ANALOG DEVICES +2.] V to +5.5 V, 400 kSPS 8-/10-Bit Sampling ADC AD 7813 FEATURES 8-/10-Bit ADC with 2.3 ps Conversion Time On-Chip Track and Hold Operating Supply Range: +2.7 V to +5.5 V Specifications at 2.7 V-3.6 V and 5 V + 10% 8-Bit Parallel Interface 8-Bit + 2-Bit Read Power Performance Normal Operation 10.5 mW, Vop =3V Automatic Power-Down 34.6 pW @ 1kSPS, Vpp = 3 V Analog Input Range: 0 V to Vper Reference Input Range: 1.2 V to Vpp GENERAL DESCRIPTION The AD7813 is a high speed, microprocessor-compatible, 8-/10-bit analog-to-digital converter with a maximum through- put of 400 kSPS. The converter operates off a single +2.7 V to +5.5 V supply and contains a 2.3 Us successive approximation A/D converter, track/hold circuitry, on-chip clock oscillator and 8-bit wide parallel interface. The parallel interface is designed to allow easy interfacing to microprocessors and DSPs. The 10-bit conversion result is read by carrying out two 8-bit read opera- dons. The first read operation accesses the 8 MSBs of the ADC conversion result and the second read accesses the 2 LSBs. Using only address decoding logic the AD7813 is easily mapped into the microprocessor address space. When used in its power-down mode, the AD7813 automatically powers down at the end of a conversion and powers up at the start of a new conversion. This feature significantly reduces the power consumption of the part at lower throughput rates. The AD7813 can also operate in a high speed mode where the part is not powered down between conversions. In this mode of opera- tion the part is capable of providing 400 kSPS throughput. The part is available in a small, 16-pin, 0.3" wide, plastic dual- in-line package (DIP), in a 16-pin, 0.15" wide, narrow body small outline IC (SOIC) and in a 16-pin thin shrink small out- line package (TSSOP). REV.0 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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. FUNCTIONAL BLOCK DIAGRAM Vpp AGND VREF ry AD7813 bB7 CHARGE |_P REDISTRIBUTION THREE. pac DRIVERS cLock DBO osc { COMP CONTROL Vin Logic BUSY CS RD CONVST PRODUCT HIGHLIGHTS 1. Low Power, Single Supply Operation The AD7813 operates from a single +2.7 V to +5.5 V sup- ply and typically consumes only 10.5 mW of power. The power dissipation can be significantly reduced at lower throughput rates by using the automatic power-down mode. i) Automatic Power-Down The automatic power-down mode, whereby the AD7813 goes into power-down mode at the end of a conversion and powers up before the next conversion, means the AD7813 is ideal for battery powered applications; e.g., 34.6 UW (@ 1 KSPS. (See Power vs. Throughput Rate section.) 3. Parallel Interface An easy to use 8-bit wide parallel interface allows interfacing to most popular microprocessors and DSPs with minimal extemal circuitry. 4. Dynamic Specifications for DSP Users In addition to the traditional ADC specifications, the AD7813 is specified for ac parameters, including signal-to-noise ratio and distortion. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 World Wide Web Site: http://www.analog.com Fax: 617/326-8703 Analog Devices, Inc., 1997AD7813-SPECIFICATIONS' (GND =O V, Vorp = +Vpp = 3 V + 10% to5 + 10%. All specifications -40C to +105C unless otherwise noted.) Parameter Y Version Units Test Conditions/Comments DYNAMIC PERFORMANCE fy = 30 KHz, feampre = 350 kHz Signal to (Noise + Distortion) Ratio! 58 dB min Total Harmonic Distortion (THD) 66 dB max Peak Harmonic or Spurious Noise! 