CA3310AD

CA3310, CA3310A August 1997 CMOS, 10-Bit, A/D Converters with Internal Track and Hold Description The Intersil CA3310 is a fast, low power, 10-bit successive approximation analog-to-digital converter, with microprocessorcompatible outputs. It uses only a single 3V to 6V supply and typically draws just 3mA when operating at 5V. It can accept full rail-to-rail input signals, and features a built-in track and hold. The track and hold will follow high bandwidth input signals, as it has only a 100ns (typical) input time constant. The ten data outputs feature full high-speed CMOS threestate bus driver capability, and are latched and held through a full conversion cycle. Separate 8 MSB and 2 LSB enables, a data ready flag, and conversion start and ready reset inputs complete the microprocessor interface. An internal, adjustable clock is provided and is available as an output. The clock may also be driven from an external source. Features • CMOS Low Power (Typ). . . . . . . . . . . . . . . . . . . . .15mW • Single Supply Voltage . . . . . . . . . . . . . . . . . . . . 3V to 6V • Conversion Time . . . . . . . . . . . . . . . . . . . . . . . . . . . 13µs • Built-In Track and Hold • Rail-to-Rail Input Range • Latched Three-state Output Drivers • Microprocessor-Compatible Control Lines • Internal or External Clock Applications • Fast, No-Droop, Sample and Hold • Voice Grade Digital Audio • DSP Modems • Remote Low Power Data Acquisition Systems • µP Controlled Systems Ordering Information PART NUMBER CA3310E CA3310AE CA3310M CA3310AM CA3310D CA3310AD LINEARITY TEMP. (INL, DNL) RANGE (oC) ±0.75 LSB ±0.5 LSB ±0.75 LSB ±0.5 LSB ±0.75 LSB ±0.5 LSB -40 to 85 -40 to 85 -40 to 85 -40 to 85 -55 to 125 -55 to 125 PACKAGE 24 Ld PDIP 24 Ld PDIP 24 Ld SOIC 24 Ld SOIC 24 Ld SBDIP 24 Ld SBDIP PKG. NO. E24.6 E24.6 M24.3 M24.3 D24.6 D24.6 Pinout CA3310, CA3310A (PDIP, SBDIP, SOIC) TOP VIEW D0 (LSB) D1 D2 D3 D4 D5 D6 D7 D8 D9 (MSB) DRDY VSS (GND) 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 VDD VIN VREF + REXT CLK STRT VREF VAA+ VAAOEL OEM DRST CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 321-724-7143 | Copyright © Intersil Corporation 1999 File Number 3095.1 6-6 CA3310, CA3310A Functional Block Diagram STRT VDD VSS VIN ALL LOGIC CONTROL AND TIMING CLOCK REXT CLK DRDY Q CLK CLR DRST VREF + 16C OEM D9 (MSB) 50Ω SUBSTRATE RESISTANCE 8C D8 4C D7 2C VAA + VAA - D6 C 32 C 31 16C 10-BIT SUCCESSIVE APPROXIMATION REGISTER 10-BIT EDGE TRIGGERED “D” LATCH D5 D4 8C D3 4C D2 2C D1 C D0 (LSB) C OEL VREF - 6-7 CA3310, CA3310A Typical Application Schematics +5V SUPPLY 4.7µF TAN 8 3 100Ω ±10% ICL7663S 1 6 ADJUST GAIN 4 A R2 A R1 + VIN R4 4 3 + 7 8 6 5 1 10K R5 47pF D ADJUST OFF SET R3 100 0.1 +8V TO +15V A 5 A A VAA DRDY A OPTIONAL CLAMP VDD VIN CLK REXT VSS UNLESS NOTED, ALL RESISTORS = 1% METAL FILM, POTS = 10 TURN, CERMET D = DIGITAL GROUND A = ANALOG GROUND 2MHz CLOCK NC DATA READY FLAG 4.5V 75V 5K 28.7K 4.7µF + TAN A OEM VREF OEL CA3310/A D0 - D9 VREF + STRT DRST START CONVERSATION RESET FLAG HIGH BYTE ENABLE LOW BYTE ENABLE OUTPUT DATA + A 0.1µF CER VAA + VDD D 2 CA3140 - 0.1 -1V TO -15V A 100 A D INPUT RANGE 0V TO 2.5V 0V TO 5V 0V TO 10V -2.5V TO +2.5V -5V TO +5V R1 4.99K 4.99K 10K 4.99K 10K R2 9.09K 4.53K 4.53K 9.09K 9.09K R3 OPEN OPEN OPEN 9.09K 9.09K R4 4.99K 4.99K 10K 4.99K 10K R5 9.09K 4.53K 4.53K 4.53K 4.53K 6-8 CA3310, CA3310A Absolute Maximum Ratings Digital Supply Voltage VDD. . . . . . . . . . . . . . . VSS -0.5V to VSS +7V Analog Supply Voltage (VAA+) . . . . . . . . . . . . . . . . . . . . . VDD ±0.5V Any Other Terminal . . . . . . . . . . . . . . . . .VSS -0.5V to VDD + 0.5V DC Input Current or Output (Protection Diode) Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±20mA DC Output Drain Current, per Output . . . . . . . . . . . . . . . . . . ±35mA Total DC Supply or Ground Current . . . . . . . . . . . . . . . . . . . ±70mA Thermal Information Thermal Resistance (Typical, Note 1) θJA (oC/W) θJC (oC/W) PDIP Package . . . . . . . . . . . . . . . . . . . . . 75 N/A SBDIP Package . . . . . . . . . . . . . . . . . . . . 70 22 SOIC Package . . . . . . . . . . . . . . . . . . . . . 