a
FEATURES
4 or 8 Analog Input Channels
Built-In Track/Hold Function
10 kHz Signal Handling on Each Channel
Fast Microprocessor Interface
Single 5 V Supply
Low Power: 50 mW
Fast Conversion Rate, 2.5 s/Channel
Tight Error Specification: 1/2 LSB
LC2MOS High-Speed
4- and 8-Channel 8-Bit ADCs
AD7824/AD7828
FUNCTIONAL BLOCK DIAGRAM
VREF (+)
AIN 1
AIN 4
DB7
DB6
DB5
DB4
4-BIT
FLASH
ADC
(4MSB)
VREF (–)
VREF (+)
16
AIN 8
THREESTATE
DRIVERS
4-BIT
DAC
MUX*
DB3
DB2
DB1
DB0
4-BIT
FLASH
ADC
(4LSB)
ADDRESS
LATCH
DECODE
TIMING AND CONTROL
CIRCUITRY
A0 A1 A2**
RDY
CS
INT
RD
*AD7824 – 4-CHANNEL MUX
**AD7828 – 8-CHANNEL MUX
A2 – AD7828 ONLY
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
The AD7824 and AD7828 are high-speed, multichannel, 8-bit
ADCs with a choice of four (AD7824) or eight (AD7828) multiplexed analog inputs. A half-flash conversion technique gives a fast
conversion rate of 2.5 µs per channel and the parts have a built-in
track/hold function capable of digitizing full-scale signals of 10 kHz
(157 mV/µs slew rate) on all channels. The AD7824 and AD7828
operate from a single 5 V supply and have an analog input range of
0 V to 5 V, using an external 5 V reference.
1. 4- or 8-channel input multiplexer gives cost effective
space-saving multichannel ADC system.
Microprocessor interfacing of the parts is simple, using standard
Chip Select (CS) and Read (RD) signals to initiate the conversion
and read the data from the three-state data outputs. The half-flash
conversion technique means that there is no need to generate a
clock signal for the ADC. The AD7824 and AD7828 can be
interfaced easily to most popular microprocessors.
2. Fast conversion rate of 2.5 µs/channel features a per-channel
sampling frequency of 100 kHz for the AD7824 or 50 kHz
for the AD7828.
3. Built-in track-hold function allows handling of four or eight
channels up to 10 kHz bandwidth (157 mV/µs slew rate).
4. Tight total unadjusted error spec and channel-to-channel
matching eliminate the need for user trims.
5. Single 5 V supply simplifies system power requirements.
6. Fast, easy-to-use digital interface allows connection to most
popular microprocessors with minimal external components.
No clock signal is required for the ADC.
The AD7824 and AD7828 are fabricated in an advanced, all
ion-implanted, linear-compatible CMOS process (LC2MOS) and
have low power dissipation of 40 mW (typ). The AD7824 is
available in a 0.3" wide, 24-lead “skinny” DIP, while the AD7828
is available in a 0.6" wide, 28-lead DIP and in 28-terminal surfacemount packages.
REV. E
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
© Analog Devices, Inc., 2002
(V = 5 V, V (+) = 5 V, V
AD7824/AD7828–SPECIFICATIONS
noted. All specifications T to T unless otherwise noted. Specifications apply for Mode 0.)
DD
MIN
ACCURACY
Resolution
Total Unadjusted Error2
Minimum Resolution for which
No Missing Codes Are Guaranteed
Channel-to-Channel Mismatch
VREF(–) Input Voltage Range
ANALOG INPUT
Input Voltage Range
Input Leakage Current
Input Capacitance3
LOGIC INPUTS
RD, CS, A0, A1, and A2
VINH
VINL
IINH
IINL
Input Capacitance3
LOGIC OUTPUTS
DB0–DB7 and INT
VOH
VOL
IOUT (DB0–DB7)
Output Capacitance3
RDY
VOL4
IOUT
Output Capacitance
SLEW RATE, TRACKING3
POWER SUPPLY
VDD
IDD5
Power Dissipation
Power Supply Sensitivity
REF(–)
= GND = O V unless otherwise
MAX
Parameter
REFERENCE INPUT
Input Resistance
VREF(+) Input Voltage Range
REF
K Version1 L Version B, T Versions
C, U Versions Unit
8
±1
8
± 1/2
8
±1
8
± 1/2
Bits
LSB max
8
± 1/4
8
± 1/4
8
± 1/4
8
± 1/4
Bits
LSB max
1.0/4.0
VREF(–)/
VDD
GND/
VREF(+)
1.0/4.0
VREF(–)/
VDD
GND/
VREF(+)
1.0/4.0
VREF(–)/
VDD
GND/
VREF(+)
1.0/4.0
VREF(–)/
VDD
GND/
VREF(+)
kΩ min/kΩ max
V min/V max
VREF(–)/
VREF(+)
±3
45
VREF(–)/
VREF(+)
±3
45
VREF(–)/
VREF(+)
±3
45
VREF(– )/
VREF(+)
±3
45
µA max
pF typ
Analog Input Any Channel
0 V to 5 V
2.4
0.8
1
–1
8
2.4
0.8
1
–1
8
2.4
0.8
1
–1
8
2.4
0.8
1
–1
8
V min
V max
µA max
µA max
pF max
Typically 5 pF
4.0
0.4
±3
8
4.0
0.4
±3
8
4.0
0.4
±3
8
4.0
0.4
±3
8
V min
V max
µA max
pF max
ISOURCE = 360 µA
ISINK = 1.6 mA
Floating State Leakage
Typically 5 pF
0.4
±3
8
0.4
±3
8
0.4
±3
8
0.4
±3
8
V max
µA max
pF max
ISINK = 2.6 mA
Floating State Leakage
Typically 5 pF
0.7
0.157
0.7
0.157
0.7
0.157
0.7
0.157
V/µs typ
V/µs max
5
5
5
5
Volts
16
50
80
± 1/4
16
50
80
± 1/4
20
50
100
± 1/4
20
50
100
± 1/4
mA max
mW typ
mW max
LSB max
Conditions/Comments
V min/V max
V min/V max
± 5% for Specified
Performance
CS = RD = 2.4 V
± 1/16 LSB typ
VDD = 5 V ± 5%
NOTES
1
Temperature ranges are as follows:
K, L Versions; 0°C to 70°C
B, C Versions; –40°C to +85°C
T, U Versions; –55°C to +125°C
2
Total Unadjusted Error includes offset, full-scale and linearity errors.
