is VA / 4096. The ideal transfer characteristic is shown in Figure 6. The transition from an output code of 0000 0000 0000 to a code of 0000 0000 0001 is at 1/2 LSB, or a voltage of VA / 8192. Other code transitions occur at steps of one LSB. 30018114 FIGURE 7. Equivalent Input Circuit 1.5 DIGITAL INPUTS AND OUTPUTS The ADC128S102's digital inputs (SCLK, CS, and DIN) have an operating range of 0 V to VA. They are not prone to latchup and may be asserted before the digital supply (VD) without any risk. The digital output (DOUT) operating range is controlled by VD. The output high voltage is VD - 0.5V (min) while the output low voltage is 0.4V (max). 30018111 FIGURE 6. Ideal Transfer Characteristic 17 www.national.com ADC128S102QML 2.0 Applications Information 2.1 TYPICAL APPLICATION CIRCUIT A typical application is shown in Figure 8. The split analog and digital supply pins are both powered in this example by the National LP2950 low-dropout voltage regulator. The analog supply is bypassed with a capacitor network located close to the ADC128S102. The digital supply is separated from the analog supply by an isolation resistor and bypassed with additional capacitors. The ADC128S102 uses the analog supply (VA) as its reference voltage, so it is very important that VA be kept as clean as possible. Due to the low power requirements of the ADC128S102, it is also possible to use a precision reference as a power supply. 30018113 FIGURE 8. Typical Application Circuit 2.2 POWER SUPPLY CONSIDERATIONS There are three major power supply concerns with this product: power supply sequencing, power management, and the effect of digital supply noise on the analog supply. 2.2.1 Power Supply Sequence The ADC128S102 is a dual-supply device. The two supply pins share ESD resources, so care must be exercised to ensure that the power is applied in the correct sequence. To avoid turning on the ESD diodes, the digital supply (VD) cannot exceed the analog supply (VA) by more than 300 mV, during a conversion cycle. Therefore, VA must ramp up before or concurrently with VD. 2.2.2 Power Management The ADC128S102 is fully powered-up whenever CS is low and fully powered-down whenever CS is high, with one exception. If operating in continuous conversion mode, the ADC128S102 automatically enters power-down mode between SCLK's 16th falling edge of a conversion and SCLK's 1st falling edge of the subsequent conversion (see Figure 1). In continuous conversion mode, the ADC128S102 can perform multiple conversions back to back. Each conversion requires 16 SCLK cycles and the ADC128S102 will perform conversions continuously as long as CS is held low. Continuous mode offers maximum throughput. In burst mode, the user may trade off throughput for power consumption by performing fewer conversions per unit time. This means spending more time in power-down mode and less time in normal mode. By utilizing this technique, the user can achieve very low sample rates while still utilizing an SCLK frequency within the electrical specifications. The Power Consumption vs. SCLK curve in the Typical Performance Curves section shows the typical power consumption of the ADC128S102. To calculate the power consumption (PC), simply multiply the fraction of time spent in the normal mode (tN) by the normal mode power consumption (PN), and add the fraction of time spent in shutdown mode (tS) multiplied by the www.national.com 18 shutdown mode power consumption (PS) as shown in Figure 9. 30018115 FIGURE 9. Power Consumption Equation 2.2.3 Power Supply Noise Considerations The charging of any output load capacitance requires current from the digital supply, VD. The current pulses required from the supply to charge the output capacitance will cause voltage variations on the digital supply. If these variations are large enough, they could degrade SNR and SINAD performance of the ADC. Furthermore, if the analog and digital supplies are tied directly together, the noise on the digital supply will be coupled directly into the analog supply, causing greater performance degradation than would noise on the digital supply alone. Similarly, discharging the output capacitance when the digital output goes from a logic high to a logic low will dump current into the die substrate, which is resistive. Load discharge currents will cause "ground bounce" noise in the substrate that will degrade noise performance if that current is large enough. The larger the output capacitance, the more current flows through the die substrate and the greater the noise coupled into the analog channel. The first solution to keeping digital noise out of the analog supply is to decouple the analog and digital supplies from each other or use separate supplies for them. To keep noise out of the digital supply, keep the output load capacitance as small as practical. If the load capacitance is greater than 50 pF, use a 100 Ω series resistor at the ADC output, located as close to the ADC output pin as practical. This will limit the charge and discharge current of the output capacitance and improve noise performance. Since the series resistor and the ADC128S102QML load capacitance form a low frequency pole, verify signal integrity once the series resistor has been added. 