REV. 0
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reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
a
AD7819
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700 World Wide Web Site: http://www.analog.com
Fax: 617/326-8703 © Analog Devices, Inc., 1997
+2.7 V to +5.5 V, 200 kSPS
8-Bit Sampling ADC
FUNCTIONAL BLOCK DIAGRAM
FEATURES
8-Bit ADC with 4.5 ms Conversion Time
On-Chip Track and Hold
Operating Supply Range: +2.7 V to +5.5 V
Specifications at +2.7 V – 3.6 V and 5 V 6 10%
8-Bit Parallel Interface
8-Bit Read
Power Performance
Normal Operation
10.5 mW, VDD = 3 V
Automatic Power-Down
57.75 mW @ 1 kSPS, VDD = 3 V
Analog Input Range: 0 V to VREF
Reference Input Range: 1.2 V to VDD
GENERAL DESCRIPTION
The AD7819 is a high speed, microprocessor-compatible, 8-bit
analog-to-digital converter with a maximum throughput of
200 kSPS. The converter operates off a single +2.7 V to +5.5 V
supply and contains a 4.5 µs successive approximation A/D
converter, track/hold circuitry, on-chip clock oscillator and 8-bit
wide parallel interface. The parallel interface is designed to
allow easy interfacing to microprocessors and DSPs. Using only
address decoding logic the AD7819 is easily mapped into the
microprocessor address space.
When used in its power-down mode, the AD7819 automatically
powers down at the end of a conversion and powers up at the
start of a new conversion. This feature significantly reduces the
power consumption of the part at lower throughput rates. The
AD7819 can also operate in a high speed mode where the part is
not powered down between conversions. In this mode of opera-
tion the part is capable of providing 200 kSPS throughput.
The part is available in a small, 16-pin 0.3" wide, plastic dual-
in-line package (DIP); in a 16-pin, 0.15" wide, narrow body
small outline IC (SOIC) and in a 16-pin, narrow body, thin
shrink small outline package (TSSOP).
PRODUCT HIGHLIGHTS
1. Low Power, Single Supply Operation
The AD7819 operates from a single +2.7 V to +5.5 V sup-
ply and typically consumes only 10.5 mW of power. The
power dissipation can be significantly reduced at lower
throughput rates by using the automatic power-down mode.
2. Automatic Power-Down
The automatic power-down mode, whereby the AD7819
goes into power-down mode at the end of a conversion and
powers up before the next conversion, means the AD7819
is ideal for battery powered applications; e.g., 57.75 µW
@ 1 kSPS. (See Power vs. Throughput Rate section.)
3. Parallel Interface
An easy to use 8-bit wide parallel interface allows interfacing
to most popular microprocessors and DSPs with minimal
external circuitry.
4. Dynamic Specifications for DSP Users
In addition to the traditional ADC specifications, the AD7819
is specified for ac parameters, including signal-to-noise ratio
and distortion.
CLOCK
OSC
CHARGE
REDISTRIBUTION
DAC THREE-
STATE
DRIVERS
CONTROL
LOGIC
BUSY CS RD CONVST
V
IN
V
DD
AGND V
REF
DB7
DB0
COMP
T/H
AD7819
–2– REV. 0
AD7819–SPECIFICATIONS
1
(GND = 0 V, VREF = +VDD = 3 V 6 10% to 5 V 6 10%). All specifications –408C
to +1258C unless otherwise noted.)
