6-5

Features

· 80C48 and 80C80/85 Bus Compatible - No Interfacing

Logic Required

· Conversion Time < 100

· Easy Interface to Most Microprocessors

· Will Operate in a "Stand Alone" Mode

· Differential Analog Voltage Inputs

· Works with Bandgap Voltage References

· TTL Compatible Inputs and Outputs

· On-Chip Clock Generator

· 0V to 5V Analog Voltage Input Range (Single + 5V Supply)

· No Zero-Adjust Required

Description

The ADC0802 family are CMOS 8-Bit, successive-approxi-
mation A/D converters which use a modified potentiometric
ladder and are designed to operate with the 8080A control
bus via three-state outputs. These converters appear to the
processor as memory locations or I/O ports, and hence no
interfacing logic is required.

The differential analog voltage input has good common-
mode-rejection and permits offsetting the analog zero-input-
voltage value. In addition, the voltage reference input can be
adjusted to allow encoding any smaller analog voltage span
to the full 8 bits of resolution.

Ordering Information

PART NUMBER

ERROR

EXTERNAL CONDITIONS

TEMP. RANGE (

PACKAGE

PKG. NO

ADC0802LCN

LSB

REF

/2 = 2.500V

(No Adjustments)

0 to 70

20 Ld PDIP

E20.3

ADC0802LCD

LSB

-40 to 85

20 Ld CERDIP

F20.3

ADC0802LD

1 LSB

-55 to 125

20 Ld CERDIP

F20.3

ADC0803LCN

LSB

REF

/2 Adjusted for Correct Full Scale

Reading

0 to 70

20 Ld PDIP

E20.3

ADC0803LCD

LSB

-40 to 85

20 Ld CERDIP

F20.3

ADC0803LCWM

1 LSB

-40 to 85

20 Ld SOIC

M20.3

ADC0803LD

1 LSB

-55 to 125

20 Ld CERDIP

F20.3

ADC0804LCN

1 LSB

REF

/2 = 2.500V

(No Adjustments)

0 to 70

20 Ld PDIP

E20.3

ADC0804LCD

1 LSB

-40 to 85

20 Ld CERDIP

F20.3

ADC0804LCWM

1 LSB

-40 to 85

20 Ld SOIC

M20.3

Pinout

ADC0802, ADC0803, ADC0804

(PDIP, CERDIP)

TOP VIEW

Typical Application Schematic

CLK IN

INTR

(-)

(+)

DGND

REF

AGND

V+ OR V

REF

CLK R

0 (LSB)

7 (MSB)

INTR

CLK IN

CLK R

V+

(-)

(+)

DGND

REF

AGND

ANY

PROCESSOR

8-BIT RESOLUTION
OVER ANY
DESIRED
ANALOG INPUT
VOLTAGE RANGE

DIFF

INPUTS

10K

150pF

REF

P B

+5V

August 1997

ADC0802, ADC0803

ADC0804

8-Bit, Microprocessor-

Compatible, A/D Converters

File Number

3094.1

CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.

6-7

Absolute Maximum Ratings

Thermal Information

Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5V
Voltage at Any Input . . . . . . . . . . . . . . . . . . . . . . -0.3V to (V

+0.3V)

Operating Conditions

Temperature Range

ADC0802/03LD. . . . . . . . . . . . . . . . . . . . . . . . . . . -55

C to 125

ADC0802/03/04LCD . . . . . . . . . . . . . . . . . . . . . . . . -40

C to 85

ADC0802/03/04LCN . . . . . . . . . . . . . . . . . . . . . . . . . .0

C to 70

ADC0803/04LCWM . . . . . . . . . . . . . . . . . . . . . . . . -40

C to 85

Thermal Resistance (Typical, Note 1)

(

C/W)

(

C/W)

PDIP Package . . . . . . . . . . . . . . . . . . . . .

125

N/A

CERDIP Package . . . . . . . . . . . . . . . . . .

SOIC Package . . . . . . . . . . . . . . . . . . . . .

120

N/A

Maximum Junction Temperature

Hermetic Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

Plastic Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

Maximum Storage Temperature Range . . . . . . . . . .-65

C to 150

Maximum Lead Temperature (Soldering, 10s) . . . . . . . . . . . . 300

(SOIC - Lead Tips Only)

CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation
of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.

NOTE:

is measured with the component mounted on an evaluation PC board in free air.

Electrical Specifications

(Notes 1, 7)

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

CONVERTER SPECIFICATIONS V+ = 5V, T

= 25

C and f

CLK

= 640kHz, Unless Otherwise Specified

Total Unadjusted Error

ADC0802

REF

/2 = 2.500V

LSB

ADC0803

REF

/2 Adjusted for Correct Full

Scale Reading

LSB

ADC0804

REF

/2 = 2.500V

LSB

REF

/2 Input Resistance

Input Resistance at Pin 9

1.0

1.3

Analog Input Voltage Range

(Note 2)

