4-Channel, 625 kSPS, 12-Bit Parallel ADC with a Sequencer AD7934-6 FEATURES GENERAL DESCRIPTION The AD7934-6 is a 12-bit, high speed, low power, successive approximation (SAR) analog-to-digital converter (ADC). The part operates from a single 2.7 V to 5.25 V power supply and features throughput rates up to 625 kSPS. The part contains a low noise, wide bandwidth, differential track-and-hold amplifier that handles input frequencies up to 50 MHz. The AD7934-6 features four analog input channels with a channel sequencer that allows a preprogrammed selection of channels to be converted sequentially. This part can accept either singleended, fully differential, or pseudo differential analog inputs. Data acquisition and conversion are controlled by standard control inputs, which allow for easy interfacing to microprocessors and DSPs. The input signal is sampled on the falling edge of CONVST, which is also the point where the conversion is initiated. The AD7934-6 has an accurate on-chip 2.5 V reference that can be used as the reference source for the analog-to-digital conversion. Alternatively, this pin can be overdriven to provide an external reference. VDD AGND AD7934-6 VREFIN/ VREFOUT 2.5V VREF VIN0 I/P MUX CLKIN 12-BIT SAR ADC AND CONTROL T/H CONVST BUSY VIN3 SEQUENCER VDRIVE PARALLEL INTERFACE/CONTROL REGISTER DB0 DB11 CS RD WR W/B DGND 04752-001 Throughput rate: 625 kSPS Specified for VDD of 2.7 V to 5.25 V Power consumption 3.6 mW max at 625 kSPS with 3 V supplies 7.5 mW max at 625 kSPS with 5 V supplies 4 analog input channels with a sequencer Software configurable analog inputs 4-channel single-ended inputs 2-channel fully differential inputs 2-channel pseudo differential inputs Accurate on-chip 2.5 V reference ±0.2% max @ 25°C, 25 ppm/°C max 70 dB SINAD at 50 kHz input frequency No pipeline delays High speed parallel interface—word/byte modes Full shutdown mode: 2 µA max 28-lead TSSOP package FUNCTIONAL BLOCK DIAGRAM Figure. 1 The AD7934-6 uses advanced design techniques to achieve very low power dissipation at high throughput rates. The part also features flexible power management options. An on-chip control register allows the user to set up different operating conditions, including analog input range and configuration, output coding, power management, and channel sequencing. PRODUCT HIGHLIGHTS 1. High throughput with low power consumption. 2. Four analog inputs with a channel sequencer. 3. Accurate on-chip 2.5 V reference. 4. Single-ended, pseudo differential, or fully differential analog inputs that are software selectable. 5. No pipeline delay. 6. Accurate control of the sampling instant via a CONVST input and once off conversion control. Table 1. Related Devices Similar Device AD7938/39 AD7933/34 AD7938-6 Number of Bits 12/10 10/12 12 Number of Channels 8 4 8 Speed 1.5 MSPS 1.5 MSPS 625 kSPS Rev. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 © 2005 Analog Devices, Inc. All rights reserved. AD7934-6 TABLE OF CONTENTS Features .............................................................................................. 1 Converter Operation.................................................................. 15 Functional Block Diagram .............................................................. 1 ADC Transfer Function............................................................. 15 General Description ......................................................................... 1 Typical Connection Diagram ................................................... 16 Product Highlights ........................................................................... 1 Analog Input Structure.............................................................. 16 Specifications..................................................................................... 3 Analog Input Configurations ................................................... 17 Timing Specifications....................................................................... 5 Analog Input Selection .............................................................. 19 Absolute Maximum Ratings............................................................ 6 Reference Section ....................................................................... 20 ESD Caution.................................................................................. 6 Parallel Interface......................................................................... 21 Pin Configuration and Function Descriptions............................. 7 Power Modes of Operation ....................................................... 24 Terminology ...................................................................................... 9 Power vs. Throughput Rate....................................................... 25 Typical Performance Characteristics ........................................... 11 Microprocessor Interfacing....................................................... 25 Control Register.............................................................................. 13 Application Hints ........................................................................... 27 Sequencer Operation ................................................................. 14 Grounding and Layout .............................................................. 27 Note on Writing to the Control Register to Program the Sequencer ............................................................. 14 Evaluating the AD7934-6 Performance .................................. 27 Circuit Information ........................................................................ 15 Outline Dimensions ....................................................................... 28 Ordering Guide .......................................................................... 28 REVISION HISTORY 10/05—Rev. 0 to Rev. A Changes to Product Highlights....................................................... 1 Inserted Table 1................................................................................. 1 Changes to Specifications ................................................................ 3 Changes to Timing Specifications .................................................. 5 Changes to Pin Function Descriptions.......................................... 7 Added Writing to the Control Register to Program the Sequencer Section.................................................... 14 Changes to the Analog Inputs Section......................................... 17 Changes to the Grounding and Layout Section ......................... 27 1/05—Revision 0: Initial Version Rev. A | Page 2 of 28 AD7934-6 SPECIFICATIONS VDD = VDRIVE = 2.7 V to 5.25 V, internal/external VREF = 2.5 V, unless otherwise noted, FCLKIN = 10 MHz, FSAMPLE = 625 kSPS; TA = TMIN to TMAX1, unless otherwise noted. Table 2. Parameter DYNAMIC PERFORMANCE Signal-to-Noise + Distortion (SINAD)2 Signal-to-Noise Ratio (SNR)2 Total Harmonic Distortion (THD)2 Peak Harmonic or Spurious Noise (SFDR)2 Intermodulation Distortion (IMD)2 Second-Order Terms Third-Order Terms Channel-to-Channel Isolation Aperture Delay2 Aperture Jitter2 Full Power Bandwidth2 DC ACCURACY Resolution Integral Nonlinearity2 Differential Nonlinearity2 Differential Mode Single-Ended Mode Single-Ended and Pseudo Differential Input Offset Error2 Offset Error Match2 Gain Error2 Gain Error Match2 Fully Differential Input Positive Gain Error2 Positive Gain Error Match2 Zero-Code Error2 Zero-Code Error Match2 Negative Gain Error2 Negative Gain Error Match2 ANALOG INPUT Single-Ended Input Range Pseudo Differential Input Range: VIN+ VIN− Fully Differential Input Range: VIN+ and VIN− VIN+ and VIN− DC Leakage Current4 Input Capacitance B Version1 Unit 70 68 71 69 −73 −70 −73 dB min dB min dB min dB min dB max dB max dB max −86 −90 −85 5 72 50 10 dB typ dB typ dB typ ns typ ps typ MHz typ MHz typ 12 ±1 ±1.5 Bits LSB max LSB max ±0.95 −0.95/+1.5 LSB max LSB max ±6 ±1 ±3 ±1 LSB max LSB max LSB max LSB max ±3 ±1 ±6 ±1 ±3 ±1 LSB max LSB max LSB max LSB max LSB max LSB max 0 to VREF 0 to 2 × VREF 0 to VREF 0 to 2 × VREF −0.3 to +0.7 −0.3 to +1.8 VCM ± VREF/2 VCM ± VREF ±1 45 10 V V V V V typ V typ V V µA max pF typ pF typ Test Conditions/Comments FIN = 50 kHz sine wave Differential mode Single-ended mode Differential mode Single-ended mode −85 dB typ, differential mode −80 dB typ, single-ended mode −82 dB typ fa = 30 kHz, fb = 50 kHz FIN = 50 kHz, FNOISE = 300 kHz @ 3 dB @ 0.1 dB Differential mode Single-ended mode Guaranteed no missed codes to 12 bits Guaranteed no missed codes to 12 bits Straight binary output coding Twos complement output coding Rev. A | Page 3 of 28 RANGE bit = 0 RANGE bit = 1 RANGE bit = 0 RANGE bit = 1 VDD = 3 V VDD = 5 V VCM = VREF/23, RANGE bit = 0 VCM = VREF3, RANGE bit = 1 When in track When in hold AD7934-6 Parameter REFERENCE INPUT/OUTPUT VREF Input Voltage5 DC Leakage Current4 VREFOUT Output Voltage VREFOUT Temperature Coefficient VREF Noise VREF Output Impedance VREF Input Capacitance LOGIC INPUTS Input High Voltage, VINH Input Low Voltage, VINL Input Current, IIN Input Capacitance, CIN4 LOGIC OUTPUTS Output High Voltage, VOH Output Low Voltage, VOL Floating-State Leakage Current Floating-State Output Capacitance4 Output Coding CONVERSION RATE Conversion Time Track-and-Hold Acquisition Time Throughput Rate POWER REQUIREMENTS VDD VDRIVE IDD6 Normal Mode (Static) Normal Mode (Operational) Autostandby Mode Full/Autoshutdown Mode (Static) Power Dissipation Normal Mode (Operational) Autostandby Mode (Static) Full/Autoshutdown Mode B Version1 Unit Test Conditions/Comments 2.5 ±1 2.5 25 5 10 130 10 15 25 V µA max V ppm/°C max ppm/°C typ µV typ µV typ Ω typ pF typ pF typ ±1% for specified performance 2.4 0.8 ±5 10 V min V max µA max pF max 2.4 0.4 ±3 10 V min V max µA max pF max Straight (natural) binary Twos complement ±0.2% max @ 25°C 0.1 Hz to 10 Hz bandwidth 0.1 Hz to 1 MHz bandwidth When in track When in hold Typically 10 nA, VIN = 0 V or VDRIVE ISOURCE = 200 µA ISINK = 200 µA CODING bit = 0 CODING bit = 1 t2 + 13 tCLK 125 80 625 ns ns max ns typ kSPS max 2.7/5.25 2.7/5.25 V min/max V min/max 0.8 1.5 1.2 0.3 160 2 mA typ mA max mA max mA typ µA typ µA max Digital I/PS = 0 V or VDRIVE VDD = 2.7 V to 5.25 V, SCLK on or off VDD = 4.75 V to 5.25 V VDD = 2.7 V to 3.6 V FSAMPLE = 100 kSPS, VDD = 5 V Static, VDD = 3 V SCLK on or off 7.5 3.6 800 480 10/6 mW max mW max µW typ µW typ µW max VDD = 5 V VDD = 3 V VDD = 5 V VDD = 3 V VDD = 5 V/3 V 1 Full-scale step input Sine wave input Temperature range is as follows: B Version: –40°C to +85°C. See the Terminology section. 