Parameter Y Version Units Test Conditions/Comments
DYNAMIC PERFORMANCE f
IN
= 30 kHz, f
SAMPLE
= 136 kHz
Signal to (Noise + Distortion) Ratio
1
48 dB min
Total Harmonic Distortion (THD)
1
–70 dB typ
Peak Harmonic or Spurious Noise
1
–70 dB typ
Intermodulation Distortion
2
fa = 29.1 kHz; fb = 29.8 kHz
2nd Order Terms –77 dB typ
3rd Order Terms –77 dB typ
DC ACCURACY
Resolution 8 Bits
Minimum Resolution for Which
No Missing Codes Are Guaranteed 8 Bits
Relative Accuracy
1
±0.5 LSB max
Differential Nonlinearity (DNL)
1
±0.5 LSB max
Total Unadjusted Error
1
±1 LSB max
Gain Error
1
±0.5 LSB max
Offset Error
1
±0.5 LSB max
ANALOG INPUT
Input Voltage Range 0 V min
V
REF
V max
Input Leakage Current
2
±1µA max
Input Capacitance
2
15 pF mx
REFERENCE INPUTS
2
V
REF
Input Voltage Range 1.2 V min
V
DD
V max
Input Leakage Current ±1µA max
Input Capacitance 20 pF max
LOGIC INPUTS
2
V
INH,
Input High Voltage 2.0 V min
V
INL,
Input Low Voltage 0.4 V max (0.8 V max, V
DD
= 5 V)
Input Current, I
IN
±1µA max Typically 10 nA, V
IN
= 0 V to V
DD
Input Capacitance, C
IN
8 pF max
LOGIC OUTPUTS
Output High Voltage, V
OH
2.4 V min I
SOURCE
= 200 µA
Output Low Voltage, V
OL
0.4 V max I
SINK
= 200 µA
High Impedance Leakage Current ±1µA max
High Impedance Capacitance 15 pF max
CONVERSION RATE
Conversion Time 4.5 µs max
Track/Hold Acquisition Time
1
100 ns max See DC Acquisition Section
POWER SUPPLY
V
DD
2.7–5.5 Volts For Specified Performance
I
DD
Digital Inputs = 0 V or V
DD
Normal Operation 3.5 mA max
Power-Down 1 µA max V
DD
= 5 V
Power Dissipation
Normal Operation 17.5 mW max V
DD
= 5 V
Power-Down 5 µW max
Auto Power-Down (Mode 2) V
DD
= 3 V
1 kSPS Throughput 57.75 µW max
10 kSPS Throughput 577.5 µW max
50 kSPS Throughput 2.89 mW max
NOTES
1
See Terminology section.
2
Sample tested during initial release and after any redesign or process change that may affect this parameter.
Specifications subject to change without notice.
AD7819
–3–
REV. 0
TIMING CHARACTERISTICS
1, 2
Parameter V
DD
= 3 V 6 10% V
DD
= 5 V 6 10% Units Conditions/Comments
t
POWER-UP
11 µs (max) Power-Up Time of AD7819 after Rising Edge of CONVST.
t
1
4.5 4.5 µs (max) Conversion Time.
t
2
30 30 ns (min) CONVST Pulse Width.
t
3
30 30 ns (max) CONVST Falling Edge to BUSY Rising Edge Delay.
t
4
0 0 ns (min) CS to RD Setup Time.
t
5
0 0 ns (min) CS Hold Time after RD High.
t
63
10 10 ns (max) Data Access Time after RD Low.
t
73, 4
10 10 ns (max) Bus Relinquish Time after RD High.
t
83
50 50 ns (min) Data Bus Relinquish to Falling Edge of CONVST Delay.
NOTES
1
Sample tested to ensure compliance.
2
See Figures 12, 13 and 14.
3
These numbers are measured with the load circuit of Figure 1. They are defined as the time required for the o/p to cross 0.8 V or 2.4 V for V
DD
= 5 V ± 10% and
0.4 V or 2 V for 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
7
, quoted in the Timing Characteristics is the true bus relinquish time
of the part and as such is independent of external bus loading capacitances.
(–408C to +1258C, unless otherwise noted)
ABSOLUTE MAXIMUM RATINGS*
V
DD
to DGND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V
Digital Input Voltage to DGND
(CONVST, RD, CS) . . . . . . . . . . . . . . –0.3 V, V
DD
+ 0.3 V
Digital Output Voltage to DGND
(BUSY, DB0–DB7) . . . . . . . . . . . . . . . –0.3 V, V
DD
+ 0.3 V
REF
IN
to AGND . . . . . . . . . . . . . . . . . . . –0.3 V, V
DD
+ 0.3 V
Analog Input . . . . . . . . . . . . . . . . . . . . . . –0.3 V, V
DD
+ 0.3 V
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . .+150°C
Plastic DIP Package, Power Dissipation . . . . . . . . . . 450 mW
θ
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . +105°C/W
Lead Temperature, (Soldering 10 sec) . . . . . . . . . . .+260°C
SOIC Package, Power Dissipation . . . . . . . . . . . . . . . 450 mW
θ
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 75°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . .+215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . .+220°C
SSOP Package, Power Dissipation . . . . . . . . . . . . . . . 450 mW
θ
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . 115°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . .+215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . .+220°C
ESD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ≤4 kV
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those listed in the operational sections
of this specification is not implied. Exposure to absolute maximum rating condi-
tions for extended periods may affect device reliability.
