Analog Devices AD7829BRU, AD7829BR, AD7829BN, AD7822BRU, AD7822BR Datasheet

3 V/5 V, 2 MSPS, 8-Bit, 1-, 4-, 8-Channel

a

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 ⴞ 10% and 5 V ⴞ 10%
Input Ranges

0 V to 2 V p-p, V

0 V to 2.5 V p-p, V
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

= 3 V ⴞ 10%

DD

= 5 V ⴞ 10%

DD

Sampling ADCs

AD7822/AD7825/AD7829

FUNCTIONAL BLOCK DIAGRAM

A0*

A2*

EOC

CONVST

V

IN1

V

*

IN2

*

V

IN3

INPUT

*

V

IN4

V
V
V
V

MUX

*

IN5

*

IN6

*

IN7

*

IN8

*A0, A1
*A2
*PD

TO V

*V

IN2

*V

IN4

TO V

IN4

IN8

A1*

CONTROL

LOGIC

T/H

V

AGND

MID

AD7825/AD7829
AD7829
AD7822/AD7825
AD7825/AD7829
AD7829

8-BIT
HALF

FLASH

ADC

PD*

DGND

V

COMP

BUF

PARALLEL

PORT

RD

CS

DD

2.5V
REF

VREF

IN /OUT

DB7

DB0

GENERAL DESCRIPTION

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 V

pin allows the user to offset the input span. This

MID

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: [phone] www.analog.com
Fax: [phone] © Analog Devices, Inc., 2001

AD7822/AD7825/AD7829–SPECIFICATIONS

V

= 2.5 V. All specifications –40ⴗC to +85ⴗC unless otherwise noted.)

REF IN/OUT

(VDD = 3 V ⴞ 10%, VDD = 5 V ⴞ 10%, GND = 0 V,

Parameter Version B Unit Test Condition/Comment

DYNAMIC PERFORMANCE f

Signal to (Noise + Distortion) Ratio
Total Harmonic Distortion
Peak Harmonic or Spurious Noise
Intermodulation Distortion

1

1

1

48 dB min

1

–55 dB max
–55 dB max

= 30 kHz. f

IN

fa = 27.3 kHz, fb = 28.3 kHz

SAMPLE

= 2 MHz

2nd Order Terms –65 dB typ
3rd Order Terms –65 dB typ

Channel-to-Channel Isolation

1

–70 dB typ fIN = 20 kHz

DC ACCURACY

Resolution 8 Bits
Minimum Resolution for Which

No Missing Codes Are Guaranteed 8 Bits
Integral Nonlinearity (INL)
Differential Nonlinearity (DNL)
Gain Error
Gain Error Match
Offset Error
Offset Error Match

ANALOG INPUTS

V

DD

V

1

1

1

1

2

= 5 V ± 10% Input Voltage Span = 2.5 V

to V

IN1

Input Voltage V

IN8

1

1

± 0.75 LSB max
± 0.75 LSB max
± 2 LSB max
± 0.1 LSB typ
± 1 LSB max
± 0.1 LSB typ

