MAX152CAP+

19-0119; Rev. 1; 12/93 l nua a M Kit eet ion ata Sh t a u l D Eva llows Fo +3V, 8-Bit ADC with 1µA Power-Down The MAX152 high-speed, microprocessor (µP)-compatible, 8-bit analog-to-digital converter (ADC) uses a half-flash technique to achieve a 1.8µs conversion time, and digitizes at a rate of 400k samples per second (ksps). It operates with single +3V or dual ±3V supplies and accepts either unipolar or bipolar inputs. –————————– A P O W E R D O W N pin reduces current consumption to a typical value of 1µA. The part returns from powerdown and acquires an input signal in less than 900ns, providing large reductions in supply current in applications with burst-mode input signals. The MAX152 is DC and dynamically tested. Its µP interface appears as a memory location or input/output port that requires no external interface logic. The data outputs use latched, three-state buffered circuitry for direct connection to a µP data bus or system input port. The ADC's input/reference arrangement enables ratiometric operation. A fullyassembled evaluation kit provides a proven PC board layout to speed prototyping and design. _______________________Applications ___________________________Features ♦ Single +3.0V to +3.6V Supply ♦ 1.8µs Conversion Time ♦ Power-Up in 900ns ♦ Internal Track/Hold ♦ 400ksps Throughput ♦ Low Power: 1.5mA (Operating Mode) 1µA (Power-Down Mode) ♦ 300kHz Full-Power Bandwidth ♦ 20-Pin DIP, SO and SSOP Packages ♦ No External Clock Required ♦ Unipolar/Bipolar Inputs ♦ Ratiometric Reference Inputs ♦ 2.7V Version Available – Contact Factory ______________Ordering Information PART PIN-PACKAGE TEMP. RANGE MAX152CPP 0°C to +70°C 20 Plastic DIP Cellular Telephones MAX152CWP 0°C to +70°C 20 Wide SO Portable Radios MAX152CAP 0°C to +70°C 20 SSOP Battery-Powered Systems MAX152C/D 0°C to +70°C Dice* Burst-Mode Data Acquisition MAX152EPP -40°C to +85°C 20 Plastic DIP MAX152EWP -40°C to +85°C 20 Wide SO MAX152EAP -40°C to +85°C 20 SSOP Digital Signal Processing Telecommunications 20 CERDIP** MAX152MJP -55°C to +125°C * Contact factory for dice specifications. ** Contact factory for availability and processing to MIL-STD-883. High-Speed Servo Loops ________________Functional Diagram VDD 12 VREF+ 11 VREFVIN 1 20 18 4-BIT FLASH ADC THREESTATE DRIVERS 4-BIT DAC VREF+ 16 4-BIT FLASH ADC (4LSB) TIMING AND CONTROL CIRCUITRY 6 7 10 13 8 GND MODE WR/RDY CS RD MAX152 19 9 INT VSS __________________Pin Configuration PWRDN D0-D7 DATA OUT PINS 2-5, 14-17 TOP VIEW VIN 1 20 VDD D0 (LSB) 2 19 VSS D1 3 18 PWRDN D2 4 17 D7 (MSB) D3 5 16 D6 WR/RDY 6 15 D5 MODE 7 14 D4 RD 8 13 CS INT 9 12 VREF+ GND 10 11 VREF- MAX152 DIP/SO/SSOP ________________________________________________________________ Maxim Integrated Products Call toll free 1-800-998-8800 for free samples or literature. 1 MAX152 _______________General Description MAX152 +3V, 8-Bit ADC with 1µA Power-Down ABSOLUTE MAXIMUM RATINGS VDD to GND .............................................................-0.3V to +7V VSS to GND ..............................................................+0.3V to -7V Digital Input Voltage to GND ........................-0.3V, (VDD + 0.3V) Digital Output Voltage to GND .....................-0.3V, (VDD + 0.3V) VREF+ to GND................................(VSS - 0.3V) to (VDD + 0.3V) VREF- to GND.................................(VSS - 0.3V) to (VDD + 0.3V) VIN to GND .....................................