+1.6V
200µA I
OL
200µA I
OH
C
L
50pF
TO
OUTPUT
PIN
Figure 1. Load Circuit for Digital Output Timing
Specifications
ORDERING GUIDE
Linearity
Error Package Package
Model (LSB) Description Option
AD7819YN ±1 LSB Plastic DIP N-16
AD7819YR ±1 LSB Small Outline IC R-16A
AD7819YRU ±1 LSB Thin Shrink Small Outline RU-16
(TSSOP)
AD7819
–4– REV. 0
PIN FUNCTION DESCRIPTIONS
Pin
No. Mnemonic Description
1V
REF
Reference Input, 1.2 V to V
DD
.
2V
IN
Analog Input, 0 V to V
REF
.
3 GND Analog and Digital Ground.
4CONVST Convert Start. A low-to-high transition on this pin initiates a 1 µs pulse on an internally generated
CONVST signal. A high-to-low transition on this line initiates the conversion process if the internal
CONVST signal is low. Depending on the signal on this pin at the end of a conversion, the AD7819
automatically powers down.
5CS Chip Select. This is a logic input. CS is used in conjunction with RD to enable outputs.
6RD Read Pin. This is a logic input. When CS is low and RD goes low, the DB7–DB0 leave their high
impedance state and data is driven onto the data bus.
7 BUSY ADC Busy Signal. This is a logic output. This signal goes logic high during the conversion process.
8–15 DB0–DB7 Data Bit 0 to 7. These outputs are three-state TTL-compatible.
16 V
DD
Positive power supply voltage, +2.7 V to +5.5 V.
PIN CONFIGURATION
DIP/SOIC
14
13
12
11
16
15
10
9
8
1
2
3
4
7
6
5TOP VIEW
(Not to Scale)
AD7819
V
REF
DB5
DB6
DB7
V
DD
V
IN
GND
CONVST
DB2
DB3
DB4
CS
RD
BUSY
DB0 DB1
AD7819
–5–
REV. 0
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
S
/2), excluding dc.
The ratio is dependent upon the number of quantization levels
in the digitization process; the more levels, the smaller the quan-
tization noise. The theoretical signal to (noise + distortion) ratio
for an ideal N-bit converter with a sine wave input is given by:
Signal to (Noise + Distortion) = (6.02N + 1.76) dB
Thus for an 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 AD7819 it is defined as:
THD (dB)=20 log V
2
2
+V
3
2
+V
4
2
+V
5
2
+V
6
2
V
1
where V
1
is the rms amplitude of the fundamental and V
2
, V
3
,
V
4
, V
5
and V
6
are the rms amplitudes of the second through the
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
S
/2 and excluding dc) to the rms value of the
fundamental. Normally, the value of this specification is deter-
mined by the largest harmonic in the spectrum, but for parts
where the harmonics are buried in the noise floor, it will be a
noise peak.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities will create distortion
products at sum and difference frequencies of mfa ± nfb where
m, n = 0, 1, 2, 3, etc. Intermodulation terms are those for which
neither m nor n are equal to zero. For example, the second
order terms include (fa + fb) and (fa – fb), while the third order
terms include (2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb).
The AD7819 is tested using the CCIF standard, where two
input frequencies near the top end of the input bandwidth are
used. In this case, the second and third order terms are of differ-
ent significance. The second order terms are usually distanced
in frequency from the original sine waves, while the third order
terms are usually at a frequency close to the input frequencies.
As a result, the second and third order terms are specified sepa-
rately. The calculation of the intermodulation distortion is as
per the THD specification where it is the ratio of the rms sum of
the individual distortion products to the rms amplitude of the
fundamental expressed in dBs.
Relative Accuracy
Relative accuracy or endpoint nonlinearity is the maximum
deviation from a straight line passing through the endpoints of
the ADC transfer function.
Differential Nonlinearity
This is the difference between the measured and the ideal
1␣ LSB change between any two adjacent codes in the ADC.
Offset Error
This is the deviation of the first code transition (0000 . . . 000)
to (0000 . . . 001) from the ideal, i.e., AGND + 1 LSB.
Offset Error Match
This is the difference in Offset Error between any two channels.
Gain Error
This is the deviation of the last code transition (1111 . . . 110)
to (1111 . . . 111) from the ideal, i.e., VREF – 1 LSB, after the
offset error has been adjusted out.