75 N/A Maximum Junction Temperature Plastic Packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150oC Hermetic Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175oC Maximum Storage Temperature (TSTG) . . . . . . . . . .-65oC to 150oC Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . 300oC (SOIC - Lead Tips Only) Operating Conditions Temperature Range (TA) Package Type D . . . . . . . . . . . . . . . . . . . . . . . . . . -55oC to 125oC Package Type E, M . . . . . . . . . . . . . . . . . . . . . . . . . -40oC to 85oC CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. NOTE: 1. θJA is measured with the component mounted on an evaluation PC board in free air. Electrical Specifications PARAMETER TA = 25oC, VDD = VAA+ = 5V, VREF + = 4.608V, VSS = VAA- = VREF - = GND, CLK = External 1MHz, Unless Otherwise Specified TEST CONDITIONS MIN TYP MAX UNITS ACCURACY (See Text For Definitions) Resolution Differential Linearity Error CA3310 CA3310A Integral Linearity Error CA3310 CA3310A Gain Error CA3310 CA3310A Offset Error CA3310 CA3310A ANALOG OUTPUT Input Resistance Input Capacitance Input Capacitance Input Current In Series with Input Sample Capacitors During Sample State During Hold State At VIN = VREF + = 5V At VIN = VREF - = 0V Static Input Current STRT = V+, CLK = V+ At VIN = VREF + = 5V At VIN = VREF - = 0V Input + Full-Scale Range Input - Full-Scale Range Input Bandwidth (Note 2) (Note 2) From Input RC Time Constant VREF - +1 VSS -0.3 330 300 20 1.5 +300 -100 1 -1 VDD +0.3 VREF + -1 Ω pF pF µA µA µA µA V V MHz 10 ±0.5 ±0.25 ±0.5 ±0.25 ±0.25 ±0.25 ±0.75 ±0.5 ±0.75 ±0.5 ±0.5 ±0.25 ±0.5 ±0.25 Bits LSB LSB LSB LSB LSB LSB LSB LSB DIGITAL INPUTS DRST, OEL, OEM, STRT, CLK High-Level Input Voltage Low-Level Input Voltage Input Leakage Current Input Capacitance Input Current Over VDD = 3V to 6V (Note 2) Over VDD = 3V to 6V (Note 2) Except CLK (Note 2) CLK Only (Note 2) 70 30 ±1 10 ±400 % of VDD % of VDD µA pF µA 6-9 CA3310, CA3310A Electrical Specifications PARAMETER DIGITAL OUTPUTS D0 - D9, DRDY High-Level Output Voltage Low-Level Output Voltage Three-State Leakage Output Capacitance CLK OUTPUT High-Level Output Voltage Low-Level Output Voltage TIMING Clock Frequency Internal, CLK and REXT Open Internal, CLK Shorted to REXT External, Applied to CLK (Note 2) (Max) (Min) Clock Pulse Width, tLOW , tHIGH Conversion Time Aperture Delay, tD APR Clock to Data Ready Delay, tD1 DRDY Clock to Data Ready Delay, tD2 DRDY Clock to Data Delay, tD Data Start Removal Time, tR STRT Start Setup Time, tSU STRT Start Pulse Width, tW STRT Start to Data Ready Delay, tD3 DRDY Clock Delay from Start, tD CLK Ready Reset Removal Time, tR DRST Ready Reset Pulse Width, tW DRST Ready Reset to Data Ready Delay, tD4 DRDY Output Enable Delay, tEN Output Disable Delay, tDIS SUPPLIES Supply Operating Range, VDD or VAA Supply Current, IDD + IAA Supply Standby Current Analog Supply Rejection Reference Input Current TEMPERATURE DEPENDENCY Offset Drift Gain Drift Internal Clock Speed NOTES: 1. A (-) removal time means the signal can be removed after the reference signal. 2. Parameter not tested, but guaranteed by design or characterization. At 0 to 1 Code Transition At 1022 to 1023 Code Transition See Figure 7 -4 -6 -0.5 µV/ oC µV/ oC %/ oC (Note 2) See Figures 14, 15 Clock Stopped During Cycle 1 At 120Hz, See Figure 13 See Figure 10 3 3 3.5 25 160 6 8 V mA mA mV/V µA External, Applied to CLK: See Figure 1 (Note 2) Internal, CLK Shorted to REXT See Figure 1 See Figure 1 See Figure 1 See Figure 1 See Figures 3 and 4 (Note 1) See Figure 4 See Figures 3 and 4 See Figures 3 and 4 See Figure 3 See Figure 50 (Note 1) See Figure 5 See Figure 5 See Figure 2 See Figure 2 200 600 100 100 13 300 800 4 10 100 150 250 200 -120 160 10 170 200 -80 10 35 40 50 400 1000 2 kHz kHz MHz kHz ns µs ns ns ns ns ns ns ns ns ns ns ns ns ns ns ISOURCE = 100µA (Note 2) ISlNK = 100µA (Note 2) 4 1 V V ISOURCE = - 4mA ISINK = 6mA Except DRDY Except DRDY (Note 2) 4.6 0.4 ±1 20 V V µA pF TA = 25oC, VDD = VAA+ = 5V, VREF + = 4.608V, VSS = VAA- = VREF - = GND, CLK = External 1MHz, Unless