See Analog Input Section

DD

V max

0 V min

V

Input Voltage VDD – 1.25 V max Default V

MID

= 1.25 V

MID

1.25 V min

= 3 V ± 10% Input Voltage Span = 2 V

V

DD

V

to V

IN1

Input Voltage V

IN8

DD

V max

0 V min

Input Voltage VDD – 1 V max Default V

V

MID

MID

= 1 V

1 V min

Input Leakage Current ± 1 µA max

V

IN

V

Input Capacitance 15 pF max

IN

V

Input Impedance 6 kΩ typ

MID

REFERENCE INPUT

V

REF IN/OUT

Input Voltage Range 2.55 V max 2.5 V + 2%

2.45 V min 2.5 V – 2%

Input Current 1 µA typ

100 µA max

ON-CHIP REFERENCE Nominal 2.5 V

Reference Error ± 50 mV max
Temperature Coefficient 50 ppm/°C typ

LOGIC INPUTS

Input High Voltage, V
Input Low Voltage, V

INL

Input High Voltage, V
Input Low Voltage, V
Input Current, I
Input Capacitance, C

INL

IN

IN

INH

INH

2.4 V min VDD = 5 V ± 10%

0.8 V max VDD = 5 V ± 10%
2 V min VDD = 3 V ± 10%

0.4 V max VDD = 3 V ± 10%
± 1 µA max Typically 10 nA, VIN = 0 V to V
10 pF max

LOGIC OUTPUTS

Output High Voltage, V

Output Low Voltage, V

OL

OH

I

4 V min V

2.4 V min V
I

0.4 V max V

0.2 V max V

= 200 µA

SOURCE

= 5 V ± 10%

DD

= 3 V ± 10%

DD

= 200 µA

SINK

= 5 V ± 10%

DD

= 3 V ± 10%

DD

High Impedance Leakage Current ± 1 µA max
High Impedance Capacitance 10 pF max

DD

–2–

REV. B

AD7822/AD7825/AD7829

Parameter Version B Unit Test Condition/Comment

CONVERSION RATE

Track/Hold Acquisition Time 200 ns max See Functional Description Section
Conversion Time 420 ns max

POWER SUPPLY REJECTION

VDD ± 10% ± 1 LSB max

POWER REQUIREMENTS

V

DD

V

DD

I

DD

Normal Operation 12 mA max 8 mA Typically
Power-Down 5 µA max Logic Inputs = 0 V or V

Power Dissipation V

Normal Operation 36 mW max Typically 24 mW
Power-Down

200 kSPS 9.58 mW typ
500 kSPS 23.94 mW typ

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.

4.5 V min 5 V ± 10%. For Specified Performance

5.5 V max

2.7 V min 3 V ± 10%. For Specified Performance

3.3 V max

0.2 µA typ

DD

= 3 V

DD

I

OL

2.1V

I

OH

TO

OUTPUT

PIN

50pF

200␮A

C

L

200␮A

Figure 1. Load Circuit for Access Time and Bus
Relinquish Time

ORDERING GUIDE

Linearity Package Package

Model Error Description Option

AD7822BN ± 0.75 LSB Plastic DIP N-20
AD7822BR ± 0.75 LSB Small Outline IC R-20
AD7822BRU ± 0.75 LSB Thin Shrink Small RU-20

Outline (TSSOP)
AD7825BN ± 0.75 LSB Plastic DIP N-24
AD7825BR ± 0.75 LSB Small Outline IC R-24
AD7825BRU ± 0.75 LSB Thin Shrink Small RU-24

Outline (TSSOP)
AD7829BN ± 0.75 LSB Plastic DIP N-28
AD7829BR ± 0.75 LSB Small Outline IC R-28
AD7829BRU ± 0.75 LSB Thin Shrink Small RU-28

Outline (TSSOP)

REV. B

–3–

AD7822/AD7825/AD7829

WARNING!

ESD SENSITIVE DEVICE

1, 2

TIMING CHARACTERISTICS

(V

Parameter 5 V ⴞ 10% 3 V ⴞ 10% Unit Conditions/Comments

t

1

t

2

t

3

t

4

420 420 ns max Conversion Time.
20 20 ns min Minimum CONVST Pulsewidth.
30 30 ns min Minimum time between the rising edge of RD and next falling edge of convert start.
110 110 ns max EOC Pulsewidth.
70 70 ns min

t

5

t

6

t

7

t

8

3

t

9

4

t

10

10 10 ns max RD rising edge to EOC pulse high.
0 0 ns min CS to RD setup time.
0 0 ns min CS to RD hold time.
30 30 ns min Minimum RD Pulsewidth.
10 20 ns max Data access time after RD low.
5 5 ns min Bus relinquish time after RD high.
20 20 ns max

t

11

t

12

t

13

t

POWER UP

t

POWER UP

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 VDD = 5 V ± 10%, and time required for
an output to cross 0.4 V or 2.0 V with VDD = 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, t10, quoted in the timing characteristics is the true bus relinquish time
of the part and as such is independent of external bus loading capacitances.

10 10 ns min Address setup time before falling edge of RD.
15 15 ns min Address hold time after falling edge of RD.
200 200 ns min Minimum time between new channel selection and convert start.
25 25 µs typ Power-up time from rising edge of CONVST using on-chip reference.
11µs max Power-up time from rising edge of CONVST using external 2.5 V reference.

= 2.5 V. All specifications –40ⴗC to +85ⴗC unless otherwise noted.)