3 VCM is the common-mode voltage. For full common-mode range, see Figure 25 and Figure 26. VIN+ and VIN− must always remain within GND/VDD. 4 Sample tested during initial release to ensure compliance. 5 This device is operational with an external reference in the range 0.1 V to VDD. See the Reference Section for more information. 6 Measured with a midscale dc analog input. 2 Rev. A | Page 4 of 28 AD7934-6 TIMING SPECIFICATIONS VDD = VDRIVE = 2.7 V to 5.25 V, internal/external VREF = 2.5 V, unless otherwise noted. FCLKIN = 10 MHz, FSAMPLE = 625 kSPS, TA = TMIN to TMAX, unless otherwise noted. Table 3. Parameter1 fCLKIN2 tQUIET t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t12 t133 t144 t15 t16 t17 t18 t19 t20 t21 t22 Limit at TMIN, TMAX 700 10 30 Unit kHz min MHz max ns min 10 15 50 0 0 10 10 10 10 0 0 30 30 3 50 0 0 10 0 10 40 15.7 7.8 ns min ns min ns min ns min ns min ns min ns min ns min ns min ns min ns min ns min ns max ns min ns max ns min ns min ns min ns min ns min ns max ns min ns min Description CLKIN Frequency Minimum time between end of read and start of next conversion, that is, time from when the data bus goes into three-state until the next falling edge of CONVST CONVST Pulse Width CONVST Falling Edge to CLKIN Falling Edge Setup Time CLKIN Falling Edge to BUSY Rising Edge CS to WR Setup Time CS to WR Hold Time WR Pulse Width Data Setup Time Before WR Data Hold after WR New Data Valid Before Falling Edge of BUSY CS to RD Setup Time CS to RD Hold Time RD Pulse Width Data Access Time After RD Bus Relinquish Time After RD Bus Relinquish Time After RD HBEN to RD Setup Time HBEN to RD Hold Time Minimum Time Between Reads/Writes HBEN to WR Setup Time HBEN to WR Hold Time CLKIN Falling Edge to BUSY Falling Edge CLKIN Low Pulse Width CLKIN High Pulse Width 1 Sample tested during initial release to ensure compliance. All input signals are specified with tr = tf = 5 ns (10% to 90% of VDD) and timed from a voltage level of 1.6 V. All timing specifications given above are with a 25 pF load capacitance. See Figure 34, Figure 35, Figure 36, and Figure 37. Minimum CLKIN for specified performance. With slower CLKIN frequencies, performance specifications apply typically. 3 The time required for the output to cross 0.4 V or 2.4 V. 4 t14 is derived from the measured time taken by the data outputs to change 0.5 V. The measured number is then extrapolated back to remove the effects of charging or discharging the 25 pF capacitor. This means that the time, t14, quoted in the timing characteristics is the true bus relinquish time of the part and is independent of the bus loading. 2 Rev. A | Page 5 of 28 AD7934-6 ABSOLUTE MAXIMUM RATINGS TA = 25°C, unless otherwise noted. Table 4. Parameter VDD to AGND/DGND VDRIVE to AGND/DGND Analog Input Voltage to AGND Digital Input Voltage to DGND VDRIVE to VDD Digital Output Voltage to DGND VREFIN to AGND AGND to DGND Input Current to Any Pin Except Supplies1 Operating Temperature Range Commercial (B Version) Storage Temperature Range Junction Temperature θJA Thermal Impedance θJC Thermal Impedance Lead Temperature, Soldering Reflow Temperature (10 sec to 30 sec) ESD 1 Rating −0.3 V to +7 V −0.3 V to VDD +0.3 V −0.3 V to VDD + 0.3 V −0.3 V to +7 V −0.3 V to VDD + 0.3 V −0.3 V to VDRIVE + 0.3 V −0.3 V to VDD + 0.3 V −0.3 V to +0.3 V ±10 mA Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. −40°C to +85°C −65°C to +150°C 150°C 97.9°C/W (TSSOP) 14°C/W (TSSOP) 255°C 1.5 kV Transient currents of up to 100 mA do not cause SCR latch-up. ESD CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Rev. A | Page 6 of 28 AD7934-6 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS VDD 1 28 VIN3 2 27 VIN2 DB0 3 26 VIN1 25 VIN0 DB1 4 DB2 5 DB3 6 DB4 7 22 CS DB5 8 21 RD DB6 9 20 WR DB7 10 VDRIVE 11 DGND 12 AD7934-6 TOP VIEW (Not to Scale) 24 VREFIN/VREFOUT 23 AGND 19 CONVST 18 CLKIN 17 BUSY DB8/HBEN 13 16 DB11 DB9 14 15 DB10 04752-006 W/B Figure 2. Pin Configuration Table 5. Pin Function Description Pin No. 1 Mnemonic VDD 2 W/B 3 to 10 DB0 to DB7 11 VDRIVE 12 DGND 13 DB8/HBEN 14 to 16 DB9 to DB11 17 BUSY 18 CLKIN 19 CONVST 20 WR Description Power Supply Input. The VDD range for the AD7934-6 is from 2.7 V to 5.25 V. The supply should be decoupled to AGND with a 0.1 µF capacitor and a 10 µF tantalum capacitor. Word/Byte Input. When this input is logic high, word transfer mode is enabled, and data is transferred to and from the AD7934-6 in 12-bit words on Pin DB0 to Pin DB11. When W/B is logic low, byte transfer mode is enabled. Data and the channel ID are transferred on Pin DB0 to Pin DB7, and Pin DB8/HBEN assumes its HBEN functionality. When operating in byte transfer mode, unused data lines should be tied off to DGND. Data Bits 0 to 7. Three-state parallel digital I/O pins that provide the conversion result, and allow the control register to be programmed. These pins are controlled by CS, RD, and WR. The logic high/low voltage levels for these pins are determined by the VDRIVE input. Logic Power Supply Input. The voltage supplied at this pin determines what voltage the parallel interface of the AD7934-6 operates. This pin should be decoupled to DGND. The voltage at this pin can be different to that at VDD, but should never exceed VDD by more than 0.3 V. Digital Ground. This is the ground reference point for all digital circuitry on the AD7934-6. This pin should connect to the DGND plane of a system. The DGND and AGND voltages should ideally be at the same potential, and must not be more than 0.3 V apart, even on a transient basis. Data Bit 8/High Byte Enable. When W/B is high, this pin acts as Data Bit 8, a three-state I/O pin that is controlled by CS, RD, and WR. When W/B is low, this pin acts as the high byte enable pin. When HBEN is low, the low byte of data written to or read from the AD7934-6 is on DB0 to DB7. When HBEN is high, the top four bits of the data being written to or read from the AD7934-6 are on DB0 to DB3. When reading from the device, DB4 and DB5 of the high byte contain the ID of the channel corresponding to the conversion result (see the channel address bits in Table 9). DB6 and DB7 are always 0. When writing to the device, DB4 to DB7 of the high byte must all be 0s. Data Bits 9 to 11. Three-state parallel digital I/O pins that provide the conversion result and allow the control register to be programmed in word mode. These pins are controlled by CS, RD, and WR. The logic high/low voltage levels for these pins are determined by the VDRIVE input. Busy Output. Logic output indicating the status of the conversion. The BUSY output goes high following the falling edge of CONVST and stays high for the duration of the conversion. Once the conversion is complete and the result is available in the output register, the BUSY output goes low. The track-and-hold returns to track mode just prior to the falling edge of BUSY, on the 13th rising edge of SCLK (see Figure 34). Master Clock Input. The clock source for the conversion process is applied to this pin. Conversion time for the AD7934-6 takes 13 clock cycles + t2. The frequency of the master clock input therefore determines the conversion time and achievable throughput rate. The CLKIN signal can be a continuous or burst clock. Conversion Start Input. A falling edge on CONVST is used to initiate a conversion. The track-and-hold goes from track to hold mode on the falling edge of CONVST, and the conversion process is initiated at this point. Following power-down, when operating in the autoshutdown or autostandby mode, a rising edge on CONVST is used to power up the device. Write Input. Active low logic input used in conjunction with CS to write data to the control register. Rev. A | Page 7 of 28 AD7934-6 Pin No. 21 Mnemonic RD 22 CS 23 AGND 24 VREFIN/VREFOUT 25 to 28 VIN0 to VIN3 Description Read Input. Active low logic input used in conjunction with CS to access the conversion result. The conversion result is placed on the data bus following the falling edge of RD read while CS is low. Chip Select. Active low logic input used in conjunction with RD and WR to read conversion data or write data to the control register. Analog Ground. This is the ground reference point for all analog circuitry on the AD7934-6. All analog input signals and any external reference signal should be referred to this AGND voltage. The AGND and DGND voltages should ideally be at the same potential and must not be more than 0.3 V apart, even on a transient basis. Reference Input/Output. This pin is connected to the internal reference, and is the reference source for the ADC. The nominal internal reference voltage is 2.5 V, and it appears at this pin. It is recommended