3
Sample tested at 25°C by Product Assurance to ensure compliance.
4
RDY is an open drain output.
5
See Typical Performance Characteristics.
Specifications subject to change without notice.
–2–
REV. E
AD7824/AD7828
TIMING CHARACTERISTICS1 (V
DD
= 5 V; VREF(+) = 5 V; VREF(–) = GND = 0 V unless otherwise noted.)
Parameter
Limit at 25C
(All Grades)
Limit at
TMIN, TMAX
(K, L, B, C Grades)
Limit at
TMIN, TMAX
(T, U Grades)
Unit
Conditions/Comments
tCSS
tCSH
tAS
tAH
tRDY2
0
0
0
30
40
0
0
0
35
60
0
0
0
40
60
ns min
ns min
ns min
ns min
ns max
tCRD
tACC13
tACC23
tlNTH2
2.0
85
50
40
75
60
500
60
600
2.4
110
60
65
100
70
500
80
500
2.8
120
70
70
100
70
600
80
400
µs max
ns max
ns max
ns typ
ns max
ns max
ns min
ns min
ns max
CS to RD Setup Time
CS to RD Hold Time
Multiplexer Address Setup Time
Multiplexer Address Hold Time
CS to RDY Delay. Pull-Up
Resistor 5 kΩ.
Conversion Time, Mode 0
Data Access Time after RD
Data Access Time after INT, Mode 0
RD to INT Delay
tDH4
tP
tRD
Data Hold Time
Delay Time between Conversions
Read Pulsewidth, Mode 1
NOTES
1
Sample tested at 25°C to ensure compliance. All input control signals are specified with tr = tf = 20 ns (10 % to 90% of 5 V) and timed from a voltage level of 1.6 V.
2
CL = 50 pF.
3
Measured with load circuits of Figure 1 and defined as the time required for an output to cross 0.8 V or 2.4 V.
4
Defined as the time required for the data lines to change 0.5 V when loaded with the circuits of Figure 2.
Specifications subject to change without notice.
Test Circuits
DBN
DBN
3k
3k
100pF
10pF
DGND
DGND
a. VOH to High-Z
a. High-Z to VOH
5V
5V
3k
3k
DBN
DBN
100pF
10pF
DGND
DGND
b. High-Z to VOL
b. VOL to High-Z
Figure 1. Load Circuits for Data Access Time Test
Figure 2. Load Circuits for Data Hold Time Test
REV. E
–3–
AD7824/AD7828
Operating Temperature Range
Commercial (K, L Versions) . . . . . . . . . . . . . . 0°C to 70°C
Industrial (B, C Versions) . . . . . . . . . . . . . –25°C to +85°C
Extended (T, U Versions) . . . . . . . . . . . –55°C to +125°C
Storage Temperature Range . . . . . . . . . . . –65°C to +150°C
Lead Temperature (Soldering, 10 secs) . . . . . . . . . . . . 300°C
Power Dissipation (Any Package) to 75°C . . . . . . . . . 450 mW
Derates above 75°C by . . . . . . . . . . . . . . . . . . . . . . 6 mW/°C
ABSOLUTE MAXIMUM RATINGS*
(TA = 25°C unless otherwise noted.)
VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V, 7 V
Digital Input Voltage to GND
(RD, CS, A0, A1, and A2) . . . . . . . . . –0.3 V, VDD + 0.3 V
Digital Output Voltage to GND
(DB0, DB7, RDY and INT) . . . . . . . –0.3 V, VDD + 0.3 V
VREF (+) to GND . . . . . . . . . . . . . . . . . VREF (–), VDD + 0.3 V
VREF (–) to GND . . . . . . . . . . . . . . . . . . . . . . . . 0 V, VREF (+)
Analog Input (Any Channel) . . . . . . . . . . –0.3 V, VDD + 0.3 V
*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 indicated 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 AD7824/AD7828 feature 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
AIN4
AIN5
AIN6
AIN7
4
3
2
1
28 27 26
VDD
AIN3
DIP/SOIC/SSOP
AIN8
LCCC
PIN CONFIGURATIONS
A0
AIN2 5
25
AIN4
1
24 VDD
AIN6 1
28 AIN7
AIN1 6
24
A1
AIN2
2
23 NC
AIN5 2
27 AIN8
NC 7
AD7828
23
A2
AIN2
3
22 A0
AIN4 3
26 VDD
DB0 8
TOP VIEW
(Not to Scale)
22
DB7
AIN1
4
21 A1
AIN3
21
DB6
DB2 10
20
DB5
NC
5
20 DB7
AIN2 5
DB3 11
19
DB4
DB0
6
AIN1 6
DB1
TOP VIEW 19 DB6
(Not to Scale) 18 DB5
7
DB2
8
17 DB4
NC 7
TOP VIEW 22 DB7
DB0 8 (Not to Scale) 21 DB6
DB3
9
24 A1
23 A2
12 13 14 15 16 17 18
VREF (–)
AD7828
NC = NO CONNECT
14 VREF (+)
DB3 11
18 CS
GND 12
13 VREF (–)
17 RDY
16 VREF (+)
GND 14
15 VREF (–)
NC = NO CONNECT
ORDERING GUIDE
NC = NO CONNECT
Model
AD7824KN
AD7824LN
AD7824KR
AD7824BQ
AD7824CQ
AD7824TQ*
AD7824UQ*
0°C to 70°C
0°C to 70°C
0°C to 70°C
–40°C to +85°C
–40°C to +85°C
–55°C to +125°C
–55°C to +125°C
±1
± 1/2
±1
±1
± 1/2
±1
± 1/2
N-24
N-24
R-24
Q-24
Q-24
Q-24
Q-24
AD7828KN
AD7828LN
AD7828KP
AD7828LP
AD7828BQ
AD7828CQ
AD7828BR
AD7828LRS
AD7828TQ*
AD7828UQ*
AD7828TE*
AD7828UE*
0°C to 70°C
0°C to 70°C
0°C to 70°C
0°C to 70°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
0°C to 70°C
–55°C to +125°C
–55°C to +125°C
–55°C to +125°C
–55°C to +125°C
±1
± 1/2
±1
± 1/2
±1
± 1/2
+1
± 1/2
±1
± 1/2
±1
± 1/2
N-28
N-28
P-28A
P-28A
Q-28
Q-28
R-28
RS-28
Q-28
Q-28
E-28A
E-28A
AIN4
AIN5
AIN6
AIN7
AIN8
AIN3
PLCC
4
3
2
1
28 27 26
PIN 1
IDENTIFIER
AIN2 5
AIN1 6
25 A0
24 A1
NC 7
AD7828
DB0 8
TOP VIEW
22 DB7
DB1 9
(Not to Scale)
21 DB6
23 A2
VREF (+)
GND
RD
INT
16
17
18
CS
19 DB4
RDY
20 DB5
DB3 11
VREF (–)
DB2 10
12 13 14 15
Total
Unadjusted Package
Error (LSBs) Option
Temperature
Range
VDD
RD 12
INT 13
CS
19 DB4
INT 11
RDY
DB2 10
GND
20 DB5
15 RDY
RD
DB1 9
RD 10
INT
16 CS
VREF (+)
AD7824
DB1 9
25 A0
4
NC = NO CONNECT
*Available to /883B processing only. Contact our local sales office for military
data sheet. For U.S. Standard Military Drawing (SMD) see DESC Drawing
#5692-88764.
–4–
REV. E
Typical Performance Characteristics–AD7824/AD7828
14
13
IDD – SUPPLY CURRENT – mA
tCRD – CONVERSION TIME – s
3
2
VDD = 5V
12
VDD = 5V
VDD = 5.25V
11
10
9
VDD = 4.75V
1
–100
–50
0
50
100
TA – AMBIENT TEMPERATURE – C
8
–100
150
TPC 1. Conversion Time vs. Temperature
0
50
100
–50
TA – AMBIENT TEMPERATURE – C
TPC 4. Power Supply Current vs. Temperature
(Not Including Reference Ladder)
2.0
2.0
VDD = 5V
VREF = 5V
TA = 25C
1.5
LINEARITY ERROR – LSB
LINEARITY ERROR – LSB*
VDD = 5V
TA = 25C
1.0
0.5
0
150
0
*1LSB =
1
2
3
4
1.5
1.0
0.5
0
300
5
VREF – V
VREF
400
500
600
700
800
900
tP – ns
256
TPC 2. Accuracy vs. VREF [VREF = VREF(+) – VREF(–)]
TPC 5. Accuracy vs. tP
–36
10
ENCODE RATE = 400kHz
INPUT SIGNAL = 5V p-p
MEASUREMENT BANDWIDTH = 80kHz
–38
VDD = 5V
8
OUTPUT CURRENT – mA
–40
SNR – dB
–42
–44
–46
–48
ISOURCE, V OUT = 2.4V
6
4
ISINK, V OUT = 0.4V
2
–50
–52
1
2
3
4 5 7
10
20 30 40 50 70
INPUT FREQUENCY – kHz
0
–100
100
TPC 3. Signal-Noise Ratio vs. Input Frequency
REV. E
–50
0
50
100
TA – AMBIENT TEMPERATURE – C
TPC 6. Output Current vs. Temperature
–5–
150
AD7824/AD7828
OPERATIONAL DIAGRAM
APPLYING THE AD7824/AD7828
REFERENCE AND INPUT
The AD7824 is a 4-channel 8-bit A/D converter and the
AD7828 is an 8-channel 8-bit A/D converter. Operational
diagrams for both of these devices are shown in Figures 3 and
4. The addition of just a 5 V reference allows the devices to
perform the analog-to-digital function.