(VSS - 0.3V) to (VDD + 0.3V) Continuous Power Dissipation (TA = +70°C) Plastic DIP (derate 11.11mW/°C above +70°C) ..........889mW Wide SO (derate 10.00mW/°C above +70°C)..............800mW SSOP (derate 8.00mW/°C above +70°C) ....................640mW CERDIP (derate 11.11mW/°C above +70°C) ...............889mW Operating Temperature Ranges: MAX152C__ ........................................................0°C to +70°C MAX152E__ .....................................................-40°C to +85°C MAX152MJP ..................................................-55°C to +125°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10sec) .............................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (Unipolar input range, VDD = 3.0V to 3.6V, GND = 0V, VSS = GND, VREF+ = 3.0V, VREF- = GND, specifications are given for RD mode (pin 7 = GND), TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS ACCURACY (Note 1) Resolution N 8 Bits Total Unadjusted Error TUE Unipolar range ±1 LSB Differential Nonlinearity DNL No-missing-codes guaranteed ±1 LSB Zero-Code Error (Note 2) Unipolar and bipolar modes ±1 LSB Full-Scale Error (Note 2) Unipolar and bipolar modes ±1 LSB DYNAMIC PERFORMANCE (Note 3) Signal-to-Noise Plus Distortion Ratio Total Harmonic Distortion S/(N+D) THD Spurious-Free Dynamic Range Input Full-Power Bandwidth MAX152C/E, fSAMPLE = 400kHz, fIN = 30.273kHz 45 MAX152M, fSAMPLE = 340kHz, fIN = 30.725kHz 45 dB MAX152C/E, fSAMPLE = 400kHz, fIN = 30.273kHz -50 MAX152M, fSAMPLE = 340kHz, fIN = 30.725kHz -50 dB MAX152C/E, fSAMPLE = 400kHz, fIN = 30.273kHz 50 MAX152M, fSAMPLE = 340kHz, fIN = 30.725kHz 50 dB VIN = 3.0Vp-p Maximum Input Slew Rate, Tracking 0.28 0.3 MHz 0.5 V/µs ANALOG INPUT Input Voltage Range VIN Input Leakage Current IIN Input Capacitance CIN VREFVSS < VIN < VDD VREF+ V ±3 µA 22 pF REFERENCE INPUT Reference Resistance 2 4 kΩ VREF+ Input Voltage Range RREF VREF- 1 2 VDD V VREF- Input Voltage Range VSS VREF+ V _______________________________________________________________________________________ +3V, 8-Bit ADC with 1µA Power-Down (Unipolar input range, VDD = 3.0V to 3.6V, GND = 0V, VSS = GND, VREF+ = 3.0V, VREF- = GND, specifications are given for RD mode (pin 7 = GND), TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS LOGIC INPUTS Input High Voltage VINH Input Low Voltage VINL Input High Current IINH CS, WR, RD, PWRDN 2.0 MODE 2.4 V CS, WR, RD, PWRDN 0.66 MODE 0.8 CS, RD, PWRDN ±1 WR ±3 MODE 15 Input Low Current IINL CS, WR, RD, PWRDN, MODE Input Capacitance (Note 4) CIN CS, WR, RD, PWRDN, MODE 5 V µA 100 ±1 µA 8 pF LOGIC OUTPUTS Output Low Voltage Output High Voltage VOL VOH INT, D0-D7, ISINK = 20µA 0.1 INT, D0-D7, ISINK = 400µA 0.4 RDY, ISINK = 1mA 0.4 INT, D0-D7, ISOURCE = 20µA VDD-0.1 INT, D0-D7, ISOURCE = 400µA VDD-0.4 Floating-State Current ILKG D0-D7, RDY Floating Capacitance (Note 4) COUT D0-D7, RDY V V 5 ±3 µA 8 pF 3.6 V POWER REQUIREMENTS Positive Supply Voltage Negative Supply Voltage VDD VSS 3.0 Unipolar operation Bipolar operation (Note 2) MAX152E/M, CS = RD = 0, PWRDN = VDD 2.5 6 MAX152C, CS = RD = 0, PWRDN = VDD 1.5 3 MAX152E/M, CS = RD = 0, PWRDN = VDD 1.5 3.5 1 50 µA CS = RD = 0, PWRDN = VDD 1 50 µA CS = RD = VDD, PWRDN = 0 1 25 µA ±1/16 ±1/4 LSB CS = RD = VDD, PWRDN = 0 ISS Power-Down VSS Current Power-Supply Rejection PSR V 5 VDD = 3.0V Negative Supply Current -3.0 2.5 IDD Power-Down VDD Current (Note 5) -3.6 MAX152C, CS = RD = 0, PWRDN = VDD VDD = 3.6V Positive Supply Current GND VDD = 3.3V ±10% MAX152C/E/M mA Note 1: Accuracy measurements performed at VDD = 3.0V, unipolar mode. Operation over supply range is guaranteed by powersupply rejection test. Note 2: Bipolar tests are performed with VREF+ = +1.5V, VREF- = -1.5V, VSS = -3.0V. Note 3: Unipolar input range, VIN = 3.0VP-P, WR-RD mode, VDD = 3.0V Note 4: Guaranteed by design. Note 5: Power-down current increases if control inputs are not driven to ground or VDD. _______________________________________________________________________________________ 3 MAX152 ELECTRICAL CHARACTERISTICS (continued) MAX152 +3V, 8-Bit ADC with 1µA Power-Down TIMING CHARACTERISTICS (Unipolar input range, VDD = 3V, VSS = 0V, TA = +25°C, unless otherwise noted.) (Note 6) PARAMETER Conversion Time (WR-RD Mode) Conversion Time (RD Mode) Power-Up Time CS to RD,WR Setup Time CS to RD,WR Hold Time CS to RDY Delay Data Access Time (RD Mode) (Note 7) RD to INT Delay (RD Mode) Data Hold Time (Note 8) Delay Time Between Conversions SYMBOL tCWR CONDITIONS ALL GRADES TA = +25°C MIN TYP MAX tRD < tINTL, CL = 100pF tCRD tUP tCSH tRDY CL = 50pF, RL = 5.1kΩ to VDD tACC0 CL = 100pF tINTH CL = 50pF tREAD1 Data Access Time (Note 7) tACC1 WR-RD mode, tRD < tINTL, CL = 100pF (Figure 6) tACC2 WR to INT Delay tIHWR Data Access Time After INT (Note 7) tID µs 1.4 µs 100 WR-RD mode, tRD < tINTL , CL = 100pF (Figure 5) Stand-alone mode, CL = 50pF Stand-alone mode, CL = 100pF 100 120 140 ns tCRD +100 tCRD +130 tCRD +150 ns 160 170 180 ns 100 130 150 ns 600 10 0.66 700 10 0.8 ns 10 µs 0.8 0.9 1.0 µs 400 500 600 ns CL = 50pF WR-RD mode, tRD > tINTL, determined by tACC2 (Figure 5) 1.2 ns tRD Data Access Time (Note 7) 2.6 0 0.6 tREAD2 2.3 0 tWR RD Pulse Width 2.0 0 Delay Time Between WR and RD Pulses tRI µs ns WR Pulse Width tINTL 2.4 0 450 WR to INT Delay 2.06 0 tP RD Pulse Width UNITS 0 tDH WR-RD mode, determined by tACC1 (Figure 6) MAX152M TA = TMIN to TMAX MIN MAX 1.8 0.9 tCSS RD to INT Delay MAX152C/E TA = TMIN to TMAX MIN MAX 0.7 400 500 600 ns 300 340 400 ns 1.45 1.6 1.8 µs 180 220 250 ns 180 220 250 ns 180 200 240 ns 100 130 150 ns Note 6: Input control signals are specified with tr = tf = 5ns, 10% to 90% of +3.0V, and timed from a voltage level of 1.3V. Timing delays get shorter at higher supply voltages. See the Converson Time vs. Supply Voltage graph in the Typical Operating Characteristics to extrapolate timing delays at other power-supply voltages. Note 7: See Figure 1 for load circuit. Parameter defined as the time required for the output to cross 0.66V or 2.0V. Note 8: See Figure 2 for load circuit. Parameter defined as the time required for the data lines to change 0.5V. 4 _________________________________________________________________________________________ _______________________________________________________________________________________ +3V, 8-Bit ADC with 1µA Power-Down EFFECTIVE BITS vs. INPUT FREQUENCY, WR-RD MODE SIGNAL-TO-NOISE RATIO 1.6 8.0 fIN = 30.27 kHz fSAMPLE = 400ksps SNR = 48.2dB 0 1.4 VDD = 3.6V 1.0 VDD = 3.3V 7.5 7.0 EFFECTIVE BITS -20 1.2 RATIO (dB) -40 -60 0.8 -80 -100 -60 -20 20 0 140 100 60 5.5 VDD = 3.0V fSAMPLE = 400kHz VIN = 2.98Vp-p TA = TMIN to TMAX 4.5 -120 0.4 6.5 6.0 5.0 VDD = 3.0V 0.6 40 TEMPERATURE (°C) CONVERSION TIME vs. SUPPLY VOLTAGE 80 120 160 4.0 200 1k 10k 100k 1M FREQUENCY (kHz) INPUT FREQUENCY (Hz) NORMALIZED TIMING vs. SUPPLY VOLTAGE AVERAGE POWER CONSUMPTION vs. CONVERSION RATE USING PWRDN 10,000 1300 tCRD (ns) 1200 1100 1000 900 1.1 VDD = 3.0V SUPPLY CURRENT (µA) TIMING (NORMALIZED TO VDD = 3.0V) 1400 1.0 0.9 0.8 1000 100 10 0.7 1 800 3.2 3.4 3.6 2.8 4.0 3.8 3.0 3.2 3.4 3.6 3.8 4.0 1 10 SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) SUPPLY CURRENT vs. SUPPLY VOLTAGE 5 CS = RD = 0V 10k 100k 1M VDD = 3.0V 4 MILITARY EXTENDED 4 1k ERROR vs. POWER-UP TIME 6 5 100 CONVERSIONS/SEC MAX186-5 3.0 SUPPLY CURRENT (mA) 2.8 ERROR (LSBs) tCRD (NORMALIZED TO VALUE AT +25°C) CONVERSION TIME vs. AMBIENT TEMPERATURE 3 COMMERCIAL 2 3 2 1 +25°C 1 VDD = 3.6V 