that this pin be decoupled to AGND with a 470 nF capacitor. This pin can be overdriven by an external reference. The input voltage range for the external reference is 0.1 V to VDD; however, care must be taken to ensure that the analog input range does not exceed VDD + 0.3 V. See the Reference Section. Analog Input 0 to Analog Input 3. Four analog input channels that are multiplexed into the on-chip track-andhold. The analog inputs can be programmed to be four single-ended inputs, two fully differential pairs, or two pseudo differential pairs by setting the MODE bits in the control register appropriately (see Table 9). The analog input channel to be converted can be selected either by writing to the address bits (ADD1 and ADD0) in the control register prior to the conversion, or by using the on-chip sequencer. The input range for all input channels can be either 0 V to VREF, or 0 V to 2 × VREF, and the coding can be binary or twos complement, depending on the states of the RANGE and CODING bits in the control register. Any unused input channels should be connected to AGND to avoid noise pickup. Rev. A | Page 8 of 28 AD7934-6 TERMINOLOGY Integral Nonlinearity (INL) This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The endpoints of the transfer function are zero scale, a point 1 LSB below the first code transition, and full scale, a point 1 LSB above the last code transition. Differential Nonlinearity (DNL) This is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC. Offset Error This is the deviation of the first code transition (00 … 000) to (00 … 001) from the ideal (that is, AGND + 1 LSB). Offset Error Match This is the difference in offset error between any two channels. Gain Error This is the deviation of the last code transition (111 … 110) to (111 … 111) from the ideal (that is, VREF – 1 LSB) after the offset error has been adjusted out. Gain Error Match This is the difference in gain error between any two channels. Zero-Code Error This applies when using the twos complement output coding option, in particular to the 2 × VREF input range, with −VREF to +VREF biased about the VREF point. It is the deviation of the midscale transition (all 0s to all 1s) from the ideal VIN voltage (that is, VREF). Negative Gain Error This applies when using the twos complement output coding option, in particular to the 2 × VREF input range, with −VREF to +VREF biased about the VREF point. It is the deviation of the first code transition (100 … 000) to (100 … 001) from the ideal (that is, −VREF + 1 LSB) after the zero-code error has been adjusted out. Negative Gain Error Match This is the difference in negative gain error between any two channels. Channel-to-Channel Isolation This is a measure of the level of crosstalk between channels. It is measured by applying a full-scale sine wave signal to the three, nonselected input channels and applying a 50 kHz signal to the selected channel. The channel-to-channel isolation is defined as the ratio of the power of the 50 kHz signal on the selected channel to the power of the noise signal on the unselected channels that appears in the fast Fourier transform (FFT) of this channel. The noise frequency on the unselected channels varies from 40 kHz to 740 kHz. The noise amplitude is at 2 × VREF, while the signal amplitude is at 1 × VREF. See Figure 4. Power Supply Rejection Ratio (PSRR) PSRR is defined as the ratio of the power in the ADC output at full-scale frequency (f) to the power of a 100 mV p-p sine wave applied to the ADC VDD supply of frequency fS. The frequency of the noise varies from 1 kHz to 1 MHz. PSRR (dB) = 10log(Pf/PfS) where: Zero-Code Error Match This is the difference in zero-code error between any two channels. Pf is the power at frequency f in the ADC output. PfS is the power at frequency fS in the ADC output. Positive Gain Error This applies when using the twos complement output coding option, in particular to the 2 × VREF input range, with −VREF to +VREF biased about the VREF point. It is the deviation of the last code transition (011 … 110) to (011 … 111) from the ideal (that is, +VREF – 1 LSB) after the zero-code error has been adjusted out. Common-Mode Rejection Ratio (CMRR) CMRR is defined as the ratio of the power in the ADC output at full-scale frequency (f) to the power of a 100 mV p-p sine wave applied to the common-mode voltage of VIN+ and VIN− of frequency fS. Positive Gain Error Match This is the difference in positive gain error between any two channels. where: CMRR (dB) = 10log(Pf/PfS) Pf is the power at frequency f in the ADC output. PfS is the power at frequency fS in the ADC output. Rev. A | Page 9 of 28 AD7934-6 Track-and-Hold Acquisition Time The track-and-hold amplifier returns to track mode at the end of conversion. The track-and-hold acquisition time is the time required for the output of the track-and-hold amplifier to reach its final value, within ±½ LSB, after the end of conversion. Signal-to-Noise and Distortion Ratio (SINAD) This is the measured ratio of signal-to-noise and distortion at the output of the ADC. The signal is the rms amplitude of the fundamental. Noise is the sum of all nonfundamental signals up to half the sampling frequency (fS/2), excluding dc. The ratio is dependent on the number of quantization levels in the digitization process; the more levels, the smaller the quantization noise. The theoretical SINAD ratio for an ideal N-bit converter with a sine wave input is given by: SINAD = (6.02 N + 1.76) dB Thus, for a 12-bit converter, SINAD is 74 dB. Total Harmonic Distortion (THD) THD is the ratio of the rms sum of harmonics to the fundamental. For the AD7934-6, it is defined as: THD (dB) = −20log V2 2 + V3 2 + V4 2 + V5 2 + V6 2 V1 where : V1 is the rms amplitude of the fundamental. V2, V3, V4, V5, and V6 are the rms amplitudes of the second through the sixth harmonics. Peak Harmonic or Spurious Noise This is defined as the ratio of the rms value of the next largest component in the ADC output spectrum (up to fS/2 and excluding dc) to the rms value of the fundamental. Normally, the value of this specification is determined by the largest harmonic in the spectrum, but for ADCs where the harmonics are buried in the noise floor, it is a noise peak. Intermodulation Distortion With inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities creates distortion products at sum and difference frequencies of mfa ± nfb, where m, n = 0, 1, 2, 3, and so on. Intermodulation distortion terms are those for which neither m nor n are equal to zero. For example, the second-order terms include (fa + fb) and (fa − fb), while the third-order terms include (2fa + fb), (2fa − fb), (fa + 2fb), and (fa − 2fb). The AD7934-6 is tested using the CCIF standard where two input frequencies near the top end of the input bandwidth are used. In this case, the second-order terms are usually distanced in frequency from the original sine waves, while the third-order terms are usually at a frequency close to the input frequencies. As a result, the second- and third-order terms are specified separately. The calculation of the intermodulation distortion is as per the THD specification, where it is the ratio of the rms sum of the individual distortion products to the rms amplitude of the sum of the fundamentals, expressed in dBs. Rev. A | Page 10 of 28 AD7934-6 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. 0 –60 100mV p-p SINE WAVE ON VDD AND/OR VDRIVE NO DECOUPLING DIFFERENTIAL/SINGLE-ENDED MODE –70 –20 –30 INT REF ??? (dB) AMPLITUDE –80 PSSR (dB) 4096 POINT FFT VDD = 5V FSAMPLE = 625kSPS FIN = 49.62kHz SINAD = 70.94dB THD = –90.09dB DIFFERENTIAL MODE –10 –90 EXT REF –100 –40 –50 –60 –70 –80 04752-007 700 600 500 400 Figure 6. FFT @ VDD = 5 V 1.0 –70 INTERNAL/EXTERNAL REFERENCE VDD = 5V VDD = 5V DIFFERENTIAL MODE 0.8 0.6 DNL ERROR (LSB) –75 –80 –85 0.4 0.2 0 –0.2 –0.4 –0.6 –90 –0.8 04752-021 –195 0 100 200 300 400 500 600 NOISE FREQUENCY (kHz) 700 04752-010 NOISE ISOLATION (dB) 300 FREQUENCY (kHz) Figure 3. PSRR vs. Supply Ripple Frequency Without Supply Decoupling –1.0 0 800 500 Figure 4. Channel-to-Channel Isolation 1000 1500 2000 2500 CODE 3000 3500 4000 Figure 7. Typical DNL @ VDD = 5 V 1.0 80 VDD = 5V VDD = 5V DIFFERENTIAL MODE 0.8 70 0.6 INL ERROR (LSB) VDD = 3V 60 SINAD (dB) 200 –110 1010 100 210 410 610 810 SUPPLY RIPPLE FREQUENCY (kHz) –100 0 –120 10 04752-009 –90 –110 50 40 0.4 0.2 0 –0.2 –0.4 20 0 100 200 300 400 500 600 700 FREQUENCY (kHz) 04752-008 FSAMPLE = 625kSPS RANGE = 0 TO VREF DIFFERENTIAL MODE 800 900 1000 Figure 5. SINAD vs. Analog Input Frequency for Various Supply Voltages Rev. A | Page 11 of 28 04752-011 –0.6 30 –0.8 –1.0 0 500 1000 1500 2000 2500 CODE 3000 Figure 8. Typical INL @ VDD = 5 V 3500 4000 AD7934-6 4 10000 SINGLE-ENDED MODE DIFFERENTIAL MODE 9000 3 9997 CODES INTERNAL REF 8000 2 6000 ??? DNL (LSB) 7000 1 5000 4000 POSITIVE DNL 3000 0 NEGATIVE DNL –1 0.25 0.50 0.75 1.00 1.25 1.50 1.75 VREF (V) 2.00 2.25 2.50 04752-015 04752-012 2000 1000 3 CODES 0 2046 2.75 2047 2048 2049 2050 CODE Figure 9. DNL vs. VREF for VDD = 3 V Figure 12. Histogram of Codes for 10 k Samples @ VDD = 5 V with the Internal Reference 12 –60 DIFFERENTIAL MODE –70 VDD = 5V DIFFERENTIAL MODE 10 –80 VDD = 5V SINGLE-ENDED MODE CMRR (dB) 9 VDD = 3V SINGLE-ENDED MODE 8 –100 VDD = 3V DIFFERENTIAL MODE 7 04752-013 –110 6 0 0.5 1.0 1.5 2.0 VREF (V) 2.5 3.0 3.5 4.0 Figure 10. ENOB vs. VREF VDD = 5V –1.0 VDD = 3V –1.5 –2.0 –2.5 –3.0 –3.5 –4.5 SINGLE-ENDED MODE –5.0 0.5 1.0 1.5 2.0 VREF (V) 2.5 3.0 04752-014 –4.0 0 –120 0 200 400 600 800 RIPPLE FREQUENCY (kHz) 1000 1200 Figure 13. CMRR vs. Input Frequency with VDD = 