Otherwise Specified (Continued) TEST CONDITIONS MIN TYP MAX UNITS 6-10 CA3310, CA3310A Timing Diagrams 1 2 3 4 5 - 12 13 1 2 3 CLK tHIGH tLOW tD2 DRDY DRDY tD1 DRDY tD DATA D0 - D9 DATA N - 1 DATA N HOLD INPUT TRACK N TRACK N + 1 tD APR FIGURE 1. FREE RUNNING, STRT TIED LOW, DRST TIED HIGH OEL OR OEM tEN D0 - D1 OR D2- D9 OFF TO HIGH OFF TO LOW 50% 10% 50% tDIS 90% ZL = 50pF TO GND 1kΩ TO GND ZL = 50pF TO GND 1kΩ TO VDD TO OUTPUT PIN FIGURE 2. OUTPUT ENABLE/DISABLE TIMING DIAGRAM 13 CLK (INTERNAL) 1 2 3 4 5 tD CLK tR STRT tW STRT STRT DON’T CARE tD3 DRDY DRDY HOLD INPUT TRACK HOLD FIGURE 3. STRT PULSED LOW, DRST TIED HIGH, INTERNAL CLOCK 6-11 CA3310, CA3310A Timing Diagrams (Continued) 13 CLK (EXTERNAL) tSU STRT tR STRT STRT tW STRT DON’T CARE tD3 DRDY DRDY 1 2 2 2 3 4 5 HOLD INPUT TRACK HOLD FIGURE 4. STRT PULSED LOW, DRST TIED HIGH, EXTERNAL CLOCK 13 CLK (INTERNAL OR EXTERNAL) 1 DON’T CARE tR DRST tW DRST DRST tD4 DRDY DRDY FIGURE 5. DRST PULSED LOW, STRT TIED HIGH Typical Performances Curves 800 700 5V 600 CLOCK FREQUENCY (kHz) 4V 500 400 3V 300 200 100 0 SHORT 10 100 1000 OPEN EXTERNAL RESISTANCE (kΩ) VDD = 6V VDD = 6V VDD = 3V - 6V = VAA+ CLOCK FREQUENCY NORMALIZED TO +5V, 25oC OPERATION, REXT = OPEN 5 VDD = VAA+ = 3V - 6V INTERNAL CLOCK MAY NOT WORK AT VDD < 4V FOR TEMPERATURE < -40oC REXT = SHORTED REXT = OPEN VDD = 6V 5V 4 3 4V 2 6V 5V 3V 1 4V 0 -55 -40 0 25 85 TEMPERATURE (oC) 125 3V FIGURE 6. INTERNAL CLOCK FREQUENCY vs EXTERNAL RESISTANCE FIGURE 7. INTERNAL CLOCK FREQUENCY vs TERMPERATURE AND SUPPLY VOLTAGE 6-12 CA3310, CA3310A Typical Performances Curves +80 +60 PEAK INPUT CURRENT (mA) VAA+ = 3 - 6V VAA+ = VDD = VREF + VAA+ = 6V PEAK INPUT CURRENT (mA) (Continued) +60 +50 +40 +30 +20 +10 0 -10 -20 5V VAA = 6V 0 1 2 3 4 5 6 INPUT VOLTAGE (V) 7 8 9 10 3V 4V VAA+ = 3 - 6V VAA+ = VDD = VREF+ CLOCK = INTERNAL, FREE RUNNING +40 (+) IPEAK +20 3V 0 6V (-) IPEAK -40 0 1 2 3 4 5 INPUT VOLTAGE (V) 6 7 4V 5V -20 FIGURE 8. PEAK INPUT CURRENT vs INPUT VOLTAGE 80 VREF+ CURRENT AVERAGE (µA) VAA+ = VDD = VREF+ CLOCK INTERNAL, FREE RUNNING IAVE 30 IPEAK 40 20 VREF+ CURRENT PEAK, mA FIGURE 9. AVERAGE INPUT CURRENT vs INPUT VOLTAGE 40 60 NORMALIZED ERROR 5 GAIN 4 3 OFFSET 2 DLE 1 ILE 0 1 2 3 4 5 20 10 0 0 1 2 3 4 5 6 VREF+ VOLTAGE (V) 7 8 9 0 REFERENCE VOLTAGE (V) FIGURE 11. NORMALIZED GAIN, OFFSET, INTEGRAL AND DIFFERENTIAL LINEARITY ERRORS vs REFERENCE VOLTAGE SENSITIVITY, REFERRED TO INPUT (mV/V) 1000 VDD = VAA = VREF + = 5V fCLOCK = 1MHz FIGURE 10. VREF+ CURRENT vs VREF+ VOLTAGE 8 7 NORMALIZED ERROR 6 5 ILE 4 3 2 1 GAIN 0 0.1 1 2 3 4 5 CLOCK FREQUENCY (MHz) OFFSET DLE VIN = (+) FULL SCALE 100 VIN = (-) FULL SCALE 10 100 1000 10,000 100,000 VAA , RIPPLE FREQUENCY (Hz) FIGURE 12. NORMALIZED GAIN, OFFSET, INTEGRAL AND DIFFERENTIAL LINEARITY ERRORS vs CLOCK SPEED FIGURE 13. VAA SUPPLY SENSITIVITY 6-13 CA3310, CA3310A Typical Performances Curves 12 SUPPLY CURRENT (IDD +IAA) (mA) VDD = VAA = VREF = 3 - 6V LOAD = 50pF/OUTPUT CONTINUOUS CONVERSIONS (Continued) 8 VDD = 3-6V 7 6 5 4 3 2 1 4V, OPEN 5V, OPEN 5V, SHORT VDD = 6V, REXT = OPEN AND REXT = OPEN OR SHORTED. CLOCK = INTERNAL, FREE RUNNING VDD = VAA+ VDD = 6V, REXT = SHORT SUPPLY CURRENT IDD +IAA (mA) 10 8 6V 6 4 5V 4V 3V 2 4V, SHORT 3V, OPEN 3V, SHORT 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 CLOCK FREQUENCY (MHz) 0 -50 -40 0 25 85 125 TEMPERATURE (oC) FIGURE 14. SUPPLY CURRENT vs CLOCK FREQUENCY FIGURE 15. SUPPLY CURRENT vs TEMPERATURE TABLE 1. PIN DESCRIPTIONS PIN NUMBER 1-10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 NAME D0 - D9 DRDY VSS DRST OEM OEL VAAVAA+ VREF STRT CLK REXT VREF + VlN VDD DESCRIPTION Three-State outputs for data bits representing 20 (LSB) through 29 (MSB). Output flag signifying new data is available. Goes high at end of clock period 13, goes low when new conversion started. Also reset asynchronously by DRST. Digital Ground. Active low input, resets DRDY. Active low input, three-state enable of D2 - D9. Active low input, three-state enable of D0, D1. Analog Ground. Analog + Supply. Reference input voltage, sets 0 code (-) end of input range. Active Low Start Conversion