ANALOG INPUTS
0V TO 5V
1 AIN4
VDD 24
2 AIN2
NC 23
3 AIN2
A0 22
4 AIN1
A1 21
AD7824
5 NC
P 4LSB
DATA BUS
P CONTROL INPUT
STATUS OUTPUT
5V
P ADDRESS
BUS
This reference flexibility also allows the input channel voltage
span to be offset from zero. The voltage at VREF (–) sets the
input level for all channels which produces a digital output of
all zeroes. Therefore, although the analog inputs are not themselves differential, they have nearly differential-input capability
in most measurement applications because of the reference
design. Figures 5 to 7 show some of the configurations that are
possible.
DB7 20
6 DB0
DB6 19
7 DB1
DB5 18
8 DB2
DB4 17
9 DB3
The two reference inputs on the AD7824/AD7828 are fully
differential and define the zero to full-scale input range of the
A/D converter. As a result, the span of the analog input voltage
for all channels can easily be varied. By reducing the reference span, VREF (+) – VREF (–), to less than 5 V the sensitivity
of the converter can be increased (e.g., if VREF = 2 V then 1
LSB = 7.8 mV). The input/reference arrangement also facilitates ratiometric operation.
CS 16
10 RD
RDY 15
11 INT
VREF (+) 14
12 GND
VREF (–) 13
P 4MSB
DATA BUS
P CONTROL INPUT
STATUS OUTPUT
5V
NC = NO CONNECT
VIN (+)
AIN1
Figure 3. AD7824 Operational Diagram
VIN (–)
GND AD7824*
AD7828*
5V
VDD
0.1F
ANALOG INPUTS
0V TO 5V
P 4LSB
DATA BUS
1
AIN6
AIN7 28
2
AIN5
AIN8 27
3
AIN4
VDD 26
4
AIN3
A0 25
5
AIN2
A1 24
AIN1
7
NC
8
DB0
DB6 21
9
DB1
DB5 20
10
DB2
DB4 19
11
DB3
CS 18
AD7828
VREF (+)
VREF (–)
5V
*ADDITIONAL PINS OMITTED FOR CLARITY.
ONLY CHANNEL 1 SHOWN.
P ADDRESS
BUS
A2 23
6
47F
ANALOG INPUTS
0V TO 5V
Figure 5. Power Supply as Reference
DB7 22
P CONTROL INPUT
12
RD
RDY 17
STATUS OUTPUT
13
INT
VREF (+) 16
14
GND
VREF (–) 15
P 4MSB
DATA BUS
P CONTROL INPUT
VIN (+)
AIN1
VIN (–)
GND AD7824*
AD7828*
5V
VDD
STATUS OUTPUT
0.1F
47F
5V
AD580
VREF (+)
0.1F
10F
VREF (–)
NC = NO CONNECT
*ADDITIONAL PINS OMITTED FOR CLARITY.
ONLY CHANNEL 1 SHOWN.
Figure 4. AD7828 Operational Diagram
Figure 6. External Reference Using the AD580, Full-Scale
Input is 2.5 V
CIRCUIT INFORMATION
BASIC DESCRIPTION
The AD7824/AD7828 uses a half-flash conversion technique
whereby two 4-bit flash A/D converters are used to achieve an
8-bit result. Each 4-bit flash ADC contains 15 comparators
which compare the unknown input to a reference ladder to get
a 4-bit result. For a full 8-bit reading to be realized, the upper
4-bit flash, the most significant (MS) flash, performs a conversion to provide the four most significant data bits. An internal
DAC, driven by the 4 MSBs, then recreates an analog approximation of the input voltage. This analog result is subtracted
from the input, and the difference is converted by the lower
flash ADC, the least significant (LS) flash, to provide the four
least significant bits of the output data.
VIN (+)
AIN1
GND AD7824*
AD7828*
5V
VDD
0.1F
47F
DB7
V1
VREF (+)
V2
VREF (–)
DATA
DB0
*ADDITIONAL PINS OMITTED FOR CLARITY.
ONLY CHANNEL 1 SHOWN.
DATA =
VIN (+)
256 (FOR ALL CHANNELS)
V1 –V2
Figure 7. Input Not Referenced to GND
–6–
REV. E
AD7824/AD7828
INPUT CURRENT
Due to the novel conversion techniques employed by the AD7824/
AD7828, the analog input behaves somewhat differently than in
conventional devices. The ADC’s sampled-data comparators
take varying amounts of input current depending on which cycle
the conversion is in.
The equivalent input circuit of the AD7824/AD7828 is shown
in Figure 8. When a conversion starts (CS and RD going low),
all input switches close, and the selected input channel is connected to the most significant and least significant comparators.
Therefore, the analog input is connected to thirty one 1 pF
input capacitors at the same time.