5 V and 3 V 0 –0.5 OFFSET (LSB) –90 04752-017 EFFECTIVE NUMBER OF BITS 11 3.5 Figure 11. Offset vs. VREF Rev. A | Page 12 of 28 AD7934-6 CONTROL REGISTER The control register on the AD7934-6 is a 12-bit, write-only register. Data is written to this register using the CS and WR pins. The control register is shown in Table 6 and the functions of the bits are described in Table 7. At power-up, the default bit settings in the control register are all 0s. Table 6. Control Register Bits MSB DB11 PM1 DB10 PM0 DB9 CODING DB8 REF DB7 ZERO DB6 ADD1 DB5 ADD0 DB4 MODE1 DB3 MODE0 DB2 SEQ1 DB1 SEQ0 LSB DB0 RANGE Table 7. Control Register Bit Function Description Bit No. 11, 10 Mnemonic PM1, PM0 9 CODING 8 REF 7 6, 5 ZERO ADD1, ADD0 4, 3 MODE1, MODE0 SEQ1 SEQ0 RANGE 2 1 0 Description Power management bits used to select the power mode of operation. The user can choose between normal mode and various power-down modes of operation as shown in Table 8. Selects the output coding of the conversion result. If set to 0, the output coding is straight (natural) binary. If set to 1, the output coding is twos complement. Selects whether the internal or external reference is used to perform the conversion. If this bit is Logic 0, an external reference should be applied to the VREF pin. If this bit is Logic 1, the internal reference is selected. See the Reference Section. Not used. This bit should always be set to Logic 0. Two address bits that either select which analog input channel is to be converted in the next conversion, if the sequencer is not used, or select the final channel in a consecutive sequence when the sequencer is used as described in Table 10. The selected input channel is decoded as shown in Table 9. Two mode pins that select the type of analog input on the four VIN pins. The AD7934-6 has four single-ended inputs, two fully differential inputs, or two pseudo differential inputs. See Table 9. Used in conjunction with the SEQ0 bit to control the sequencer function. See Table 10. Used in conjunction with the SEQ1 bit to control the sequencer function. See Table 10. Selects the analog input range of the AD7934-6. If set to 0, the analog input range extends from 0 V to VREF. If it is set to 1, the analog input range extends from 0 V to 2 × VREF. When this range is selected, AVDD must be 4.75 V to 5.25 V if a 2.5 V reference is used; otherwise, care must be taken to ensure that the analog input remains within the supply rails. See the Analog Input Configurations section for more information. Table 8. Power Mode Selection Using the Power Management Bits in the Control Register PM1 0 0 PM0 0 1 Mode Normal Mode Autoshutdown 1 0 Autostandby 1 1 Full Shutdown Description When operating in normal mode, all circuitry is fully powered up at all times. When operating in autoshutdown mode, the AD7934-6 enters full shutdown mode at the end of each conversion. In this mode, all circuitry is powered down. When the AD7934-6 enters this mode, the reference remains fully powered, the reference buffer is partially powered down, and all other circuitry is fully powered down. This mode is similar to autoshutdown mode, but it allows the part to power-up in 7 µs (or 600 ns if an external reference is used). See the Power Modes of Operation section for more information. When the AD7934-6 enters this mode, all circuitry is powered down. The information in the control register is retained. Table 9. Analog Input Type Selection Channel Address ADD1 ADD0 0 0 0 1 1 0 1 1 MODE0 = 0, MODE1 = 0 Four Single-Ended I/P Channels VIN+ VIN− VIN0 AGND VIN1 AGND VIN2 AGND VIN3 AGND MODE0 = 0, MODE1 = 1 Two Fully Differential I/P Channels VIN+ VIN− VIN0 VIN1 VIN1 VIN0 VIN2 VIN3 VIN3 VIN2 Rev. A | Page 13 of 28 MODE0 = 1, MODE1 = 0 Two Pseudo Differential I/P Channels VIN+ VIN− VIN0 VIN1 VIN1 VIN0 VIN2 VIN3 VIN3 VIN2 MODE0 = 1, MODE1 = 1 Not Used AD7934-6 SEQUENCER OPERATION The configuration of the SEQ0 and SEQ1 bits in the control register allow the user to use the sequencer function. Table 10 outlines the two sequencer modes of operation. Table 10. Sequence Selection Modes SEQ0 0 SEQ1 0 0 1 1 1 0 1 Sequence Type This configuration is selected when the sequence function is not used. The analog input channel selected on each individual conversion is determined by the contents of the channel address bits, ADD1 and ADD0, in each prior write operation. This mode of operation reflects the normal operation of a multichannel ADC, without the sequencer function being used, where each write to the AD7934-6 selects the next channel for conversion. Not used. Not used. This configuration is used in conjunction with the channel address bits, ADD1 and ADD0, to program continuous conversions on a consecutive sequence of channels from Channel 0 to a selected final channel, as determined by the channel address bits in the control register. When in differential or pseudo-differential mode, inverse channels (for example, VIN1, VIN0) are not converted in this mode. NOTE ON WRITING TO THE CONTROL REGISTER TO PROGRAM THE SEQUENCER The AD7933 and AD7934 need 13 full CLKIN periods to perform a conversion. If the ADC does not receive the full 13 CLKIN periods, the conversion is aborted. If a conversion is aborted after applying 12.5 CLKIN periods to the ADC, ensure that a rising edge of CONVST or a falling edge of CLKIN is applied to the part before writing to the control register to program the sequencer. If these conditions are not met, then the sequencer is not in the correct state to handle being reprogrammed for another sequence of conversions. As a result, the performance of the converter is not guaranteed. Rev. A | Page 14 of 28 AD7934-6 CIRCUIT INFORMATION The AD7934-6 provides the user with an on-chip track-andhold, an accurate internal reference, an analog-to-digital converter, and a parallel interface housed in a 28-lead TSSOP package. The AD7934-6 has four analog input channels that can be configured to be four single-ended inputs, two fully differential pairs or two pseudo differential pairs. An on-chip channel sequencer allows the user to select a consecutive sequence of channels through which the ADC can cycle with each falling edge of CONVST. When the ADC starts a conversion (Figure 15), SW3 opens, and SW1 and SW2 move to Position B, causing the comparator to become unbalanced. Both inputs are disconnected once the conversion begins. The control logic and charge redistribution DACs are used to add and subtract fixed amounts of charge from the sampling capacitor arrays to bring the comparator back into a balanced condition. When the comparator is rebalanced, the conversion is complete. The control logic generates the output code of the ADC. The output impedances of the sources driving the VIN+ and the VIN− pins must match; otherwise, the two inputs have different settling times, resulting in errors. CAPACITIVE DAC COMPARATOR The analog input range for the AD7934-6 is 0 to VREF or 0 to 2 × VREF, depending on the status of the RANGE bit in the control register. The output coding of the ADC can be either straight binary or twos complement, depending on the status of the CODING bit in the control register. CS B VIN+ A SW1 A B SW2 CONTROL LOGIC SW3 VIN– VREF CS CAPACITIVE DAC 04752-024 The AD7934-6 is a fast, 4-channel, 12-bit, single-supply, successive approximation analog-to-digital converter. The part operates from a 2.7 V to 5.25 V power supply and features throughput rates up to 625 kSPS. Figure 15. ADC Conversion Phase CONVERTER OPERATION The AD7934-6 is a successive approximation ADC based on two capacitive digital-to-analog converters (DACs). Figure 14 and Figure 15 show simplified schematics of the ADC in acquisition and conversion phase, respectively. The ADC comprises control logic, SAR, and two capacitive DACs. Both figures show the operation of the ADC in differential/pseudo differential mode. Single-ended mode operation is similar but VIN− is internally tied to AGND. In the acquisition phase, SW3 is closed, SW1 and SW2 are in Position A, the comparator is held in a balanced condition, and the sampling capacitor arrays acquire the differential signal on the input. ADC TRANSFER FUNCTION The output coding for the AD7934-6 is either straight binary or twos complement, depending on the status of the CODING bit in the control register. The designed code transitions occur at successive LSB values (that is, 1 LSB, 2 LSBs, and so on), and the LSB size is VREF/4096. The ideal transfer characteristics of the AD7934-6 for both straight binary and twos complement output coding are shown in Figure 16 and Figure 17, respectively. 