REF IN/OUT

ABSOLUTE MAXIMUM RATINGS*

(TA = 25°C unless otherwise noted)

VDD to AGND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V

to DGND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V

V

DD

Analog Input Voltage to AGND

V

to V

IN1

Reference Input Voltage to AGND . . . –0.3 V to V
V

Input Voltage to AGND . . . . . . . –0.3 V to VDD + 0.3 V

MID

Digital Input Voltage to DGND . . . . . –0.3 V to V

Digital Output Voltage to DGND . . . . –0.3 V to V

. . . . . . . . . . . . . . . . . . . –0.3 V to VDD + 0.3 V

IN8

DD

DD

DD

+ 0.3 V

+ 0.3 V
+ 0.3 V

Operating Temperature Range

Industrial (B Version) . . . . . . . . . . . . . . . . –40°C to +85°C

Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C

Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 150°C

Plastic DIP Package, Power Dissipation . . . . . . . . . . 450 mW

Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 105°C/W

θ

JA

SOIC Package, Power Dissipation . . . . . . . . . . . . . . . 450 mW

Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 75°C/W

θ

JA

Lead Temperature, Soldering

Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . 215°C

Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . 220°C

TSSOP Package, Power Dissipation . . . . . . . . . . . . . 450 mW

Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 128°C/W

θ

JA

Lead Temperature, Soldering

Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . 215°C

Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . 220°C

ESD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 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
conditions for extended periods may affect device reliability.

Lead Temperature, (Soldering, 10 sec) . . . . . . . . . . . 260°C

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.

–4–

REV. B

AD7822/AD7825/AD7829

PIN FUNCTION DESCRIPTIONS

Mnemonic Description

to V

V

IN1

IN8

V

DD

AGND Analog Ground. Ground reference for track/hold, comparators, reference circuit and multiplexer.
DGND Digital Ground. Ground reference for digital circuitry.

CONVST Logic Input Signal. The convert start signal initiates an 8-bit analog-to-digital conversion on the falling edge of

EOC Logic Output. The End of Conversion signal indicates when a conversion has finished. The signal can be used

CS Logic input signal. The chip select signal is used to enable the parallel port of the AD7822, AD7825, and AD7829.

PD Logic Input. The Power-Down pin is present on the AD7822 and AD7825 only. Bringing the PD pin low

RD Logic Input Signal. The read signal is used to take the output buffers out of their high impedance state and

A0–A2 Channel Address Inputs. The address of the next multiplexer channel must be present on these inputs when the

DB0–DB7 Data Output Lines. They are normally held in a high impedance state. Data is driven onto the data bus when

V

REF IN/OUT

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 (V

). This span may be centered anywhere in the range AGND to VDD using the V

DD

default input range (V

unconnected) is AGND to 2 V (VDD = 3 V ± 10%) or AGND to 2.5 V (VDD = 5 V

MID

Pin. The

MID

± 10%). See Analog Input section of the data sheet for more information.
Positive supply voltage, 3 V ± 10% and 5 V ± 10%.

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.)

to interrupt a microcontroller when a conversion has finished or latch data into a gate array. (See Parallel Inter­face section of this data sheet.)

This is necessary if the ADC is sharing a common data bus with another device.

places the AD7822 and AD7825 in Power-Down mode. The ADCs will power up when PD is brought logic
high again.

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.

RD signal goes low.

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.

1

DB2

2

DB1

3

DB0

CONVST

4

5

CS

AD7822

TOP VIEW

6

RD

DGND

(Not to Scale)

7

8

EOC

9

PD

10

NC V

NC = NO CONNECT

20

19

18

17

16

15

14

13

12

11

DB3

DB4

DB5

DB6

DB7

AGND

V

DD

V

REF IN/ OUT

V

MID

IN1

PIN CONFIGURATIONS

DIP/SOIC/TSSOP

1

DB2

DB1

DB0

CONVST

DGND

EOC

V

CS

RD

A1

A0

PD

IN4

2

3

4

5

AD7825

6

TOP VIEW

(Not to Scale)

7

8

9

10

11

12

24

23

22

21

20

19

18

17

16

15

14

13

DB3

DB4

DB5

DB6

DB7

AGND

V

V

V

V

V

V

–5–REV. B

DD

REF IN/OUT

MID

IN1

IN2

IN3

DB2

DB1

DB0

CONVST

RD

DGND

EOC

V

V

V

CS

A2

A1

A0

IN8

IN7

IN6

1

2

3

4

5

6

AD7829

7

TOP VIEW

8

(Not to Scale)

9

10

11

12

13

14

28

27

26

25

24

23

22

21

20

19

18

17

16

15

DB3

DB4

DB5

DB6

DB7

AGND

V

DD

V

REF IN/OUT

V

MID

V

IN1

V

IN2

V

IN3

V

IN4

V

IN5

AD7822/AD7825/AD7829

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.

