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a
3 V/5 V, 2 MSPS, 8-Bit, 1-, 4-, 8-Channel Sampling ADCs AD7822/AD7825/AD7829
FUNCTIONAL BLOCK DIAGRAM
CONVST EOC A0* A1* A2* PD* VDD
FEATURES 8-Bit Half-Flash ADC with 420 ns Conversion Time 1, 4 and 8 Single-Ended Analog Input Channels Available with Input Offset Adjust On-Chip Track-and-Hold SNR Performance Given for Input Frequencies Up to 10 MHz On-Chip Reference (2.5 V) Automatic Power-Down at the End of Conversion Wide Operating Supply Range 3 V 10% and 5 V 10% Input Ranges 0 V to 2 V p-p, VDD = 3 V 10% 0 V to 2.5 V p-p, VDD = 5 V 10% Flexible Parallel Interface with EOC Pulse to Allow Stand-Alone Operation APPLICATIONS Data Acquisition Systems, DSP Front Ends Disk Drives Mobile Communication Systems, Subsampling Applications GENERAL DESCRIPTION
CONTROL LOGIC
COMP
2.5V REF
VIN1 VIN2* VIN3* VIN4* VIN5* VIN6* VIN7* VIN8*
BUF
VREFIN / OUT
INPUT MUX
T/H
8-BIT HALF FLASH ADC
PARALLEL PORT
DB7 DB0
VMID *A0, A1 *A2 *PD *VIN2 TO VIN4 *VIN4 TO VIN8
AGND
DGND
CS RD
AD7825/AD7829 AD7829 AD7822/AD7825 AD7825/AD7829 AD7829
The AD7822, AD7825, and AD7829 are high speed, 1-, 4-, and 8-channel, microprocessor-compatible, 8-bit analog-to-digital converters with a maximum throughput of 2 MSPS. The AD7822, AD7825, and AD7829 contain an on-chip reference of 2.5 V (2% tolerance), a track/hold amplifier, a 420 ns 8-bit half-flash ADC and a high speed parallel interface. The converters can operate from a single 3 V 10% and 5 V 10% supply. The AD7822, AD7825, and AD7829 combine the convert start and power-down functions at one pin, i.e., the CONVST pin. This allows a unique automatic power-down at the end of a conversion to be implemented. The logic level on the CONVST pin is sampled after the end of a conversion when an EOC (End of Conversion) signal goes high, and if it is logic low at that point, the ADC is powered down. The AD7822 and AD7825 also have a separate power-down pin. (See Operating Modes section of the data sheet.) The parallel interface is designed to allow easy interfacing to microprocessors and DSPs. Using only address decoding logic, the parts are easily mapped into the microprocessor address space. The EOC pulse allows the ADCs to be used in a standalone manner. (See Parallel Interface section of the data sheet.)
The AD7822 and AD7825 are available in a 20-/24-lead 0.3" wide, plastic dual-in-line package (DIP), a 20-/24-lead small outline IC (SOIC) and a 20-/24-lead thin shrink small outline package (TSSOP). The AD7829 is available in a 28-lead 0.6" wide, plastic dual-in-line package (DIP), a 28-lead small outline IC (SOIC) and in a 28-lead thin shrink small outline package (TSSOP).
PRODUCT HIGHLIGHTS
1. Fast Conversion Time The AD7822, AD7825, and AD7829 have a conversion time of 420 ns. Faster conversion times maximize the DSP processing time in a real-time system. 2. Analog Input Span Adjustment The VMID pin allows the user to offset the input span. This feature can reduce the requirements of single-supply op amps and take into account any system offsets. 3. FPBW (Full Power Bandwidth) of Track-and-Hold The track-and-hold amplifier has an excellent high-frequency performance. The AD7822, AD7825, and AD7829 are capable of converting full-scale input signals up to a frequency of 10 MHz. This makes the parts ideally suited to subsampling applications. 4. Channel Selection Channel selection is made without the necessity of writing to the part.
REV. B
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. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 2001
AD7822/AD7825/AD7829-SPECIFICATIONS (V V = 2.5 V. All specifications -40 C to +85 C unless otherwise noted.)
REF IN/OUT
DD
=3V
10%, VDD = 5 V
10%, GND = 0 V,
Parameter DYNAMIC PERFORMANCE Signal to (Noise + Distortion) Ratio1 Total Harmonic Distortion1 Peak Harmonic or Spurious Noise1 Intermodulation Distortion1 2nd Order Terms 3rd Order Terms Channel-to-Channel Isolation1 DC ACCURACY Resolution Minimum Resolution for Which No Missing Codes Are Guaranteed Integral Nonlinearity (INL)1 Differential Nonlinearity (DNL)1 Gain Error1 Gain Error Match1 Offset Error1 Offset Error Match1 ANALOG INPUTS2 VDD = 5 V 10% VIN1 to VIN8 Input Voltage VMID Input Voltage VDD = 3 V 10% VIN1 to VIN8 Input Voltage VMID Input Voltage VIN Input Leakage Current VIN Input Capacitance VMID Input Impedance REFERENCE INPUT VREF IN/OUT Input Voltage Range Input Current ON-CHIP REFERENCE Reference Error Temperature Coefficient LOGIC INPUTS Input High Voltage, VINH Input Low Voltage, VINL Input High Voltage, VINH Input Low Voltage, VINL Input Current, IIN Input Capacitance, CIN LOGIC OUTPUTS Output High Voltage, VOH
Version B 48 -55 -55 -65 -65 -70 8 8 0.75 0.75 2 0.1 1 0.1
Unit dB min dB max dB max
Test Condition/Comment fIN = 30 kHz. fSAMPLE = 2 MHz
fa = 27.3 kHz, fb = 28.3 kHz dB typ dB typ dB typ Bits Bits LSB max LSB max LSB max LSB typ LSB max LSB typ See Analog Input Section Input Voltage Span = 2.5 V VDD 0 VDD - 1.25 1.25 VDD 0 VDD - 1 1 1 15 6 2.55 2.45 1 100 50 50 2.4 0.8 2 0.4 1 10 V max V min V max V min V max V min V max V min A max pF max k typ V max V min A typ A max mV max ppm/C typ V min V max V min V max A max pF max VDD = 5 V 10% VDD = 5 V 10% VDD = 3 V 10% VDD = 3 V 10% Typically 10 nA, VIN = 0 V to VDD
fIN = 20 kHz
Default VMID = 1.25 V Input Voltage Span = 2 V
Default VMID = 1 V
2.5 V + 2% 2.5 V - 2%
Nominal 2.5 V
4 2.4 Output Low Voltage, VOL High Impedance Leakage Current High Impedance Capacitance 0.4 0.2 1 10
V min V min V max V max A max pF max
ISOURCE = 200 A VDD = 5 V 10% VDD = 3 V 10% ISINK = 200 A VDD = 5 V 10% VDD = 3 V 10%
-2-
REV. B
AD7822/AD7825/AD7829
Parameter CONVERSION RATE Track/Hold Acquisition Time Conversion Time POWER SUPPLY REJECTION VDD 10% POWER REQUIREMENTS VDD VDD IDD Normal Operation Power-Down Power Dissipation Normal Operation Power-Down 200 kSPS 500 kSPS Version B 200 420 1 4.5 5.5 2.7 3.3 12 5 0.2 36 9.58 23.94 Unit ns max ns max LSB max V min V max V min V max mA max A max A typ mW max mW typ mW typ 5 V 10%. For Specified Performance 3 V 10%. For Specified Performance 8 mA Typically Logic Inputs = 0 V or VDD VDD = 3 V Typically 24 mW Test Condition/Comment See Functional Description Section
NOTES 1 See Terminology section of this data sheet. 2 Refer to the Analog Input section for an explanation of the Analog Input(s). Specifications subject to change without notice.