111...111 111...110 ADC CODE The AD7934-6 provides flexible power management options to allow users to achieve the best power performance for a given throughput rate. These options are selected by programming the power management bits, PM1 and PM0, in the control register. SW1 A B SW2 0V SW3 VREF +VREF – 1 LSB 1 LSB ANALOG INPUT CONTROL LOGIC NOTE: VREF IS EITHER VREF OR 2 × VREF CS Figure 16. Ideal Transfer Characteristic with Straight Binary Output Coding CAPACITIVE DAC 04752-023 VIN– 000...000 04752-025 A 1 LSB = VREF/4096 000...001 COMPARATOR CS B 011...111 000...010 CAPACITIVE DAC VIN+ 111...000 Figure 14. ADC Acquisition Phase Rev. A | Page 15 of 28 AD7934-6 ANALOG INPUT STRUCTURE 1 LSB = 2 × VREF/4096 Figure 19 shows the equivalent circuit of the analog input structure of the AD7934-6 in differential/pseudo differential mode. In single-ended mode, VIN− is internally tied to AGND. The four diodes provide ESD protection for the analog inputs. Care must be taken to ensure that the analog input signals never exceed the supply rails by more than 300 mV. This causes the diodes to become forward-biased and start conducting into the substrate. These diodes can conduct up to 10 mA without causing irreversible damage to the part. ADC CODE 011...110 000...001 000...000 111...111 100...010 100...001 –VREF + 1 LSB VREF +VREF – 1 LSB 04752-026 100...000 Figure 17. Ideal Transfer Characteristic with Twos Complement Output Coding and 2 x VREF Range TYPICAL CONNECTION DIAGRAM Figure 18 shows a typical connection diagram for the AD7934-6. The AGND and DGND pins are connected together at the device for good noise suppression. The VREFIN/VREFOUT pin is decoupled to AGND with a 0.47 µF capacitor to avoid noise pickup if the internal reference is used. Alternatively, VREFIN/VREFOUT can be connected to an external reference source. In this case, the reference pin should be decoupled with a 0.1 µF capacitor. In both cases, the analog input range can either be 0 V to VREF (RANGE bit = 0) or 0 V to 2 × VREF (RANGE bit = 1). The analog input configuration is either four single-ended inputs, two differential pairs or two pseudo differential pairs (see Table 9). The VDD pin connects to either a 3 V or 5 V supply. The voltage applied to the VDRIVE input controls the voltage of the digital interface. Here in Figure 18 it is connected to the same 3 V supply of the microprocessor to allow a 3 V logic interface (see the Digital Inputs section). 0.1µF VDD 3V/5V SUPPLY 10µF AD7934-6 W/B VIN0 0 TO VREF/ 0 TO 2 × VREF CLKIN CS RD VIN3 µC/µP WR BUSY CONVST AGND DB0 DGND DB11/DB9 VREFIN/VREFOUT 0.1µF 10µF 3V SUPPLY 0.1µF EXTERNAL VREF 0.47µF INTERNAL VREF 04752-027 2.5V VREF VDRIVE The C1 capacitors in Figure 19 are typically 4 pF, and can primarily be attributed to pin capacitance. The resistors are lumped components made up of the on resistance of the switches. The value of these resistors is typically about 100 Ω. The C2 capacitors are the sampling capacitors of the ADC and typically have a capacitance of 45 pF. VDD D R1 C2 R1 C2 VIN+ C1 D VDD D VIN– C1 D 04752-028 011...111 Figure 19. Equivalent Analog Input Circuit, Conversion Phase—Switches Open, Track Phase—Switches Closed For ac applications, removing high frequency components from the analog input signal is recommended by the use of an RC lowpass filter on the relevant analog input pins. In applications where harmonic distortion and signal-to-noise ratio are critical, the analog input should be driven from a low impedance source. Large source impedances significantly affect the ac performance of the ADC. This can necessitate the use of an input buffer amplifier. The choice of the op amp is a function of the particular application. When no amplifier is used to drive the analog input, the source impedance should be limited to low values. The maximum source impedance depends on the amount of THD that can be tolerated. The THD increases as the source impedance increases and performance degrades. Figure 20 and Figure 21 show a graph of the THD vs. source impedance with a 50 kHz input tone for both VDD = 5 V and 3 V, in single-ended mode and differential mode, respectively. Figure 18. Typical Connection Diagram Rev. A | Page 16 of 28 AD7934-6 ANALOG INPUT CONFIGURATIONS –40 FIN = 50kHz –45 The AD7934-6 has software selectable analog input configurations. The user can choose either four singleended inputs, two fully differential pairs, or two pseudo differential pairs. The analog input configuration is chosen by setting the MODE0/MODE1 bits in the internal control register (see Table 9). –50 VDD = 3V THD (dB) –55 –60 –65 –70 Single-Ended Mode –75 The AD7934-6 can have four single-ended analog input channels by setting the MODE0 and MODE1 bits in the control register to 0. In applications where the signal source has a high impedance, it is recommended to buffer the analog input before applying it to the ADC. An op amp suitable for this function is the AD8021. The analog input range of the AD7934-6 can be programmed to be either 0 to VREF or 0 to 2 × VREF. VDD = 5V 04752-018 –80 –85 –90 10 100 RSOURCE (Ω) 1k Figure 20. THD vs. Source Impedance in Single-Ended Mode –60 FIN = 50kHz If the analog input signal to be sampled is bipolar, the internal reference of the ADC can be used to externally bias up this signal to make it the correct format for the ADC. –65 –70 THD (dB) –75 Figure 23 shows a typical connection diagram when operating the ADC in single-ended mode. This diagram shows a bipolar signal of amplitude ±1.25 V being preconditioned before it is applied to the AD7934-6. In cases where the analog input amplitude is ±2.5 V, the 3R resistor can be replaced with a resistor of value R. The resultant voltage on the analog input of the AD7934-6 is a signal ranging from 0 V to 5 V. In this case, the 2 × VREF mode can be used. –80 –85 VDD = 3V –90 VDD = 5V 04752-019 –95 –100 10 100 1k RSOURCE (Ω) R Figure 21. THD vs. Source Impedance in Differential Mode Figure 22 shows a graph of the THD vs. the analog input frequency for various supplies, while sampling at 625 kHz with an SCLK of 10 MHz. In this case, the source impedance is 10 Ω. +1.25V 0V –1.25V +2.5V 0V R VIN VIN0 3R R –50 AD7934-61 VIN7 VREFOUT VDD = 3V SINGLE-ENDED MODE –60 THD (dB) 1ADDITIONAL –80 VDD = 5V/3V DIFFERENTIAL MODE –90 Differential Mode –100 FSAMPLE = 625kSPS RANGE = 0 TO VREF 0 100 200 300 400 500 INPUT FREQUENCY (kHz) The AD7934-6 can have two differential analog input pairs by setting the MODE0 and MODE1 bits in the control register to 0 and 1, respectively. 04752-020 –110 –120 PINS OMITTED FOR CLARITY. Figure 23. Single-Ended Mode Connection Diagram 600 700 Figure 22. THD vs. Analog Input Frequency for Various Supply Voltages Differential signals have some benefits over single-ended signals, including noise immunity based on the device’s common-mode rejection, and improvements in distortion performance. Figure 24 defines the fully differential analog input of the AD7934-6. Rev. A | Page 17 of 28 04752-031 0.47µF VDD = 5V SINGLE-ENDED MODE –70 AD7934-6 4.5 TA = 25°C VIN+ 4.0 *ADDITIONAL PINS OMITTED FOR CLARITY 04752-032 COMMON-MODE VOLTAGE VIN– Figure 24. Differential Input Definition The amplitude of the differential signal is the difference between the signals applied to the VIN+ and VIN− pins in each differential pair (that is, VIN+ − VIN−). VIN+ and VIN− should be simultaneously driven by two signals, each of amplitude VREF (or 2 × VREF depending on the range chosen), which are 180° out of phase. The amplitude of the differential signal is therefore −VREF to +VREF peak-to-peak (that is, 2 × VREF), regardless of the common mode (CM). The common mode is the average of the two signals, (VIN+ + VIN−)/2, and is therefore the voltage on which the two inputs are centered. This results in the span of each input being CM ± VREF/2. This voltage must be set up externally, and its range varies with the reference value VREF. As the value of VREF increases, the common-mode range decreases. When driving the inputs with an amplifier, the actual common-mode range is determined by the amplifier’s output voltage swing. Figure 25 and Figure 26 show how the common-mode range typically varies with VREF for a 5 V power supply using the 0 to VREF range or 0 to 2 × VREF range, respectively. The common mode must be in this range to guarantee the functionality of the AD7934-6. When a conversion takes place, the common mode is rejected. This results in a virtually noise-free signal of amplitude −VREF to +VREF, corresponding to the digital codes 0 to 4096. If the 0 to 2 × VREF range is used, then the input signal amplitude extends from −2 VREF to +2 VREF. 3.5 TA = 25°C COMMON-MODE RANGE (V) 3.0 2.5 3.5 3.0 2.5 2.0 1.5 1.0 04752-034 AD7934-6* VREF p-p COMMON-MODE RANGE (V) VREF p-p 0.5 0 0.1 0.6 1.1 1.6 2.1 2.6 VREF (V) Figure 26. Input Common-Mode Range vs. VREF (2 × VREF Range, VDD = 5 V) Driving Differential Inputs Differential operation requires that VIN+ and VIN− be simultaneously driven with two equal signals that are 180° out of phase. The common mode must be set up externally and has a range that is determined by VREF, the power supply, and the particular amplifier used to drive the analog inputs. Differential modes of operation with either an ac or a dc input provide the best THD performance over a wide frequency range. Not all applications have a signal preconditioned for differential operation, so there is often a need to perform single-ended-todifferential conversion. Using an Op Amp Pair An op amp pair can be used to directly couple a differential signal to one of the analog input pairs of the AD7934-6. The circuit configurations shown in Figure 27 and Figure 28 show how a dual op amp can be used to convert a single-ended signal into a differential signal for both a bipolar and unipolar input signal, respectively. The voltage applied to Point A sets up the common-mode voltage. In both diagrams, it is connected in some way to the reference, but any value in the common-mode range can be input here to set up the common mode. A suitable dual op amp for use in this configuration to provide differential drive to the AD7934-6 is the AD8022. 