ADC081S051CISDX/NOPB

ADC081S051 www.ti.com SNAS309F – APRIL 2005 – REVISED JANUARY 2014 ADC081S051 Single Channel, 200 to 500 ksps, 8-Bit A/D Converter Check for Samples: ADC081S051 FEATURES DESCRIPTION • • • • • The ADC081S051 is a low-power, single channel CMOS 8-bit analog-to-digital converter with a highspeed serial interface. Unlike the conventional practice of specifying performance at a single sample rate only, the ADC081S051 is fully specified over a sample rate range of 200 ksps to 500 ksps. The converter is based on a successive-approximation register architecture with an internal track-and-hold circuit. 1 2 Specified Over a Range of Sample Rates 6-lead WSON and SOT-23 Packages Variable Power Management Single Power Supply with 2.7V - 5.25V Range SPI™/QSPI™/MICROWIRE/DSP Compatible KEY SPECIFICATIONS • • • • DNL: +0.06 / -0.045 LSB (Typ) INL: +0.06 / -0.05 LSB (Typ) SNR: 49.6 dB (Typ) Power Consumption: – 3.6V Supply: 1.6 mW (Typ) – 5.25V Supply: 8.5 mW (Typ) 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 ADC081S051 operates with a single supply that can range from +2.7V to +5.25V. Normal power consumption using a +3.6V or +5.25V supply is 1.6 mW and 8.5 mW, respectively. The power-down feature reduces the power consumption to as low as 2.6 µW using a +5.25V supply. APPLICATIONS • • • Portable Systems Remote Data Acquisition Instrumentation and Control Systems The ADC081S051 is packaged in 6-lead WSON and SOT-23 packages. Operation over the industrial temperature range of −40°C to +85°C is ensured. Table 1. Pin-Compatible Alternatives by Resolution and Speed (1) Resolution (1) Specified for Sample Rate Range of: 50 to 200 ksps 200 to 500 ksps 500 ksps to 1 Msps 12-bit ADC121S021 ADC121S051 ADC121S101 10-bit ADC101S021 ADC101S051 ADC081S101 8-bit ADC081S021 ADC081S051 ADC081S101 All devices are fully pin and function compatible. Connection Diagram VA 1 GND 2 VIN 3 ADC081S051 6 CS 5 SDATA 4 SCLK Figure 1. 6-Lead WSON or SOT-23 See NGF0006A or DBV Package 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2005–2014, Texas Instruments Incorporated ADC081S051 SNAS309F – APRIL 2005 – REVISED JANUARY 2014 www.ti.com Block Diagram VIN T/H 8-BIT SUCCESSIVE APPROXIMATION ADC SCLK CONTROL LOGIC CS SDATA PIN DESCRIPTIONS and EQUIVALENT CIRCUITS Pin No. Symbol Description ANALOG I/O 3 VIN Analog input. This signal can range from 0V to VA. DIGITAL I/O 4 SCLK 5 SDATA Digital clock input. This clock directly controls the conversion and readout processes. 6 CS Chip select. On the falling edge of CS, a conversion process begins. 1 VA Positive supply pin. This pin should be connected to a quiet +2.7V to +5.25V source and bypassed to GND with a 1 µF capacitor and a 0.1 µF monolithic capacitor located within 1 cm of the power pin. 2 GND The ground return for the supply and signals. PAD GND For package suffix CISD(X) only, it is recommended that the center pad should be connected to ground. Digital data output. The output samples are clocked out of this pin on falling edges of the SCLK pin. POWER SUPPLY 2 Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 ADC081S051 www.ti.com SNAS309F – APRIL 2005 – REVISED JANUARY 2014 These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. Absolute Maximum Ratings (1) (2) (3) −0.3V to 6.5V Analog Supply Voltage VA −0.3V to (VA +0.3V) Voltage on Any Analog Pin to GND −0.3V to 6.5V Voltage on Any Digital Pin to GND Input Current at Any Pin (4) ±10 mA Package Input Current (4) ±20 mA See (5) Power Consumption at TA = 25°C Human Body Model ESD Susceptibility (6) 3500V Machine Model 300V Junction Temperature +150°C Storage Temperature −65°C to +150°C (1) (2) (3) (4) (5) (6) 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 ensure specific performance limits. For ensured specifications and test conditions, see the Electrical Characteristics. The ensured specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. All voltages are measured with respect to GND = 0V, unless otherwise specified. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications. When the input voltage at any pin exceeds the power supply (that is, VIN < GND or VIN > VA), 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. The Absolute Maximum Rating specification does not apply to the VA pin. The current into the VA pin is limited by the Analog Supply Voltage specification. The absolute maximum junction temperature (TJmax) for this device is 150°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 device 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. Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through zero ohms Operating Ratings (1) (2) −40°C ≤ TA ≤ +85°C Operating Temperature Range VA Supply Voltage +2.7V to +5.25V −0.3V to 5.25V Digital Input Pins Voltage Range (regardless of supply voltage) Analog Input Pins Voltage Range 0V to VA Clock Frequency 25 kHz to 20 MHz Sample Rate (1) (2) up to 1Msps 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 ensure specific performance limits. For ensured specifications and test conditions, see the Electrical Characteristics. The ensured specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. All voltages are measured with respect to GND = 0V, unless otherwise specified. Package Thermal Resistance (1) θJA Package (1) 6-lead WSON 94°C / W 6-lead SOT-23 265°C / W Soldering process must comply with Reflow Temperature Profile specifications. Refer to www.ti.com/packaging. Reflow temperature profiles are different for lead-free and non-lead-free packages. Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 3 ADC081S051 SNAS309F – APRIL 2005 – REVISED JANUARY 2014 www.ti.com ADC081S051 Converter Electrical Characteristics (1) (2) The following specifications apply for VA = +2.7V to 5.25V, GND = 0V, fSCLK = 4 MHz to 10 MHz, fSAMPLE = 200 ksps to 500 ksps, CL = 15 pF, unless otherwise noted. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25°C. Symbol Parameter Conditions Typical Limits (2) Units 8 Bits ±0.3 LSB (max) STATIC CONVERTER CHARACTERISTICS Resolution with No Missing Codes VA = +2.7V to +3.6V INL Integral Non-Linearity ±0.04 +0.06 VA = +4.75V to +5.25V −0.045 VA = +2.7V to +3.6V DNL VOFF GE Differential Non-Linearity Offset Error Gain Error ±0.05 +0.06 VA = +4.75V to +5.25V −0.05 ±0.2 ±0.2 LSB (max) LSB (min) LSB (max) LSB (max) LSB (min) VA = +2.7V to +3.6V −0.01 ±0.2 LSB (max) VA = +4.75V to +5.25V +0.04 ±0.2 LSB (max) VA = +2.7V to +3.6V +0.01 ±0.4 LSB (max) VA = +4.75V to +5.25V −0.075 ±0.4 LSB (max) +0.04 VA = +2.7V to +3.6V TUE ±0.3 −0.045 Total Unadjusted Error +0.07 VA = +4.75V to +5.25V −0.055 ±0.3 ±0.3 LSB (max) LSB (min) LSB (max) LSB (min) DYNAMIC CONVERTER CHARACTERISTICS SINAD Signal-to-Noise Plus Distortion Ratio VA = +2.7 to 5.25V fIN = 100 kHz, −0.02 dBFS 49.5 49 dB (min) SNR Signal-to-Noise Ratio VA = +2.7 to 5.25V fIN = 100 kHz, −0.02 dBFS 49.6 49 dB (min) THD Total Harmonic Distortion VA = +2.7 to 5.25V fIN = 100 kHz, −0.02 dBFS −77 −65 dB (max) SFDR Spurious-Free Dynamic Range VA = +2.7 to 5.25V fIN = 100 kHz, −0.02 dBFS 68 65 dB (min) ENOB Effective Number of Bits VA = +2.7 to 5.25V fIN = 100 kHz, −0.02 dBFS 7.9 7.8 Bits (min) Intermodulation Distortion, Second Order Terms VA = +5.25V fa = 103.5 kHz, fb = 113.5 kHz −83 dB Intermodulation Distortion, Third Order Terms VA = +5.25V fa = 103.5 kHz, fb = 113.5 kHz −82 dB VA = +5V 11 MHz VA = +3V 8 MHz IMD FPBW -3 dB Full Power Bandwidth ANALOG INPUT CHARACTERISTICS VIN Input Range IDCL DC Leakage Current CINA Input Capacitance 0 to VA V ±1 µA (max) Track Mode 30 pF Hold Mode 4 pF DIGITAL INPUT CHARACTERISTICS VIH Input High Voltage VIL Input Low Voltage IIN Input Current CIND Digital Input Capacitance (1) (2) 4 VA = +5.25V 2.4 VA = +3.6V 2.1 V (min) VA = +5.25V 0.8 V (max) VA = +3.6V 0.4 V (max) ±0.1 ±1 µA (max) 2 4 pF (max) VIN = 0V or VA V (min) Tested limits are ensured to AOQL (Average Outgoing Quality Level). Data sheet min/max specification limits are ensured by design, test, or statistical analysis. Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 ADC081S051 www.ti.com SNAS309F – APRIL 2005 – REVISED JANUARY 2014 ADC081S051 Converter Electrical Characteristics(1)(2) (continued) The following specifications apply for VA = +2.7V to 5.25V, GND = 0V, fSCLK = 4 MHz to 10 MHz, fSAMPLE = 200 ksps to 500 ksps, CL = 15 pF, unless otherwise noted. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25°C. Symbol Typical Limits (2) Units ISOURCE = 200 µA VA − 0.07 VA − 0.2 V (min) ISOURCE = 1 mA VA − 0.1 ISINK = 200 µA 0.03 0.4 V (max) ISINK = 1 mA 0.1 Parameter Conditions DIGITAL OUTPUT CHARACTERISTICS VOH Output High Voltage VOL Output Low Voltage IOZH, IOZL TRI-STATE Leakage Current COUT TRI-STATE Output Capacitance V V ±0.1 ±10 µA (max) 2 4 pF (max) Output Coding Straight (Natural) Binary POWER SUPPLY CHARACTERISTICS VA Supply Voltage Supply Current, Normal Mode (Operational, CS low) IA Supply Current, Shutdown (CS high) Power Consumption, Normal Mode (Operational, CS low) PD Power Consumption, Shutdown (CS high) 2.7 V (min) 5.25 V (max) VA = +5.25V, fSAMPLE = 200 ksps 1.61 2.4 mA (max) VA = +3.6V, fSAMPLE = 200 ksps 0.43 1.0 mA (max) fSCLK= 0 MHz, VA = +5.25V fSAMPLE = 0 ksps 500 nA VA = +5.25V, fSCLK = 10 MHz, fSAMPLE = 0 ksps 60 µA VA = +5.25V 8.5 12.6 mW (max) VA = +3.6V 1.6 3.6 mW (max) fSCLK = 0 MHz, VA = +5.25V fSAMPLE = 0 ksps 2.6 µW VA = +5.25V, fSCLK = 10 MHz, fSAMPLE = 0 ksps 315 µW AC ELECTRICAL CHARACTERISTICS 4 MHz (min) 10 MHz (max) fSCLK Clock Frequency See (3) fS Sample Rate See (3) DC SCLK Duty Cycle fSCLK = 10 MHz tACQ Minimum Time Required for Acquisition tQUIET See (4) tAD Aperture Delay 3 ns tAJ Aperture Jitter 30 ps (3) (4) 50 50 200 ksps (min) 500 ksps (max) 40 % (min) 60 % (max) 350 ns (max) 50 ns (min) This is the frequency range over which the electrical performance is ensured. The device is functional over a wider range which is specified under Operating Ratings. Minimum Quiet Time required by Bus relinquish and start of the next conversion. Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 5 ADC081S051 SNAS309F – APRIL 2005 – REVISED JANUARY 2014 www.ti.com ADC081S051 Timing Specifications The following specifications apply for VA = +2.7V to 5.25V, GND = 0V, fSCLK = 4 MHz to 10 MHz, CL = 25 pF, fSAMPLE = 200 ksps to 500 ksps, Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25°C. Symbol Limits Units tCS Minimum CS Pulse Width Parameter Conditions Typical 10 ns (min) tSU CS to SCLK Setup Time 10 ns (min) tEN Delay from CS Until SDATA TRI-STATE Disabled (1) 20 ns (max) tACC Data Access Time after SCLK Falling Edge (2) VA = +2.7V to +3.6V 40 ns (max) VA = +4.75V to +5.25V 20 ns (max) tCL SCLK Low Pulse Width 0.4 x tSCLK ns (min) tCH SCLK High Pulse Width 0.4 x tSCLK ns (min) 7 ns (min) tH VA = +2.7V to +3.6V SCLK to Data Valid Hold Time VA = +4.75V to +5.25V VA = +2.7V to +3.6V SCLK Falling Edge to SDATA High Impedance (3) tDIS VA = +4.75V to +5.25V tPOWER- Power-Up Time from Full Power-Down 1 5 ns (min) 25 ns (max) 6 ns (min) 25 ns (max) 5 ns (min) µs UP (1) (2) (3) 6 Measured with the timing test circuit shown in Figure 2 and defined as the time taken by the output signal to cross 1.0V. Measured with the timing test circuit shown in Figure 2 and defined as the time taken by the output signal to cross 1.0V or 2.0V. tDIS is derived from the time taken by the output to change by 0.5V with the timing test circuit shown in Figure 2. The measured number is then adjusted to remove the effects of charging or discharging the load capacitance. This means that tDIS is the true bus relinquish time, independent of the bus loading. Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 ADC081S051 www.ti.com SNAS309F – APRIL 2005 – REVISED JANUARY 2014 Timing Diagrams IOL 200 PA 1.6 V To Output Pin CL 25 pF IOH 200 PA Figure 2. Timing Test Circuit Hold Track | CS tCS tSU tACQ tCL 1 2 3 4 12 13 14 15 16 17 Z1 Z0 DB7 3 leading zero bits 18 19 20 tQUIET tCH tH | Z2 5 tACC tEN SDATA | SCLK tDIS TRI-STATE Zero Zero 8 data bits Zero Zero 4 trailing zeroes Figure 3. ADC081S051 Serial Timing Diagram Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 7 ADC081S051 SNAS309F – APRIL 2005 – REVISED JANUARY 2014 www.ti.com Specification Definitions ACQUISITION TIME is the time required to acquire the input voltage. That is, it is time required for the hold capacitor to charge up to the input voltage. Acquisition time is measured backwards from the falling edge of CS when the signal is sampled and the part moves from track to hold. The start of the time interval that contains TACQ is the 13th rising edge of SCLK of the previous conversion when the part moves from hold to track. The user must ensure that the time between the 13th rising edge of SCLK and the falling edge of the next CS is not less than TACQ to meet performance specifications. APERTURE DELAY is the time after the falling edge of CS when the input signal is acquired or held for conversion. APERTURE JITTER (APERTURE UNCERTAINTY) is the variation in aperture delay from sample to sample. Aperture jitter manifests itself as noise in the output. CONVERSION TIME is the time required, after the input voltage is acquired, for the ADC to convert the input voltage to a digital word. This is from the falling edge of CS when the input signal is sampled to the 16th falling edge of SCLK when the SDATA output goes into TRI-STATE. 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 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 the ADC input at the same time. It is defined as the ratio of the power in the second and third order intermodulation products to the sum of the power in both of the original frequencies. IMD is usually expressed in dB. MISSING CODES are those output codes that will never appear at the ADC outputs. The ADC081S051 is ensured 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 + 1 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. 8 Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 ADC081S051 www.ti.com SNAS309F – APRIL 2005 – REVISED JANUARY 2014 TOTAL HARMONIC DISTORTION (THD) is the ratio, expressed in dB or 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 THD = 20 ‡ log10 A f 22 +  + A f 6 2 A f 12 where • Af1 is the RMS power of the input frequency at the output and Af2 through Af6 are the RMS power in the first 5 harmonic frequencies. (1) THROUGHPUT TIME is the minimum time required between the start of two successive conversion. It is the acquisition time plus the conversion time. TOTAL UNADJUSTED ERROR is the worst deviation found from the ideal transfer function. As such, it is a comprehensive specification which includes full scale error, linearity error, and offset error. Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 9 ADC081S051 SNAS309F – APRIL 2005 – REVISED JANUARY 2014 www.ti.com Typical Performance Characteristics TA = +25°C, fSAMPLE = 200 ksps to 500 ksps, fSCLK = 4 MHz to 10 MHz, fIN = 100 kHz unless otherwise stated. 10 DNL fSCLK = 4 MHz INL fSCLK = 4 MHz Figure 4. Figure 5. DNL fSCLK = 10 MHz INL fSCLK = 10 MHz Figure 6. Figure 7. DNL vs. Clock Frequency INL vs. Clock Frequency Figure 8. Figure 9. Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 ADC081S051 www.ti.com SNAS309F – APRIL 2005 – REVISED JANUARY 2014 Typical Performance Characteristics (continued) TA = +25°C, fSAMPLE = 200 ksps to 500 ksps, fSCLK = 4 MHz to 10 MHz, fIN = 100 kHz unless otherwise stated. Total Unadjusted Error vs. Clock Frequency SNR vs. Clock Frequency Figure 10. Figure 11. SINAD vs. Clock Frequency THD vs. Clock Frequency Figure 12. Figure 13. SFDR vs.Clock Frequency Spectral Response, VA = 5V, fSCLK = 4 MHz Figure 14. Figure 15. Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 11 ADC081S051 SNAS309F – APRIL 2005 – REVISED JANUARY 2014 www.ti.com Typical Performance Characteristics (continued) TA = +25°C, fSAMPLE = 200 ksps to 500 ksps, fSCLK = 4 MHz to 10 MHz, fIN = 100 kHz unless otherwise stated. 12 Spectral Response, VA = 5V, fSCLK = 10 MHz Power Consumption vs.Throughput, fSCLK = 10 MHz Figure 16. Figure 17. Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 ADC081S051 www.ti.com SNAS309F – APRIL 2005 – REVISED JANUARY 2014 APPLICATIONS INFORMATION ADC081S051 OPERATION The ADC081S051 is a successive-approximation analog-to-digital converter designed around a chargeredistribution digital-to-analog converter core. Simplified schematics of the ADC081S051 in both track and hold modes are shown in Figure 18 and Figure 19, respectively. In Figure 18, the device is in track mode: switch SW1 connects the sampling capacitor to the input and SW2 balances the comparator inputs. The device is in this state until CS is brought low, at which point the device moves to hold mode. Figure 19 shows the device 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 chargeredistribution DAC to add or subtract fixed amounts of charge 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 device moves from hold mode to track mode on the 13th rising edge of SCLK. CHARGE REDISTRIBUTION DAC VIN SAMPLING CAPACITOR SW1 + SW2 GND - CONTROL LOGIC VA 2 Figure 18. ADC081S051 in Track Mode CHARGE REDISTRIBUTION DAC VIN SAMPLING CAPACITOR SW1 + SW2 GND - CONTROL LOGIC VA 2 Figure 19. ADC081S051 in Hold Mode Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 13 ADC081S051 SNAS309F – APRIL 2005 – REVISED JANUARY 2014 www.ti.com USING THE ADC081S051 The serial interface timing diagram for the ADC is shown in Figure 3. CS is chip select, which initiates conversions on the ADC and frames the serial data transfers. SCLK (serial clock) controls both the conversion process and the timing of serial data. SDATA is the serial data out pin, where a conversion result is found as a serial data stream. Basic operation of the ADC begins with CS going low, which initiates a conversion process and data transfer. Subsequent rising and falling edges of SCLK will be labelled with reference to the falling edge of CS; for example, "the third falling edge of SCLK" shall refer to the third falling edge of SCLK after CS goes low. At the fall of CS, the SDATA pin comes out of TRI-STATE and the converter moves from track mode to hold mode. The input signal is sampled and held for conversion on the falling edge of CS. The converter moves from hold mode to track mode on the 13th rising edge of SCLK (see Figure 3). It is at this point that the interval for the TACQ specification begins. At least 350ns must pass between the 13th rising edge of SCLK and the next falling edge of CS. The SDATA pin will be placed back into TRI-STATE after the 16th falling edge of SCLK, or at the rising edge of CS, whichever occurs first. After a conversion is completed, the quiet time (tQUIET) must be satisfied before bringing CS low again to begin another conversion. Sixteen SCLK cycles are required to read a complete sample from the ADC. The sample bits (including leading or trailing zeroes) are clocked out on falling edges of SCLK, and are intended to be clocked in by a receiver on subsequent rising edges of SCLK. The ADC will produce three leading zero bits on SDATA, followed by eight data bits, most significant first. After the data bits, the ADC will clock out four trailing zeros. If CS goes low before the rising edge of SCLK, an additional (fourth) zero bit may be captured by