GND-0.05

(V+) + 0.05

DC Common-Mode Rejection

Over Analog Input Voltage Range

LSB

Power Supply Sensitivity

V+ = 5V

10% Over Allowed Input

Voltage Range

LSB

CONVERTER SPECIFICATIONS V+ = 5V, 0

C to 70

C and f

CLK

= 640kHz, Unless Otherwise Specified

Total Unadjusted Error

ADC0802

REF

/2 = 2.500V

LSB

ADC0803

REF

/2 Adjusted for Correct Full

Scale Reading

LSB

ADC0804

REF

/2 = 2.500V

LSB

REF

/2 Input Resistance

Input Resistance at Pin 9

1.0

1.3

Analog Input Voltage Range

(Note 2)

GND-0.05

(V+) + 0.05

DC Common-Mode Rejection

Over Analog Input Voltage Range

LSB

Power Supply Sensitivity

V+ = 5V

10% Over Allowed Input

Voltage Range

LSB

CONVERTER SPECIFICATIONS V+ = 5V, -25

C to 85

C and f

CLK

= 640kHz, Unless Otherwise Specified

Total Unadjusted Error

ADC0802

REF

/2 = 2.500V

LSB

ADC0803

REF

/2 Adjusted for Correct Full

Scale Reading

LSB

ADC0804

REF

/2 = 2.500V

LSB

REF

/2 Input Resistance

Input Resistance at Pin 9

1.0

1.3

Analog Input Voltage Range

(Note 2)

GND-0.05

(V+) + 0.05

DC Common-Mode Rejection

Over Analog Input Voltage Range

LSB

Power Supply Sensitivity

V+ = 5V

10% Over Allowed Input

Voltage Range

LSB

ADC0802, ADC0803, ADC0804

6-8

CONVERTER SPECIFICATIONS V+ = 5V, -55

C to 125

C and f

CLK

= 640kHz, Unless Otherwise Specified

Total Unadjusted Error

ADC0802

REF

/2 = 2.500V

LSB

ADC0803

REF

/2 Adjusted for Correct Full

Scale Reading

LSB

REF

/2 Input Resistance

Input Resistance at Pin 9

1.0

1.3

Analog Input Voltage Range

(Note 2)

GND-0.05

(V+) + 0.05

DC Common-Mode Rejection

Over Analog Input Voltage Range

LSB

Power Supply Sensitivity

V+ = 5V

10% Over Allowed Input

Voltage Range

LSB

AC TIMING SPECIFICATIONS V+ = 5V, and T

C, Unless Otherwise Specified

Clock Frequency, f

CLK

V+ = 6V (Note 3)

100

640

1280

kHz

V+ = 5V

100

640

800

kHz

Clock Periods per Conversion
(Note 4), t

CONV

Clocks/Conv

Conversion Rate In Free-Running
Mode, CR

INTR tied to WR with CS = 0V,
f

CLK

= 640kHz

8888

Conv/s

Width of WR Input (Start Pulse
Width), t

W(WR)I

CS = 0V (Note 5)

100

Access Time (Delay from Falling
Edge of RD to Output Data Valid),
t

ACC

= 100pF (Use Bus Driver IC for

Larger C

135

200

Three-State Control (Delay from
Rising Edge of RD to Hl-Z State),
t

, t

= 10pF, R

= 10K

(See Three-State Test Circuits)

125

250

Delay from Falling Edge of WR to
Reset of INTR, t

, t

300

450

Input Capacitance of Logic
Control Inputs, C

Three-State Output Capacitance
(Data Buffers), C

OUT

DC DIGITAL LEVELS AND DC SPECIFICATIONS V+ = 5V, and T

MIN

to T

MAX

, Unless Otherwise Specified

CONTROL INPUTS (Note 6)

Logic "1" Input Voltage (Except
Pin 4 CLK IN), V

INH

V+ = 5.25V

2.0

V+

Logic "0" Input Voltage (Except
Pin 4 CLK IN), V

INL

V+ = 4.75V

0.8

CLK IN (Pin 4) Positive Going
Threshold Voltage, V+

CLK

2.7

3.1

3.5

CLK IN (Pin 4) Negative Going
Threshold Voltage, V-

CLK

1.5

1.8

2.1

CLK IN (Pin 4) Hysteresis, V

0.6

1.3

2.0

Logic "1" Input Current
(All Inputs), I

INHI

= 5V

0.005

Logic "0" Input Current
(All Inputs), I

INLO

= 0V

-1

-0.005

Supply Current (Includes Ladder
Current), I+

CLK

= 640kHz,T

= 25

and CS = Hl

1.3

2.5

DATA OUTPUTS AND INTR

Logic "0" Output Voltage, V

= 1.6mA, V+ = 4.75V

0.4

Electrical Specifications

(Notes 1, 7) (Continued)

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

ADC0802, ADC0803, ADC0804

6-9

Logic "1" Output Voltage, V

= -360

A, V+ = 4.75V

2.4

Three-State Disabled Output
Leakage (All Data Buffers)

, I

OUT

= 0V

-3

OUT

= 5V

Output Short Circuit Current,
I

SOURCE

OUT

Short to Gnd T

= 25

4.5

Output Short Circuit Current,
I

SINK

OUT

Short to V+ T

= 25

9.0

NOTES:

1. All voltages are measured with respect to GND, unless otherwise specified. The separate AGND point should always be wired to the

DGND, being careful to avoid ground loops.