0 2.8 3.0 3.2 3.4 SUPPLY VOLTAGE (V) 3.6 3.8 120 160 200 240 280 320 tUP (ns) _________________________________________________________________________________________________ 5 MAX152 __________________________________________Typical Operating Characteristics (TA=+25°C, unless otherwise noted). MAX152 +3V, 8-Bit ADC with 1µA Power-Down VDD VDD 3k DATA OUTPUTS DATA OUTPUTS CL 3k A. HIGH-Z TO VOH CL B. HIGH-Z TO VOL Figure 1. Load Circuits for Data-Access Time Test ____________________Pin Description PIN NAME FUNCTION 1 VIN Analog Input. Range is VREF- ≤ VIN ≤ VREF+. 2 D0 Three-State Data Output (LSB) 3-5 D1-D3 6 WR/RDY Three-State Data Outputs Write Control Input/Ready Status Output* Mode Selection Input is internally pulled low with a 15µA current source. MODE = 0 activates read mode MODE = 1 activates write-read mode* 7 MODE 8 RD Read Input must be low to access data.* 9 INT Interrupt Output goes low to indicate end of conversion.* 10 GND Ground 11 VREF- Lower limit of reference span. Sets the zero-code voltage. Range is VSS ≤ VREF- < VREF+. 12 VREF+ Upper limit to reference span. Sets the full-scale input voltage. Range is VREF- < VREF+ ≤ VDD. 13 CS 14-16 D4-D6 17 D7 Chip-Select Input must be low for the device recognize WR or RD inputs. Three-State Data Outputs Three-State Data Output (MSB) Powerdown Input reduces supply current when low. 18 PWRDN 19 VSS Negative Supply. Unipolar: VSS = 0V, Bipolar: VSS = -3V. 20 VDD Positive Supply, +3V. *See Digital Inferface Section. 6 3k DATA OUTPUTS DATA OUTPUTS 10pF 3k A. VOH TO HIGH-Z 10pF B. VOL TO HIGH-Z Figure 2. Load Circuits for Data-Hold TIme Test _______________Detailed Description Converter Operation The MAX152 uses a half-flash conversion technique (see Functional Diagram) in which two 4-bit flash ADC sections achieve an 8-bit result. Using 15 comparators, the flash ADC compares the unknown input voltage to the reference ladder and provides the upper 4 data bits. An internal digital-to-analog converter (DAC) uses the 4 most significant bits (MSBs) to generate the analog result from the first flash conversion and a residue voltage that is the difference between the unknown input and the DAC voltage. The residue is then compared again with the flash comparators to obtain the lower 4 data bits (LSBs). The MAX152 is characterized for operation between +3.0V and +3.6V. Conversion times decrease as the supply voltage increases. The supply current decreases rapidly with decreasing supply voltage. (See Typical Operating Characteristics.) Power-Down Mode In burst-mode or low sample-rate applications, the MAX152 can be shut down between conversions, reducing supply current to microamp levels (see Typical Operating Characteristics). A logic low on the PWRDN pin shuts the device down, reducing supply current to typically 1µA when powered from a single 3V supply. A logic high on PWRDN wakes up the MAX152. A new conversion can be started within 900ns of the PWRDN pin being driven high (this includes both the power-up delay and the track/hold acquisition time). If power-down mode is not required, connect PWRDN to VDD. _______________________________________________________________________________________ +3V, 8-Bit ADC with 1µA Power-Down ___________________Digital Interface The MAX152 has two basic interface modes set by the status of the MODE input pin. When MODE is low, the converter is in the RD mode; when MODE is high, the converter is set up for the WR-RD mode. Write-Read Mode (MODE = 1) Figures 4 and 5 show the operating sequence for the write-read (WR-RD) mode. The comparator inputs track the analog input voltage for the duration of