2.0 1.5 1.0 04752-033 0.5 0 0 0.5 1.0 1.5 VREF (V) 2.0 2.5 3.0 Figure 25. Input Common-Mode Range vs. VREF (0 to VREF Range, VDD = 5 V) It is advisable to take care when choosing the op amp; the selection depends on the required power supply and system performance objectives. The driver circuits in Figure 27 and Figure 28 are optimized for dc coupling applications requiring best distortion performance. The circuit configuration in Figure 27 converts and level shifts a single-ended, groundreferenced, bipolar signal to a differential signal centered at the VREF level of the ADC. The circuit configuration shown in Figure 28 converts a unipolar, single-ended signal into a differential signal. Rev. A | Page 18 of 28 AD7934-6 220Ω VREF p-p 2 × VREF p-p GND 27Ω V– 220Ω VIN+ 3.75V 2.5V 1.25V AD7934-6* VIN– VIN+ 220Ω VREF AD7934-6 220Ω V+ 27Ω A 3.75V 2.5V 1.25V VIN– DC INPUT VOLTAGE 0.47µF VREF 04752-037 440Ω V+ *ADDITIONAL PINS OMITTED FOR CLARITY V– Figure 29. Pseudo Differential Mode Connection Diagram 10kΩ 04752-035 20kΩ 0.47µF As shown in Table 9, users can set up their analog input configuration by setting the values in the MODE0 and MODE1 bits in the control register. Assuming the configuration has been chosen, there are two different ways of selecting the analog input to be converted, depending on the state of the SEQ0 and SEQ1 bits in the control register. Figure 27. Dual Op Amp Circuit to Convert a Single-Ended Bipolar Signal into a Differential Unipolar Signal 220Ω VREF p-p VREF 440Ω V+ 27Ω GND 3.75V 2.5V 1.25V V– AD7934-6 220Ω V+ 27Ω A Traditional Multichannel Operation (SEQ0 = SEQ1 = 0) VIN+ 220Ω 3.75V 2.5V 1.25V VIN– VREF 0.47µF 04752-036 V– 10kΩ ANALOG INPUT SELECTION Figure 28. Dual Op Amp Circuit to Convert a Single-Ended Unipolar Signal into a Differential Signal Any one of four analog input channels or two pairs of channels can be selected for conversion in any order by setting the SEQ0 and SEQ1 bits in the control register to 0. The channel to be converted is selected by writing to the address bits, ADD1 and ADD0, in the control register to program the multiplexer prior to the conversion. This mode of operation is that of a traditional multichannel ADC, where each data write selects the next channel for conversion. Figure 30 shows a flow chart of this mode of operation. The channel configurations are shown in Table 9. POWER ON Another method of driving the AD7934-6 is to use the AD8138 differential amplifier. The AD8138 can be used as a singleended-to-differential amplifier or as a differential-to-differential amplifier. The device is as easy to use as an op amp and greatly simplifies differential signal amplification and driving. WRITE TO THE CONTROL REGISTER TO SET UP OPERATING MODE, ANALOG INPUT, AND OUTPUT CONFIGURATION. SET SEQ0 = SEQ1 = 0. SELECT THE DESIRED CHANNEL TO CONVERT ON (ADD1 TO ADD0). The AD7934-6 can have two pseudo differential pairs by setting the MODE0 and MODE1 bits in the control register to 1 and 0, respectively. VIN+ is connected to the signal source, which must have an amplitude of VREF (or 2 × VREF depending on the range chosen) to make use of the full dynamic range of the part. A dc input is applied to the VIN− pin. The voltage applied to this input provides an offset from ground or a pseudo ground for the VIN+ input. The benefit of pseudo differential inputs is that they separate the analog input signal ground from the ADC ground, allowing dc common-mode voltages to be cancelled. Typically, the voltage range for the VIN− pin while in pseudo differential mode can extend from −0.3 V to +0.7 V when VDD = 3 V, or from −0.3 V to +1.8V when VDD = 5 V. Figure 29 shows a connection diagram for the pseudo differential mode. INITIATE A WRITE CYCLE TO SELECT THE NEXT CHANNEL TO BE CONVERTED ON BY CHANGING THE VALUES OF BITS ADD2 TO ADD0 IN THE CONTROL REGISTER. SET SEQ0 = SEQ1 = 0. 04752-038 ISSUE CONVST PULSE TO INITIATE A CONVERSION ON THE SELECTED CHANNEL. INITIATE A READ CYCLE TO READ THE DATA FROM THE SELECTED CHANNEL. Pseudo Differential Mode Figure 30. Traditional Multichannel Operation Flow Chart Using the Sequencer: Consecutive Sequence (SEQ0 = SEQ1 = 1) A sequence of consecutive channels can be converted beginning with Channel 0, and ending with a final channel selected by writing to the ADD1 and ADD0 bits in the control register. This is done by setting the SEQ0 and SEQ1 bits in the control register to 1. In this mode, once the control register is written to, the next conversion is on Channel 0, then Channel 1, and so on, until the channel selected by the address bits (ADD1 and ADD0) is reached. Rev. A | Page 19 of 28 AD7934-6 The ADC then returns to Channel 0 and starts the sequence again. The WR input must be kept high to ensure that the control register is not accidentally overwritten and the sequence interrupted. This pattern continues until the AD7934-6 is written to. Figure 31 shows the flowchart of the consecutive sequence mode. POWER ON WRITE TO THE CONTROL REGISTER TO SET UP OPERATING MODE, ANALOG INPUT, AND OUTPUT CONFIGURATION. SELECT FINAL CHANNEL (ADD1 AND ADD0) IN CONSECUTIVE SEQUENCE. SET SEQ0 = SEQ1 = 1. In all cases, the specified reference is 2.5 V. The performance of the part with different reference values is shown in Figure 9 , Figure 10, and Figure 11. The value of the reference sets the analog input span and the common-mode voltage range. Errors in the reference source result in gain errors in the AD7934-6 transfer function and add to the specified full-scale errors on the part. Table 11 lists suitable voltage references available from Analog Devices that can be used. Figure 33 shows a typical connection diagram for an external reference. Table 11. Examples of Suitable Voltage References 04752-039 CONTINUOUSLY CONVERT ON A CONSECUTIVE SEQUENCE OF CHANNELS FROM CHANNEL 0 UP TO AND INCLUDING THE PREVIOUSLY SELECTED FINAL CHANNEL ON ADD1 AND ADD0 WITH EACH CONVST PULSE. Reference AD780 ADR421 ADR420 Figure 31. Consecutive Sequence Mode Flow Chart Output Voltage 2.5/3 2.5 2.048 Initial Accuracy (% max) 0.04 0.04 0.05 Operating Current (µA) 1000 500 500 REFERENCE SECTION AD7934-6 04752-040 REFERENCE ADC NC VDD 1 O/PSELECT 8 2 +VIN 7 3 TEMP VOUT 0.1µF 10nF 0.1µF 4 GND 6 TRIM 5 NC VREF NC 2.5V NC 0.1µF NC = NO CONNECT *ADDITIONAL PINS OMITTED FOR CLARITY Figure 33. Typical VREF Connection Diagram Digital Inputs The digital inputs applied to the AD7934-6 are not limited by the maximum ratings that limit the analog inputs. Instead, the digital inputs applied can go to 7 V. They are not restricted by the AVDD + 0.3 V limit that is on the analog inputs. BUFFER VREFIN/ VREFOUT AD7934-6* AD780 04752-041 The AD7934-6 can operate with either the on-chip reference or external reference. The internal reference is selected by setting the REF bit in the internal control register to 1. A block diagram of the internal reference circuitry is shown in Figure 32. The internal reference circuitry includes an on-chip 2.5 V band gap reference and a reference buffer. When using the internal reference, the VREFIN/VREFOUT pin should be decoupled to AGND with a 0.47 µF capacitor. This internal reference not only provides the reference for the analog-to-digital conversion, but it can also be used externally in the system. It is recommended that the reference output is buffered using an external precision op amp before applying it anywhere in the system. Figure 32. Internal Reference Circuit Block Diagram Alternatively, an external reference can be applied to the VREFIN/VREFOUT pin of the AD7934-6. An external reference input is selected by setting the REF bit in the internal control register to 0. The external reference input range is 0.1 V to VDD. It is important to ensure that when choosing the reference value, the maximum analog input range (VIN MAX) is never greater than VDD + 0.3 V, in order to comply with the maximum ratings of the device. For example, if operating in differential mode and the reference is sourced from VDD, then the 0 to 2 × VREF range cannot be used. This is because the analog input signal range would now extend to 2 × VDD, which would exceed maximum rating conditions. In the pseudo differential modes, the user must ensure that (VREF + VIN−) ≤ VDD when using the 0 to VREF range, or that (2 × VREF + VIN−) ≤ VDD when using the 2 × VREF range. Another advantage of the digital inputs not being restricted by the AVDD + 0.3 V limit is that the power supply sequencing issues are avoided. If any of these inputs are applied before AVDD, then there is no risk of latch-up as there is on the analog inputs if a signal greater than 0.3 V is applied prior to AVDD. VDRIVE Input The AD7934-6 also has a VDRIVE feature. VDRIVE controls the voltage at which the parallel interface operates. VDRIVE allows the ADC to easily interface to 3 V and 5 V processors. For example, if the AD7934-6 is operated with an AVDD of 5 V, and the VDRIVE pin is powered from a 3 V supply, the AD7934-6 has better dynamic performance with an AVDD of 5 V while still being able to interface to 3 V processors. Care should be taken to ensure VDRIVE does not exceed AVDD by more than 0.3 V (see the Absolute Maximum Ratings section). Rev. A | Page 20 of 28 AD7934-6 At the end of the conversion, BUSY goes low and can be used to activate an interrupt service routine. The CS and RD lines are then activated in parallel to read the 12 bits of conversion data. When power supplies are first applied to the device, a rising edge on CONVST is necessary to put the track-and-hold into track. The acquisition time of 125 ns minimum must be allowed before CONVST is brought low to initiate a conversion. The ADC then goes into hold on the falling edge of CONVST, and back into track on the 13th rising edge of CLKIN (see Figure 34). When operating the device in autoshutdown or autostandby mode, where the ADC powers down at the end of each conversion, a rising edge on the CONVST signal is used to power up the device. PARALLEL INTERFACE The AD7934-6 has a flexible, high speed, parallel interface. This interface is 12-bits wide and is capable of operating in either word (W/B tied