the next falling edge of SCLK. Determining Throughput Throughput depends on the frequency of SCLK and how much time is allowed to elapse between the end of one conversion and the start of another. At the maximum specified SCLK frequency, the maximum specified throughput is obtained by using a 20 SCLK frame. As shown in Figure 3, the minimum allowed time between CS falling edges is determined by 1) 12.5 SCLKs for Hold mode, 2) the larger of two quantities: either the minimum required time for Track mode (tACQ) or 2.5 SCLKs to finish reading the result and 3) 0, 1/2 or 1 SCLK padding to ensure an even number of SCLK cycles so there is a falling SCLK edge when CS next falls. For example, at the fastest rate for this family of parts, SCLK is 20MHz and 2.5 SCLKs are 125ns, so the minimum time between CS falling edges is calculated by 12.5*50ns + 350ns + 0.5*50ns = 1000ns (2) (12.5 SCLKs + tACQ + 1/2 SCLK) which corresponds to a maximum throughput of 1MSPS. At the slowest rate for this family, SCLK is 1MHz. Using a 20 cycle conversion frame as shown in Figure 3 yields a 20μs time between CS falling edges for a throughput of 50KSPS. It is possible, however, to use fewer than 20 clock cycles provided the timing parameters are met. With a 1MHz SCLK, there are 2500ns in 2.5 SCLK cycles, which is greater than tACQ. After the last data bit has come out, the clock will need one full cycle to return to a falling edge. Thus the total time between falling edges of CS is 12.5*1μs +2.5*1μs +1*1μs=16μs which is a throughput of 62.5KSPS. 14 Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 ADC081S051 www.ti.com SNAS309F – APRIL 2005 – REVISED JANUARY 2014 ADC081S051 TRANSFER FUNCTION The output format of the ADC is straight binary. Code transitions occur midway between successive integer LSB values. The LSB width for the ADC is VA/256. The ideal transfer characteristic is shown in Figure 20. The transition from an output code of 0000 0000 to a code of 0000 0001 is at 1/2 LSB, or a voltage of VA/512. Other code transitions occur at steps of one LSB. 111...111 111...000 | | ADC CODE 111...110 1 LSB = VA/256 011...111 000...010 | 000...001 000...000 1 LSB 0V ANALOG INPUT +VA-1 LSB Figure 20. Ideal Transfer Characteristic TYPICAL APPLICATION CIRCUIT A typical application of the ADC is shown in Figure 21. Power is provided in this example by the LP2950 lowdropout voltage regulator, available in a variety of fixed and adjustable output voltages. The power supply pin is bypassed with a capacitor network located close to the ADC. Because the reference for the ADC is the supply voltage, any noise on the supply will degrade device noise performance. To keep noise off the supply, use a dedicated linear regulator for this device, or provide sufficient decoupling from other circuitry to keep noise off the ADC supply pin. Because of the ADC's low power requirements, it is also possible to use a precision reference as a power supply to maximize performance. The three-wire interface is shown connected to a microprocessor or DSP. LP2950 1 PF VA VIN 0.1 PF 5V 1 PF 0.1 PF SCLK ADC081S051 CS SDATA MICROPROCESSOR DSP GND Figure 21. Typical Application Circuit Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 15 ADC081S051 SNAS309F – APRIL 2005 – REVISED JANUARY 2014 www.ti.com ANALOG INPUTS An equivalent circuit of the ADC's input is shown in Figure 22. Diodes D1 and D2 provide ESD protection for the analog inputs. At no time should the analog input go beyond (VA + 300 mV) or (GND − 300 mV), as these ESD diodes will begin to conduct, which could result in erratic operation. For this reason, the ESD diodes should not be used to clamp the input signal. The capacitor C1 in Figure 22 has a typical value of 4 pF, and is mainly the package pin capacitance. Resistor R1 is the on resistance of the track / hold switch, and is typically 