tP. The conversion is initiated by a falling edge of WR. When WR returns high, the 4 MSBs' flash result is latched into the output buffers and the 4 LSBs' conversion begins. INT goes low, indicating conversion end, and the lower 4 data bits are latched into the output buffers. The data is then accessible after RD goes low (see Timing Characteristics). Read Mode (MODE = 0) In RD mode, conversion control and data access are controlled by the RD input (Figure 3). The comparator inputs track the analog input voltage for the duration of tP. A conversion is initiated by driving RD low. With µPs that can be forced into a wait state, hold RD low until output data appears. The µP starts the conversion, waits, and then reads data with a single read instruction. WR/RDY is configured as a status output (RDY) in RD mode, where it can drive the ready or wait input of a µP. RDY is an open-collector output (with no internal pull-up) that goes low after the falling edge of CS and goes high at the end of the conversion. If not used, the WR/RDY pin can be left unconnected. The INT output goes low at the end of the conversion and returns high on the rising edge of CS or RD. PWRDN tUP CS WR tWR tCSS tP tCSH RD tREAD2 tRD INT tINTL D0-D7 VALID DATA tACC2 tDH Figure 4. WR-RD Mode Timing (tRD > tINTL) (MODE = 1) PWRDN tUP tCSH CS PWRDN tUP CS RD WR tCSH tCSS RDY tRDY tWR tCSS RD tP tRD tREAD1 tP WITH EXTERNAL PULL-UP tINTH INT tRI INT tINTH tCRD VALID DATA D0-D7 tACCO tDH Figure 3. RD Mode Timing (MODE = 0) VALID DATA tACC1 tCWR tDH Figure 5. WR-RD Mode Timing (tRD < tINTL), Fastest Operating Mode (MODE = 1) _______________________________________________________________________________________ 7 MAX152 Once the MAX152 is in power-down mode, lowest supply current is drawn with MODE low (RD mode) due to an internal pull-down resistor at this pin. In addition, for minimum current consumption, other digital inputs should remain high in power-down. Refer to the Reference section for information on reducing reference current during power-down. MAX152 +3V, 8-Bit ADC with 1µA Power-Down tWR D0-D7 tINTL OLD DATA 10 VIN- tP tIHWR INT 1 V IN VIN+ WR +3V 0.1µF GND MAX152 20 V DD 12 VREF+ 11 VREF- 4.7µF tID NEW DATA Figure 6. Stand-Alone Mode Timing (CS = RD = 0) (MODE = 1) Figure 7a. Power Supply as Reference VIN+ VIN- A minimum acquisition time (tP) is required from INT going low to the start of another conversion (WR going low). +3V 20 4.7 µF 0.1 µF 8 1 3 Using Internal Delay The µP waits for the INT output to go low before reading the data (Figure 4). INT goes low after the rising edge of WR, indicating that the conversion is complete and the result is available in the output latch. With CS low, data outputs D0-D7 can be accessed by pulling RD low. INT is then reset by the rising edge of CS or RD. Fastest Conversion: Reading Before Delay An external method of controlling the conversion time is shown in Figure 5. The internally generated delay tINTL varies slightly with temperature and supply voltage, and can be overridden with RD to achieve the fastest conversion time. RD is brought low after the rising edge of WR, but before INT goes low. This completes the conversion and enables the output buffers (D0-D7) that contain the conversion result. INT also goes low after the falling edge of RD and is reset on the rising edge of RD or CS. The total conversion time is therefore: tCWR = tWR (600ns) + tRD (800ns) + tACC1 (400ns) = 1800ns. 8 6 +2.5V 12 2 LM10 1 VDD VREF+ MAX152 0.1 µF VREF- 4 11 Figure 7b. External Reference, +2.5V Full Scale 1 V IN VIN+ 10 GND 20 V MAX152 DD +3V 0.1µF 12 4.7µF VIN- 1.2V 11 0.1µF *CURRENT PATH MUST STILL EXIST FROM VIN- TO GND. VREF+ VREF- 0.1µF Figure 7c. Input Not Referenced to GND +3V VDD MAX152 VREF+ + MAX872 C1 2.2µF Stand-Alone Operation Besides the two standard WR-RD mode options, standalone operation can be achieved by connecting CS and RD low (Figure 6). A conversion is initiated by pulling WR low. Output data can be read by either edge of the next WR pulse. 