2. For V

IN(-)

IN(+)

the digital output code will be 0000 0000. Two on-chip diodes are tied to each analog input (see Block Diagram) which

will forward conduct for analog input voltages one diode drop below ground or one diode drop greater than the V+ supply. Be careful,
during testing at low V+ levels (4.5V), as high level analog inputs (5V) can cause this input diode to conduct - especially at elevated tem-
peratures, and cause errors for analog inputs near full scale. As long as the analog V

does not exceed the supply voltage by more than

50mV, the output code will be correct. To achieve an absolute 0V to 5V input voltage range will therefore require a minimum supply volt-
age of 4.950V over temperature variations, initial tolerance and loading.

3. With V+ = 6V, the digital logic interfaces are no longer TTL compatible.

4. With an asynchronous start pulse, up to 8 clock periods may be required before the internal clock phases are proper to start the conversion

process.

5. The CS input is assumed to bracket the WR strobe input so that timing is dependent on the WR pulse width. An arbitrarily wide pulse

width will hold the converter in a reset mode and the start of conversion is initiated by the low to high transition of the WR pulse (see
Timing Diagrams).

6. CLK IN (pin 4) is the input of a Schmitt trigger circuit and is therefore specified separately.

7. None of these A/Ds requires a zero-adjust. However, if an all zero code is desired for an analog input other than 0V, or if a narrow full scale span

exists (for example: 0.5V to 4V full scale) the V

IN(-)

input can be adjusted to achieve this. See the Zero Error description in this data sheet.

Electrical Specifications

(Notes 1, 7) (Continued)

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

Timing Waveforms

FIGURE 1A. t

FIGURE 1B. t

, C

= 10pF

FIGURE 1C. t

FIGURE 1D. t

, C

= 10pF

FIGURE 1. THREE-STATE CIRCUITS AND WAVEFORMS

10K

V+

DATA

OUTPUT

2.4V

90%

50%

10%

0.8V

DATA

OUTPUTS

GND

= 20ns

90%

10K

V+

DATA

OUTPUT

V+

2.4V

90%

50%

10%

0.8V

DATA

OUTPUTS

= 20ns

V+

10%

ADC0802, ADC0803, ADC0804

6-10

Typical Performance Curves

FIGURE 2. LOGIC INPUT THRESHOLD VOLTAGE vs SUPPLY

VOLTAGE

FIGURE 3. DELAY FROM FALLING EDGE OF RD TO OUTPUT

DATA VALID vs LOAD CAPACITANCE

FIGURE 4. CLK IN SCHMITT TRIP LEVELS vs SUPPLY VOLTAGE

FIGURE 5. f

CLK

vs CLOCK CAPACITOR

FIGURE 6. FULL SCALE ERROR vs f

CLK

FIGURE 7. EFFECT OF UNADJUSTED OFFSET ERROR

-55

C TO 125

1.8

1.7

1.6

1.5

1.4

1.3

4.75

4.50

5.00

5.25

5.50

V+ SUPPLY VOLTAGE (V)

LOGIC INPUT THRESHOLD V

GE (V)

DELA

Y (ns)

500

400

300

200

100

LOAD CAPACITANCE (pF)

200

400

600

800

1000

CLK IN THRESHOLD V

GE (V)

3.5

3.1

2.7

2.3

1.9

1.5

4.50

V+ SUPPLY VOLTAGE (V)

-55

C TO 125

T(-)

T(+)

4.75

5.00

5.25

5.50

1000

CLOCK CAPACITOR (pF)

CLK

(kHz)

100

1000

R = 10K

R = 50K

R = 20K

FULL SCALE ERR

OR (LSBs)

CLK

(kHz)

400

800

1200

1600

2000

V+ = 4.5V

V+ = 5V

V+ = 6V

IN(+)

= V

IN(-)

= 0V

ASSUMES V

= 2mV

THIS SHOWS THE NEED
FOR A ZERO ADJUSTMENT
IF THE SPAN IS REDUCED

OFFSET ERR

OR (LSBs)

REF

/2 (V)

0.01

0.1

1.0

ADC0802, ADC0803, ADC0804

6-12

Understanding A/D Error Specs

A perfect A/D transfer characteristic (staircase wave-form) is
shown in Figure 11A. The horizontal scale is analog input volt-
age and the particular points labeled are in steps of 1 LSB
(19.53mV with 2.5V tied to the V

REF

/2 pin). The digital output

codes which correspond to these inputs are shown as D-1, D,
and D+1. For the perfect A/D, not only will center-value (A - 1,
A, A + 1, . . .) analog inputs produce the correct output digital
codes, but also each riser (the transitions between adjacent
output codes) will be located

LSB away from each center-

value. As shown, the risers are ideal and have no width. Correct
digital output codes will be provided for a range of analog input
voltages which extend

LSB from the ideal center-values.

Each tread (the range of analog input voltage which provides
the same digital output code) is therefore 1 LSB wide.

The error curve of Figure 11B shows the worst case transfer
function for the ADC0802. Here the specification guarantees
that if we apply an analog input equal to the LSB analog volt-
age center-value, the A/D will produce the correct digital code.

Next to each transfer function is shown the corresponding error
plot. Notice that the error includes the quantization uncertainty of
the A/D. For example, the error at point 1 of Figure 11A is
+

LSB because the digital code appeared

LSB in advance

of the center-value of the tread. The error plots always have a

constant negative slope and the abrupt upside steps are always
1 LSB in magnitude, unless the device has missing codes.