S

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

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:

2

2

2

2

2

+V

5

6

THD (dB) = 20 log

+V

+V

V

2

+V

3

4

V

1

where V1 is the rms amplitude of the fundamental and V2, V3,

, V5, and V6 are the rms amplitudes of the second through the

V

4

sixth harmonics.

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 f

/2 and excluding dc) to the rms value of the

S

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

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

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.

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

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., V

Offset Error Match

MID

.

The difference in offset error between any two channels.

Zero-Scale Error

The deviation of the first code transition (00000000) to
(00000001) from the ideal, i.e., V
5 V ± 10%), or V

Full-Scale Error

– 1.0 V + 1 LSB (VDD = 3 V ± 10%).

MID

– 1.25 V + 1 LSB (VDD =

MID

The deviation of the last code transition (11111110) to
(11111111) from the ideal, i.e., V
5 V ± 10%), or V

Gain Error

+ 1.0 V – 1 LSB (VDD = 3 V ± 10%).

MID

+ 1.25 V – 1 LSB (VDD =

MID

The deviation of the last code transition (1111 . . . 110) to
(1111 . . . 111) from the ideal, i.e., V

– 1 LSB, after the off-

REF

set 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 V

input of the AD7822/

IN

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 V

before starting another conversion, to

IN

ensure that the part operates to specification.

PSR (Power Supply Rejection)

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

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

R16

SW2

A

T/H 1

V

IN

HOLD

B

TIMING AND

CONTROL

LOGIC

R15

SAMPLING

CAPACITOR

R14

R13

15

14

LOGIC

OUTPUT

DECODE

13

1

R1

REGISTER

OUTPUT

DRIVERS

D7

D6

D5

D4

D3

D2

D1

D0

Figure 2. ADC Acquisition Phase

REFERENCE

R16

SW2

A

T/H 1

V

IN

HOLD

B

TIMING AND

CONTROL

LOGIC

R15

SAMPLING

CAPACITOR

R14

R13

15

14

LOGIC

OUTPUT

DECODE

13

1

R1

REGISTER

OUTPUT

DRIVERS

D7

D6

D5

D4

D3

D2

D1

D0

CONVST

EOC

CS

RD

DB0–DB7

TRACK

120ns

HOLD HOLD

t

2

t

1

TRACK

VALID
DATA

t

3

Figure 4. Track-and-Hold Timing

TYPICAL CONNECTION DIAGRAM

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.) V

REF

and V

such as the AD780, while V

are connected to a voltage source

MID

is connected to a voltage source

DD

that can vary from 4.5 V to 5.5 V. (See Table I in Analog Input
section.) When V

is first connected, the AD7822, AD7825, and

DD

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 V

is applied, as this could put the AD7822/AD7825/

DD

AD7829 into an unknown state. A suggestion is to tie CONVST

or DGND through a pull-up or pull-down resistor. A rising

to V

DD

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.)

V

DD

2.5V

AD780

V

REF

AD7822/
AD7825/
AD7829

V

MID

DB0–DB7

EOC

RD

CS

CONVST

A0

A1

A2

PD

PARALLEL

INTERFACE

␮C/␮P

SUPPLY

4.5V TO 5.5V

1.25V TO

3.75V INPUT

10␮F 0.1␮F

V

IN1

V

IN2

V

IN4(8)

AGND

DGND

Figure 3. ADC Conversion Phase

Figure 5. Typical Connection Diagram

–7–REV. B

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
(V

/256 (VDD = 5 V) or the LSB size = (0.8 V

REF

= 3 V). The ideal transfer characteristic for the AD7822,

DD

AD7825, and AD7829 is shown in Figure 6, below.