Gain Error Match
This is the difference in Gain Error between any two channels.
Track/Hold Acquisition Time
Track/hold acquisition time is the time required for the output
of the track/hold amplifier to reach its final value, within
±1/2 LSB, after the end of conversion (the point at which the
track/hold returns to track mode). It also applies to situations
where a change in the selected input channel takes place or
where there is a step input change on the input voltage applied
to the selected V
IN
input of the AD7819. It means that the user
must wait for the duration of the track/hold acquisition time
after the end of conversion or after a step input change to V
IN
before starting another conversion, to ensure that the part
operates to specification.
AD7819
–6– REV. 0
CIRCUIT DESCRIPTION
Converter Operation
The AD7819 is a successive approximation analog-to-digital
converter based around a charge redistribution DAC. The ADC
can convert analog input signals in the range 0 V to V
DD
. Fig-
ures 2 and 3 below show simplified schematics of the ADC.
Figure 2 shows the ADC during its acquisition phase. SW2 is
closed and SW1 is in Position A, the comparator is held in a
balanced condition and the sampling capacitor acquires the
signal on V
IN+
.
CHARGE
RESTRIBUTION
DAC
CONTROL
LOGIC
CLOCK
OSC
COMPARATOR
SW2
V
DD
/3
ACQUISITION
PHASE
SAMPLING
CAPACITOR
SW1
A
B
AGND
V
IN
Figure 2. ADC Track Phase
When the ADC starts a conversion, see Figure 3, SW2 will open
and SW1 will move to Position B causing the comparator to
become unbalanced. The Control Logic and the Charge Redis-
tribution DAC are used to add and subtract fixed amounts of
charge from the sampling capacitor to bring the comparator
back into a balanced condition. When the comparator is rebal-
anced the conversion is complete. The Control Logic generates
the ADC output code. Figure 7 shows the ADC transfer function.
CHARGE
RESTRIBUTION
DAC
CONTROL
LOGIC
CLOCK
OSC
COMPARATOR
SW2
V
DD
/3
CONVERSION
PHASE
SAMPLING
CAPACITOR
SW1
A
B
AGND
V
IN
Figure 3. ADC Conversion Phase
TYPICAL CONNECTION DIAGRAM
Figure 4 shows a typical connection diagram for the AD7819. The
parallel interface is implemented using an 8-bit data bus, the
falling edge of CONVST brings the BUSY signal high and at
the end of conversion, the falling edge of BUSY is used to
initiate an ISR on a microprocessor. (See Parallel Interface
section for more details.) V
REF
is connected to a well decoupled
V
DD
pin to provide an analog input range of 0 V to V
DD
. When
V
DD
is first connected the AD7819 powers up in a low current
mode, i.e., power down. A rising edge on the CONVST input
will cause the part to power up. (See Power-Up Times section.)
If power consumption is of concern, the automatic power-down
at the end of a conversion should be used to improve power
performance. See Power vs. Throughput Rate section of the
data sheet.
BUSY
RD
CS
CONVST
DB0-DB7
V
DD
V
REF
V
IN
GND
AD7819
mC/mP
PARALLEL
INTERFACE
0V TO V
REF
INPUT
0.1
m
F10
m
F
SUPPLY
+2.7V TO +5.5V
Figure 4. Typical Connection Diagram
Analog Input
Figure 5 shows an equivalent circuit of the analog input struc-
ture of the AD7819. 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 with-
out causing irreversible damage to the part. The capacitor C2 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 a multiplexer and a switch. This resistor
is typically about 125 Ω. The capacitor C1 is the ADC sampling
capacitor and has a capacitance of 3.5 pF.
VDD
VIN
C2
4pF
D1
D2
R1
125ΩC1
3.5pF VDD/3
CONVERT PHASE – SWITCH OPEN
TRACK PHASE – SWITCH CLOSED
Figure 5. Equivalent Analog Input Circuit
DC Acquisition Time
The ADC starts a new acquisition phase at the end of a conver-
sion and ends on the falling edge of the CONVST signal. At the
end of a conversion there is a settling time associated with the
sampling circuit. This settling time lasts approximately 100 ns.
The analog signal on V
IN
is also being acquired during this set-
tling time. The minimum acquisition time needed is approxi-
mately 100 ns. Figure 6 shows the equivalent charging circuit
for the sampling capacitor when the ADC is in its acquisition
phase. R2 represents the source impedance of a buffer amplifier
or resistive network, R1 is an internal multiplexer resistance and
C1 is the sampling capacitor.