66 dB max Intermodulation Distortion" fa = 29.1 kHz, fb = 29.8 kHz 2nd Order Terms 67 dB typ 3rd Order Terms 67 dB typ DC ACCURACY Resolution 10 Bits Minimum Resolution for Which No Missing Codes Are Guaranteed 10 Bits Relative Accuracy! +1 LSB max Differential Nonlinearity (ONL)! +1 LSB max Gain Error! +2 LSB max Offset Error! +2.0 LSB max ANALOG INPUT Input Voltage Range 0 V min VRer V max Input Leakage Current? +1 HA max Input Capacitance" 20 pF max REFERENCE INPUTS? Vrur Input Voltage Range 1.2 V min Vop V max Input Leakage Current +3 pA max Input Capacitance 15 pF max LOGIC INPUTS? Vin, Input High Voltage 2.0 VY min Vint, Input Low Voltage 0.4 V max (0.8 Vmax, Vpp = 5 V) Input Current, In +1 HA max Typically 10 nA, Vay = 0 V to Vpp Input Capacitance, Cpy 8 pF max LOGIC OUTPUTS Output High Voltage, Vou 2.4 V min Isournce = 200 pA Output Low Voltage, Voy 0.4 V max Towk = 200 pA High Impedance Leakage Current +1 pA max High Impedance Capacirance 15 pF max CONVERSION RATE Conversion Time 2.3 pis max Track/Hold Acquisition Time! 100 ns max POWER SUPPLY Vop 2.7-3.5 Volts For Specified Performance Ipp Digital Inputs = 0 V or Vop Normal Operation 3.5 mA max Power-Down 1 HA max Vop =5V Power Dissipation Normal Operation 17.5 mW max Vop=5V Power-Down 5 LW max Auto Power-Down Vpp=3V 1 KSPS Throughput 34.6 pW max 10 kSPS Throughput 346.5 pW max 100 kSPS Throughput 3.46 mW max NOTES 'See Terminology section. "Sample tested during initial release and after any redesign or process change that may affect this parameter. Specifications subject to change without notice. REV. 0AD7813 Tl MING CHARACTERISTI cs! 2 (40C to +125C, unless otherwise noted) Parameter Vpp = 3 V+410% | Vpp=5V410% | Units Conditions/Comments tpowER-UP 1 1 pis (max) Power-Up Time of AD7813 after Rising Edge of CONVST. ty 2.3 2.3 pis (max) Conversion Time. tz 20 20 ns (min) CONVST Pulse Width. ts 30 30 ns (max) CONVST Falling Edge to BUSY Rising Edge Delay. ty 0 0 ns (min) CS to RD Setup Time. ts 0 0 ns (min) CS Hold Time after RD High. ts? 10 10 ns (max) Data Access Time after RD Low. ty24 10 10 ns (max) Bus Relinquish Time after RD High. 5 5 ns (min) ts 10 10 ns (min) Minimum Time Between MSB and LSB Reads. ty 50 50 us(min) | Rising Edge of CS or RD to Falling Edge of CONVST Delay. NOTES Sample tested to ensure compliance. "See Figures 12, 13 and 14. ?These numbers are measured with the load circuit of Figure 1. They are defined as the time required for the o/p to cross 0.8 V or 2.4 V for Vop = 5 V+ 10% and 0.4V or 2 V for Vpp = 3 Vt 10%. Derived from the measured time taken by the data outputs to change 0.5 V when loaded with the circuit of Figure 1. The measured number is then extrapolated back to remove the effects of charging or discharging the 50 pF capacitor. This means that the time, t;, quoted in the Timing Characteristics is the true bus relinquish time of the part and as such is independent of external bus loading capacitances. ABSOLUTE MAXIMUM RATINGS* Vop to DGND Digital Input Voltage to DGND (CONVST, RD, CS) Digital Output Voltage to DGND (BUSY, DBO-DB7) REF, to AGND Analog Input Storage Temperature Range -0.3Vtot+7V -0.3.V, Vop + 0.3V 0.3 V, Vop + 0.3V -0.3 V; Vpp + 0.3V 0.3 V, Vop + 0.3V 65C to +150C +1.6V Figure 1. Load Circuit for Digital Output Timing Specifications Junction Temperature ..........-0.000-00000 cee +150C Plastic DIP Package, Power Dissipation .......... 450 mW 05, Thermal Impedance ................... +105C AW Lead Temperature, (Soldering 10 sec) ........... +260C SOIC Package, Power Dissipation ............... 450 mW Oj, Thermal Impedance ......... 0.000000. 00, 75 CW Lead Temperature, Soldering Vapor Phase (60 sec) .......0..0-0.02000000005 +215C Infrared (15 sec) 2... eee eee +220C SSOP Package, Power Dissipation ............... 450 mW @;, Thermal Impedance ...........000 seas 115C Ww Lead Temperature, Soldering Vapor Phase (60 sec) .. 0... 02. +215C Infrared (15 sec) oc ees +220C ESD oo eee eee eens <4 kV *Stresses above those listed under Absolute Maximum Ratings may cause perma- nent 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 condi- tions for extended periods may affect device reliability. REV. 0 ORDERING GUIDE Linearity Error Package Package Model (LSB) Description Option AD7813YN [+1 LSB | Plastic DIP N-16 AD7813YR |+1LSB_ | Small CudineIC R-16A AD7813YRU |+1 LSB | Thin Shrmk Small Cutline | RU-16 (TSSOP)AD7813 PIN FUNCTION DESCRIPTIONS Pin No. Mnemonic Description 1 VeEF Reference Input, 1.2 V to Vpp. 2 Vin Analog Input, 0 V to Vpgp. 3 GND Analog and Digital Ground. 