Input. Recognized after end of clock period 13. Clock input or output. Conversion functions are synchronous to high-going edge. Clock adjust input when using internal clock. Reference input voltage, set 1023 code (+) end of input range. Analog Input. Digital + Supply. TABLE 2. OUTPUT CODES CODE DESCRIPTION ( V REF+ – V REF- ) LSB = --------------------------------------------1024 INPUT VOLTAGE (NOTE 1) ( V REF+ – V REF- ) = 4.608V (V) 0.000 0.0045 1.152 2.304 3.456 4.6035 BINARY OUTPUT CODE MSB D9 0 0 0 1 1 1 D8 0 0 1 0 1 1 D7 0 0 0 0 0 1 D6 0 0 0 0 0 1 D5 0 0 0 0 0 1 D4 0 0 0 0 0 1 D3 0 0 0 0 0 1 D2 0 0 0 0 0 1 D1 0 0 0 0 0 1 LSB D0 0 1 0 0 0 1 DECIMAL COUNT 0 1 256 512 768 1023 Zero 1 LSB 1/ (V 4 REF+ - VREF -) 1/ (V 2 REF+ - VREF -) 3/ (V 4 REF+ - VREF -) (VREF+ - VREF -) - 1 LSB NOTE: 1. The voltages listed above are the ideal centers of each output code shown as a function of its associated reference voltage. 6-14 CA3310, CA3310A Device Operation The CA3310 is a CMOS 10-bit, analog-to-digital converter that uses capacitor-charge balancing to successively approximate the analog input. A binarily weighted capacitor network forms the D-to-A “Heart” of the device. See the Functional Diagram of the CA3310. The capacitor network has a common node which is connected to a comparator. The second terminal of each capacitor is individually switchable to the input, VREF + or VREF -. During the first three clock periods of a conversion cycle, the switchable end of every capacitor is connected to the input. The comparator is being auto-balanced at its trip point, thus setting the voltage at the capacitor common node. During the fourth period, all capacitors are disconnected from the input, the one representing the MSB (D9) is connected to the VREF + terminal, and the remaining capacitors to VREF -. The capacitor-common node, after the charges balance out, will represent whether the input was above or below 1/2 of (VREF + - VREF). At the end of the fourth period, the comparator output is stored and the MSB capacitor is either left connected to VREF + (if the comparator was high) or returned to VREF -. This allows the next comparison to be at either 3/4 or 1/4 of (VREF + - VREF -). At the end of periods 5 through 12, capacitors representing the next to MSB (D8) through the next to LSB (D1) are tested, the result stored, and each capacitor either left at VREF + or at VREF -. At the end of the 13th period, when the LSB (D0) capacitor is tested, D0 and all the previous results are shifted to the output registers and drivers. The capacitors are reconnected to the input, the comparator returns to the balance state, and the data-ready output goes active. The conversion cycle is now complete. Clock The CA3310 can operate either from its internal clock or from one externally supplied. The CLK pin functions either as the clock output or input. All converter functions are synchronous with the rising edge of the clock signal. Figure 16 shows the configuration of the internal clock. The clock output drive is low power: if used as an output, it should not have more than 1 CMOS gate load applied, and wiring capacitance should be kept to a minimum. INTERNAL ENABLE The REXT pin allows adjusting of the internal clock frequency by connecting a resistor between REXT and CLK. Figure 6 shows the typical relationship between the resistor and clock speed, while Figure 7 shows clock speed versus temperature and supply voltage. The internal clock will shut down if the A/D is not restarted after a conversion. This is described under Control Timing. The clock could also be shut down with an open collector driver applied to the CLK pin. This should only be done during the sample portion (the first three periods) of a conversion cycle, and might be useful for using the device as a digital sample and hold: this is described further under Applications. If an external clock is supplied to the CLK pin, it must have sufficient drive to overcome the internal clock source. The external clock can be shut off, but again only during the sample portion of a conversion cycle. At other times, it must be above