(V

= 5V)

11111111

111...110

111...000

10000000

000...111

ADC CODE

000...010

000...001

00000000

(VDD = 5V) V

= 3V) V

(V

DD

DD

1LSB = V

1LSB

MID

MID

– 1.25V
– 1V

/256

REF

1LSB = 0.8V

V

MID

V

MID

V

ANALOG INPUT VOLTAGE

MID

(V

= 3V)

DD

/256

REF

+ 1.25V – 1LSB
+ 1V – 1LSB

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 (V
up by an on-chip “V
ADCs is detected when V
detected when V

). This input span is automatically set

DD

Detector” circuit. 5 V operation of the

DD

exceeds 4.1 V and 3 V operation is

DD

falls below 3.8 V. This circuit also possesses

DD

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 V

The V
range AGND to V

pin is used to center this input span anywhere in the

MID

. If no input voltage is applied to V

DD

default input range is AGND to 2.0 V (V
centered about 1.0 V, or AGND to 2.5 V (V

detector.

DD

= 3 V ± 10%) i.e.,

DD

= 5 V ± 10%)

DD

i.e., centered about 1.25 V. When using the default input range,
the V

pin can be left unconnected or, in some cases, it can be

MID

decoupled to AGND with a 0.1␮F capacitor.

If, however, an external V
will be from V
or from V

MID

– 1.0 V to V

MID

– 1.25 V to V

The range of values of V
value of V
can be applied to V
to V

DD

evant ranges of V
V

. Figure 7 illustrates the input signal range available with

DD

various values of V

. For VDD = 3 V ± 10%, the range of values that

DD

MID

– 1.25 V when VDD= 5 V ± 10%. Table I shows the rel-

and the input span for various values of

MID

MID

is applied, the analog input range

MID

MID

+ 1.0 V (VDD = 3 V ± 10%),

MID

+ 1.25 V (VDD = 5 V ± 10%).

MID

that can be applied depends on the

is from 1.0 V to VDD – 1.0 V and is 1.25 V

.

Table I.

REF

)/256

MID

, the

= 5V

V

DD

5V

4V

3V

V

= 2.5V

MID

2V

V

= N/C (1.25V)

MID

1V

V

= 3V

DD

3V

2V

V

= 1.5V

MID

V

1V

= N/C (1V)

MID

Figure 7. Analog Input Span Variation with V

V

may be used to remove offsets in a system by applying the

MID

offset to the V

pin as shown in Figure 8, or it may be used to

MID

accommodate bipolar signals by applying V
circuit before V

, as shown in Figure 9. When V

IN

V

= 3.75V

MID

INPUT SIGNAL RANGE

FOR VARIOUS V

V

= 2V

MID

INPUT SIGNAL RANGE

FOR VARIOUS V

MID

MID

MID

MID

to a level-shifting

is being

MID

driven by an external source, the source may be directly tied to
the level-shifting circuitry (see Figure 9); however, if the internal

, i.e., the default value, is being used as an output, it must

V

MID

be buffered before applying it to the level-shifting circuitry, as
the V

pin has an impedance of approximately 6 kΩ (see

MID

Figure 10).

V

IN

V

MID

V

IN

AD7822/
AD7825/
AD7829

V

MID

V

V

MID

Internal Max VIN Span Min VIN Span

DD

V

Ext V

MID

MID

Ext

5.5 1.25 4.25 3.0 to 5.5 1.25 0 to 2.5

5.0 1.25 3.75 2.5 to 5.0 1.25 0 to 2.5

4.5 1.25 3.25 2.0 to 4.5 1.25 0 to 2.5

3.3 1.00 2.3 1.3 to 3.3 1.00 0 to 2.0

3.0 1.00 2.0 1.0 to 3.0 1.00 0 to 2.0

2.7 1.00 1.7 0.7 to 2.7 1.00 0 to 2.0

–8–

V

MID

Figure 8. Removing Offsets Using V

MID

REV. B

AD7822/AD7825/AD7829

V

IN

C2

4pF

D1

D2

R1

310⍀

SW1

C1

0.5pF
A

B

SW2

V

DD

2.5V

V

REF

V

MID

R4

R3

V

0V

R2

V

R1

V

IN

2.5V

0V

AD7822/
AD7825/
AD7829

V

IN

Figure 9. Accommodating Bipolar Signals Using
External V

V

0V

MID

EXTERNAL

2.5V

V

REF

V

R4

R3

R2

V

R1

V

V

MID

0V

MID

AD7822/
AD7825/
AD7829

V

IN

IN

Figure 10. Accommodating Bipolar Signals Using
Internal V

NOTE: Although there is a V

MID

pin from which a voltage refer-

REF

ence 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)

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 Ω. 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.