4 CONVST Convert Start. A low-to-high transition on this pin initiates a 1 ps pulse on an internally generated CONVST signal. A high-to-low transition on this line initiates the conversion process if the internal CONVST signal is low. Depending on the signal on this pin at the end of a conversion, the AD7813 automatically powers down. cs Chip Selecr. This is a logic input. CS is used in conjunction with RD ro enable ourpurs. 6 RD Read Pin. This is a logic input. When CS is low and RD goes low, the DB7-DB0 leave their high impedance state and data is driven onto the data bus. 7 BUSY ADC Busy Signal. This is a logic output. This signal goes logic high during the conversion process. 8-15 DBo-DB7 Data Bit 0 to 7. These ourputs are three-state I'[L-compatible. 16 Vop Positive power supply voltage, +2.7 V to +5.5 V. PIN CONFIGURATION DIP/SOIC Vrer [1] @ 6] Yop Vin [2] ig] 087 enb [3 | fa] Be convat [a] AD7813 ra] DBS ts [5] (Not to Seale) 2] 054 Ap [6 | fa] 56s BUSY ro] bez peo [a] [a] 051 _4- REV. 0AD7813 TERMINOLOGY Signal to (Noise + Distortion) Ratio This is the measured ratio of signal to (noise + distortion) at the output of the A/D converter. The signal is the rms amplitude of the fundamental. Noise is the rms sum of all nonfundamental signals up to half the sampling frequency (f,/2), excluding dc. The ratio is dependent upon the number of quantization levels in the digitization process; the more levels, the smaller the quan- tization noise. The theoretical signal to (noise + distortion) ratio for an ideal N-bit converter with a sine wave input is given by: Signal to (Noise + Distortion) = (6.02N + 1.76) dB Thus for an 10-bit converter, this is 62 dB. Total Harmonic Distortion Total harmonic distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7813 it is defined as: Vr es Pe Ps Ve where I; is the rms amplitude of the fundamental and V2, V3, V,, V; and V, are the rms amplitudes of the second through the sixth harmonics. THD (dB) = 20 log Peak Harmonic or Spurious Noise Peak harmonic or spurious noise is defined as the ratio of the rms value of the next largest component in the ADC output spectrum (up to fe/2 and excluding dc) to the rms value of the fundamental. Normally, the value of this specification is deter- mined by the largest harmonic in the spectrum, but for parts where the harmonics are buried in the noise floor, it will be a noise peak. Intermodulation Distortion With inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities will create distortion products at sum and difference frequencies of mfa + nfb where m,n=0, 1, 2, 3, etc. Intermodulation 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 AD7813 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 and third order terms are of differ- ent significance. 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 sepa- rately. 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 fundamental expressed in dBs. REV. 0 Relative Accuracy Relative accuracy or endpoint nonlinearity is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. Differential Nonlinearity 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 (0000... 000) to (0000. ..001) fromm the ideal, i.e., 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 (1111... 110) to (1111...111) from the ideal, i.c., 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. Track/Hold Acquisition Time Track/hold acquisition time is the time required for the output of the track/hold amplifier to reach its final value, within +1/2 LSB, after the end of conversion (the point at which the track/hold returns to track mode). It also applies to situations where a change in the selected input channel takes place or where there is a step input change on the input voltage applied to the selected V4 input of the AD7813. It means that the user must wait for the duration of the track/hold acquisition time after the end of conversion, or after a step input change to Vay, before starting another conversion, to ensure that the part operates to specification.AD7813 CIRGUIT DESCRIPTION Converter Operation The AD7813 is a successive approximation analog-ro-digital converter based around a charge redistribution DAC. The ADC can convert analog input signals in the range 0 V to Vpp. Fig- ures 2 and 3 below show simplified schematics of the ADC. Figure 2 shows the ADC during its acquisition phase. SW2 is closed and SW'1 is in Position A, the comparator is held in a balanced condition and the sampling capacitor acquires the signal on Vyy.