ORDERING GUIDE
200 A IOL
Model
TO OUTPUT PIN CL 50pF 2.1V
Linearity Error 0.75 LSB 0.75 LSB 0.75 LSB 0.75 LSB 0.75 LSB 0.75 LSB 0.75 LSB 0.75 LSB 0.75 LSB
Package Description Plastic DIP Small Outline IC Thin Shrink Small Outline (TSSOP) Plastic DIP Small Outline IC Thin Shrink Small Outline (TSSOP) Plastic DIP Small Outline IC Thin Shrink Small Outline (TSSOP)
Package Option N-20 R-20 RU-20 N-24 R-24 RU-24 N-28 R-28 RU-28
AD7822BN AD7822BR AD7822BRU AD7825BN AD7825BR AD7825BRU AD7829BN AD7829BR AD7829BRU
200 A
IOH
Figure 1. Load Circuit for Access Time and Bus Relinquish Time
REV. B
-3-
AD7822/AD7825/AD7829 TIMING CHARACTERISTICS1, 2 (V
Parameter 5 V t1 t2 t3 t4 t5 t6 t7 t8 t9 3 t104 t11 t12 t13 tPOWER UP tPOWER UP 420 20 30 110 70 10 0 0 30 10 5 20 10 15 200 25 1 10% 3V 420 20 30 110 70 10 0 0 30 20 5 20 10 15 200 25 1 10% Unit
REF IN/OUT
= 2.5 V. All specifications -40 C to +85 C unless otherwise noted.)
Conditions/Comments Conversion Time. Minimum CONVST Pulsewidth. Minimum time between the rising edge of RD and next falling edge of convert start. EOC Pulsewidth. RD rising edge to EOC pulse high. CS to RD setup time. CS to RD hold time. Minimum RD Pulsewidth. Data access time after RD low. Bus relinquish time after RD high. Address setup time before falling edge of RD. Address hold time after falling edge of RD. Minimum time between new channel selection and convert start. Power-up time from rising edge of CONVST using on-chip reference. Power-up time from rising edge of CONVST using external 2.5 V reference.
ns max ns min ns min ns max ns min ns max ns min ns min ns min ns max ns min ns max ns min ns min ns min s typ s max
NOTES 1 Sample tested to ensure compliance. 2 See Figures 20, 21, and 22. 3 Measured with the load circuit of Figure 1 and defined as the time required for an output to cross 0.8 V or 2.4 V with V DD = 5 V 10%, and time required for an output to cross 0.4 V or 2.0 V with V DD = 3 V 10%. 4 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 10, 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*
(TA = 25C unless otherwise noted)
VDD to AGND . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to +7 V VDD to DGND . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to +7 V Analog Input Voltage to AGND VIN1 to VIN8 . . . . . . . . . . . . . . . . . . . -0.3 V to VDD + 0.3 V Reference Input Voltage to AGND . . . -0.3 V to VDD + 0.3 V VMID Input Voltage to AGND . . . . . . . -0.3 V to VDD + 0.3 V Digital Input Voltage to DGND . . . . . -0.3 V to VDD + 0.3 V Digital Output Voltage to DGND . . . . -0.3 V to VDD + 0.3 V Operating Temperature Range Industrial (B Version) . . . . . . . . . . . . . . . . -40C to +85C Storage Temperature Range . . . . . . . . . . . . -65C to +150C Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 150C Plastic DIP Package, Power Dissipation . . . . . . . . . . 450 mW JA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 105C/W Lead Temperature, (Soldering, 10 sec) . . . . . . . . . . . 260C
SOIC Package, Power Dissipation . . . . . . . . . . . . . . . 450 mW JA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 75C/W Lead Temperature, Soldering Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . 215C Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . 220C TSSOP Package, Power Dissipation . . . . . . . . . . . . . 450 mW JA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 128C/W Lead Temperature, Soldering Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . 215C Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . 220C ESD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 kV
*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.
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 the AD7822/AD7825/AD7829 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.
WARNING!