Figure 11. Equivalent Analog Input Circuit

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 V
to normal operation from power-down, the V

. When returning

IN1

selected will be

IN

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 V

IN1

to V

for the AD7825 or AD7829.

IN4(8)

Table II.

A2 A1 A0 Analog Input Selected

00 0V
00 1V
01 0V
01 1V
10 0V
10 1V
11 0V
11 1V

IN1

IN2

IN3

IN4

IN5

IN6

IN7

IN8

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.

–9–REV. B

AD7822/AD7825/AD7829

120ns

TRACK CHx

CONVST

EOC

CS

RD

DB0–DB7

A0–A2

HOLD CHx

t

2

TRACK CHx

t

1

ADDRESS CHANNEL y

TRACK CHy

t

13

VALID

DATA

t

HOLD CHy

3

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, t

. This is the

13

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 V
V

IN1

and V

with 0 V on Channel 4 and 0.5 V on Channel 1.

IN4

8.5

8.0

7.5

7.0

ENOB

6.5

6.0

5.5

5.0
500 10200

while channel hopping between

MID

100 50 40 30 20 15

ACQUISITION TIME – ns

Figure 13. Effective Number of Bits vs. Acquisition Time
for the AD7825

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.

50

f

= 2MHz

48

46

44

SNR – dB

42

40

38

0.2 101

34568

INPUT FREQUENCY – MHz

SAMPLE

Figure 14. SNR vs. Input Frequency on the AD7825

POWER-UP TIMES

The AD7822/AD7825/AD7829 have a 1 µs power-up time when
using an external reference and a 25 µs power-up time when using
the on-chip reference. When V

is first connected, the AD7822,

DD

AD7825, and AD7829 are in a low current mode of operation.
Ensure that the CONVST line is not floating when V
as if there is a glitch on CONVST while V
attempt to power up before V

has fully settled and could enter

DD

is rising, the part will

DD

is applied,

DD

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 V

is first connected or after the

DD

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 µs. 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 µs
before initiating a conversion; i.e., a falling edge on CONVST
may not occur before the required power-up time has elapsed,
when V

is first connected or after the AD7829 has been powered

DD

down using the CONVST pin as shown in Figure 15.

EXTERNAL REFERENCE

V

CONVST

V

CONVST

DD

DD

t

POWER-UP

1␮s

CONVERSION

INITIATED HERE

ON-CHIP REFERENCE

t

POWER-UP

25␮s

–10–

CONVERSION

INITIATED HERE

Figure 15. AD7829 Power-Up Time

REV. B

AD7822/AD7825/AD7829

Figure 16 shows how to power up the AD7822 or AD7825 when
V

is first connected or after the ADCs have been powered

DD

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 µs. 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 µs 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

V

DD

PD

CONVST

t

POWER-UP

1␮s

t

POWER-UP

1␮s

CONVST

t

POWER-UP

1␮s

t

CONVERT

330ns

POWER-DOWN

t

CYCLE

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,

= 3 V. If the power-up time is 1 µs and the conversion time

V

DD

is 330 ns (@ +25°C), the AD7822 can be said to dissipate
36 mW (maximum) for 1.33 µs during each conversion cycle.
If the throughput rate is 100 kSPS, the cycle time is 10 µs
and the average power dissipated during each cycle is (1.33/10)
× (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

10

1

V

PD

CONVST

CONVERSION

INITIATED HERE

ON-CHIP REFERENCE

DD

t

POWER-UP

25␮s

CONVERSION

INITIATED HERE

CONVERSION

INITIATED HERE

t

POWER-UP

25␮s

CONVERSION

INITIATED HERE

Figure 16. AD7822/AD7825 Power-Up Time

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.

POWER – mW

0.1

0

0 500100

50 150 250 350 450

200 300 400

THROUGHPUT – kSPS

Figure 18. AD7822/AD7825/AD7829 Power vs. Throughput

0

–10

–20

–30

–40

dB

–50

–60

–70

–80

0

85

28

57

113

142

170

198

227

255

283

312

481

425

368

453

396

340

FREQUENCY – kHz

510

538

566

595

623

651

2048 POINT FFT
SAMPLING
2MSPS

f

= 200kHz

IN

736

765

793

821

850

878

680

708

906

935

963

991

Figure 19. AD7822/AD7825/AD7829 SNR

–11–REV. B

AD7822/AD7825/AD7829

OPERATING MODES

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.