- CHARGE REDISTRIBUTION DAC SAMPLING a CAPACITOR Vint O-O-0] ee ew CONTROL Loaic ACQUISITION PHASE COMPARATOR } AGND Vpp/3 ose Figure 2. ADC Track Phase When the ADC starts a conversion (see Figure 3), SW2 will open and SW 1 will move to Position B, causing the comparator to become unbalanced. The Control Logic and the Charge Redistribution DAC are used to add and subtract fixed amounts of charge from the sampling capacitor so as to bring the com- parator back into a balanced condition. When the comparator is rebalanced the conversion is complete. The Control Logic gen- erates the ADC output code. Figure 7 shows the ADC transfer function. CHARGE REDISTRIBUTION DAC SAMPLING A CAPACITOR Vint O-O Int Swi CONTROL Sw Logic CONVERSION PHASE COMPARATOR # AGND Vpp/3 oan Figure 3. ADC Conversion Phase TYPICAL CONNECTION DIAGRAM Figure 4 shows a typical connection diagram for the AD7813. The parallel interface is implemented using an 8-bit data bus, the falling edge of CONVST brings the BUSY signal high, and at the end of conversion the falling edge of BUSY is used to ini- tiate an Interrupt Service Routine (SR) on a microprocessor see Parallel Interface section for more details. Vgpp is connected to a well decoupled Vpp pin to provide an analog input range of 0 V to Vop. When Vpp is first connected the AD7813 powers up in alow current mode, i.e., power-down. A rising edge on an internal CONVST input will cause the part to power upsee Power-Up Times. If power consumption is of concern, the automatic power-down at the end of a conversion should be used to improve power performance. See Power vs. Throughput Rate section of the data sheet. PARALLEL INTERFACE DB0-DB7 AD7813 OV TO Vper INPUT pOipP Figure 4. Typical Connection Diagram Analog Input Figure 5 shows an equivalent circuit of the analog imput struc- ture of the AD7813. The two diodes, D1 and D2, provide ESD protection for the analog inputs. Care must be taken to ensure that the analog input signal never exceeds the supply rails by more than 200 mV. This will cause these diodes to become forward biased and start conducting current into the substrate. The maximum current these diodes can conduct without caus- ing irreversible damage to the part is 20 mA. The capacitor C2, in Figure 5, is typically about 4 pF and can be primarily attrib- uted to pin capacitance. The resistor R1 is a lumped component made up of the on resistance of a multiplexer and a switch. This resistor is cypically about 125 . The capacitor C1 is the ADC sampling capacitor and has a capacitance of 3.5 pF. ci Ri 125Q | 3-5pF - Voo2 CONVERT PHASE SWITCH OPEN TRACK PHASE SWITCH CLOSED Figure 5. Equivalent Analog Input Circuit DC Acquisition Time The ADC starts a new acquisition phase at the end of a conver- sion and ends on the falling edge of the CONVST signal. Ar the end of a conversion there is a settling time associated with the sampling circuit. This settling time lasts approximately 100 ns. The analog signal on Vpy is also being acquired during this settling ume; therefore, the minimum acquisition time needed is ap- proximately 100 ns. Figure 6 shows the equivalent charging circuit for the sampling capacitor when the ADC is in its acquisition phase. R2 repre- sents the source impedance of a buffer amplifier or resistive network, R1 is an internal multiplexer resistance and C1 is the sampling capacitor. R1 Vin 1250 ct rl Figure 6. Equivalent Sampling Circuit REV. 0AD7813 During the acquisition phase the sampling capacitor must be charged cto within a 1/2 LSB of its final value. The time it rakes to charge the sampling capacitor (Teyapas) is given by the following formula: Tonarge = 7.6 X (R2 + 125 ) x 3.5 pF For small values of source impedance, the settling time associ- ated with the sampling circuit (100 ns) is, in effect, the acquisi- ton time of the ADC. For example, with a source impedance (R2) of 10 