ESD SENSITIVE DEVICE
-4-
REV. B
AD7822/AD7825/AD7829
PIN FUNCTION DESCRIPTIONS
Mnemonic VIN1 to VIN8
Description Analog Input Channels. The AD7822 has a single input channel; the AD7825 and AD7829 have four and eight analog input channels respectively. The inputs have an input span of 2.5 V and 2 V depending on the supply voltage (VDD). This span may be centered anywhere in the range AGND to VDD using the VMID Pin. The default input range (VMID unconnected) is AGND to 2 V (VDD = 3 V 10%) or AGND to 2.5 V (VDD = 5 V 10%). See Analog Input section of the data sheet for more information. Positive supply voltage, 3 V 10% and 5 V 10%. Analog Ground. Ground reference for track/hold, comparators, reference circuit and multiplexer. Digital Ground. Ground reference for digital circuitry. Logic Input Signal. The convert start signal initiates an 8-bit analog-to-digital conversion on the falling edge of this signal. The falling edge of this signal places the track/hold in hold mode. The track/hold goes into track mode again 120 ns after the start of a conversion. The state of the CONVST signal is checked at the end of a conversion. If it is logic low, the AD7822/AD7825/AD7829 will power down. (See Operating Modes section of the data sheet.) Logic Output. The End of Conversion signal indicates when a conversion has finished. The signal can be used to interrupt a microcontroller when a conversion has finished or latch data into a gate array. (See Parallel Interface section of this data sheet.) Logic input signal. The chip select signal is used to enable the parallel port of the AD7822, AD7825, and AD7829. This is necessary if the ADC is sharing a common data bus with another device. Logic Input. The Power-Down pin is present on the AD7822 and AD7825 only. Bringing the PD pin low places the AD7822 and AD7825 in Power-Down mode. The ADCs will power up when PD is brought logic high again. Logic Input Signal. The read signal is used to take the output buffers out of their high impedance state and drive data onto the data bus. The signal is internally gated with the CS signal. Both RD and CS must be logic low to enable the data bus. Channel Address Inputs. The address of the next multiplexer channel must be present on these inputs when the RD signal goes low. Data Output Lines. They are normally held in a high impedance state. Data is driven onto the data bus when both RD and CS go active low. Analog Input and Output. An external reference can be connected to the AD7822, AD7825, and AD7829 at this pin. The on-chip reference is also available at this pin. When using the internal reference, this pin can be left unconnected or, in some cases, it can be decoupled to AGND with a 0.1 F capacitor.
VDD AGND DGND CONVST
EOC
CS PD
RD
A0-A2 DB0-DB7 VREF IN/OUT
PIN CONFIGURATIONS DIP/SOIC/TSSOP
DB2 1 DB1 2 DB0 3 CONVST 4 CS 5 RD 6 DGND 7 28 DB3 27 DB4 26 DB5 25 DB6 24 DB7 23 AGND
DB2 1 DB1 2 DB0 3 CONVST 4 CS 5 RD 6
20 DB3 19 DB4 18 DB5 17 DB6
DB2 1 DB1 2 DB0 3 CONVST 4 CS 5 RD 6
24 DB3 23 DB4 22 DB5 21 DB6
AD7822
16 DB7
AD7825
20 DB7
TOP VIEW 15 AGND (Not to Scale) 14 VDD DGND 7 EOC 8 PD 9 NC 10 13 VREF IN/OUT 12 VMID 11 VIN1
TOP VIEW 19 AGND DGND 7 (Not to Scale) 18 VDD EOC 8 A1 9 A0 10 PD 11 VIN4 12 17 VREF IN/OUT 16 VMID 15 VIN1 14 VIN2 13 VIN3
22 VDD TOP VIEW EOC 8 (Not to Scale) 21 VREF IN/OUT A2 9 20 VMID A1 10 A0 11 VIN8 12 VIN7 13 VIN6 14 19 VIN1 18 VIN2 17 VIN3 16 VIN4 15 VIN5
AD7829
NC = NO CONNECT
REV. B
-5-
AD7822/AD7825/AD7829
TERMINOLOGY Signal-to-(Noise + Distortion) Ratio Relative Accuracy
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 (fS/2), excluding dc. The ratio is dependent upon the number of quantization levels in the digitization process; the more levels, the smaller the quantization 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 8-bit converter, this is 50 dB.
Total Harmonic Distortion
Relative accuracy or endpoint nonlinearity is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function.
Differential Nonlinearity
The difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC.
Offset Error
The deviation of the 128th code transition (01111111) to (10000000) from the ideal, i.e., VMID.
Offset Error Match
The difference in offset error between any two channels.
Zero-Scale Error
Total harmonic distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7822/AD7825/AD7829 it is defined as: THD (dB) = 20 log
2 2 2 2 V22 +V3 +V4 +V5 +V6
The deviation of the first code transition (00000000) to (00000001) from the ideal, i.e., VMID - 1.25 V + 1 LSB (VDD = 5 V 10%), or VMID - 1.0 V + 1 LSB (VDD = 3 V 10%).
Full-Scale Error
V1
where V1 is the rms amplitude of the fundamental and V2, V3, V4, V5, and V6 are the rms amplitudes of the second through the sixth harmonics.
Peak Harmonic or Spurious Noise
The deviation of the last code transition (11111110) to (11111111) from the ideal, i.e., VMID + 1.25 V - 1 LSB (VDD = 5 V 10%), or VMID + 1.0 V - 1 LSB (VDD = 3 V 10%).
Gain Error
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 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 parts where the harmonics are buried in the noise floor, it will be a noise peak.
Intermodulation Distortion
The deviation of the last code transition (1111 . . . 110) to (1111 . . . 111) from the ideal, i.e., VREF - 1 LSB, after the offset error has been adjusted out.
Gain Error Match
The difference in gain error between any two channels.
Track/Hold Acquisition Time
The time required for the output of the track/hold amplifier to reach its final value, within 1/2 LSB, after the point at which the track/hold returns to track mode. This happens approximately 120 ns after the falling edge of CONVST. 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 VIN input of the AD7822/ AD7825/AD7829. It means that the user must wait for the duration of the track/hold acquisition time after a channel change/step input change to VIN before starting another conversion, to ensure that the part operates to specification.
PSR (Power Supply Rejection)
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 AD7822/AD7825/AD7829 are 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 different 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 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 fundamental expressed in dBs.
Channel-to-Channel Isolation
Variations in power supply will affect the full-scale transition, but not the converter's linearity. Power supply rejection is the maximum change in the full-scale transition point due to a change in power supply voltage from the nominal value.
CIRCUIT DESCRIPTION
Channel-to-channel isolation is a measure of the level of crosstalk between channels. It is measured by applying a full-scale 20 kHz sine wave signal to one input channel and determining how much that signal is attenuated in each of the other channels. The figure given is the worst case across all four or eight channels of the AD7825 and AD7829, respectively.
The AD7822, AD7825, and AD7829 consist of a track-and-hold amplifier followed by a half-flash analog-to-digital converter. These devices use a half-flash conversion technique where one 4-bit flash ADC is used to achieve an 8-bit result. The 4-bit flash ADC contains a sampling capacitor followed by fifteen comparators that compare the unknown input to a reference ladder to achieve a 4-bit result. This first flash, i.e., coarse conversion, provides the 4 MSBs. For a full 8-bit reading to be realized, a second flash, i.e., a fine conversion, must be performed to provide the 4 LSBs. The 8-bit word is then placed on the data output bus.