the minimum frequency shown in the specifications. If the internal or external clock was shut off during the conversion time (clock cycles 4 through 13) of the A/D, the output might be invalid due to balancing capacitor droop. An external clock must also meet the minimum tLOW and tHIGH times shown in the specifications. A violation may cause an internal miscount and invalidate the results. Control Signals The CA3310 may be synchronized from an external source by using the STRT (Start Conversion) input to initiate conversions, or if STRT is tied low, may be allowed to free-run. In the free-running mode, illustrated in Figure 1, each conversion takes 13 clock periods. The input is tracked from clock period 1 through period 3, then disconnected as the successive approximation takes place. After the start of the next period 1 (specified by TD data), the output is updated. The DRDY (Data Ready) status output goes high (specified by tD1 DRDY) after the start of clock period 1, and returns low (specified by tD2 DRDY) after the start of clock period 2. DRDY may also be asynchronously reset by a low on DRST (to be discussed later). If the output data is to be latched externally by the DRDY signal, the trailing edge of DRDY should be used: there is no guaranteed set-up time to the leading edge. The 10 output data bits are available in parallel on threestate bus driver outputs. When low, the OEM input enables the most significant byte (D2 through D9) while the OEL input enables the two least significant bits (D0, D1). tEN and tDIS specify the output enable and disable times, respectively. See Figure 2. When the STRT input is used to initiate conversions, operation is slightly different depending on whether an internal or external clock is used. OPTIONAL EXTERNAL CLOCK CLK INTERNAL CLOCK OPTIONAL CLOCK ADJUST REXT 50K 100K 18pF FIGURE 16. CLOCK CIRCUITRY Figure 3 illustrates operation with an internal clock. If the STRT signal is removed (at least tR STRT) before clock period 1, and is not reapplied during that period, the clock 6-15 CA3310, CA3310A will shut off after entering period 2. The input will continue to track the DRDY output will remain high during this time. A low signal applied to STRT (at least tW STRT wide) can now initiate a new conversion. The STRT signal (after a delay of tD3 DRDY) will cause the DRDY flag to drop, and (after a delay of tD CLK) cause the clock to restart. Depending on how long the clock was shut off, the low portion of clock period 2 may be longer than during the remaining cycles. The input will continue to track until the end of period 3, the same as when free-running. Figure 4 illustrates the same operation as above, but with an external clock. If STRT is removed (at least tR STRT) before clock period 1, and not reapplied during that period, the clock will continue to cycle in period 2. A low signal applied to STRT will drop the DRDY flag as before, and with the first positive-going clock edge that meets the tSU STRT set-up time, the converter will continue with clock period 3. The DRDY flag output, as described previously, goes active at the start of period 1, and drops at the start of period 2 or upon a new STRT command, whichever is later. It may also be controlled with the DRST (Data Ready Reset) input. Figure 5 depicts this operation. DRST must be removed (at least tR DRST) before the start of period 1 to allow DRDY to go high. A low level on DRST (at least tW DRST wide) will (after a delay of tD4 DRDY) drop DRDY. Analog Input The analog input pin is a predominantly capacitive load that changes between the track and hold periods of a conversion cycle. During hold, clock period 4 through 13, the input loading is leakage and stray capacitance, typically less than 0.1µA and 20pF. At the start of input tracking, clock period 1, some charge is dumped back to the input pin. The input source must have low enough impedance to dissipate the charge by the end of the tracking period. The amount of charge is dependent on supply and input voltages. Figure 8 shows typical peak input currents for various supply and input voltages, while Figure 