CS
2pF
RS
R MUX
AIN1
VIN
CS
12pF
1pF
RON
TO LS
LADDER
•
•
•
1pF
15LSB
COMPARATORS
1pF
RON
AD7824/
AD7828
TO MS
LADDER
•
•
•
Figure 8. AD7824/AD7828 Equivalent Input Circuit
The input capacitors must charge to the input voltage through
the on resistance of the analog switches (about 3 kΩ to 6 kΩ). In
addition, about 14 pF of input stray capacitance must be charged.
The analog input for any channel can be modelled as an RC
network as shown in Figure 9. As RS increases, it takes longer
for the input capacitance to charge.
VIN
AIN 1
R MUX
800
CS1
12pF
INHERENT SAMPLE-HOLD
A major benefit of the AD7824’s and AD7828’s analog input
structure is its ability to measure a variety of high-speed signals
without the help of an external sample-and-hold. In a conventional SAR type converter, regardless of its speed, the input
must remain stable to at least 1/2 LSB throughout the conversion
process if rated accuracy is to be maintained. Consequently, for
many high-speed signals, this signal must be externally sampled
and held stationary during the conversion. The AD7824/AD7828
input comparators, by nature of their input switching inherently
accomplish this sample-and-hold function. Although the conversion time for AD7824/AD7828 is 2 µs, the time for which any
selected analog input must be 1/2 LSB stable is much smaller.
The AD7824/AD7828 tracks the selected input channel for
approximately 1 µs after conversion start. The value of the analog
input at that instant (1 µs from conversion start) is the measured
value. This value is then used in the least significant flash to
generate the lower 4 bits of data.
SINUSOIDAL INPUTS
The AD7824/AD7828 can measure input signals with slew rates
as high as 157 mV/µs to the rated specifications. This means that
the analog input frequency can be up to 10 kHz without the aid
of an external sample and hold. Furthermore, the AD7828 can
measure eight 10 kHz signals without a sample and hold. The
Nyquist criterion requires that the sampling rate be twice the
input frequency (i.e., 2 × 10 kHz). This requires an ideal antialiasing filter with an infinite roll-off. To ease the problem of
antialiasing filter design, the sampling rate is usually much greater
than the Nyquist criterion. The maximum sampling rate (FMAX)
for the AD7824/AD7828 can be calculated as follows:
RON
350
CS2
2pF
FMAX =
1
tCRD + t P
FMAX =
1
= 400 kHz
2E – 6 + 0.5E – 6
32pF
Figure 9. RC Network Model
The time for which the input comparators track the analog input
is approximately 1 µs at the start of conversion. Because of input
transients on the analog inputs, it is recommended that a source
impedance no greater than 100 Ω be connected to the analog
inputs. The output impedance of an op amp is equal to the open
REV. E
Suitable op amps for driving the AD7824/AD7828 are the AD544
or AD644.
1pF
15MSB
COMPARATORS
RS
loop output impedance divided by the loop gain at the frequency of
interest. It is important that the amplifier driving the AD7824/
AD7828 analog inputs have sufficient loop gain at the input signal
frequency as to make the output impedance low.
tCRD = AD7824/AD7828 Conversion Time
tP = Minimum Delay Between Conversion
This permits a maximum sampling rate of 50 kHz for each of
the 8 channels when using the AD7828 and 100 kHz for each of
the 4 channels when using the AD7824.
–7–
AD7824/AD7828
UNIPOLAR OPERATION
25k
The analog input range for any channel of the AD7824/ AD7828 is
0 V to 5 V as shown in the unipolar operational diagram of Figure
10. Figure 11 shows the designed code transitions which occur
midway between successive integer LSB values (i.e., 1/2 LSB, 3/2
LSB, 5/2 LSB, FS 3/2 LSBs). The output code is Natural Binary
with 1 LSB = FS/256 = (5/256) V = 19.5 mV.
VIN
5V
40k
27k
AD544
12k
AIN1
VREF (+)
5V
5V
VDD
0.1F
47F
VREF (–)
0.1F
47F V
REF
5V
VIN
0V TO 5V
VREF (+)
*ADDITIONAL PINS OMITTED FOR CLARITY.
ONLY CHANNEL 1 SHOWN.
AD7824*
AD7828*
AIN1
Figure 12. AD7824/AD7828 Bipolar ± 4 V Operation
DB7
VREF (–)
DB7
DB0
GND
VDD
5V
AD7824*
AD7828*
DB0
GND
11111111
*ADDITIONAL PINS OMITTED FOR CLARITY.
ONLY CHANNEL 1 SHOWN.
FS = 8V
1LSB = FS/256
11111110
11111101
OUTPUT CODE
Figure 10. AD7824/AD7828 Unipolar 0 V to 5 V Operation
FULL-SCALE
TRANSITION
11111111
10000010
10000001
10000000
01111111
01111110
11111101
00000010
OUTPUT CODE
11111110
+FS
2
–FS
+ 1LSB
2
00000001
00000000
1LSB =
FS
256
0V
AIN, INPUT VOLTAGE – LSB
00000011
Figure 13. Ideal Input/Output Transfer Characteristic for
± 4 V Operation
00000010
00000001
00000000
0 1LSB 2LSB 3LSB
TIMING AND CONTROL
FS
The AD7824/AD7828 has two digital inputs for timing and
control. These are Chip Select (CS) and Read (RD). A READ
operation brings CS and RD low, which starts a conversion on
the channel selected by the multiplexer address inputs (see
Table I). There are two modes of operation as outlined by the
timing diagrams of Figures 14 and 15. Mode 0 is designed for
microprocessors which can be driven into a WAIT state. A
READ operation (i.e., CS and RD are taken low) starts a conversion and data is read when conversion is complete. Mode l
does not require microprocessor WAIT states. A READ operation
initiates a conversion and reads the previous conversion results.