-6-
REV. B
AD7822/AD7825/AD7829
Figures 2 and 3 below show simplified schematics of the ADC. When the ADC starts a conversion, the track-and-hold goes into hold mode and holds the analog input for 120 ns. This is the acquisition phase as shown in Figure 2, when Switch 2 is in Position A. At the point when the track-and-hold returns to its track mode, this signal is sampled by the sampling capacitor as Switch 2 moves into Position B. The first flash occurs at this instant and is then followed by the second flash. Typically, the first flash is complete after 100 ns, i.e., at 220 ns, while the end of the second flash and hence the 8-bit conversion result is available at 330 ns (minimum). The maximum conversion time is 420 ns. As shown in Figure 4, the track-and-hold returns to track mode after 120 ns, and starts the next acquisition before the end of the current conversion. Figure 6 shows the ADC transfer function.
REFERENCE
120ns
TRACK HOLD TRACK HOLD
CONVST EOC CS
t2 t1
RD
t3
DB0-DB7
VALID DATA
Figure 4. Track-and-Hold Timing
TYPICAL CONNECTION DIAGRAM
R16 15 R15 14 D7 D6 D5
OUTPUT REGISTER
B HOLD
SAMPLING CAPACITOR R14 R13 13
OUTPUT DRIVERS
DECODE LOGIC
VIN
T/H 1
A
SW2
D4 D3 D2 D1
1 R1 TIMING AND CONTROL LOGIC
D0
Figure 2. ADC Acquisition Phase
Figure 5 shows a typical connection diagram for the AD7822, AD7825, and AD7829. The AGND and DGND are connected together at the device for good noise suppression. The parallel interface is implemented using an 8-bit data bus. The end of conversion signal (EOC) idles high, the falling edge of CONVST initiates a conversion and at the end of conversion the falling edge of EOC is used to initiate an Interrupt Service Routine (ISR) on a microprocessor. (See Parallel Interface section for more details.) VREF and VMID are connected to a voltage source such as the AD780, while VDD is connected to a voltage source that can vary from 4.5 V to 5.5 V. (See Table I in Analog Input section.) When VDD is first connected, the AD7822, AD7825, and AD7829 power up in a low current mode, i.e., power-down, with the default logic level on the EOC pin on the AD7822 and AD7825 equal to a low. Ensure the CONVST line is not floating when VDD is applied, as this could put the AD7822/AD7825/ AD7829 into an unknown state. A suggestion is to tie CONVST to VDD or DGND through a pull-up or pull-down resistor. A rising edge on the CONVST pin will cause the AD7829 to fully power up while a rising edge on the PD pin will cause the AD7822 and AD7825 to fully power up. For applications where power consumption is of concern, the automatic power-down at the end of a conversion should be used to improve power performance. (See Power-Down Options section of the data sheet.)
SUPPLY 4.5V TO 5.5V 10 F 0.1 F 2.5V AD780 PARALLEL INTERFACE VREF VMID DB0-DB7 VIN1 1.25V TO 3.75V INPUT VIN2 EOC
REFERENCE
R16 15 R15 14 D7 D6 D5
VDD
A VIN T/H 1
SW2
OUTPUT REGISTER
OUTPUT DRIVERS
DECODE LOGIC
B HOLD
SAMPLING CAPACITOR R14 R13 13
D4 D3 D2 D1
AD7822/ AD7825/ AD7829
C/ P RD CS CONVST A0
VIN4(8) AGND
1 R1
D0
A1 A2 PD
DGND
TIMING AND CONTROL LOGIC
Figure 3. ADC Conversion Phase
Figure 5. Typical Connection Diagram
REV. B
-7-
AD7822/AD7825/AD7829
ADC TRANSFER FUNCTION
The output coding of the AD7822, AD7825, and AD7829 is straight binary. The designed code transitions occur at successive integer LSB values (i.e., 1 LSB, 2 LSBs, etc.). The LSB size is = V REF/256 (VDD = 5 V) or the LSB size = (0.8 VREF)/256 (VDD = 3 V). The ideal transfer characteristic for the AD7822, AD7825, and AD7829 is shown in Figure 6, below.
(VDD = 5V) 1LSB = VREF /256
VDD = 5V 5V
4V VMID = 3.75V 3V
11111111 111...110
ADC CODE
VMID = 2.5V 2V VMID = N/C (1.25V)
111...000 10000000 000...111 000...010 000...001 00000000 (VDD = 3V) 1LSB = 0.8VREF /256
1V
INPUT SIGNAL RANGE FOR VARIOUS VMID
1LSB
VMID VMID + 1.25V - 1LSB VMID + 1V - 1LSB
VDD = 3V 3V
(VDD = 5V) VMID - 1.25V (VDD = 3V) VMID - 1V
ANALOG INPUT VOLTAGE
Figure 6. Transfer Characteristic
ANALOG INPUT
The AD7822 has a single input channel and the AD7825 and AD7829 have four and eight input channels respectively. Each input channel has an input span of 2.5 V or 2.0 V, depending on the supply voltage (VDD). This input span is automatically set up by an on-chip "VDD Detector" circuit. 5 V operation of the ADCs is detected when VDD exceeds 4.1 V and 3 V operation is detected when VDD falls below 3.8 V. This circuit also possesses a degree of glitch rejection; for example, a glitch from 5.5 V to 2.7 V up to 60 ns wide will not trip the VDD detector. The VMID pin is used to center this input span anywhere in the range AGND to VDD. If no input voltage is applied to VMID, the default input range is AGND to 2.0 V (VDD = 3 V 10%) i.e., centered about 1.0 V, or AGND to 2.5 V (VDD = 5 V 10%) i.e., centered about 1.25 V. When using the default input range, the VMID pin can be left unconnected or, in some cases, it can be decoupled to AGND with a 0.1 F capacitor. If, however, an external VMID is applied, the analog input range will be from VMID - 1.0 V to VMID + 1.0 V (VDD = 3 V 10%), or from VMID - 1.25 V to VMID + 1.25 V (VDD = 5 V 10%). The range of values of VMID that can be applied depends on the value of VDD. For VDD = 3 V 10%, the range of values that can be applied to VMID is from 1.0 V to VDD - 1.0 V and is 1.25 V to VDD - 1.25 V when VDD = 5 V 10%. Table I shows the relevant ranges of VMID and the input span for various values of V DD. Figure 7 illustrates the input signal range available with various values of VMID.
Table I.