V
IN
R1
125Ω
R2
C1
3.5pF
Figure 6. Equivalent Sampling Circuit
AD7819
–7–
REV. 0
During the acquisition phase the sampling capacitor must be
charged to within a 1/2 LSB of its final value. The time it takes
to charge the sampling capacitor (T
CHARGE
) is given by the
following formula:
T
CHARGE
= 6.2 × (R2 + 125 Ω) × 3.5 pF
For small values of source impedance, the settling time associ-
ated with the sampling circuit (100 ns) is, in effect, the acquisi-
tion time of the ADC. For example, with a source impedance
(R2) of 10 Ω, the charge time for the sampling capacitor is
approximately 3 ns. The charge time becomes significant for
source impedances of 2 kΩ and greater.
AC Acquisition Time
In ac applications it is recommended to always buffer analog
input signals. The source impedance of the drive circuitry must
be kept as low as possible to minimize the acquisition time of
the ADC. Large values of source impedance will cause the
THD to degrade at high throughput rates.
ADC TRANSFER FUNCTION
The output coding of the AD7819 is straight binary. The de-
signed code transitions occur at successive integer LSB values
(i.e., 1 LSB, 2 LSBs, etc.). The LSB size is = V
REF
/256. The
ideal transfer characteristic for the AD7819 is shown in Figure 7
below.
111...111
111...110
111...000
011...111
000...010
000...001
000...000
ADC CODE
1LSB = V
REF
/256
0V 1LSB +V
REF
–1LSB
ANALOG INPUT
Figure 7. Transfer Characteristic
POWER-UP TIMES
The AD7819 has a 1 µs power-up time. When V
DD
is first con-
nected, the AD7819 is in a low current mode of operation. In
order to carry out a conversion the AD7819 must first be pow-
ered up. The ADC is powered up by a rising edge on an inter-
nally generated CONVST signal, which occurs as a result of a
rising edge on the external CONVST pin. The rising edge of the
external CONVST signal initiates a 1 µs pulse on the internal
CONVST signal. This pulse is present to ensure the part has
enough time to power-up before a conversion is initiated, as a
conversion is initiated on the falling edge of gated CONVST.
See Timing and Control section. Care must be taken to ensure
that the CONVST pin of the AD7819 is logic low when V
DD
is first applied.
When operating in Mode 2, the ADC is powered down at the
end of each conversion and powered up again before the next
conversion is initiated. (See Figure 8.)
t
POWER-UP
1 s
t
POWER-UP
1 s
t
POWER-UP
1 s
MODE 1
MODE 2
V
DD
EXT
INT
V
DD
EXT
INT
Figure 8. Power-Up Times
POWER VS. THROUGHPUT RATE
By operating the AD7819 in Mode 2, the average power con-
sumption of the AD7819 decreases at lower throughput rates.
Figure 9 shows how the Automatic Power-Down is implemented
using the external CONVST signal to achieve the optimum
power performance for the AD7819. The AD7819 is operated
in Mode 2 and the duration of the external CONVST pulse is
set to be equal to or less than the power-up time of the device.
As the throughput rate is reduced, the device remains in its power-
down state longer and the average power consumption over time
drops accordingly.
EXT
INT
POWER-DOWN
t
POWER-UP
1 s
t
CONVERT
5.0 s
t
CYCLE
100 s @ 10kSPS
Figure 9. Automatic Power-Down
If, for example, the AD7819 is operated in a continuous sam-
pling mode with a throughput rate of 10 kSPS, the power con-
sumption is calculated as follows. The power dissipation during
normal operation is 10.5 mW, V
DD
= 3 V. If the power-up time
is 1 µs and the conversion time is 4.5 µs, the AD7819 can be
said to dissipate 10.5 mW for 5.5 µs (worst case) during each
conversion cycle. If the throughput rate is 10 kSPS, the cycle
time is then 100 µs and the average power dissipated during
each cycle is (5.5/100) × (10.5 mW) = 577.5 µW.