FS – 1LSB
AIN, INPUT VOLTAGE – LSB
Figure 11. Ideal Input/Output Transfer Characteristic for
Unipolar 0 V to 5 V Operation
BIPOLAR OPERATION
The circuit of Figure 12 is designed for bipolar operation. An
AD544 op amp conditions the signal input (VIN) so that only
positive voltages appear at AIN 1. The closed loop transfer
function of the op amp for the resistor values shown is given
below:
AIN 1 = (2.5 − 0.625 VIN ) Volts
Table I. Truth Table for Input Channel Selection
The analog input range is ± 4 V and the LSB size is 31.25 mV.
The output code is complementary offset binary. The ideal
input/output characteristic is shown in Figure 13.
AD7824
A1
A0
0
0
1
1
–8–
0
1
0
1
A2
0
0
0
0
1
1
1
1
AD7828
A1 A0
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Channel
AIN 1
AIN 2
AIN 3
AIN 4
AIN 5
AIN 6
AIN 7
AIN 8
REV. E
AD7824/AD7828
MODE 0
MODE 1
Figure 14 shows the timing diagram for Mode 0 operation. This
mode can only be used for microprocessors which have a WAIT
state facility, whereby a READ instruction cycle can be extended
to accommodate slow memory devices. A READ operation brings
CS and RD low which starts a conversion. The analog multiplexer
address inputs must remain valid while CS and RD are low. The
data bus (DB7–DB0) remains in the three-state condition until
conversion is complete. There are two converter status outputs on
the AD7824/AD7828, interrupt (INT) and ready (RDY), which
can be used to drive the microprocessor READY/WAIT input.
The RDY is an open drain output (no internal pull-up device) that
goes low on the falling edge of CS and goes high impedance at the
end of conversion, when the 8-bit conversion result appears on the
data outputs. If the RDY status is not required, then the external
pull-up resistor can be omitted and the RDY output tied to GND.
The INT goes low when conversion is complete and returns high
on the rising edge of CS or RD.
Mode 1 operation is designed for applications where the microprocessor is not forced into a WAIT state. A READ operation takes
CS and RD low, which triggers a conversion (see Figure 15). The
multiplexer address inputs are latched on the rising edge of RD.
Data from the previous conversion is read from the three-state
data outputs (DB7–DB0). This data may be disregarded if not
required. Note, the RDY output (open drain output) does not
provide any status information in this mode and must be connected to GND. At the end of conversion INT goes low. A second
READ operation is required to access the new conversion result.
This READ operation latches a new address into the multiplexer
inputs and starts another conversion. INT returns high at the end
of the second READ operation, when CS or RD returns high.
A delay of 2.5 µs must be allowed between READ operations.
CS
tCSH
tCSS
tCSS
RD
tP
tAS
ANALOG
CHANNEL
ADDRESS
ADDRESS
VALID
tAS
ADDRESS
VALID
tAH
RDY
tRDY
tINTH
INT
tCRD
tACC2
HIGH IMPEDANCE
DATA
tDH
DATA
VALID
Figure 14. Mode 0 Timing Diagram
CS
tCSS
tCSH
tRD
tCSS
tRD
tCSH
RD
tP
tAS
ANALOG
CHANNEL
ADDRESS
tAS
ADDRESS
VALID
ADDRESS
VALID
tAH
tAH
tCRD
tINTH
tINTH
INT
tACC1
DATA
tDH
tACC1
OLD
VALID
Figure 15. Mode 1 Timing Diagram
REV. E
tDH
NEW
VALID
–9–
AD7824/AD7828
to any of the addresses in Table II starts a conversion and reads
the conversion result.
MICROPROCESSOR INTERFACING
The AD7824/AD7828 is designed to interface to microprocessors as Read Only Memory (ROM). Analog channel selection,
conversion start and data read operations are controlled by CS,
RD and the channel address inputs. These signals are common
to all memory peripheral devices.
MOVE × B $C000, D0
Once conversion has begun, the MC68000 inserts WAIT states,
until INT goes low asserting DTACK at the end of conversion.
The microprocessor then places the conversion results in the
D0 register.
Z80 MICROPROCESSOR
Figure 16 shows a typical AD7824/AD7828–Z80 interface. The
AD7824/AD7828 is operating in Mode 0. Assume the ADC is
assigned a memory block starting at address C000. The following LOAD instruction to any of the addresses listed in Table II
will start a conversion of the selected channel and read the
conversion result.
A23
A1
ADDRESS BUS
A1
A0
EN ADDRESS
DECODE
AS
LD B, (C000)
A1
A2**
CS
R/W
At the beginning of the instruction cycle when the ADC
address is selected, RDY asserts the WAIT input, so that the
Z80 is forced into a WAIT state. At the end of conversion RDY
returns high and the conversion result is placed in the B register
of the microprocessor.