2V VMID = 2V VMID = 1.5V 1V VMID = N/C (1V) INPUT SIGNAL RANGE FOR VARIOUS VMID
Figure 7. Analog Input Span Variation with VMID
VMID may be used to remove offsets in a system by applying the offset to the VMID pin as shown in Figure 8, or it may be used to accommodate bipolar signals by applying VMID to a level-shifting circuit before VIN, as shown in Figure 9. When VMID is being driven by an external source, the source may be directly tied to the level-shifting circuitry (see Figure 9); however, if the internal VMID, i.e., the default value, is being used as an output, it must be buffered before applying it to the level-shifting circuitry, as the V MID pin has an impedance of approximately 6 k (see Figure 10).
VIN VIN
VMID
AD7822/ AD7825/ AD7829
VMID
VDD 5.5 5.0 4.5 3.3 3.0 2.7
VMID VMID Ext Internal Max 1.25 1.25 1.25 1.00 1.00 1.00 4.25 3.75 3.25 2.3 2.0 1.7
VIN Span 3.0 to 5.5 2.5 to 5.0 2.0 to 4.5 1.3 to 3.3 1.0 to 3.0 0.7 to 2.7
VMID Ext Min 1.25 1.25 1.25 1.00 1.00 1.00
VIN Span 0 to 2.5 0 to 2.5 0 to 2.5 0 to 2.0 0 to 2.0 0 to 2.0 -8-
VMID
Figure 8. Removing Offsets Using VMID
REV. B
AD7822/AD7825/AD7829
2.5V VREF VMID R4 R3 V V R2 R1 0V VIN 2.5V VIN
AD7822/ AD7825/ AD7829
being conducted into the substrate due to an over voltage on an unselected channel, can cause inaccurate conversions on a selected channel. The capacitor C2 in Figure 11 is typically about 4 pF and can be primarily attributed to pin capacitance. The resistor, R1, is a lumped component made up of the on resistance of several components, including that of the multiplexer and the track and hold. This resistor is typically about 310 . The capacitor C1 is the track-and-hold capacitor and has a capacitance of 0.5 pF. Switch 1 is the track-and-hold switch, while Switch 2 is that of the sampling capacitor as shown in Figures 2 and 3.
VDD
0V
D1 VIN C2 4pF D2
R1 310 SW1
C1 0.5pF A SW2 B
Figure 9. Accommodating Bipolar Signals Using External VMID
EXTERNAL 2.5V
Figure 11. Equivalent Analog Input Circuit
VREF VMID R4 R3 V V R2 R1 0V VIN VMID VIN
AD7822/ AD7825/ AD7829
When in track phase, Switch 1 is closed and Switch 2 is in Position A; when in hold mode, Switch 1 opens while Switch 2 remains in Position A. The track-and-hold remains in hold mode for 120 ns--see Circuit Description--after which it returns to track mode and the ADC enters its conversion phase. At this point, Switch 1 opens and Switch 2 moves to Position B. At the end of the conversion, Switch 2 moves back to Position A.
Analog Input Selection
On power-up, the default VIN selection is VIN1. When returning to normal operation from power-down, the VIN selected will be the same one that was selected prior to power-down being initiated. Table II below shows the multiplexer address corresponding to each analog input from VIN1 to VIN4(8) for the AD7825 or AD7829.
Table II.
0V
Figure 10. Accommodating Bipolar Signals Using Internal VMID
A2 0 0 0 0 1 1 1 1
A1 0 0 1 1 0 0 1 1
A0 0 1 0 1 0 1 0 1
Analog Input Selected VIN1 VIN2 VIN3 VIN4 VIN5 VIN6 VIN7 VIN8
NOTE: Although there is a VREF pin from which a voltage reference of 2.5 V may be sourced, or to which an external reference may be applied, this does not provide an option of varying the value of the voltage reference. As stated in the specifications for the AD7822, AD7825, and AD7829, the input voltage range at this pin is 2.5 V 2%.
Analog Input Structure
Figure 11 shows an equivalent circuit of the analog input structure of the AD7822, AD7825, and the AD7829. 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. 20 mA is the maximum current these diodes can conduct without causing irreversible damage to the part. However, it is worth noting that a small amount of current (1 mA)
Channel selection on the AD7825 and AD7829 is made without the necessity of a write operation. The address of the next channel to be converted is latched at the start of the current read operation, i.e., on the falling edge of RD while CS is low, as shown in Figure 12. This allows for improved throughput rates in "channel hopping" applications.
REV. B
-9-
AD7822/AD7825/AD7829
120ns TRACK CHx HOLD CHx TRACK CHx TRACK CHy HOLD CHy
50
fSAMPLE = 2MHz
48
t2
CONVST
t1
EOC
46
SNR - dB
44
CS
42
RD
t3
40
t13
DB0-DB7
VALID DATA
38 0.2
1
3 4 5 6 INPUT FREQUENCY - MHz
8
10
A0-A2
ADDRESS CHANNEL y
Figure 14. SNR vs. Input Frequency on the AD7825
POWER-UP TIMES
Figure 12. Channel Hopping Timing
There is a minimum time delay between the falling edge of RD and the next falling edge of the CONVST signal, t13. This is the minimum acquisition time required of the track-and-hold in order to maintain 8-bit performance. Figure 13 shows the typical performance of the AD7825 when channel hopping for various acquisition times. These results were obtained using an external reference and internal VMID while channel hopping between VIN1 and VIN4 with 0 V on Channel 4 and 0.5 V on Channel 1.
8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 500
200
100
50 40 30 20 ACQUISITION TIME - ns
15
10
Figure 13. Effective Number of Bits vs. Acquisition Time for the AD7825
The AD7822/AD7825/AD7829 have a 1 s power-up time when using an external reference and a 25 s power-up time when using the on-chip reference. When VDD is first connected, the AD7822, AD7825, and AD7829 are in a low current mode of operation. Ensure that the CONVST line is not floating when VDD is applied, as if there is a glitch on CONVST while VDD is rising, the part will attempt to power up before VDD has fully settled and could enter an unknown state. In order to carry out a conversion, the AD7822, AD7825, and AD7829 must first be powered up. The AD7829 is powered up by a rising edge on the CONVST pin and a conversion is initiated on the falling edge of CONVST. Figure 15 shows how to power up the AD7829 when VDD is first connected or after the AD7829 has been powered down using the CONVST pin when using either the on-chip, or an external, reference. When using an external reference, the falling edge of CONVST may occur before the required power-up time has elapsed; however, the conversion will not be initiated on the falling edge of CONVST but rather at the moment when the part has completely powered up, i.e., after 1 s. If the falling edge of CONVST occurs after the required power-up time has elapsed, then it is upon this falling edge that a conversion is initiated. When using the on-chip reference, it is necessary to wait the required power-up time of approximately 25 s before initiating a conversion; i.e., a falling edge on CONVST may not occur before the required power-up time has elapsed, when VDD is first connected or after the AD7829 has been powered down using the CONVST pin as shown in Figure 15.