120ns

TRACK

CONVST

HOLD

t

2

t

1

Mode 2 Operation (Automatic Power-Down)

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.

TRACK

HOLD

DB0–DB7

CONVST

EOC

CS

RD

EOC

CS

RD

t

POWER-UP

Figure 20. Mode 1 Operation

t

1

VALID
DATA

POWER

DOWN

HERE

t

3

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

t

CONVST

EOC

CS

RD

DB0–DB7

A0–A2

2

t

1

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.

t

4

t

5

t

8

VALID

DATA

t

7

t

3

t

10

t

13

t

6

t

11

NEXT
CHANNEL
ADDRESS

t

9

t

12

Figure 22. AD7822/AD7825/AD7829 Parallel Port Timing

–13–REV. B

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

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.

8051*

AD0–AD7

LATCH

ALE

A8–A15

RD
INT

*ADDITIONAL PINS OMITTED FOR CLARITY

DECODER

DB0–DB7

AD7822/
AD7825/
AD7829*

CS

RD
EOC

Figure 23. Interfacing to the 8051

AD7822/AD7825/AD7829 to PIC16C6x/7x

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

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*

PSP0–PSP7

CS

RD

INT

*ADDITIONAL PINS OMITTED FOR CLARITY

AD7822/
AD7825/
AD7829*

DB0–DB7

CS

RD

EOC

Figure 24. Interfacing to the PIC16C6x/7x

AD7822/AD7825/AD7829 to ADSP-21xx

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*

D7–D0

A13–A0

ADDRESS

DECODE

LOGIC

DMS

RD

IRQ

*ADDITIONAL PINS OMITTED FOR CLARITY

EN

DB0–DB7

AD7822/
AD7825/
AD7829*

CS

RD

EOC

Figure 25. Interfacing to the ADSP-21xx

–14–

REV. B

AD7822/AD7825/AD7829

Interfacing Multiplexer Address Inputs

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.

A0
A1

A2

AD7825/

A15–A3

SYSTEM BUS

ADDRESS

DECODE

AD7829

CS

RD

DB7–DB0

A15–A3

A2–A0

DB0–DB7

AD7822 Stand–Alone Operation

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

CS

RD

ADC I/O ADDRESS

MUX ADDRESS

A/D RESULT

MUX ADDRESS

(CHANNEL SELECTION A0–A2)

LATCHED

CONVST

AD7822

DB7–DB0

RD

CS

EOC

Figure 26. AD7825/AD7829 Simplified Microinterfacing Scheme

t

1

DSP/

LATCH/ASIC

CONVST

EOC

CS

RD

DB0–DB7 A/D RESULT

t

Figure 27. AD7822 Stand-Alone Operation

4

–15–REV. B

AD7822/AD7825/AD7829

0.210 (5.33)

0.160 (4.06)

0.115 (2.93)

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

20-Lead Plastic DIP

(N-20)

1.060 (26.90)

0.925 (23.50)

20

110

PIN 1

MAX

0.022 (0.558)

0.014 (0.356)

0.100
(2.54)

BSC

11

0.070 (1.77)

0.045 (1.15)

0.280 (7.11)

0.240 (6.10)

0.060 (1.52)

0.015 (0.38)

SEATING
PLANE

20-Lead Small Outline Package

(R-20)

0.5118 (13.00)

0.4961 (12.60)

0.130
(3.30)
MIN

0.325 (8.25)

0.300 (7.62)

0.015 (0.381)

0.008 (0.204)

0.195 (4.95)

0.115 (2.93)

20 11

0.2992 (7.60)

0.2914 (7.40)

0.4193 (10.65)

0.3937 (10.00)

0.0125 (0.32)

0.0091 (0.23)

0.0118 (0.30)

0.0040 (0.10)

PIN 1

0.0500
(1.27)

BSC

0.1043 (2.65)

0.0926 (2.35)

0.0192 (0.49)

0.0138 (0.35)

101

SEATING
PLANE

20-Lead Thin Shrink Small Outline Package

(RU-20)

0.260 (6.60)

0.252 (6.40)

20 11

0.177 (4.50)

0.006 (0.15)

0.002 (0.05)

SEATING

PLANE

0.169 (4.30)

1

PIN 1

0.0256 (0.65)
BSC

0.0118 (0.30)

0.0075 (0.19)

10

0.256 (6.50)