9 shows typical average input currents. The average current is also proportional to clock frequency, and should be scaled accordingly. During tracking, the input appears as approximately a 300pF capacitor in series with 330Ω, for a 100ns time constant. A full-scale input swing would settle to 1/2 LSB (1/2048) in 7RC time constants. Doing continuous conversions with a 1MHz clock provides 3µs of tracking time, so up to 1kΩ of external source impedance (400ns time constant) would allow proper settling of a step input. If the clock was slower, or the converter was not restarted immediately (causing a longer sample lime), a higher source impedance could be used. The CA3310s low-input time constant also allows good tracking of dynamic input waveforms. The sampling rate with a 1MHz clock is approximately 80kHz. A Nyquist rate (fSAMPLE/2) input sine wave of 40kHz would have negligible attenuation and a phase lag of only 1.5 degrees. Accuracy Specifications The CA3310 accepts an analog input between the values of VREF - and VREF +, and quantizes it into one of 210 or 1024 output codes. Each code should exist as the input is varied through a range of 1/1024 X (VREF+ - VREF -), referred to as 1 LSB of input voltage. A differential Iinearity error, illustrated in Figure 17, occurs if an output code occurs over other than the ideal (1 LSB) input range. Note that as long as the error does not reach -1 LSB, the converter will not miss any codes. UNIFORM TRANSFER CURVE A B OUTPUT CODE C ACTUAL TRANSFER CURVE A = IDEAL 1 LSB STEP B-A = + DIFFERENTIAL LINEARITY ERROR A-C = - DIFFERENTIAL LINEARITY ERROR INPUT VOLTAGE FIGURE 17. DIFFERENTIAL LINEARITY ERROR The CA3310 output should change from a code of 00016 to 00116 at an input voltage of (VREF - +1 LSB). It should also change from a code of 3FE16 to 3FF16 at an input of (VREF + -1 LSB). Any differences between the actual and expected input voltages that cause these transitions are the offset and gain errors, respectively. Figure 18 illustrates these errors. As the input voltage is increased linearly from the point that causes the 00016 to 00116 transition to the point that causes the 3FE16 to 3FF16 transition, the output code should also increase linearly. Any deviation from this input-to-output correspondence is integral linearity error, illustrated in Figure 19. Note that the integral linearity is referenced to a straight line drawn through the actual end points, not the ideal end points. For absolute accuracy to be equal to the integral linearity, the gain and offset would have to be adjusted to ideal. Offset and Gain Adjustments The VREF + and VREF - pins, references for the two ends of the analog input range, are the only means of doing offset or gain adjustments. In a typical system, the VREF - might be returned to a clean ground, and offset adjustment done on an input amplifier. VREF + would then be adjusted for gain. VREF - could be raised from ground to adjust offset or to accommodate an input source that can’t drive down to ground. There are current pulses that occur, however, during the successive approximation part of a conversion cycle, as the charge-balancing capacitors are switched between VREF - and VREF +. For that reason, VREF - and VREF + should be well bypassed. Figure 10 shows peak and average VREF + current. 6-16 CA3310, CA3310A 3FF 3FE OUTPUT CODE (HEX) EXPECTED TRANSFER CURVE OFFSET ERROR 002 GAIN ERROR ACTUAL TRANSFER CURVE 001 000 0 1 2 1022 1023 1024 1024 1024 1024 INPUT VOLTAGE AS A FRACTION OF (VREF + - VREF -) 1 FIGURE 18. GAIN AND OFFSET ERROR 3FF 3FE ACTUAL TRANSFER CURVE IDEAL TRANSFER CURVE OUTPUT CODE (HEX) INTEGRAL LINEARITY ERROR 001 000 OFFSET POINT INPUT VOLTAGE GAIN POINT FIGURE 19. NORMALIZED GAIN, OFFSET, INTEGRAL AND DIFFERENTIAL LINEARITY ERRORS vs REFERENCE VOLTAGE 6-17 CA3310, CA3310A Other Accuracy Effects Linearity, offset, and gain errors are dependent on the magnitude of the full-scale input range, VREF + - VREF -. Figure 11 shows how these errors vary with full-scale range. The clocking speed is a second factor that affects conversion accuracy. Figure 12 shows the typical