EXTERNAL REFERENCE
VDD
The on-chip track-and-hold can accommodate input frequencies to 10 MHz, making the AD7822, AD7825, and AD7829 ideal for subsampling applications. When the AD7825 is converting a 10 MHz input signal at a sampling rate of 2 MSPS, the effective number of bits typically remains above seven, corresponding to a signal-to-noise ratio of 42 dBs as shown in Figure 14.
ENOB
tPOWER-UP
1s
CONVST CONVERSION INITIATED HERE
ON-CHIP REFERENCE
VDD
tPOWER-UP
25 s
CONVST CONVERSION INITIATED HERE
Figure 15. AD7829 Power-Up Time
-10-
REV. B
AD7822/AD7825/AD7829
Figure 16 shows how to power up the AD7822 or AD7825 when VDD is first connected or after the ADCs have been powered down using the PD pin, or the CONVST pin, with either the on-chip or an external reference. When the supplies are first connected or after the part has been powered down by the PD pin, only a rising edge on the PD pin will cause the part to power up. When the part has been powered down using the CONVST pin, a rising edge on either the PD pin or the CONVST pin will power the part up again. As with the AD7829, when using an external reference with the AD7822 or AD7825, the falling edge of CONVST may occur before the required power-up time has elapsed, however, if this is the case, the conversion will not be initiated on the falling edge of CONVST, but rather at the moment when the part has powered up completely, i.e., after 1 s. If the falling edge of CONVST occurs after the required power-up time has elapsed, it is upon this falling edge that a conversion is initiated. When using the on-chip reference, it is necessary to wait the required powerup time of approximately 25 s before initiating a conversion; i.e., a falling edge on CONVST may not occur before the required power-up time has elapsed, when supplies are first connected to the AD7822 or AD7825, or when the ADCs have been powered down using the PD pin or the CONVST pin as shown in Figure 16.
EXTERNAL REFERENCE
VDD PD
10
tPOWER-UP tCONVERT
1s CONVST 330ns POWER-DOWN
tCYCLE
10 s @ 100kSPS
Figure 17. Automatic Power-Down
For example, if the AD7822 is operated in a continuous sampling mode, with a throughput rate of 100 kSPS and using an external reference, the power consumption is calculated as follows. The power dissipation during normal operation is 36 mW, VDD = 3 V. If the power-up time is 1 s and the conversion time is 330 ns (@ +25C), the AD7822 can be said to dissipate 36 mW (maximum) for 1.33 s during each conversion cycle. If the throughput rate is 100 kSPS, the cycle time is 10 s and the average power dissipated during each cycle is (1.33/10) x (36 mW) = 4.79 mW. This calculation uses the minimum conversion time, thus giving the best case power dissipation at this throughput rate. However, the actual power dissipated during each conversion cycle could increase depending on the actual conversion time (up to a maximum of 420 ns). Figure 18 shows the power vs. throughput rate for automatic full power-down.
100
tPOWER-UP
1s CONVST
1s
POWER - mW
tPOWER-UP
1
CONVERSION INITIATED HERE
CONVERSION INITIATED HERE
0.1
ON-CHIP REFERENCE
VDD PD
0 0 50 100 150 200 250 300 350 THROUGHPUT - kSPS 400 450 500
tPOWER-UP
25 s CONVST CONVERSION INITIATED HERE
tPOWER-UP
25 s
Figure 18. AD7822/AD7825/AD7829 Power vs. Throughput
0 2048 POINT FFT SAMPLING 2MSPS fIN = 200kHz
CONVERSION INITIATED HERE
-10 -20
Figure 16. AD7822/AD7825 Power-Up Time
-30
dB
POWER VS. THROUGHPUT
Superior power performance can be achieved by using the automatic power-down (Mode 2) at the end of a conversion--see Operating Modes section of the data sheet. Figure 17 shows how the automatic power-down is implemented using the CONVST signal to achieve the optimum power performance for the AD7822, AD7825, and AD7829. The duration of the CONVST pulse is set to be equal to or less than the power-up time of the devices--see Operating Modes section. As the throughput rate is reduced, the device remains in its powerdown state longer and the average power consumption over time drops accordingly.
-40 -50 -60 -70 -80
Figure 19. AD7822/AD7825/AD7829 SNR
REV. B
-11-
0 28 57 85 113 142 170 198 227 255 283 312 340 368 396 425 453 481 510 538 566 595 623 651 680 708 736 765 793 821 850 878 906 935 963 991
FREQUENCY - kHz
AD7822/AD7825/AD7829
OPERATING MODES Mode 2 Operation (Automatic Power-Down)
The AD7822, AD7825, and AD7829 have two possible modes of operation, depending on the state of the CONVST pulse approximately 100 ns after the end of a conversion, i.e., upon the rising edge of the EOC pulse.
Mode 1 Operation (High-Speed Sampling)
When the AD7822, AD7825, and AD7829 are operated in Mode 1 they are not powered-down between conversions. This mode of operation allows high throughput rates to be achieved. Figure 20 shows how this optimum throughput rate is achieved by bringing CONVST high before the end of a conversion, i.e., before the EOC pulses low. When operating in this mode, a new conversion should not be initiated until 30 ns after the end of a read operation. This is to allow the track/hold to acquire the analog signal to 0.5 LSB accuracy.
When the AD7822, AD7825, and AD7829 are operated in Mode 2 (see Figure 21), they automatically power down at the end of a conversion. The CONVST signal is brought low to initiate a conversion and is left logic low until after the EOC goes high, i.e., approximately 100 ns after the end of the conversion. The state of the CONVST signal is sampled at this point (i.e., 530 ns maximum after CONVST falling edge) and the AD7822, AD7825, and AD7829 will power down as long as CONVST is low. The ADC is powered up again on the rising edge of the CONVST signal. Superior power performance can be achieved in this mode of operation by only powering up the AD7822, AD7825, and AD7829 to carry out a conversion. The parallel interface of the AD7822, AD7825, and AD7829 is still fully operational while the ADCs are powered down. A read may occur while the part is powered down, and so it does not necessarily need to be placed within the EOC pulse as shown in Figure 21.