A2
A0
RD
CLR
MC68000
7474
AD7824*
AD7828*
5V
D
5k
DTACK
Q
CK
RDY
D7
DB7
DATA BUS
A15
ADDRESS BUS
A1
A2
D0
DB0
A0
A0
EN
MREQ
ADDRESS
DECODE
A0
A1
A2**
*LINEAR CIRCUITRY OMITTED FOR CLARITY.
** FOR THE AD7828 ONLY
5V
Z80
CS
5k
AD7824*
AD7828*
Figure 17. AD7824/AD7828–MC68000 Interface
RDY
WAIT
RD
RD
TMS32010 MICROCOMPUTER
D7
DB7
A TMS32010 interface is shown in Figure 18. The AD7824/
AD7828 is operating in Mode 1 (i.e., no µP WAIT states). The
ADC is mapped at a port address. The following I/O instruction
starts a conversion and reads the previous conversion result into
the accumulator.
DATA BUS
DB0
D0
IN, A PA (PA = PORT ADDRESS)
*LINEAR CIRCUITRY OMITTED FOR CLARITY.
** FOR THE AD7828 ONLY
Figure 16. AD7824/AD7828–Z80 lnterface
Table II. Address Channel Selection
Address
C000
C001
C002
C003
C004
C005
C006
C007
AD7824
Channel
1
2
3
4
The port address (000 to 111) selects the analog channel to be
converted. When conversion is complete a second I/O instruction (IN, A PA) reads the up-to-date data into the accumulator
and starts another conversion. A delay of 2.5 µs must be allowed
between conversions.
AD7828
Channel
1
2
3
4
5
6
7
8
PA2
A2**
PA1
A1
PA0
A0
MEN
CS
DEN
RD
TMS32010
D7
AD7824*
AD7828*
DB7
DATA BUS
D0
DB0
MC68000 MICROPROCESSOR
Figure 17 shows a MC68000 interface. The AD7824/AD7828
is operating in Mode 0. Assume the ADC is again assigned a
memory block starting at address C000. A MOVE instruction
*LINEAR CIRCUITRY OMITTED FOR CLARITY.
** FOR THE AD7828 ONLY
Figure 18. AD7824/AD7828–TMS32010 Interface
–10–
REV. E
AD7824/AD7828
5V
BANDPASS
FILTER 1
BANDPASS
FILTER 2
SPEECH
INPUT
VDD
AIN 1
VDD
DB7
AIN 1
AIN 2
AIN 3
AIN 4
AD7828
DATA
BANDPASS
FILTER 7
AIN 7
DB0
BANDPASS
FILTER 8
AIN 8
A2
A1
A0
5V
VREF (+)
15V
10V
RD
AIN 2
AMP
SAMPLE
PULSE
5V
CS
CS
RD
INT
WR
DB7
DB7
DB0
AD7824
VREF
AD7226
DB0
VREF (+)
VREF (–)
GND
VDD
A1
A1
A0
A0
VOUT A
VOUT B
VOUT C
VOUT D
VSS
VO1
VO 2
VO 3
VO 4
DGND
AGND
VREF (–) GND
Figure 20. 4-Channel Fast Infinite Sample-and-Hold
Figure 19. Speech Analysis Using Real-Time Filtering
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
24-Lead Plastic DIP (N-24)
1.228 (31.19)
1.226 (31.14)
24
13
12
1
0.260 0.001
(6.61 0.03)
0.32 (8.128)
0.30 (7.62)
PIN 1
0.130 (3.30)
0.128 (3.25)
SEATING
PLANE
0.02 (0.5)
0.07 (1.78)
0.05 (1.27) 0.016 (0.41)
0.11 (2.79)
0.09 (2.28)
15
0
0.011 (0.28)
0.009 (0.23)
NOTES
1. LEAD NO. 1 IDENTIFIED BY DOT OR NOTCH
2. PLASTIC LEADS WILL BE EITHER SOLDER DIPPED OR TIN/LEAD PLATED
IN ACCORDANCE WITH MIL-M-38510 REQUIREMENTS
24-Lead Cerdip (Q-24)*
1.290 (32.77) MAX
24
13
0.295
(7.493)
MAX
PIN 1
1
12
0.320 (8.128)
0.290 (7.366)
0.070 (1.778)
0.020 (0.508)
0.180
0.225
(4.572)
(5.715)
MAX
MAX
0.125
(3.175)
SEATING
PLANE
MIN
0.012 (0.305)
0.021 (0.533) 0.110 (2.794) 0.065 (1.651)
15
0.008 (0.203)
0
0.015 (0.381) 0.090 (2.286) 0.055 (1.397)
TYP
TYP
TYP
NOTES
1. LEAD NO. 1 IDENTIFIED BY DOT OR NOTCH
2. CERDIP LEADS WILL BE EITHER TIN/LEAD PLATED OR SOLDER DIPPED
IN ACCORDANCE WITH MIL-M-38510 REQUIREMENTS
* ANALOG DEVICES RESERVES THE RIGHT TO SHIP EITHER CERDIP (Q-24, Q-28)
OR CERAMIC (D-24A, D-28) HERMETIC PACKAGES
REV. E
–11–
AD7824/AD7828
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