500Ω. Capacitor C2 is the ADC sampling capacitor and is typically 26 pF. The ADC will deliver best performance when driven by a low-impedance source to eliminate distortion caused by the charging of the sampling capacitance. This is especially important when using the ADC to sample AC signals. Also important when sampling dynamic signals is an anti-aliasing filter. VA D1 R1 C2 26 pF VIN C1 4 pF D2 Conversion Phase - Switch Open Track Phase - Switch Closed Figure 22. Equivalent Input Circuit DIGITAL INPUTS AND OUTPUTS The ADC digital inputs (SCLK and CS) are not limited by the same maximum ratings as the analog inputs. The digital input pins are instead limited to +5.25V with respect to GND, regardless of VA, the supply voltage. This allows the ADC to be interfaced with a wide range of logic levels, independent of the supply voltage. MODES OF OPERATION The ADC has two possible modes of operation: normal mode, and shutdown mode. The ADC enters normal mode (and a conversion process is begun) when CS is pulled low. The device will enter shutdown mode if CS is pulled high before the tenth falling edge of SCLK after CS is pulled low, or will stay in normal mode if CS remains low. Once in shutdown mode, the device will stay there until CS is brought low again. By varying the ratio of time spent in the normal and shutdown modes, a system may trade-off throughput for power consumption, with a sample rate as low as zero. Normal Mode The fastest possible throughput is obtained by leaving the ADC in normal mode at all times, so there are no power-up delays. To keep the device in normal mode continuously, CS must be kept low until after the 10th falling edge of SCLK after the start of a conversion (remember that a conversion is initiated by bringing CS low). If CS is brought high after the 10th falling edge, but before the 16th falling edge, the device will remain in normal mode, but the current conversion will be aborted, and SDATA will return to TRI-STATE (truncating the output word). Sixteen SCLK cycles are required to read all of a conversion word from the device. After sixteen SCLK cycles have elapsed, CS may be idled either high or low until the next conversion. If CS is idled low, it must be brought high again before the start of the next conversion, which begins when CS is again brought low. After sixteen SCLK cycles, SDATA returns to TRI-STATE. Another conversion may be started, after tQUIET has elapsed, by bringing CS low again. Shutdown Mode Shutdown mode is appropriate for applications that either do not sample continuously, or it is acceptable to trade throughput for power consumption. When the ADC is in shutdown mode, all of the analog circuitry is turned off. 16 Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 ADC081S051 www.ti.com SNAS309F – APRIL 2005 – REVISED JANUARY 2014 To enter shutdown mode, a conversion must be interrupted by bringing CS high anytime between the second and tenth falling edges of SCLK, as shown in Figure 23. Once CS has been brought high in this manner, the device will enter shutdown mode, the current conversion will be aborted and SDATA will enter TRI-STATE. If CS is brought high before the second falling edge of SCLK, the device will not change mode; this is to avoid accidentally changing mode as a result of noise on the CS line. Figure 23. Entering Shutdown Mode Figure 24. Entering Normal Mode To exit shutdown mode, bring CS back low. Upon bringing CS low, the ADC will begin powering up (power-up time is specified in the Timing Specifications table). This microsecond of power-up delay results in the first conversion result being unusable. The second conversion performed after power-up, however, is valid, as shown in Figure 24. If CS is brought back high before the 10th falling edge of SCLK, the device will return to shutdown mode. This is done to avoid accidentally