Detailed Description

The functional diagram of the ADC0802 series of A/D
converters operates on the successive approximation princi-
ple (see Application Notes AN016 and AN020 for a more
detailed description of this principle). Analog switches are
closed sequentially by successive-approximation logic until
the analog differential input voltage [V

lN(+)

- V

lN(-)

] matches

a voltage derived from a tapped resistor string across the
reference voltage. The most significant bit is tested first and
after 8 comparisons (64 clock cycles), an 8-bit binary code
(1111 1111 = full scale) is transferred to an output latch.

The normal operation proceeds as follows. On the high-to-low
transition of the WR input, the internal SAR latches and the
shift-register stages are reset, and the INTR output will be set
high. As long as the CS input and WR input remain low, the
A/D will remain in a reset state. Conversion will start from 1 to
8 clock periods after at least one of these inputs makes a low-
to-high transition. After the requisite number of clock pulses to
complete the conversion, the INTR pin will make a high-to-low
transition. This can be used to interrupt a processor, or
otherwise signal the availability of a new conversion. A RD
operation (with CS low) will clear the INTR line high again.

TRANSFER FUNCTION

ERROR PLOT

FIGURE 11A. ACCURACY =

0 LSB; PERFECT A/D

TRANSFER FUNCTION

ERROR PLOT

FIGURE 11B. ACCURACY =

LSB

FIGURE 11. CLARIFYING THE ERROR SPECS OF AN A/D CONVERTER

ANALOG INPUT (V

)

DIGIT

AL OUTPUT CODE

D + 1

D - 1

A + 1

A - 1

5 6

ERR

+1 LSB

-1 LSB

LSB

* QUANTIZATION ERROR

ANALOG INPUT (V

)

A + 1

A - 1

ANALOG INPUT (V

)

DIGIT

AL OUTPUT CODE

D + 1

D - 1

A + 1

A - 1

+1 LSB

-1 LSB

QUANTIZATION

ERR

ANALOG INPUT (V

)

A + 1

A - 1

ERROR

ADC0802, ADC0803, ADC0804

6-13

The device may be operated in the free-running mode by con-
necting INTR to the WR input with CS = 0. To ensure start-up
under all possible conditions, an external WR pulse is
required during the first power-up cycle. A conversion-in-pro-
cess can be interrupted by issuing a second start command.

Digital Operation

The converter is started by having CS and WR simultaneously
low. This sets the start flip-flop (F/F) and the resulting "1" level
resets the 8-bit shift register, resets the Interrupt (INTR) F/F
and inputs a "1" to the D flip-flop, DFF1, which is at the input
end of the 8-bit shift register. Internal clock signals then trans-
fer this "1" to the Q output of DFF1. The AND gate, G1, com-
bines this "1" output with a clock signal to provide a reset
signal to the start F/F. If the set signal is no longer present
(either WR or CS is a "1"), the start F/F is reset and the 8-bit
shift register then can have the "1" clocked in, which starts the
conversion process. If the set signal were to still be present,
this reset pulse would have no effect (both outputs of the start
F/F would be at a "1" level) and the 8-bit shift register would
continue to be held in the reset mode. This allows for asyn-
chronous or wide CS and WR signals.

After the "1" is clocked through the 8-bit shift register (which
completes the SAR operation) it appears as the input to
DFF2. As soon as this "1" is output from the shift register, the
AND gate, G2, causes the new digital word to transfer to the
Three-State output latches. When DFF2 is subsequently
clocked, the Q output makes a high-to-low transition which
causes the INTR F/F to set. An inverting buffer then supplies
the INTR output signal.

When data is to be read, the combination of both CS and RD
being low will cause the INTR F/F to be reset and the three-
state output latches will be enabled to provide the 8-bit digital
outputs.

Digital Control Inputs

The digital control inputs (CS, RD, and WR) meet standard
TTL logic voltage levels. These signals are essentially equiva-
lent to the standard A/D Start and Output Enable control sig-
nals, and are active low to allow an easy interface to
microprocessor control busses. For non-microprocessor
based applications, the CS input (pin 1) can be grounded and
the standard A/D Start function obtained by an active low
pulse at the WR input (pin 3). The Output Enable function is
achieved by an active low pulse at the RD input (pin 2).

Analog Operation

The analog comparisons are performed by a capacitive
charge summing circuit. Three capacitors (with precise
ratioed values) share a common node with the input to an
auto-zeroed comparator. The input capacitor is switched
between V

lN(+)

and V

lN(-)

, while two ratioed reference capaci-

tors are switched between taps on the reference voltage
divider string. The net charge corresponds to the weighted dif-
ference between the input and the current total value set by
the successive approximation register. A correction is made to
offset the comparison by

LSB (see Figure 11A).

Analog Differential Voltage Inputs and Common-Mode
Rejection

This A/D gains considerable applications flexibility from the ana-
log differential voltage input. The V

lN(-)

input (pin 7) can be used

to automatically subtract a fixed voltage value from the input
reading (tare correction). This is also useful in 4mA - 20mA cur-
rent loop conversion. In addition, common-mode noise can be
reduced by use of the differential input.