high) or byte (W/B tied low) mode. The CONVST signal is used to initiate conversions, and when operating in autoshutdown or autostandby mode, it is used to initiate power up. A falling edge on the CONVST signal is used to initiate conversions, and it also puts the ADC track-and-hold into track. Once the CONVST signal goes low, the BUSY signal goes high for the duration of the conversion. Between conversions, CONVST must be brought high for a minimum time of t1. This must occur after the 14th falling edge of CLKIN; otherwise, the conversion is aborted and the track-and-hold goes back into track. B t1 A CONVST tCONVERT 1 CLKIN 2 3 4 5 12 13 14 t2 t20 BUSY t3 t9 INTERNAL TRACK/HOLD tAQUISITION CS t10 RD t12 t13 DB0 TO DB11 t14 DATA THREE-STATE t11 THREE-STATE tQUIET DB0 TO DB11 OLD DATA DATA Figure 34. AD7934-6 Parallel Interface—Conversion and Read Cycle in Word Mode (W/B = 1) Rev. A | Page 21 of 28 04752-004 WITH CS AND RD TIED LOW AD7934-6 Reading Data from the AD7934-6 The CS and RD signals are gated internally and level triggered active low. In either word mode or byte mode, CS and RD can be tied together as the timing specification t10 and t11 are 0 ns minimum. This means the bus is constantly driven by the AD7934-6. With the W/B pin tied logic high, the AD7934-6 interface operates in word mode. In this case, a single read operation from the device accesses the conversion data-word on Pins DB0 to DB11. The DB8/HBEN pin assumes its DB8 function. With the W/B pin tied to logic low, the AD7934-6 interface operates in byte mode. In this case, the DB8/HBEN pin assumes its HBEN function. The data is placed onto the data bus a time, t13, after both CS and RD go low. The RD rising edge can be used to latch data out of the device. After a time, t14, the data lines become threestated. Conversion data from the AD7934-6 must be accessed in two read operations with 8 bits of data provided on DB0 to DB7 for each of the read operations. The HBEN pin determines whether the read operation accesses the high byte or the low byte of the 12-bit word. For a low byte read, DB0 to DB7 provide the eight LSBs of the 12-bit word. For a high byte read, DB0 to DB3 provide the 4 MSBs of the 12-bit word. DB4 and DB5 of the high byte provide the channel ID. DB6 and DB7 are always 0. Figure 34 shows the read cycle timing diagram for a 12-bit transfer. When operated in word mode, the HBEN input does not exist and only the first read operation is required to access data from the device. When operated in byte mode, the two read cycles shown in Figure 35 are required to access the full data-word from the device. Alternatively, CS and RD can be tied permanently low, and the conversion data is valid and placed onto the data bus a time, t9, before the falling edge of BUSY. Note that if RD is pulsed during the conversion time then this causes a degradation in linearity performance of approximately 0.25 LSB. Reading during conversion by way of tying CS and RD low does not cause any degradation. HBEN/DB8 t15 t16 t15 t16 CS t10 t11 t17 t12 t13 DB0 TO DB7 t14 LOW BYTE HIGH BYTE Figure 35. AD7934-6 Parallel Interface—Read Cycle Timing for Byte Mode Operation (W/B = 0) Rev. A | Page 22 of 28 04752-005 RD AD7934-6 When operated in byte mode, the two write cycles shown in Figure 37 are required to write the full data-word to the AD7934-6. In Figure 37, the first write transfers the lower 8 bits of the data-word from DB0 to DB7, and the second write transfers the upper 4 bits of the data-word. Writing Data to the AD7934-6 With W/B tied logic high, a single write operation transfers the full data-word on DB0 to DB11 to the control register on the AD7934-6. The DB8/HBEN pin assumes its DB8 function. Data written to the AD7934-6 should be provided on the DB0 to DB11 inputs, with DB0 being the LSB of the data-word. With W/B tied logic low, the AD7934-6 requires two write operations to transfer a full 12-bit word. DB8/HBEN assumes its HBEN function. Data written to the AD7934-6 should be provided on the DB0 to DB7 inputs. HBEN determines whether the byte written is high byte or low byte data. The low byte of the dataword has DB0 being the LSB of the full data-word. For the high byte write, HBEN should be high, and the data on the DB0 input should be data Bit 8 of the 12-bit word. When writing to the AD7934-6, the top 4 bits in the high byte must be 0s. The data is latched into the device on the rising edge of WR. The data needs to be set up a time, t7, before the WR rising edge and held for a time, t8, after the WR rising edge. The CS and WR signals are gated internally. CS and WR can be tied together as the timing specification for t4, and t5 is 0 ns minimum (assuming CS and RD have not already been tied together). Figure 36 shows the write cycle timing diagram of the AD7934-6. When operated in word mode, the HBEN input does not exist, and only one write operation is required to write the word of data to the device. Data should be provided on DB0 to DB11. CS t5 t6 t8 t7 DB0 TO DB11 04752-002 t4 WR DATA Figure 36. AD7934-6 Parallel Interface—Write Cycle Timing for Word Mode Operation (W/B = 1) HBEN/DB8 t18 t19 t18 t19 CS t4 t5 t17 t6 t7 DB0 TO DB7 t8 LOW BYTE HIGH BYTE Figure 37. AD7934-6 Parallel Interface—Write Cycle Timing for Byte Mode Operation (W/B = 0) Rev. A | Page 23 of 28 04752-003 WR AD7934-6 POWER MODES OF OPERATION Autostandby Mode (PM1 = 1; PM0 = 0) The AD7934-6 has four different power modes of operation. These modes are designed to provide flexible power management options. Different options can be chosen to optimize the power dissipation/throughput rate ratio for differing applications. The mode of operation is selected by the power management bits, PM1 and PM0, in the control register (see Table 8). When power is first applied to the AD7934-6, an onchip, power-on reset circuit ensures that the default power-up condition is normal mode. In this mode, the AD7934-6 automatically enters standby mode at the end of each conversion, shown as Point A in Figure 34. When this mode is entered, all circuitry on the AD7934-6 is powered down except for the reference and reference buffer. The track-and-hold also goes into hold at this point and remains in hold as long as the device is in standby. The part remains in standby until the next rising edge of CONVST powers up the device. The power-up time required depends on whether the internal or external reference is used. With an external reference, the power-up time required is a minimum of 600 ns. When using the internal reference, the power-up time required is a minimum of 7 µs. The user should ensure this power-up time has elapsed before initiating another conversion as shown in Figure 38. This rising edge of CONVST also places the track-and-hold back into track mode. Note that, after power-on, the track-and-hold is in hold mode, and the first rising edge of CONVST places the track-and-hold into track mode. Normal Mode (PM1 = PM0 = 0) This mode is intended for the fastest throughput rate performance because the user does not have to allow for power-up times associated with the AD7934-6. It remains fully powered up at all times. At power-on reset, this mode is the default setting in the control register. Autoshutdown Mode (PM1 = 0; PM0 = 1) In this mode of operation, the AD7934-6 automatically enters full shutdown at the end of each conversion, shown at Point A in Figure 34 and Figure 38. In shutdown mode, all internal circuitry on the device is powered down. The part retains information in the control register during shutdown. The trackand-hold also goes into hold at this point, and remains in hold as long as the device is in shutdown. The AD7934-6 remains in shutdown mode until the next rising edge of CONVST (see Point B in Figure 34 and Figure 38). To keep the device in shutdown for as long as possible, CONVST should idle low between conversions as shown in Figure 38. On this rising edge, the part begins to power-up and the track-and-hold returns to track mode. The power-up time required is 10 ms minimum regardless of whether the user is operating with the internal or external reference. The user should ensure that the power-up time has elapsed before initiating a conversion. Full Shutdown Mode (PM1 = 1; PM0 = 1) When this mode is entered, all circuitry on the AD7934-6 is powered down upon completion of the write operation, that is, on rising edge of WR. The track-and-hold enters hold mode at this point. The part retains the information in the control register while the part is in shutdown. The AD7934-6 remains in full shutdown mode, and the track-and-hold in hold mode, until the power management bits (PM1 and PM0) in the control register are changed. If a write to the control register occurs while the part is in full shutdown mode, and the power management bits are changed to PM0 = PM1 = 0 (normal mode), the part begins to power up on the WR rising edge, and the track-and-hold returns to track. To ensure the part is fully powered up before a conversion is initiated, the power-up time of 10 ms minimum should be allowed before the CONVST falling edge; otherwise, invalid data is read. Note that all power-up times quoted apply with a 470 nF capacitor on the VREFIN pin. tPOWER-UP B A CONVST 1 14 1 14 04752-048 CLKIN BUSY Figure 38. Autoshutdown/Autostandby Modes Rev. A | Page 24 of 28 AD7934-6 POWER VS. THROUGHPUT RATE 7 TA = 25°C 6 VDD = 5V 5 POWER (mW) A considerable advantage of powering the ADC down after a conversion is that the part’s power consumption is significantly reduced at lower throughput rates. When using the different power modes, the AD7934-6 is only powered up for the duration of the conversion. Therefore, the average power consumption per cycle is significantly reduced. Figure 39 shows a plot of the power vs. the throughput rate when operating in autostandby mode for both VDD = 5 V and 3 V. 4 3 VDD = 3V 2 For example, if the device runs at a throughput rate of 10 kSPS, then the overall cycle time would be 100 µs. If the maximum CLKIN frequency of 10 MHz is used, the conversion time accounts for only 1.315 µs of the overall cycle time while the AD7938-6 stays in standby mode for the remainder of the cycle. If an external reference is used, the power-up time reduces to 600 ns; therefore, the AD7934-6 remains in standby for a greater time in every cycle. Additionally, the current consumption when converting should be lower than the specified maximum of 1.5 mA or 1.2 mA with VDD = 5 V or 3 V, respectively. Figure 40 shows a plot of the power vs. the throughput rate when operating in normal mode for both VDD = 5 V and 3 V. Again, when using an external reference, the current consumption when converting is lower than the specified maximum. In both plots, the figures apply when using the internal reference. 