AD7819
–8– REV. 0
Typical Performance Characteristics
THROUGHPUT – kSPS
POWER – mW
10
1
0.01 0505 1015202530354045
0.1
Figure 10. Power vs. Throughput
0
–60
–100
dBs
–10
–50
–70
–90
–30
–40
–80
–20
FREQUENCY – kHz
0667 1320273340475360
AD7819
2048 POINT FFT
SAMPLING 136.054kHz
FIN 29.961kHz
Figure 11. SNR
TIMING AND CONTROL
The AD7819 has only one input for timing and control, i.e.,
the CONVST (convert start signal). The rising edge of this
CONVST signal initiates a 1 µs pulse on an internally generated
CONVST signal. This pulse is present to ensure the part has
enough time to power up before a conversion is initiated. If the
external CONVST signal is low, the falling edge of the inter-
nal CONVST signal will cause the sampling circuit to go into
hold mode and initiate a conversion. If, however, the external
CONVST signal is high when the internal CONVST goes low,
it is upon the falling edge of the external CONVST signal that
the sampling circuitry will go into hold mode and initiate a
conversion. The use of the internally generated 1 µs pulse as
previously described can be likened to the configuration shown
in Figure 12. The application of a CONVST signal at the
CONVST pin triggers the generation of a 1 µs pulse. Both the
external CONVST and this internal CONVST are input to an
OR gate. The resultant signal has the duration of the longer of
the two input signals. Once a conversion has been initiated, the
BUSY signal goes high to indicate a conversion is in progress. At
the end of conversion the sampling circuit returns to its track-
ing mode. The end of conversion is indicated by the BUSY
signal going low. This signal may be used to initiate an ISR on a
microprocessor. At this point the conversion result is latched
into the output register where it may be read. The AD7819 has
an 8-bit wide parallel interface. The state of the external CONVST
signal at the end of conversion also establishes the mode of
operation of the AD7819.
Mode 1 Operation (High Speed Sampling)
If the external CONVST is logic high when BUSY goes low, the
part is said to be in Mode 1 operation. While operating in Mode
1 the AD7819 will not power down between conversions. The
AD7819 should be operated in Mode 1 for high speed sampling
applications, i.e., throughputs greater than 100 kSPS. Figure 13
shows the timing for Mode 1 operation. From this diagram one
can see that a minimum delay of the sum of the conversion time
and read time must be left between two successive falling edges of
the external CONVST. This is to ensure that a conversion is not
initiated during a read.
Mode 2 Operation (Automatic Power-Down)
At slower throughput rates the AD7819 may be powered down
between conversion to give a superior power performance.
This is Mode 2 Operation and it is achieved by bringing the
CONVST signal logic low before the falling edge of BUSY.
Figure 14 shows the timing for Mode 2 Operation. The falling
edge of the external CONVST signal may occur before or after
the falling edge of the internal CONVST signal, but it is the
later occurring falling edge of both that controls when the first
conversion will take place. If the falling edge of the external
CONVST occurs after that of the internal CONVST, it means
that the moment of the first conversion is controlled exactly,
regardless of any jitter associated with the internal CONVST
signal. The parallel interface is still fully operational while the
AD7819 is powered down. The AD7819 is powered up again
on the rising edge of the CONVST signal. The gated CONVST
pulse will now remain high long enough for the AD7819 to fully
power up, which takes about 1 µs. This is ensured by the
internal CONVST signal, which will remain high for 1 µs.
1 s
EXT
INT
(PIN 4) GATED
Figure 12.
AD7819
–9–
REV. 0
PARALLEL INTERFACE
The parallel interface of the AD7819 is eight bits wide. The
output data buffers are activated when both CS and RD are
logic low. At this point the contents of the data register are
placed on the 8-bit data bus. Figure 15 shows the timing diagram
for the parallel port. The Parallel Interface of the AD7819 is reset
8 MSBs
t
1
t
2
t
3
t
POWER-UP
EXT CONVST
INT CONVST
BUSY
CS/RD
DB7–DB0
Figure 13. Mode 1 Operation
8 MSBs
t
1
t
3
EXT CONVST
INT CONVST
BUSY
CS/RD
DB7–DB0
t
POWER-UP
Figure 14. Mode 2 Operation
when BUSY goes logic high. Care must be taken to ensure that
a read operation does not occur while BUSY is high. Data
read from the AD7819 while BUSY is high will be invalid. For
optimum performance the read operation should end at least
100 ns (t
10
) prior to the falling edge of the next CONVST.