The time interval between sampling V

IN(+)

and V

lN(-)

is 4

clock periods. The maximum error voltage due to this slight
time difference between the input voltage samples is given by:

where:

is the error voltage due to sampling delay,

PEAK

is the peak value of the common-mode voltage,

is the common-mode frequency.

For example, with a 60Hz common-mode frequency, f

and a 640kHz A/D clock, f

CLK

, keeping this error to

LSB

(~5mV) would allow a common-mode voltage, V

PEAK

, given

by:

The allowed range of analog input voltage usually places
more severe restrictions on input common-mode voltage
levels than this.

An analog input voltage with a reduced span and a relatively
large zero offset can be easily handled by making use of the
differential input (see Reference Voltage Span Adjust).

Analog Input Current

The internal switching action causes displacement currents to
flow at the analog inputs. The voltage on the on-chip capaci-
tance to ground is switched through the analog differential
input voltage, resulting in proportional currents entering the
V

IN(+)

input and leaving the V

IN(-)

input. These current tran-

sients occur at the leading edge of the internal clocks. They
rapidly decay and do not inherently cause errors as the on-
chip comparator is strobed at the end of the clock perIod.

Input Bypass Capacitors

Bypass capacitors at the inputs will average these charges
and cause a DC current to flow through the output resistances
of the analog signal sources. This charge pumping action is
worse for continuous conversions with the V

IN(+)

input voltage

at full scale. For a 640kHz clock frequency with the V

IN(+)

input at 5V, this DC current is at a maximum of approximately
5

A. Therefore, bypass capacitors should not be used at

the analog inputs or the V

REF

/2 pin for high resistance

sources (>1k

). If input bypass capacitors are necessary for

noise filtering and high source resistance is desirable to mini-
mize capacitor size, the effects of the voltage drop across this
input resistance, due to the average value of the input current,
can be compensated by a full scale adjustment while the
given source resistor and input bypass capacitor are both in
place. This is possible because the average value of the input
current is a precise linear function of the differential input
voltage at a constant conversion rate.

MAX

(

)

PEAK

(

)

(

)

4.5

CLK

------------

PEAK

E MAX

(

)

CLK

(

)

(

)

4.5

(

)

--------------------------------------------------

PEAK

(

)

640

(

)

6.28

(

)

( )

4.5

(

)

----------------------------------------------------------

1.9V

ADC0802, ADC0803, ADC0804

6-14

Input Source Resistance

Large values of source resistance where an input bypass
capacitor is not used will not cause errors since the input
currents settle out prior to the comparison time. If a low-
pass filter is required in the system, use a low-value series
resistor (

) for a passive RC section or add an op amp

RC active low-pass filter. For low-source-resistance
applications (

), a 0.1

F bypass capacitor at the inputs

will minimize EMI due to the series lead inductance of a long
wire. A 100

series resistor can be used to isolate this

capacitor (both the R and C are placed outside the feedback
loop) from the output of an op amp, if used.

Stray Pickup

The leads to the analog inputs (pins 6 and 7) should be kept
as short as possible to minimize stray signal pickup (EMI).
Both EMI and undesired digital-clock coupling to these inputs
can cause system errors. The source resistance for these
inputs should, in general, be kept below 5k

. Larger values of

source resistance can cause undesired signal pickup. Input
bypass capacitors, placed from the analog inputs to ground,
will eliminate this pickup but can create analog scale errors as
these capacitors will average the transient input switching cur-
rents of the A/D (see Analog Input Current). This scale error
depends on both a large source resistance and the use of an
input bypass capacitor. This error can be compensated by a
full scale adjustment of the A/D (see Full Scale Adjustment)
with the source resistance and input bypass capacitor in
place, and the desired conversion rate.

Reference Voltage Span Adjust

For maximum application flexibility, these A/Ds have been
designed to accommodate a 5V, 2.5V or an adjusted voltage
reference. This has been achieved in the design of the IC as
shown in Figure 12.

Notice that the reference voltage for the IC is either

of the

voltage which is applied to the V+ supply pin, or is equal to
the voltage which is externally forced at the V

REF

/2 pin. This

allows for a pseudo-ratiometric voltage reference using, for
the V+ supply, a 5V reference voltage. Alternatively, a volt-
age less than 2.5V can be applied to the V

REF

/2 input. The

internal gain to the V

REF

/2 input is 2 to allow this factor of 2

reduction in the reference voltage.

Such an adjusted reference voltage can accommodate a
reduced span or dynamic voltage range of the analog input
voltage. If the analog input voltage were to range from 0.5V to
3.5V, instead of 0V to 5V, the span would be 3V. With 0.5V
applied to the V

lN(-)

pin to absorb the offset, the reference

voltage can be made equal to

of the 3V span or 1.5V. The

A/D now will encode the V

lN(+)

signal from 0.5V to 3.5V with

the 0.5V input corresponding to zero and the 3.5V input corre-
sponding to full scale. The full 8 bits of resolution are therefore
applied over this reduced analog input voltage range. The req-
uisite connections are shown in Figure 13. For expanded
scale inputs, the circuits of Figures 14 and 15 can be used.