7 34.8k 3.01k Options for reading data from the converter include the following: 10 GND VIN VREFPWRDN PWRDN MTD3055EL N Figure 7d. An N-channel MOSFET switches off the reference load during power-down. _______________________________________________________________________________________ +3V, 8-Bit ADC with 1µA Power-Down Reference Figures 7a-7c show some reference connections. VREF+ and VREF- inputs set the full-scale and zeroinput voltages of the ADC. The voltage at VREFdefines the input that produces an output code of all zeros, and the voltage at VREF+ defines the input that produces an output code of all ones. The internal resistance from VREF+ to VREF- may be as low as 1kΩ, and current will flow through it even when the MAX152 is shut down. Figure 7d shows how an Nchannel MOSFET may be connected to VREF- to break this path during power-down. The FET should have an on resistance < 2Ω with a 3V gate drive. Although VREF+ is frequently connected to VDD, this circuit uses a low current, low-dropout, 2.5V voltage reference – the MAX872. Since the MAX872 cannot continuously furnish enough current for the reference resistance, this circuit is intended for applications where the MAX152 is normally in standby and is turned on in order to make measurements at intervals greater than 20µs. The capacitor C1 connected to VREF+ is slowly charged by the MAX872 during the standby period and furnishes the reference current during the short measurement period. The 2.2µF value of C1 is chosen so that its voltage drops by less than 1/2LSB during the conversion process. Larger capacitors reduce the error still further. Use ceramic or tantalum capacitors for C1. When VREF- is switched, as in Figure 7d, a new conversion can be initiated after waiting a time equal to the power-up delay (tUP) plus the turn-on time of the N-channel FET. Bypassing A 4.7µF electrolytic in parallel with a 0.1µF ceramic capacitor should be used to bypass V DD to GND. These capacitors should have minimal lead length. The reference inputs should be bypassed with 0.1µF capacitors, as shown in Figures 7a-7c. Input Current Figure 8 shows the equivalent circuit of the converter input. When the conversion starts and WR is low, VIN is connected to sixteen 0.6pF capacitors. During this acquisition phase, the input capacitors charge to the input voltage through the resistance of the internal analog switches. In addition, about 12pF of stray capacitance must be charged. The input can be modeled as an equivalent RC network (Figure 9). As source impedance increases, the capacitors take longer to charge. The typical 22pF input capacitance allows source resistance as high as 2.2kΩ without setup problems. For larger resistances, the acquisition time (tP) must be increased. MAX152 RIN VIN RON 1 VIN C Figure 8. Equivalent Input Circuit R VIN 1 VIN 4k 12pF 10pF MAX152 Figure 9. RC Network Equivalent Input Model _______________________________________________________________________________________ 9 MAX152 ____________Analog Considerations MAX152 +3V, 8-Bit ADC with 1µA Power-Down Conversion Rate Total Harmonic Distortion The maximum sampling rate (fmax) for the MAX152 is achieved in the WR-RD mode (tRD < tINTL) and is calculated as follows: Total harmonic distortion (THD) is the ratio of the RMS sum of all harmonics of the input signal (in the frequency band above DC and below one-half the sample rate) to the fundamental itself. This is expressed as: fmax = 1 t WR + t RD + t RI + t P e.g. at TA = +25°C, VDD = +3.0V : fmax = 1 600ns + 800ns + 300ns + 450ns fmax = 465kHz where t WR = Write pulse width t RD = Delay between WR and RD pulses t RI = RD to INT delay t P = Delay time between conversons.  