the charge time for the sampling capacitor is approximately 4 ns. The charge time becomes significant for source impedances of 2 kQ and greater. AC Acquisition Time In ac applications it is recommended to always buffer analog input signals. The source impedance of the drive circuitry must be kept as low as possible to minimize the acquisition time of the ADC. Large values of source impedance will cause the THD to degrade at high throughput rates. ADC TRANSFER FUNCTION The output coding of the AD7813 is straight binary. The de- signed code transitions occur at successive integer LSB values (i.e., 1 LSB, 2 LSBs, etc.). The LSB size is = Vppp/1024. The ideal transfer characteristic for the AD7813 is shown in Figure 7. 114...111 111...110 WwW Q 111...000 8 : 1LSB = Vper024 o Boot a . . 000...010 000...001 000...000 ==} we T py (LSB +VREF-1LSB ANALOG INPUT Figure 7. Transfer Characteristic POWER-UP TIMES The AD7813 has a 1 ps power-up time. When Vopp is first con- nected, the AD7813 is in a low current mode of operation. In order to carry out a conversion the AD7813 must first be pow- ered up. The ADC is powered up by a rising edge on an inter- nally generated CONVST signal, which occurs as a result of a rising edge on the external CONVST pin. The rising edge of the external CONVST signal initiates a 1 ps pulse on the internal CONVST signal. This pulse is presenr to ensure the part has enough time to power up before a conversion is initiated, as a conversion is initiated on the falling edge of gared CONVST. See Timing and Control section. Care must be taken to ensure that the CONVST pin of the AD7813 is logic low when Vpp is first applied. REV. 0 When operating in Mode 2, the ADC is powered down at the end of each conversion and powered up again before the next conversion is initiated. (See Figure 8.) MODE 1 S 7 te te Vpp + 31 tL EXT CONVST f x i \ f x f tpower-uP _ ips 3 INT CONVST je MODE 2 31 51. 5 Yop Sf At Me Lea EXT CONVST / % / X tpower-uP tpower-uP - Ips Ips a 3 dE INT CONVST ys * Figure 8. Power-Up Times POWER VS. THROUGHPUT RATE By operating the AD7813 in Mode 2, the average power con- sumption of the AI7813 decreases at lower throughput rates. Figure 9 shows how the Automatic Power-Down is implemented using the external CONVST signal to achieve the optimum power performance for the AD7813. The AD7813 is operated in Mode 2, and the duration of the external CONVST pulse is set to be equal to or less than the power-up time of the device. As the throughput rate is reduced, the device remains in its power- down state longer and the average power consumption over time drops accordingly. EXT CONVET / aa wt w tpower-uptconvert ry bag 1.5-peleg 2.015 pole POWER-DOWN ? 32 re rey INT CONVST . a Ei * teveLe 100s @ 10kSPS Figure 9. Automatic Power-Down For example, if the AD7813 is operated in a continuous sam- pling mode, with a throughpur rate of 10 kSPS, the power con- sumption is calculated as follows. The power dissipation during normal operation is 10.5 mW, Vpp = 3 V. If the power-up time is 1 us and the conversion time is 2.3 Us, the AI)7813 can then be said to dissipate 10.5 mW for 3.3 us (worst case) during each conversion cycle. If the throughput rate is 10 kKSPS, the cycle Ume is 100 us and the average power dissipated during each cycle is (3.3/100) x (10.5 mW) = 346.5 pW.AD7813 Typical Performance Characteristics 10 POWER mW O14 0.04 a 5 10 15 20 25 30 THROUGHPUT kSPS 35 40 45 50 Figure 10. Power vs. Throughput AD7B13 2048 POINT FFT SAMPLING 357.142kHz 30.168kHz dBs W635 52 70 87 86105 122 FREQUENCY kHz 140 157 174 Figure 17. SNR TIMING AND CONTROL The AD7813 has only one input for timing and control, j.e., the CONVST (convert start signal). The rising edge of this CONVST signal initiates a 1 us pulse on an internally generated CONVST signal. This pulse is present to ensure the part has enough time to power up before a conversion is initiated. If the external CONVST signal is low, the falling edge of the internal CONVST signal will cause the sampling circuit to go into hold mode and initiate a conversion. If, however, the external CONVST