120ns
TRACK HOLD TRACK HOLD
t2
CONVST
t1
EOC
CS
t3
RD
DB0-DB7
VALID DATA
Figure 20. Mode 1 Operation
tPOWER-UP
CONVST POWER DOWN HERE
t1
EOC
CS
RD
DB0-DB7
VALID DATA
Figure 21. Mode 2 Operation
-12-
REV. B
AD7822/AD7825/AD7829
PARALLEL INTERFACE
The parallel interface of the AD7822, AD7825, and AD7829 is eight bits wide. Figure 22 shows a timing diagram illustrating the operational sequence of the AD7822/AD7825/AD7829 parallel interface. The multiplexer address is latched into the AD7822/AD7825/AD7829 on the falling edge of the RD input. The on-chip track/hold goes into hold mode on the falling edge of CONVST and a conversion is also initiated at this point. When the conversion is complete, the end of conversion line (EOC) pulses low to indicate that new data is available in the output register of the AD7822, AD7825, and AD7829. The EOC pulse will stay logic low for a maximum time of 110 ns. However, the EOC pulse can be reset high by a rising edge of
t2
CONVST
RD. This EOC line can be used to drive an edge-triggered interrupt of a microprocessor. CS and RD going low accesses the 8-bit conversion result. It is possible to tie CS permanently low and use only RD to access the data. In systems where the part is interfaced to a gate array or ASIC, this EOC pulse can be applied to the CS and RD inputs to latch data out of the AD7822, AD7825, and AD7829 and into the gate array or ASIC. This means that the gate array or ASIC does not need any conversion status recognition logic and it also eliminates the logic required in the gate array or ASIC to generate the read signal for the AD7822, AD7825, and AD7829.
t1
EOC
t4
t5
CS
t6
RD
t7 t8 t9 t10
VALID DATA
t3
DB0-DB7
t11
A0-A2
t12
t13
NEXT CHANNEL ADDRESS
Figure 22. AD7822/AD7825/AD7829 Parallel Port Timing
REV. B
-13-
AD7822/AD7825/AD7829
MICROPROCESSOR INTERFACING
The parallel port on the AD7822/AD7825/AD7829 allows the ADCs to be interfaced to a range of many different microcontrollers. This section explains how to interface the AD7822, AD7825, and AD7829 with some of the more common microcontroller parallel interface protocols.
AD7822/AD7825/AD7829 to 8051
parallel slave port when control bit PSPMODE in the TRISE register is set. Setting PSPMODE enables the port pin RE0 to be the RD output and RE2 to be the CS (chip select) output. 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.
PIC16C6x/7x*
Figure 23 below shows a parallel interface between the AD7822, AD7825, and AD7829 and the 8051 microcontroller. The EOC signal on the AD7822, AD7825, and AD7829 provides an interrupt request to the 8051 when a conversion ends and data is ready. 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 output of the 8051 is used to latch the low byte of the address during accesses to the device, while the high order address byte is supplied from Port 2. Port 2 latches remain stable when the AD7822, AD7825, and AD7829 are addressed, as they do not have to be turned around (set to 1) for data input as is the case for Port 0.
AD7822/ AD7825/ AD7829*
DB0-DB7
PSP0-PSP7
CS
CS
RD INT *ADDITIONAL PINS OMITTED FOR CLARITY
RD EOC
Figure 24. Interfacing to the PIC16C6x/7x
8051*
DB0-DB7
AD7822/AD7825/AD7829 to ADSP-21xx
AD0-AD7 LATCH DECODER
AD7822/ AD7825/ AD7829*
CS
Figure 25 below shows a parallel interface between the AD7822, AD7825, and AD7829 and the ADSP-21xx series of DSPs. As before, the EOC signal on the AD7822, AD7825, and AD7829 provides an interrupt request to the DSP when a conversion ends.
ADSP-21xx*
ALE A8-A15 RD INT *ADDITIONAL PINS OMITTED FOR CLARITY
RD EOC
D7-D0 A13-A0 ADDRESS DECODE LOGIC DMS RD IRQ *ADDITIONAL PINS OMITTED FOR CLARITY EN
DB0-DB7
Figure 23. Interfacing to the 8051
AD7822/AD7825/AD7829 to PIC16C6x/7x
AD7822/ AD7825/ AD7829*
CS RD EOC
Figure 24 shows a parallel interface between the AD7822, AD7825, and AD7829 and the PIC16C64/65/74. The EOC signal on the AD7822, AD7825, and AD7829 provides an interrupt request to the microcontroller when a conversion begins. Of the PIC16C6x/7x range of microcontrollers only the PIC16C64/65/74 can provide the option of a parallel slave port. Port D of the microcontroller will operate as an 8-bit wide
Figure 25. Interfacing to the ADSP-21xx
-14-
REV. B
AD7822/AD7825/AD7829
Interfacing Multiplexer Address Inputs AD7822 Stand-Alone Operation
Figure 26 shows a simplified interfacing scheme between the AD7825/AD7829 and any microprocessor or microcontroller, which facilitates easy channel selection on the ADCs. The multiplexer address is latched on the falling edge of the RD signal, as outlined in the Parallel Interface section, which allows the use of the 3 LSBs of the address bus to select the channel address. As shown in Figure 26, only address bits A3 to A15 are address decoded allowing A0 to A2 to be changed according to desired channel selection without affecting chip selection.
The AD7822, being the single channel device, does not have any multiplexer addressing associated with it and can in fact be controlled with just one signal, i.e., the CONVST signal. As shown in Figure 27, the RD and CS pins are both tied to the EOC pin, and the resulting signal may be used as an interrupt request signal (IRQ) on a DSP, as a WR signal to memory, or as a CLK to a latch or ASIC. The timing for this interface, as shown in Figure 27, demonstrates how with the CONVST signal alone, a conversion may be initiated, data is latched out, and the operating mode of the AD7822 can be selected.