FIGURE 12. THE V

REFERENCE

DESIGN ON THE IC

FIGURE 13. OFFSETTING THE ZERO OF THE ADC0802 AND

PERFORMING AN INPUT RANGE (SPAN)
ADJUSTMENT

FIGURE 14. HANDLING

10V ANALOG INPUT RANGE

V+

DGND

REF

AGND

REF

)

DIGITAL

CIRCUITS

ANALOG

CIRCUITS

DECODE

300

TO V

REF

TO V

IN(-)

ZERO SHIFT VOLTAGE

0.1

REF

(5V)

ADJ.

"SPAN"/2

ICL7611

IN(-)

10V

IN(+)

REF

)

V+

ADC0802-

ADC0804

ADC0802, ADC0803, ADC0804

6-15

Reference Accuracy Requirements

The converter can be operated in a pseudo-ratiometric
mode or an absolute mode. In ratiometric converter applica-
tions, the magnitude of the reference voltage is a factor in
both the output of the source transducer and the output of
the A/D converter and therefore cancels out in the final digi-
tal output code. In absolute conversion applicatIons, both the
initial value and the temperature stability of the reference
voltage are important accuracy factors in the operation of the
A/D converter. For V

REF

/2 voltages of 2.5V nominal value,

initial errors of

10mV will cause conversion errors of

LSB due to the gain of 2 of the V

REF

/2 input. In reduced

span applications, the initial value and the stability of the
V

REF

/2 input voltage become even more important. For

example, if the span is reduced to 2.5V, the analog input LSB
voltage value is correspondingly reduced from 20mV (5V
span) to 10mV and 1 LSB at the V

REF

/2 input becomes

5mV. As can be seen, this reduces the allowed initial toler-
ance of the reference voltage and requires correspondingly
less absolute change with temperature variations. Note that
spans smaller than 2.5V place even tighter requirements on
the initial accuracy and stability of the reference source.

In general, the reference voltage will require an initial
adjustment. Errors due to an improper value of reference
voltage appear as full scale errors in the A/D transfer func-
tion. IC voltage regulators may be used for references if the
ambient temperature changes are not excessive.

Zero Error

The zero of the A/D does not require adjustment. If the
minimum analog input voltage value, V

lN(MlN)

, is not ground, a

zero offset can be done. The converter can be made to output
0000 0000 digital code for this minimum input voltage by bias-
ing the A/D V

IN(-)

input at this V

lN(MlN)

value (see Applications

section). This utilizes the differential mode operation of the A/D.

The zero error of the A/D converter relates to the location of
the first riser of the transfer function and can be measured by
grounding the V

IN(-)

input and applying a small magnitude

positive voltage to the V

IN(+)

input. Zero error is the difference

between the actual DC input voltage which is necessary to
just cause an output digital code transition from 0000 0000 to
0000 0001 and the ideal

LSB value (

LSB = 9.8mV for

REF

/2 = 2.500V).

Full Scale Adjust

The full scale adjustment can be made by applying a
differential input voltage which is 1

LSB down from the

desired analog full scale voltage range and then adjusting
the magnitude of the V

REF

/2 input (pin 9) for a digital output

code which is just changing from 1111 1110 to 1111 1111.
When offsetting the zero and using a span-adjusted V

REF

voltage, the full scale adjustment is made by inputting V

MlN

to the V

IN(-)

input of the A/D and applying a voltage to the

IN(+)

input which is given by:

where:

MAX

= the high end of the analog input range,

and

MIN

= the low end (the offset zero) of the analog range.

(Both are ground referenced.)

Clocking Option

The clock for the A/D can be derived from an external source
such as the CPU clock or an external RC network can be
added to provIde self-clocking. The CLK IN (pin 4) makes
use of a Schmitt trigger as shown in Figure 16.

Heavy capacitive or DC loading of the CLK R pin should be
avoided as this will disturb normal converter operation.
Loads less than 50pF, such as driving up to 7 A/D converter
clock inputs from a single CLK R pin of 1 converter, are
allowed. For larger clock line loading, a CMOS or low power
TTL buffer or PNP input logic should be used to minimize the
loading on the CLK R pin (do not use a standard TTL buffer).

Restart During a Conversion

If the A/D is restarted (CS and WR go low and return high)
during a conversion, the converter is reset and a new con-
version is started. The output data latch is not updated if the
conversion in progress is not completed. The data from the
previous conversion remain in this latch.

Continuous Conversions

In this application, the CS input is grounded and the WR
input is tied to the INTR output. This WR and INTR node
should be momentarily forced to logic low following a power-
up cycle to insure circuit operation. See Figure 17 for details.

FIGURE 15. HANDLING

5V ANALOG INPUT RANGE

IN(-)

IN(+)

REF

)

V+

ADC0802-

ADC0804

IN +

( )

SADJ

MAX

1.5

MAX

MIN

(

)

256

-----------------------------------------

CLK R

CLK IN

CLK

ADC0802-

ADC0804

CLK

1.1 RC

10k

FIGURE 16. SELF-CLOCKING THE A/D

ADC0802, ADC0803, ADC0804

6-16

Driving the Data Bus

This CMOS A/D, like MOS microprocessors and memories,
will require a bus driver when the total capacitance of the
data bus gets large. Other circuItry, which is tied to the data
bus, will add to the total capacitive loading, even in three-
state (high-impedance mode). Back plane busing also
greatly adds to the stray capacitance of the data bus.