8 MSBs
CONVST
BUSY
CS
DB7–DB0
t
2
t
3
t
1
t
4
t
6
t
7
t
5
t
8
RD
Figure 15. Parallel Port Timing
AD7819
–10– REV. 0
MICROPROCESSOR INTERFACING
The parallel port on the AD7819 allows the device to be inter-
faced to a range of many different microcontrollers. This section
explains how to interface the AD7819 with some of the more
common microcontroller parallel interface protocols.
AD7819 to 8051
Figure 16 shows a parallel interface between the AD7819 and
the 8051 microcontroller. The BUSY signal on the AD7819 pro-
vides an interrupt request to the 8051 when a conversion begins.
Port 0 of the 8051 may serve as an input or output port, or as in
this case when used together, may be used as a bidirectional
low-order address and data bus. The address latch enable out-
put of the 8051 is used to latch the low byte of the address dur-
ing accesses to the device, while the high-order address byte is
supplied from Port 2. Port 2 latches remain stable when the
AD7819 is addressed, as they do not have to be turned around
(set to 1) for data input as is the case for Port 0.
AD7819
*
8051*
AD0–AD7
ALE
A8–A15
RD
INT
LATCH DECODER
DB0–DB7
CS
RD
BUSY
*
ADDITIONAL PINS OMITTED FOR CLARITY
Figure 16. Interfacing to the 8051
AD7819 to PIC16C6x/7x
Figure 17 shows a parallel interface between the AD7819 and the
PIC16C64/65/74. The BUSY signal on the AD7819 provides an
interrupt request to the microcontroller when a conversion be-
gins. 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 output.
For this functionality, the corresponding data direction bits
of the TRISE register must be configured as outputs (reset to
0). See user PIC16/17 Microcontroller User Manual.
PIC16C6x/7x*
PSP0–PSP7
RD
INT
*
ADDITIONAL PINS OMITTED FOR CLARITY
CS
AD7819
*
DB0–DB7
CS
RD
BUSY
Figure 17. Interfacing to the PIC16C6x/7x
AD7819 to ADSP-21xx
Figure 18 shows a parallel interface between the AD7819 and
the ADSP-21xx series of DSPs. As before, the BUSY signal on
the AD7819 provides an interrupt request to the DSP when a
conversion begins.
*
ADDITIONAL PINS OMITTED FOR CLARITY
ADDRESS
DECODE
LOGIC
EN
AD7819
*
DB0–DB7
CS
RD
BUSY
ADSP-21xx*
D0–D7
DMS
A13–A0
RD
IRQ
Figure 18. Interfacing to the ADSP-21xx
AD7819
–11–
REV. 0
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
16-Lead Plastic DIP
(N-16)
16
18
9
0.840 (21.33)
0.745 (18.93)
0.280 (7.11)
0.240 (6.10)
PIN 1
SEATING
PLANE
0.022 (0.558)
0.014 (0.356)
0.060 (1.52)
0.015 (0.38)
0.210 (5.33)
MAX 0.130
(3.30)
MIN
0.070 (1.77)
0.045 (1.15)
0.100
(2.54)
BSC
0.160 (4.06)
0.115 (2.93)
0.325 (8.25)
0.300 (7.62)
0.015 (0.381)
0.008 (0.204)
0.195 (4.95)
0.115 (2.93)
16-Lead Small Outline Package
(R-16A)
16 9
81
0.3937 (10.00)
0.3859 (9.80)
0.2440 (6.20)
0.2284 (5.80)
0.1574 (4.00)
0.1497 (3.80)
PIN 1
SEATING
PLANE
0.0098 (0.25)
0.0040 (0.10)
0.0192 (0.49)
0.0138 (0.35)
0.0688 (1.75)
0.0532 (1.35)
0.0500
(1.27)
BSC 0.0099 (0.25)
0.0075 (0.19) 0.0500 (1.27)
0.0160 (0.41)
8°
0°
0.0196 (0.50)
0.0099 (0.25) x 45°
16-Lead Thin Shrink Small Outline Package
(RU-16)
16 9
8
1
0.201 (5.10)
0.193 (4.90)
0.256 (6.50)
0.246 (6.25)
0.177 (4.50)
0.169 (4.30)
PIN 1
SEATING
PLANE
0.006 (0.15)
0.002 (0.05)
0.0118 (0.30)
0.0075 (0.19)
0.0256
(0.65)
BSC
0.0433
(1.10)
MAX
0.0079 (0.20)
0.0035 (0.090)
0.028 (0.70)
0.020 (0.50)
8°
0°
–12–
C3059–12–6/97
PRINTED IN U.S.A.