MICROPROCESSOR READ CYCLE
A0 A1 A2 CS
SYSTEM BUS
A15-A3
ADDRESS DECODE
CS RD
AD7825/ AD7829
RD A15-A3 ADC I/O ADDRESS
A2-A0 DB7-DB0 DB0-DB7
MUX ADDRESS
A/D RESULT MUX ADDRESS (CHANNEL SELECTION A0-A2) LATCHED
Figure 26. AD7825/AD7829 Simplified Microinterfacing Scheme
t1
CONVST RD
DSP/ LATCH/ASIC
CONVST
t4
EOC CS RD
AD7822
CS EOC
DB7-DB0
DB0-DB7
A/D RESULT
Figure 27. AD7822 Stand-Alone Operation
REV. B
-15-
AD7822/AD7825/AD7829
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
20-Lead Plastic DIP (N-20)
1.060 (26.90) 0.925 (23.50)
20 1 11 10
0.280 (7.11) 0.240 (6.10) 0.060 (1.52) 0.015 (0.38) 0.130 (3.30) MIN
PIN 1 0.210 (5.33) MAX 0.160 (4.06) 0.115 (2.93) 0.022 (0.558) 0.014 (0.356) 0.100 (2.54) BSC
0.325 (8.25) 0.300 (7.62) 0.195 (4.95) 0.115 (2.93)
0.070 (1.77) SEATING 0.045 (1.15) PLANE
0.015 (0.381) 0.008 (0.204)
20-Lead Small Outline Package (R-20)
0.5118 (13.00) 0.4961 (12.60)
20 11
1
10
PIN 1
0.1043 (2.65) 0.0926 (2.35)
0.4193 (10.65) 0.3937 (10.00)
0.2992 (7.60) 0.2914 (7.40)
0.0291 (0.74) x 45 0.0098 (0.25)
0.0118 (0.30) 0.0040 (0.10)
8 0.0500 (1.27) 0.0500 0.0192 (0.49) 0 0.0157 (0.40) SEATING 0.0125 (0.32) (1.27) 0.0138 (0.35) PLANE 0.0091 (0.23) BSC
20-Lead Thin Shrink Small Outline Package (RU-20)
0.260 (6.60) 0.252 (6.40)
20 11
0.177 (4.50) 0.169 (4.30)
1
10
0.006 (0.15) 0.002 (0.05)
PIN 1 0.0433 (1.10) MAX 0.0256 (0.65) 0.0118 (0.30) BSC 0.0075 (0.19) 0.0079 (0.20) 0.0035 (0.090)
0.256 (6.50) 0.246 (6.25)
SEATING PLANE
8 0
0.028 (0.70) 0.020 (0.50)
-16-
REV. B
AD7822/AD7825/AD7829
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
24-Lead Plastic DIP (N-24)
1.275 (32.30) 1.125 (28.60)
24 1 13 12
PIN 1 0.210 (5.33) MAX 0.200 (5.05) 0.125 (3.18)
0.325 (8.25) 0.300 (7.62) 0.195 (4.95) 0.060 (1.52) 0.115 (2.93) 0.015 (0.38) 0.150 (3.81) MIN
0.280 (7.11) 0.240 (6.10)
0.022 (0.558) 0.014 (0.356)
0.100 (2.54) BSC
0.070 (1.77) SEATING 0.045 (1.15) PLANE
0.015 (0.381) 0.008 (0.204)
24-Lead Small Outline Package (R-24)
0.6141 (15.60) 0.5985 (15.20)
24 13
1
12
PIN 1
0.1043 (2.65) 0.0926 (2.35)
0.2992 (7.60) 0.2914 (7.40) 0.4193 (10.65) 0.3937 (10.00)
0.0291 (0.74) x 45 0.0098 (0.25)
0.0118 (0.30) 0.0040 (0.10)
0.0500 (1.27) BSC
8 0.0192 (0.49) 0 SEATING 0.0125 (0.32) 0.0138 (0.35) PLANE 0.0091 (0.23)
0.0500 (1.27) 0.0157 (0.40)
24-Lead Thin Shrink Small Outline Package (RU-24)
0.311 (7.90) 0.303 (7.70)
24
13
0.177 (4.50) 0.169 (4.30)
1
12
0.006 (0.15) 0.002 (0.05)
PIN 1 0.0433 (1.10) MAX 0.0256 (0.65) 0.0118 (0.30) BSC 0.0075 (0.19) 0.0079 (0.20) 0.0035 (0.090) 0.028 (0.70) 0.020 (0.50)
0.256 (6.50) 0.246 (6.25)
SEATING PLANE
8 0
REV. B
-17-
AD7822/AD7825/AD7829
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
28-Lead Plastic DIP (N-28)
1.565 (39.70) 1.380 (35.10)
28 15
0.580 (14.73) 0.485 (12.32)
1 14
PIN 1 0.250 (6.35) MAX 0.200 (5.05) 0.022 (0.558) 0.125 (3.18) 0.014 (0.356)
0.060 (1.52) 0.015 (0.38) 0.150 (3.81) MIN 0.100 (2.54) BSC 0.070 (1.77) MAX SEATING PLANE
0.625 (15.87) 0.600 (15.24)
0.195 (4.95) 0.125 (3.18)
0.015 (0.381) 0.008 (0.204)
28-Lead Small Outline Package (R-28)
0.7125 (18.10) 0.6969 (17.70)
28 15
1
14
PIN 1
0.1043 (2.65) 0.0926 (2.35)
0.4193 (10.65) 0.3937 (10.00)
0.0291 (0.74) x 45 0.0098 (0.25)
0.0118 (0.30) 0.0040 (0.10)
0.0500 (1.27) BSC
8 0.0500 (1.27) 0.0192 (0.49) 0 0.0157 (0.40) SEATING 0.0125 (0.32) 0.0138 (0.35) PLANE 0.0091 (0.23)
28-Lead Thin Shrink Small Outline Package (RU-28)
0.386 (9.80) 0.378 (9.60)
28 15
0.177 (4.50) 0.169 (4.30)
1
14
PIN 1 0.006 (0.15) 0.002 (0.05)
0.256 (6.50) 0.246 (6.25)
0.0433 (1.10) MAX 0.0079 (0.20) 0.0035 (0.090)
0.2992 (7.60) 0.2914 (7.40)
SEATING PLANE
0.0256 (0.65) 0.0118 (0.30) BSC 0.0075 (0.19)
8 0
0.028 (0.70) 0.020 (0.50)
-18-
REV. B
10/24/01 10:15 AM_LM
AD7822/AD7825/AD7829 Revision History
Location Page
Data Sheet changed from REV. A to REV. B. Edit to POWER REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Edit to PIN FUNCTION DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Edit to CIRCUIT DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Edit toTYPICAL CONNECTION DIAGRAM section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Edit to ANALOG INPUT section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Edit to ANALOG INPUT SELECTION section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Edit to POWER-UP TIMES section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Edit to POWER vs. THROUGHPUT section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 AD7822 Stand-Alone Operation section created . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
REV. B
-19-
-20-
C01321a-0-10/01(B)
PRINTED IN U.S.A.
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