There are some alternatives available to the designer to han-
dle this problem. Basically, the capacitive loading of the data
bus slows down the response time, even though DC specifi-
cations are still met. For systems operating with a relatively
slow CPU clock frequency, more time is available in which to
establish proper logic levels on the bus and therefore higher
capacitive loads can be driven (see Typical Performance
Curves).

At higher CPU clock frequencies time can be extended for
I/O reads (and/or writes) by inserting wait states (8080) or
using clock-extending circuits (6800).

Finally, if time is short and capacitive loading is high,
external bus drivers must be used. These can be three-state
buffers (low power Schottky is recommended, such as the
74LS240 series) or special higher-drive-current products
which are designed as bus drivers. High-current bipolar bus
drivers with PNP inputs are recommended.

Power Supplies

Noise spikes on the V+ supply line can cause conversion
errors as the comparator will respond to this noise. A
low-inductance tantalum filter capacitor should be used
close to the converter V+ pin, and values of 1

F or greater

are recommended. If an unregulated voltage is available in
the system, a separate 5V voltage regulator for the converter
(and other analog circuitry) will greatly reduce digital noise
on the V+ supply. An lCL7663 can be used to regulate such
a supply from an input as low as 5.2V.

Wiring and Hook-Up Precautions

Standard digital wire-wrap sockets are not satisfactory for
breadboarding with this A/D converter. Sockets on PC
boards can be used. All logic signal wires and leads should
be grouped and kept as far away as possible from the analog

signal leads. Exposed leads to the analog inputs can cause
undesired digital noise and hum pickup; therefore, shielded
leads may be necessary in many applications.

A single-point analog ground should be used which is separate
from the logic ground points. The power supply bypass capaci-
tor and the self-clockIng capacitor (if used) should both be
returned to digital ground. Any V

REF

/2 bypass capacitors, ana-

log input filter capacitors, or input signal shielding should be
returned to the analog ground point. A test for proper grounding
is to measure the zero error of the A/D converter. Zero errors in
excess of

LSB can usually be traced to improper board

layout and wiring (see Zero Error for measurement). Further
information can be found in Application Note AN018.

Testing the A/D Converter

There are many degrees of complexity associated with testing
an A/D converter. One of the simplest tests is to apply a
known analog input voltage to the converter and use LEDs to
display the resulting digital output code as shown in Figure 18.

For ease of testing, the V

REF

/2 (pin 9) should be supplied

with 2.560V and a V+ supply voltage of 5.12V should be
used. This provides an LSB value of 20mV.

If a full scale adjustment is to be made, an analog input volt-
age of 5.090V (5.120 - 1

LSB) should be applied to the

IN(+)

pin with the V

IN(-)

pin grounded. The value of the

REF

/2 input voltage should be adjusted until the digital out-

put code is just changing from 1111 1110 to 1111 1111. This
value of V

REF

/2 should then be used for all the tests.

The digital-output LED display can be decoded by dividing the 8
bits into 2 hex characters, one with the 4 most-significant bits
(MS) and one with the 4 least-significant bits (LS). The output is
then interpreted as a sum of fractions times the full scale voltage:

For example, for an output LED display of 1011 0110, the
MS character is hex B (decimal 11) and the LS character is
hex (and decimal) 6, so:

ADC0802 - ADC0804

INTR

CLK IN

(-)

(+)

DGND

REF

AGND

CLK R

V+

10K

5V (V

REF

)

DATA

START

ANALOG

INPUTS

150pF

OUTPUTS

N.O.

MSB

LSB

FIGURE 17. FREE-RUNNING CONNECTION

O UT

---------

256

----------

5.12

(

)

START

(+)

DGND

2.560V

AGND

150pF

N.O.

0.1

TANTALUM

5.120V

1.3k

LEDs

(8)

MSB

LSB

10k

REF

ADC0802-

ADC0804

FIGURE 18. BASIC TESTER FOR THE A/D

O UT

11
16

------

256

----------

5.12

(

)

3.64V

ADC0802, ADC0803, ADC0804

6-17

Figures 19 and 20 show more sophisticated test circuits.

Typical Applications

Interfacing 8080/85 or Z-80 Microprocessors

This converter has been designed to directly interface with
8080/85 or Z-80 Microprocessors. The three-state output
capability of the A/D eliminates the need for a peripheral
interface device, although address decoding is still required
to generate the appropriate CS for the converter. The A/D
can be mapped into memory space (using standard mem-
ory-address decoding for CS and the MEMR and MEMW
strobes) or it can be controlled as an I/O device by using the
I/OR and I/OW strobes and decoding the address bits A0

A7 (or address bits A8

A15, since they will contain the

same 8-bit address information) to obtain the CS input.
Using the I/O space provides 256 additional addresses and
may allow a simpler 8-bit address decoder, but the data can
only be input to the accumulator. To make use of the addi-
tional memory reference instructions, the A/D should be
mapped into memory space. See AN020 for more discus-
sion of memory-mapped vs I/O-mapped interfaces. An
example of an A/D in I/O space is shown in Figure 21.