0.246 (6.25)

0.0433
(1.10)
MAX

0.0079 (0.20)

0.0035 (0.090)

0.0291 (0.74)

0.0098 (0.25)

8°
0°

0.028 (0.70)

8°
0°

0.020 (0.50)

x 45°

0.0500 (1.27)

0.0157 (0.40)

–16–

REV. B

0.210

24

13

121

0.6141 (15.60)

0.5985 (15.20)

0.4193 (10.65)

0.3937 (10.00)

0.2992 (7.60)

0.2914 (7.40)

PIN 1

SEATING
PLANE

0.0118 (0.30)

0.0040 (0.10)

0.0192 (0.49)

0.0138 (0.35)

0.1043 (2.65)

0.0926 (2.35)

0.0500
(1.27)

BSC

0.0125 (0.32)

0.0091 (0.23)

0.0500 (1.27)

0.0157 (0.40)

8°
0°

0.0291 (0.74)

0.0098 (0.25)

x 45°

(5.33)

MAX

0.200 (5.05)

0.125 (3.18)

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

24-Lead Plastic DIP

(N-24)

1.275 (32.30)

1.125 (28.60)

24

112

PIN 1

0.022 (0.558)

0.014 (0.356)

0.100 (2.54)
BSC

13

0.070 (1.77)

0.045 (1.15)

0.280 (7.11)

0.240 (6.10)

0.060 (1.52)

0.015 (0.38)

0.150
(3.81)
MIN

SEATING
PLANE

0.325 (8.25)

0.300 (7.62)

24-Lead Small Outline Package

(R-24)

AD7822/AD7825/AD7829

0.195 (4.95)

0.115 (2.93)

0.015 (0.381)

0.008 (0.204)

0.177 (4.50)

0.006 (0.15)

0.002 (0.05)

SEATING

PLANE

24-Lead Thin Shrink Small Outline Package

(RU-24)

0.311 (7.90)

0.303 (7.70)

24

0.169 (4.30)

1

PIN 1

0.0256 (0.65)
BSC

0.0118 (0.30)

0.0075 (0.19)

13

12

0.256 (6.50)

0.246 (6.25)

0.0433
(1.10)
MAX

0.0079 (0.20)

0.0035 (0.090)

8°
0°

0.028 (0.70)

0.020 (0.50)

–17–REV. B

AD7822/AD7825/AD7829

0.250
(6.35)

MAX

0.200 (5.05)

0.125 (3.18)

28

1

PIN 1

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

28-Lead Plastic DIP

(N-28)

1.565 (39.70)

1.380 (35.10)

15

0.580 (14.73)

0.485 (12.32)

14

0.060 (1.52)

0.015 (0.38)

0.150
(3.81)

0.022 (0.558)

0.014 (0.356)

0.100
(2.54)

BSC

0.070
(1.77)

MAX

MIN

SEATING
PLANE

28-Lead Small Outline Package

(R-28)

0.625 (15.87)

0.600 (15.24)

0.015 (0.381)

0.008 (0.204)

0.195 (4.95)

0.125 (3.18)

0.7125 (18.10)

0.6969 (17.70)

28 15

PIN 1

0.0118 (0.30)

0.0040 (0.10)

0.0500
(1.27)

BSC

0.0192 (0.49)

0.0138 (0.35)

28-Lead Thin Shrink Small Outline Package

0.386 (9.80)

0.378 (9.60)

28 15

0.177 (4.50)

0.169 (4.30)

1

141

0.1043 (2.65)

0.0926 (2.35)

SEATING

PLANE

(RU-28)

14

0.2992 (7.60)

0.2914 (7.40)

0.0125 (0.32)

0.0091 (0.23)

0.256 (6.50)

0.246 (6.25)

0.4193 (10.65)

0.3937 (10.00)

0.0291 (0.74)

0.0098 (0.25)

0.0500 (1.27)

8°
0°

0.0157 (0.40)

x 45°

0.006 (0.15)

0.002 (0.05)

SEATING

PLANE

PIN 1

0.0256 (0.65)
BSC

0.0118 (0.30)

0.0075 (0.19)

–18–

0.0433
(1.10)

MAX

0.0079 (0.20)

0.0035 (0.090)

8°
0°

0.028 (0.70)

0.020 (0.50)

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–

C01321a–0–10/01(B)

–20–

PRINTED IN U.S.A.