variation of linearity, offset, and gain errors versus clocking speed. Gain and offset drift due to temperature are kept very low by means of auto-balancing the comparator. The specifications show typical offset and gain dependency on temperature. There is also very little linearity change with temperature, only that caused by the slight slowing of CMOS with increasing temperature. At 85oC, for instance, the lLE and DLE would be typically those for a 20% faster clock than at 25oC. Power Supplies and Grounding VDD(+) and VSS(GND) are the digital supply pins: they operate all internal logic and the output drivers. Because the output drivers can cause fast current spikes in the VDD and VSS lines, VSS should have a low impedance path to digital ground and VDD should be well bypassed. Except for VDD +, which is a substrate connection to VDD , all pins have protection diodes connected to VDD and VSS : input transients above VDD or below VSS will get steered to the digital supplies. Current on these pins must be limited by external means to the values specified under maximum ratings. The VAA + and VAA - terminals supply the charge-balancing comparator only. Because the comparator is autobalanced between conversions, it has good low frequency supply rejection. It does not reject well at high frequencies, however: VAA - should be returned to a clean analog ground, and VAA + should be RC decoupled from the digital supply. There is approximately 50Ω of substrate impedance between VDD and VAA +. This can be used, for example, as part of a low-pass RC filter to attenuate switching supply noise. A 10pF capacitor from VAA + to ground would attenuate 30kHz noise by approximately 40dB. Note that back-to-back diodes should be placed from VDD to VAA + to handle supply to capacitor turn-on or turn-off current spikes. Figure 16 shows VAA + supply rejection versus frequency. Note that the frequency to be rejected scales with the clock: the 100Hz rejection with a 100kHz clock would be roughly equivalent to the 1kHz rejection with a 1MHz clock. The supply current for the CA3310 is dependent on clock frequency, supply voltage, and temperature. Figure 14 shows the typical current versus frequency and voltage, while Figure 15 shows it versus temperature and voltage. Note that if stopped in auto-balance, the supply current is typically somewhat higher than if free-running. See Specifications. Application Circuits Differential Input A/D System As the CA3310 accepts a unipolar positive-analog input, the accommodation of other ranges requires additional circuitry. The input capacitance and the input energy also force using a low-impedance source for all but slow speed use. Figure 20 shows the CA3310 with a reference, input amplifier, and input-scaling resistors for several input ranges. The ICL7663S regulator was chosen as the reference, as it can deliver less than 0.25V input-to-output (dropout) voltage and uses very little power. As high a reference as possible is generally desirable, resulting in the best linearity and rejection of noise at the CA3310. The tantalum capacitor sources the VREF current spikes during a conversion cycle. This relieves the response and peak current requirements of the reference. The CA3140 operational amplifier provides good slewing capability for high bandwidth input signals and can quickly settle the energy that the CA3310 outputs at its VlN terminal. It can also drive close to the negative supply rail. If system supply sequencing or an unknown input voltage is likely to cause the operational amplifier to drive above the VDD supply, a diode clamp can be added from pin 8 of the operational amplifier to the VDD supply. The minus drive current is low enough not to require protection. With a 2MHz clock (~150kHz sampling), Nyquist criteria would give a maximum input bandwidth of 75kHz. The resistor values chosen are low enough to not seriously degrade system bandwidth (an operational amplifier settling) at that clock frequency. If A/D clock frequency and bandwidth requirements are lower, the resistor values (and input impedance) can be made correspondingly