THD = 20 log   2 2 2 2 (V2 + V3 + V4 + L + VN )  V1 where V1 is the fundamental RMS amplitude, and V2 to VN are the amplitudes of the 2nd through Nth harmonics. Spurious-Free Dynamic Range Spurious-free dynamic range is the ratio of the fundamental RMS amplitude to the amplitude of the next largest spectral component (in the frequency band above DC and below one-half the sample rate). Usually the next largest spectral component occurs at some harmonic of the input frequency. However, if the ADC is exceptionally linear, it may occur only at a random peak in the ADC's noise floor. See "Signal to Noise Ratio" plot in Typical Operating Characteristics. Signal-to-Noise Ratio and Effective Number of Bits Signal-to-noise plus distortion ratio (SINAD) is the ratio of the fundamental input frequency's RMS amplitude to the RMS amplitude of all other ADC output signals. The output band is limited to frequencies above DC and below one-half the ADC sample rate. The theoretical minimum A/D noise is caused by quantization error, and results directly from the ADC's resolution: SNR = (6.02N + 1.76)dB, where N is the number of bits of resolution. Therefore, a perfect 8-bit ADC can do no better than 50dB. The FFT plot (Typical Operation Characteristics) shows the result of sampling a pure 30.27kHz sinusoid at a 400kHz rate. This FFT plot of the output shows the output level in various spectral bands. The effective resolution, or "effective number of bits," the ADC provides can be measured by transposing the equation that converts resolution to SNR: N = (SINAD 1.76)/6.02 (see Typical Operating Characteristics). 10   ______________________________________________________________________________________ +3V, 8-Bit ADC with 1µA Power-Down MAX152 ___________________Chip Topography MAX152 D0 VIN VDD VSS D1 PWRDN D2 D7 D3 D6 0.104" 2.64mm D5 WR/RDY D4 MODE CS RD INT GND VREF- VREF+ 0.098" 2.49mm TRANSISTOR COUNT: 1856 SUBSTRATE CONNECTED TO VDD ________________________________________________________Package Information DIM A A1 A2 A3 B B1 C D D1 E E1 e eA eB L α D1 E E1 D A2 A A3 INCHES MAX MIN 0.200 – – 0.015 0.150 0.125 0.080 0.055 0.022 0.016 0.065 0.050 0.012 0.008 1.045 1.015 0.070 0.040 0.325 0.300 0.280 0.240 0.100 BSC 0.300 BSC 0.400 – 0.150 0.115 15˚ 0˚ MILLIMETERS MIN MAX – 5.08 0.38 – 3.18 3.81 1.40 2.03 0.41 0.56 1.27 1.65 0.20 0.30 25.78 26.54 1.02 1.78 7.62 8.26 6.10 7.11 2.54 BSC 7.62 BSC – 10.16 2.92 3.81 0˚ 15˚ 21-333A α A1 L C e B1 B eA eB 20-PIN PLASTIC DUAL-IN-LINE PACKAGE ______________________________________________________________________________________ 11 MAX152 +3V, 8-Bit ADC with 1µA Power-Down __________________________________________Package Information (continued) DIM E A A1 B C D E e H h L α H INCHES MAX MIN 0.104 0.093 0.012 0.004 0.019 0.014 0.013 0.009 0.512 0.496 0.299 0.291 0.050 BSC 0.419 0.394 0.030 0.010 0.050 0.016 8˚ 0˚ MILLIMETERS MIN MAX 2.35 2.65 0.10 0.30 0.35 0.49 0.23 0.32 12.60 13.00 7.40 7.60 1.27 BSC 10.00 10.65 0.25 0.75 0.40 1.27 0˚ 8˚ 21-334A h x 45˚ D α A 0.127mm 0.004in. e 12 B A1 C L 20-PIN PLASTIC SMALL-OUTLINE PACKAGE ______________________________________________________________________________________