entering normal mode as a result of noise on the CS line. To exit shutdown mode and remain in normal mode, CS must be kept low until after the 10th falling edge of SCLK. The ADC will be fully powered-up after 16 SCLK cycles. POWER MANAGEMENT The ADC takes time to power-up, either after first applying VA, or after returning to normal mode from shutdown mode. This corresponds to one "dummy" conversion for any SCLK frequency within the specifications in this document. After this first dummy conversion, the ADC will perform conversions properly. Note that the tQUIET time must still be included between the first dummy conversion and the second valid conversion. When the VA supply is first applied, the ADC may power up in either of the two modes: normal or shutdown. As such, one dummy conversion should be performed after start-up, as described in the previous paragraph. The part may then be placed into either normal mode or the shutdown mode, as described in Sections 7.1 and 7.2. When the ADC is operated continuously in normal mode, the maximum specified throughput is fSCLK / 20 at the maximum specified fSCLK . Throughput may be traded for power consumption by running fSCLK at its maximum specified rate and performing fewer conversions per unit time, raising the ADC CS line after the 10th and before the 15th fall of SCLK of each conversion. A plot of typical power consumption versus throughput is shown in the Typical Performance Characteristics section. To calculate the power consumption for a given throughput, multiply the fraction of time spent in the normal mode by the normal mode power consumption and add the fraction of time spent in shutdown mode multiplied by the shutdown mode power consumption. Note that the curve of power consumption vs. throughput is essentially linear. This is because the power consumption in the shutdown mode is so small that it can be ignored for all practical purposes. Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 17 ADC081S051 SNAS309F – APRIL 2005 – REVISED JANUARY 2014 www.ti.com POWER SUPPLY NOISE CONSIDERATIONS The charging of any output load capacitance requires current from the power supply, VA. The current pulses required from the supply to charge the output capacitance will cause voltage variations on the supply. If these variations are large enough, they could degrade SNR and SINAD performance of the ADC. Furthermore, 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 is the noise coupled into the analog channel, degrading noise performance. To keep noise out of the power supply, keep the output load capacitance as small as practical. It is good practice to 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 maintain noise performance . 18 Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 ADC081S051 www.ti.com SNAS309F – APRIL 2005 – REVISED JANUARY 2014 REVISION HISTORY Changes from Revision D (March 2013) to Revision E • Page Changed layout of National Data Sheet to TI format .......................................................................................................... 18 Changes from Revision E (March 2013) to Revision F • Page Changed sentence in the "Using the ADC081S051" section ............................................................................................. 14 Submit Documentation Feedback Copyright © 2005–2014, Texas Instruments Incorporated Product Folder Links: ADC081S051 19 PACKAGE OPTION ADDENDUM www.ti.com 10-Dec-2020 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan (2) Lead finish/ Ball material MSL Peak Temp Op Temp (°C) Device Marking (3) (4/5) (6) ADC081S051CIMF/NOPB ACTIVE SOT-23 DBV 6 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 85 X15C ADC081S051CISD/NOPB ACTIVE WSON NGF 6 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 85 X6C (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of