higher. The A/D system would generally be calibrated by tying VlN - to ground and applying a voltage to VIN + that is 0.5 LSB (1/2048 of full-scale range) above ground. The operational amplifier offset should be adjusted for an output code dithering between 00016 and 00116 for unipolar use, or 10016 and 10116 for bipolar use. The gain would then be adjusted by applying a voltage that is 1.5 LSB below the positive full scale input, and adjusting the reference for an output dithering between 3FE16 and 3FF16 . Note that R1 through R5 should be very well matched, as they affect the common-mode rejection of the A/D system. Also, if R2 and R3 are not matched, the offset adjust of the operational amplifier may not have enough adjustment range in bipolar systems. The common-mode input range of the system is set by the supply voltage available to the operational amplifier. The range that can be applied to the VIN - terminal can be calculated by:  R4 + 1 ------ R5   R4 + 1 ------ R5  VIN- for the most negative, (VIN+ -2.5V) - ( ------- )VREF+ for the most positive. R4 R5 6-18 CA3310, CA3310A Single +5V Supply If only a single +5V supply is available, an ICL7660 can be used to provide approximately +8V and -4V to the operational amplifier. Figure 20 shows this approach. Note that the converter and associated capacitors should be grounded to the digital supply. The 1kΩ in series with each supply at the operational amplifier isolates digital and analog grounds. +5V 10Ω 8 2 + ICL7660S 4 5 D -4V + D ALL CAPACITORS - 10µF, 10V D = DIGITAL GROUND + IN914 D + + +8V end as it goes positive. Ten cycles later, the conversion will be complete, and DRDY will go active. Operating and Handling Considerations HANDLING All inputs and outputs of Intersil CMOS devices have a network for electrostatic protection during handling. Recommended handling practices for CMOS devices are described in lCAN-6526, “Guide to Better Handling and Operation of CMOS Integrated Circuits”. OPERATING Operating Voltage During operation near the maximum supply voltage limit, care should be taken to avoid or suppress power supply turn-on and turn-off transients, power supply ripple, or ground noise; any of these conditions must not cause VDD - VSS to exceed the absolute maximum rating. Input Signals To prevent damage to the input protection circuit, input signals should never be greater than VDD +0.3V nor less than VSS -0.3V. Input currents must not exceed 20mA even when the power supply is off. Unused Inputs A connection must be provided at every input terminal. All unused Input terminals must be connected to either VDD or VSS , whichever is appropriate. Output Short Circuits Shorting of outputs to VDD or VSS may damage CMOS devices by exceeding the maximum device dissipation. 3 D Digital Sample and Hold With a minimum of external logic, the CA3310 can be made to wait at the verge of ending a sample. A start pulse will then, after the internal aperture delay, capture the input and finish the conversion cycle. Figure 21 illustrates this application. The CA3310 is connected as if to free run. The Data Ready signal is shifted through a CD74HC175, and at the low-going clock edge just before the sample would end, is used to hold the clock low. The same signal, active high, is available to indicate the CA3310 is ready to convert. A low pulse to reset the CD74HC175 will now release the clock, and the sample will CA3310/A +5V D A VREF + A ANALOG INPUT INPUT BUFFED AS REQUIRED VIN VREF VAA A VSS D OEL OEM DRDY REXT CLK IN914 1/16 CD74HCO4E READY TO CONVERT D2 Q2 Q2 VDD CP KEEP CAPACITANCE AT REXT/CLK NODE AS LOW AS POSSIBLE D = DIGITAL GROUND A = ANALOG GROUND CD74HC175E GND D3 D NC Q0 Q1 Q3 Q3 MR D START CONVERT +5V DATA READY OUTPUT ENABLES VDD VAA + D0 - D9 FULL SCALE REFERENCE DRST STRT D DATA TO SYSTEM +5V D0 Q0 D1 Q1 FIGURE 20. DIGITAL TRACK-AND-HOLD BLOCK DIAGRAM 6-19 CA3310, CA3310A All Intersil semiconductor products are manufactured, assembled and tested under ISO9000 quality systems certification. Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. 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