2.0 04752-030 0 0 100 200 300 400 500 THROUGHPUT (kSPS) MICROPROCESSOR INTERFACING AD7934-6 to ADSP-21xx Interface Figure 41 shows the AD7934-6 interfaced to the ADSP-21xx series of DSPs as a memory-mapped device. A single wait state could be necessary to interface the AD7934-6 to the ADSP21xx, depending on the clock speed of the DSP. The wait state can be programmed via the data memory wait state control register of the ADSP-21xx (see the ADSP-21xx family User’s Manual for details). The following instruction reads from the AD7934-6: MR = DM (ADC) ADC is the address of the AD7934-6. DSP/USER SYSTEM VDD = 5V 1.2 A0 TO A15 DMS 0.8 VDD = 3V CONVST ADDRESS BUS AD7934-61 ADSP-21xx1 1.0 ADDRESS DECODER CS IRQ2 0.4 WR WR RD RD 04752-029 0.6 0.2 0 20 40 60 80 THROUGHPUT (kSPS) 100 Figure 39. Power vs. Throughput in Autostandby Mode Using Internal Reference BUSY DB0 TO DB11 120 D0 TO D23 1ADDITIONAL DATA BUS PINS OMITTED FOR CLARITY. Figure 41. Interfacing to the ADSP-21xx Rev. A | Page 25 of 28 04752-044 1.4 0 700 Figure 40. Power vs. Throughput in Normal Mode Using Internal Reference 1.6 POWER (mW) 600 where: TA = 25°C 1.8 1 AD7934-6 DSP/USER SYSTEM AD7934-6 to ADSP-21065L Interface Figure 42 shows a typical interface between the AD7934-6 and the ADSP-21065L SHARC processor. This interface is an example of one of three DMA handshake modes. The MSx control line is actually three memory select lines. Internal ADDR25–24 are decoded into MS3-0. These lines are then asserted as chip selects. The DMAR1 (DMA request 1) is used in this setup as the interrupt to signal the end of the conversion. The rest of the interface is a standard handshaking operation. A0 TO A15 TMS32020/ TMS320C25/ TMS320C501 CONVST ADDRESS BUS AD7934-61 IS ADDRESS EN DECODER CS READY TMS320C25 ONLY MSC STRB WR R/W DSP/USER SYSTEM MSX INTX CONVST ADDRESS BUS BUSY DMD0 TO DMD15 ADDRESS LATCH DATA BUS DB11 TO DB0 1ADDITIONAL PINS OMITTED FOR CLARITY. AD7934-61 04752-046 ADDR0 TO ADDR23 RD Figure 43. Interfacing to the TMS32020/C25/C5x ADDRESS BUS ADDRESS DECODER DMAR1 AD7934-6 to 80C186 Interface CS BUSY RD RD WR WR DB0 TO DB11 DATA BUS 04752-045 D0 TO D31 1ADDITIONAL PINS REMOVED FOR CLARITY. Figure 42. Interfacing to the ADSP-21065L AD7934-6 to TMS32020, TMS320C25, and TMS320C5x Interface Parallel interfaces between the AD7934-6 and the TMS32020, TMS320C25, and TMS320C5x family of DSPs are shown in Figure 43. The memory-mapped address chosen for the AD7934-6 should be chosen to fall in the I/O memory space of the DSPs. The parallel interface on the AD7934-6 is fast enough to interface to the TMS32020 with no extra wait states. If high speed glue logic devices, such as the 74AS, are used to drive the RD and the WR lines when interfacing to the TMS320C25, no wait states are necessary. However, if slower logic is used, data accesses could be slowed sufficiently when reading from, and writing to, the part to require the insertion of one wait state. Extra wait states are necessary when using the TMS320C5x at their fastest clock speeds (see the TMS320C5x User’s Guide for details). Figure 44 shows the AD7934-6 interfaced to the 80C186 microprocessor. The 80C186 DMA controller provides two independent high speed DMA channels where data transfer can occur between memory and I/O spaces. Each data transfer consumes two bus cycles, one cycle to fetch data and the other to store data. After the AD7934-6 has finished a conversion, the BUSY line generates a DMA request to Channel 1 (DRQ1). Because of the interrupt, the processor performs a DMA READ operation that also resets the interrupt latch. Sufficient priority must be assigned to the DMA channel to ensure that the DMA request is serviced before the completion of the next conversion. µP/USER SYSTEM AD0 TO AD15 A16 TO A19 ALE ADDRESS/DATA BUS CONVST ADDRESS LATCH AD7934-61 ADDRESS BUS 80C1861 ADDRESS DECODER DRQ1 Q CS R S BUSY RD RD WR WR DATA BUS DB0 TO DB11 1ADDITIONAL PINS OMITTED FOR CLARITY. Figure 44. Interfacing to the 80C186 Data is read from the ADC using the following instruction: IN D, ADC where: D is the data memory address. ADC is the AD7934-6 address. Rev. A | Page 26 of 28 04752-047 ADSP-21065L1 AD7934-6 APPLICATION HINTS GROUNDING AND LAYOUT The printed circuit board that houses the AD7934-6 should be designed so that the analog and digital sections are separated and confined to certain areas of the board. This facilitates the use of ground planes that can be easily separated. Generally, a minimum etch technique is best for ground planes since it gives the best shielding. Digital and analog ground planes should be joined in only one place, and the connection should be a star ground point established as close to the ground pins on the AD7934-6 as possible. Avoid running digital lines under the device as this couples noise onto the die. The analog ground plane should be allowed to run under the AD7934-6 to avoid noise coupling. The power supply lines to the AD7934-6 should use as large a trace as possible to provide low impedance paths and reduce the effects of glitches on the power supply line. Fast switching signals, such as clocks, should be shielded with digital ground to avoid radiating noise to other sections of the board, and clock signals should never run near the analog inputs. Avoid crossover of digital and analog signals. Traces on opposite sides of the board should run at right angles to each other. This reduces the effects of feedthrough through the board. A microstrip technique is by far the best but is not always possible with a double-sided board. In this technique, the component side of the board is dedicated to ground planes, while signals are placed on the solder side. Good decoupling is also important. All analog supplies should be decoupled with 10 µF tantalum capacitors in parallel with 0.1 µF capacitors to GND. To achieve the best from these decoupling components, they must be placed as close as possible to the device, ideally right up against the device. The 0.1 µF capacitors should have low effective series resistance (ESR) and effective series inductance (ESI), such as the common ceramic types or surface-mount types, which provide a low impedance path to ground at high frequencies to handle transient currents due to internal logic switching. EVALUATING THE AD7934-6 PERFORMANCE The recommended layout for the AD7934-6 is outlined in the evaluation board documentation. The evaluation board package includes a fully assembled and tested evaluation board, documentation, and software for controlling the board from the PC via the evaluation board controller. The evaluation board controller can be used in conjunction with the AD7934-6 evaluation board, as well as with many other ADI evaluation boards ending in the CB designator, to demonstrate/evaluate the ac and dc performance of the AD7934-6. The software allows the user to perform ac (fast Fourier transform) and dc (histogram of codes) tests on the AD7934-6. The software and documentation are on the CD that ships with the evaluation board. Rev. A | Page 27 of 28 AD7934-6 OUTLINE DIMENSIONS 9.80 9.70 9.60 28 15 4.50 4.40 4.30 6.40 BSC 1 14 PIN 1 0.65 BSC 0.15 0.05 COPLANARITY 0.10 0.30 0.19 1.20 MAX SEATING PLANE 0.20 0.09 8° 0° 0.75 0.60 0.45 COMPLIANT TO JEDEC STANDARDS MO-153-AE Figure 45. 28-Lead Thin Shrink Small Outline Package [TSSOP] (RU-28) Dimensions shown in millimeters ORDERING GUIDE Model AD7934BRU-6 AD7934BRU-6REEL7 AD7934BRUZ-62 AD7934BRUZ-6REEL72 EVAL-AD7934-6CB3 EVAL-CONTROL BRD24 Temperature Range −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C Linearity Error (LSB)1 ±1 ±1 ±1 ±1 1 Package Descriptions 28-Lead TSSOP 28-Lead TSSOP 28-Lead TSSOP 28-Lead TSSOP Evaluation Board Controller Board Package Option RU-28 RU-28 RU-28 RU-28 Linearity error here refers to integral linearity error. Z = Pb-free part. 3 This can be used as a standalone evaluation board or in conjunction with the Evaluation Board Controller for evaluation/demonstration purposes. 4 The Evaluation Board Controller is a complete unit that allows a PC to control and communicate with all Analog Devices evaluation boards ending in the CB designators. The following needs to be ordered to obtain a complete evaluation kit: the ADC Evaluation Board (e.g. EVAL-AD7934CB), the EVAL-CONTROL BRD2, and a 12 V ac transformer. See the relevant evaluation board technical note for more details. 2 © 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04752-0-10/05(A) Rev. A | Page 28 of 28