2.3 LAYOUT AND GROUNDING Capacitive coupling between the noisy digital circuitry and the sensitive analog circuitry can lead to poor performance. The solution is to keep the analog circuitry separated from the digital circuitry and the clock line as short as possible. Digital circuits create substantial supply and ground current transients. The logic noise generated could have significant impact upon system noise performance. To avoid performance degradation of the ADC128S102 due to supply noise, do not use the same supply for the ADC128S102 that is used for digital logic. Generally, analog and digital lines should cross each other at 90° to avoid crosstalk. However, to maximize accuracy in high resolution systems, avoid crossing analog and digital lines altogether. It is important to keep clock lines as short as possible and isolated from ALL other lines, including other digital lines. In addition, the clock line should also be treated as a transmission line and be properly terminated. The analog input should be isolated from noisy signal traces to avoid coupling of spurious signals into the input. Any external component (e.g., a filter capacitor) connected between the converter's input pins and ground or to the reference input pin and ground should be connected to a very clean point in the ground plane. We recommend the use of a single, uniform ground plane and the use of split power planes. The power planes should be located within the same board layer. All analog circuitry (input amplifiers, filters, reference components, etc.) should be placed over the analog power plane. All digital circuitry and I/ O lines should be placed over the digital power plane. Furthermore, all components in the reference circuitry and the input signal chain that are connected to ground should be connected together with short traces and enter the analog ground plane at a single, quiet point. 3.0 Radiation Environments Careful consideration should be given to environmental conditions when using a product in a radiation environment. 3.1 TOTAL IONIZING DOSE Radiation hardness assured (RHA) products are those part numbers with a total ionizing dose (TID) level specified in the Ordering Information table on the front page. Testing and qualification of these products is done on a wafer level according to MIL-STD-883G, Test Method 1019.7. Testing is done according to Condition A and the “Extended room temperature anneal test” described in section 3.11 for application environment dose rates less than 0.16 rad(Si)/s. Wafer level TID data is available with lot shipments. 3.2 SINGLE EVENT LATCH-UP One time single event latchup testing (SEL) was performed according to EIA/JEDEC Standard, EIA/JEDEC57. Testing was done at maximum operating temperature and supply voltage. The linear energy transfer threshold (LETth) shown in the Key Specifications table on the front page is the maximum LET tested. A test report is available upon request. 3.3 SINGLE EVENT UPSET A report on single event upset (SEU) is available upon request. 19 www.national.com ADC128S102QML Revision History Date Released 08/21/08 11/03/08 Revision A B Section New Data Sheet, Initial Release Timing Diagrams Changes New product data sheet, Initial Release Typo, Changed Figure 2, tDIS lower left hand side changed to tDS and tDIH lower left hand side change to tDH. Revision A will be Archived. Corrected package reference from 16-lead TSSOP to 16-lead Ceramic SOIC, Removed QV NSID reference and Added SMD Number to RQV NSID. Revision B will be Archived. 01/09/09 C Features, Ordering Information 06/02/09 D Features, Ordering Information, Electrical Moved Rad information from Key Specifications to Section Features. Deleted ADC128S102WGMLS reference. Added Burn In Delta Table. Revision C will be Archived. Operating Ratings, Electricals, Note and Typical Performance Characteristics Spec Typo for Clock Frequency range, Electrical headings, currently shows 8 Mhz to 16 Mhz, Should be 0.8 Mhz and 16 Mhz. Reword Note 10. Reformatted Burn In Delta table. Added new ENOB vs SCLK Plot. Revision D will be Archived. 10/27/09 E 03/11/2010 F AC Electrical Characteristics - SCLK Duty AC Electrical Characteristics - SCLK Duty Cycle, Cycle typ limits. Revision E will be Archived. www.national.com 20 ADC128S102QML Physical Dimensions inches (millimeters) unless otherwise noted 16-Lead Ceramic SOIC NS Package Number WG16A 21 www.national.com ADC128S102QML 8-Channel, 50 kSPS to 1 MSPS, 12-Bit A/D Converter Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Amplifiers Audio Clock and Timing Data Converters Interface LVDS Power Management Switching Regulators LDOs LED Lighting Voltage References PowerWise® Solutions Temperature Sensors PLL/VCO www.national.com/amplifiers www.national.com/audio www.national.com/timing www.national.com/adc www.national.com/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/vref www.national.com/powerwise WEBENCH® Tools App Notes Reference Designs Samples Eval Boards Packaging Green Compliance Distributors Quality and Reliability Feedback/Support Design Made Easy Design Support www.national.com/webench www.national.com/appnotes www.national.com/refdesigns www.national.com/samples www.national.com/evalboards www.national.com/packaging www.national.com/quality/green www.national.com/contacts www.national.com/quality www.national.com/feedback www.national.com/easy www.national.com/solutions www.national.com/milaero www.national.com/solarmagic www.national.com/training Applications & Markets Mil/Aero PowerWise® Design University Serial Digital Interface (SDI) www.national.com/sdi www.national.com/wireless www.national.com/tempsensors SolarMagic™ THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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