signal is high when the internal CONVST goes low, it is upon the falling edge of rhe external CONVS'T signal that the sampling circuitry will go into hold mode and initiate a conversion. The use of the internally generated 1 us pulse, as previously described, can be likened to the configuration shown in Figure 12. The application of a CONVST signal at the CONVST pin triggers the generation of a 1 ps pulse. Both the external CONVST and this internal CONVST are input to an OR gate. The resulting signal has the duration of the longer of the two input signals. Once a conversion has been initiated the BUSY signal goes high to indicate a conversion is in progress. At the end of conversion the sampling circuit goes back into its tracking mode again. The end of conversion is indicated by the BUSY signal going low. This signal may be used to initiate an ISR on a microprocessor. At this point the conversion result is latched into the output register where it may be read. The AD7813 has an 8-bit wide parallel interface. The 10-bit conversion result is accessed by performing two successive read operations. The first 8-bit read accesses the 8 MSBs of the conversion result and the second read accesses the 2 LSBs, as illustrated in Figure 13, where one performance of the rwo successive reads is highlighted after the falling edge of BUSY. The state of the external CONVST signal at the end of conversion also establishes the mode of opera- tion of the AD7813. Mode 1 Operation (High Speed Sampling) If the external CONVST is logic high when BUSY goes low, the part is said to be in Mode 1 operation. While operating in Mode 1, the AD7813 will not power down between conversions. The AD7813 should be operated in Mode 1 for high speed sampling applications, i.e., throughputs grearer than 100 kSPS. Figure 13 shows the timing for Mode 1 operation. From this diagram one can see that a minimum delay of the sum of the conversion time and read time must be left between two successive falling edges of the external CONVST. This is to ensure that a conversion is not initiated during a read. Mode 2 Operation (Automatic Power-Down) At slower throughput rates the AD7813 may be powered down between conversions to give a superior power performance. This is Mode 2 Operation and it is achieved by bringing the CONVST signal logic low before the falling edge of BUSY. Figure 14, overleaf, shows the timing for Mode 2 Operation. The falling edge of the external CONVST signal may occur before or after the falling edge of the internal CONVST signal, but it is the later occurring fallmg edge of both that controls when the first conversion will take place. If the falling edge of the external CONVS'T occurs after that of the internal CONVST, it means that the moment of the first conversion is controlled exactly, regardless of any jitter associated with the internal CONVST signal. The parallel interface is still fully operational while the AD7813 is powered down. The AD7813 is powered up again on the rising edge of the CONVST signal. The gated CONVST pulse will now remain high long enough for the AD7813 to fully power up, which takes about 1 ps. This is ensured by the internal CONVST signal, which will remain high for 1 ps. TONVET ExT (PIN 4) GATED ! INT | LJ L ips I Figure 72. REV. 0AD7813 2 i oy 31 bh MM q A EXT CONVST / 3 trower-up ty, INT CONVST i x te \ f te \ f we BUSY a =] DB?7-DBO Figure 13. Mode 7 Operation EXT CONVST i tpowen-up bt, INTCONVST a ts - BUSY h SAD we Me DB7-DBO 7 2 Figure 14. Mode 2 Operation PARALLEL INTERFACE The parallel interface of the AID7813 is eight bits wide. The ourput data buffers are activated when both CS and RD are logic low. At this point the contents of the data register are placed on the 8-bir data bus. Figure 15 shows the timing dia- gram for the parallel port. As previously explained, two succes- sive read operations must take place in order to access the 10-bit conversion result. The first read places the 8 MSBs on the data bus and the second read places the 2 LSBs on the data bus. The 2 LSBs appear on DB7 and DB6, with DB5DB0 set to logic zero. 7{ | 7c cal ty ts F BUSY \ CONVST Further read operations will access the 8 MSBs and 2 LSBs of the 10-bit ADC conversion result again. The parallel interface of the AD7813 is reset when BUSY goes logic high. This feature allows the AD7813 to be used as an 8-bit converter if the user only wishes to access rhe 8 MSBs of the conversion. Care must be taken to ensure that a read operation does not occur while BUSY is high. Data read from the AD7813 while BUSY is high will be invalid. For optimum performance the read operation should end at least 100 ns (t,,) prior to the falling edge of the next CONVST. laa thy UW DB7-DBoO a 3 Figure 15. Parallel Port Timing REV. 0AD7813 MICROPROCESSOR INTERFACING The parallel port on the AD7813 allows the device to be inter- faced to a range of many different microcontrollers. This section explains how to interface the AD7813 with some of the more common microcontroller parallel interface protocols. AD7813 to 8051 Figure 16 shows a parallel interface between the AD7813 and the 8051 microcontroller. The BUSY signal on the AD7813 pro- vides an interrupt request to the 8051 when a conversion begins. Port 0 of the 8051 may serve as an input or output port, or as in this case when used together, may be used as a bidirectional low-order address and data bus. The address latch enable out- put of the 8051 is used to latch the low byte of the address dur- ing accesses to the device, while the high-order address byte is supplied from Port 2. Port 2 latches remain stable when the AD7813 is addressed, as they do not have to be turned around (set to 1) for data input as is the case for Port 0. 8051" DBO-DB7 ADO-AD7 LATCH AD7813* DECODER ALE cs AB-A15 AD - AD INT [= BUSY *ADDITIONAL PINS OMITTED FOR CLARITY Figure 16. Interfacing to the 8057 AD7813 to PICI6C6x/7x Figure 17 shows a parallel mterface between the AD7813 and the PIC16C64/65/74. The BUSY signal on the AD7813 provides an interrupt request to the microcontroller when a conversion begins. Of the PIC 16C6x/7x range of microcontrollers only the PIC16C 64/65/74 can provide the option of a parallel slave port. Port D of the microcontroller will operate as an 8-bit wide parallel slave port when control bit PSPMODE in the TRISE register is set. Setting PSPMODE enables the port pin REO to be the RD output and RE2 to be the CS outpur. For this functionality, the corresponding data direction bits of the TRISE register must be configured as outputs (reset to 0). See PIC16/17 Microcontroller User Manual. PSPO-PSP7 PIC16C6X/7x* DBO-DB? AD7813* BUSY ADDITIONAL PINS OMITTED FOR CLARITY Figure 17. Interfacing to the PIC 16C6x/7x AD7813 to ADSP-21xx Figure 18 shows a parallel interface between the AD7813 and the ADSP-21xx series of DSPs. As before, the BUSY signal on the AD7813 provides an interrupt request to the DSP when a conversion begins. D7-D0 A13-A0 ADSP-21 xx* 3 A a Oo =} EN ADDRESS DECODE Logic IL RD DBO-DB7 AD7813* BUSY *ADDITIONAL PINS OMITTED FOR CLARITY Figure 18. Interfacing to the ADSP-2 Ixx -10- REV. 0AD7813 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 16-Lead Plastic DIP (N-16) 0.840 (21.39) 0.745 (18.93) * | F 9] 0.280 7.11) = || O40 6-10) 0.325 (8.25) i 0.080 (1.52) 0.900 (762) a 0.210 (5.33) 0.015 (0.38) + MAX g UU 0.130 0.160 (4.06) | i (830) OSE R) Coie =< 0.015 (0.381) 0.022 (0.558) 0.100 0.070 (1.77) SEATING 5.008 (0.204) 0.014 (0.356) (254) o.045 (1.15) PLANE BSC 16-Lead Small Outline Package (R-16A) 0.3937 (10.00) 9.3880 , 8 16 0.2440 (6.20) + 0.1574 (4.00) 0.2284 (5.80) 0.1497 (3.80) )71 8 PIN 1 0.0688 (1.75) 0.0196 (0.50) 0.0098 (0.25) 0.0832 (1.35) *| 0.0099 (0.25) 0.0040 (0.10) Cos L hfe oe lt 8 ol Lag O.0s00 0.0182 (0.49) ange (0.25) o,0s00 (1.27) soaNe (27) gorges) 70009 (0.28 PLANE . (0.85) 0.0075 (0.18) 0.0760 (0.41) 16-Lead Thin Shrink Small Outline Package (RU- 16) 3.183 42.90 LAA RRL a 16 9 ai 0.177 (4.50) 0.169 (4.30) 0.256 (6.50) 0.246 (6.25) MITT: PIN 4 0.008 (0.15) 0.002 (0.05) 0.0433 BREET Fi ia MAX 0.028 (0.70) Th . 0.0118 (0.20 a ANE (85) 0.0075 a 5) o. ars (0.20) none @s) BSC 0.0085 (0.090) REV. 0 -11-16/3-ZL-090E9 ST NI GALNIdd -12-