24-Lead Small Outline Package (R-24)
0.6141 (15.60)
0.5985 (15.20)
24
13
0.2992 (7.60)
0.2914 (7.40)
1
0.4193 (10.65)
0.3937 (10.00)
12
PIN 1
0.1043 (2.65)
0.0926 (2.35)
0.0118 (0.30) 0.0500
0.0040 (0.10) (1.27)
BSC
0.0291 (0.74)
45
0.0098 (0.25)
8
0
0.0192 (0.49) SEATING
0.0125 (0.32)
PLANE
0.0138 (0.35)
0.0091 (0.23)
0.0500 (1.27)
0.0157 (0.40)
28-Lead Plastic DIP (N-28)
1.45 (36.83)
1.44 (36.58)
15
28
0.55 (13.97)
0.53 (13.47)
1
14
PIN 1
0.2
(5.08)
MAX
0.175 (4.45)
0.12 (3.05)
0.16 (4.07)
0.15 (3.56)
0.606 (15.4)
0.594 (15.09)
SEATING
0.065 (1.66) 0.02 (0.508) 0.105 (2.67) PLANE
0.045 (1.15) 0.015 (0.381) 0.095 (2.42)
15
0
0.012 (0.305)
0.008 (0.203)
NOTES
1. LEAD NO. 1 IDENTIFIED BY DOT OR NOTCH
2. PLASTIC LEADS WILL BE EITHER SOLDER DIPPED OR TIN/LEAD PLATED
IN ACCORDANCE WITH MIL-M-38510 REQUIREMENTS
28-Lead Cerdip (Q-28)*
1.490 (37.84) MAX
28
15
0.525 (13.33)
0.515 (13.08)
PIN 1
1
14
0.62 (15.74)
0.59 (14.93)
GLASS SEALANT
0.22
(5.59)
MAX
0.11 (2.79)
0.099 (2.28)
0.125
(3.175)
MIN
0.02 (0.5) 0.06 (1.52) SEATING
0.016 (0.406) 0.05 (1.27) PLANE
15
0
0.18
(4.57)
MAX
0.012 (0.305)
0.008 (0.203)
NOTES
1. LEAD NO. 1 IDENTIFIED BY DOT OR NOTCH
2. CERDIP LEADS WILL BE EITHER TIN PLATED OR SOLDER DIPPED
IN ACCORDANCE WITH MIL-M-38510 REQUIREMENTS
* ANALOG DEVICES RESERVES THE RIGHT TO SHIP EITHER CERDIP (Q-24, Q-28)
OR CERAMIC (D-24A, D-28) HERMETIC PACKAGES
–12–
REV. E
AD7824/AD7828
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
28-Lead PLCC (P-28A)
0.180 (4.51)
0.165 (4.20)
0.495 (12.57)
SQ
0.485 (12.32)
4
5
26
25
PIN 1
IDENTIFIER
0.021 (0.533)
0.013 (0.331)
0.050 0.005)
(1.27 0.13)
TOP VIEW
(PINS DOWN)
11
12
0.032 (0.812)
0.026 (0.661)
19
18
0.456 (11.582)
SQ
0.450 (11.430)
0.430 (10.5)
0.390 (9.9)
0.120 (3.04)
0.090 (2.29)
28-Lead Small Outline Package (R-28)
0.7125 (18.10)
0.6969 (17.70)
28
15
0.2992 (7.60)
0.2914 (7.40)
1
0.4193 (10.65)
0.3937 (10.00)
14
PIN 1
0.1043 (2.65)
0.0926 (2.35)
0.0118 (0.30)
0.0040 (0.10)
0.0500
(1.27)
BSC
8
0
0.0192 (0.49) SEATING
0.0125 (0.32)
PLANE
0.0138 (0.35)
0.0091 (0.23)
0.0291 (0.74)
45
0.0098 (0.25)
0.0500 (1.27)
0.0157 (0.40)
28-Lead Shrink Small Outline Package (RS-28)
0.407 (10.34)
0.397 (10.08)
15
1
14
0.311 (7.9)
0.301 (7.64)
0.212 (5.38)
0.205 (5.21)
28
0.078 (1.98) PIN 1
0.068 (1.73)
0.008 (0.203) 0.0256
(0.65)
0.002 (0.050) BSC
REV. E
0.07 (1.79)
0.066 (1.67)
8
0.015 (0.38)
0
SEATING 0.009 (0.229)
0.010 (0.25)
PLANE
0.005 (0.127)
–13–
0.03 (0.762)
0.022 (0.558)
AD7824/AD7828
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
28-Terminal LCCC (E-28A)
0.100 (2.54)1
0.064 (1.63)
0.055 (1.40)
0.045 (1.14)
0.075 (1.91)
REF
19
25
26
18
0.458 (11.63)2
0.442 (11.23)
0.050 0.005
(1.27 0.13)
0.040 45
(1.02 45)
REF 3 PLCS
BOTTOM
VIEW
12
11
0.028 (0.71)
0.022 (0.56)
28
1
NO. 1 PIN
INDEX
4
5
0.020 45
(0.51 45)
REF
NOTES
1 THIS DIMENSION CONTROLS THE OVERALL PACKAGE THICKNESS
2 APPLIES TO ALL FOUR SIDES
*ALL TERMINALS ARE GOLD PLATED
–14–
REV. E
AD7824/AD7828
Revision History
Location
Page
Data Sheet changed from REV. D to REV. E.
Edits to ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
REV. E
–15–
–16–
PRINTED IN U.S.A.
C01323–0–4/02(E)
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