The standard control-bus signals of the 8080 (CS, RD and
WR) can be directly wired to the digital control inputs of the
A/D, since the bus timing requirements, to allow both starting
the converter, and outputting the data onto the data bus, are
met. A bus driver should be used for larger microprocessor
systems where the data bus leaves the PC board and/or
must drive capacitive loads larger than 100pF.

It is useful to note that in systems where the A/D converter is
1 of 8 or fewer I/O-mapped devices, no address-decoding
circuitry is necessary. Each of the 8 address bits (A0 to A7)
can be directly used as CS inputs, one for each I/O device.

Interfacing the Z-80 and 8085

The Z-80 and 8085 control buses are slightly different from
that of the 8080. General RD and WR strobes are provided
and separate memory request, MREQ, and I/O request,
IORQ, signals have to be combined with the generalized
strobes to provide the appropriate signals. An advantage of
operating the A/D in I/O space with the Z-80 is that the CPU
will automatically insert one wait state (the RD and WR
strobes are extended one clock period) to allow more time
for the I/O devices to respond. Logic to map the A/D in I/O
space is shown in Figure 22. By using MREQ in place of
IORQ, a memory-mapped configuration results.

Additional I/O advantages exist as software DMA routines are
available and use can be made of the output data transfer
which exists on the upper 8 address lines (A8 to A15) during
I/O input instructions. For example, MUX channel selection for
the A/D can be accomplished with this operating mode.

The 8085 also provides a generalized RD and WR strobe, with
an IO/M line to distinguish I/O and memory requests. The cir-
cuit of Figure 22 can again be used, with IO/M in place of IORQ
for a memory-mapped interface, and an extra inverter (or the
logic equivalent) to provide IO/M for an I/O-mapped connection.

Interfacing 6800 Microprocessor Derivatives (6502, etc.)

The control bus for the 6800 microprocessor derivatives does
not use the RD and WR strobe signals. Instead it employs a
single R/W line and additional timing, if needed, can be derived
from the

2 clock. All I/O devices are memory-mapped in the

6800 system, and a special signal, VMA, indicates that the cur-
rent address is valid. Figure 23 shows an interface schematic
where the A/D is memory-mapped in the 6800 system. For sim-
plicity, the CS decoding is shown using

DM8092. Note that

in many 6800 systems, an already decoded 4/5 line is brought
out to the common bus at pin 21. This can be tied directly to the
CS pin of the A/D, provided that no other devices are
addressed at HEX ADDR: 4XXX or 5XXX.

In Figure 24 the ADC0802 series is interfaced to the MC6800
microprocessor through (the arbitrarily chosen) Port B of the
MC6820 or MC6821 Peripheral Interface Adapter (PlA). Here
the CS pin of the A/D is grounded since the PlA is already
memory-mapped in the MC6800 system and no CS decoding
is necessary. Also notice that the A/D output data lines are con-
nected to the microprocessor bus under program control
through the PlA and therefore the A/D RD pin can be grounded.

Application Notes

ANALOG

INPUTS

"A"

"B"

"C"

100R

8-BIT

A/D UNDER

TEST

10-BIT

DAC

ANALOG OUTPUT

100X ANALOG

ERROR VOLTAGE

FIGURE 19. A/D TESTER WITH ANALOG ERROR OUTPUT. THIS

CIRCUIT CAN BE USED TO GENERATE "ERROR
PLOTS" OF FIGURE 11.

A/D UNDER

TEST

10-BIT

DAC

DIGITAL

ANALOG

INPUTS

DIGITAL

OUTPUTS

FIGURE 20. BASIC "DIGITAL" A/D TESTER

NOTE #

DESCRIPTION

AnswerFAX

DOC. #

AN016

"Selecting A/D Converters"

9016

AN018

"Do's and Don'ts of Applying A/D
Converters"

9018

AN020

"A Cookbook Approach to High Speed
Data Acquisition and Microprocessor
Interfacing"

9020

AN030

"The ICL7104 - A Binary Output A/D
Converter for Microprocessors"

9030

ADC0802, ADC0803, ADC0804

6-19

FIGURE 22. MAPPING THE A/D AS AN

I/O DEVICE FOR USE
WITH THE Z-80 CPU

FIGURE 23. ADC0802 TO MC6800 CPU INTERFACE

FIGURE 24. ADC0802 TO MC6820 PIA INTERFACE

IORQ

74C32

ADC0802-

ADC0804

ADC0802 - ADC0804

INTR

CLK IN

(-)

(+)

DGND

REF

AGND

CLK R

V+

10K

5V (8)

ANALOG

INPUTS

150pF

MSB

LSB

(32) [29]

(33) [31]

(29) [32]

(30) [H]

(31) [K]

(26) [J]

(27) [L]

(28) [30]

(22) [34]

(23) [N]

(24) [M]

(25) [33]

VMA (5) [F]

IRQ (4)

[D]

R/W (34) [6]

DM8092

A B C

1 2 3

Numbers in parentheses refer to MC6800 CPU Pinout.

Numbers or letters in brackets refer to standard MC6800 System Common Bus Code.

ADC0802 - ADC0804

INTR

CLK IN

(-)

(+)

DGND

REF

AGND

CLK R

V+

10K

ANALOG

INPUTS

150pF

MSB

LSB

MC6820

(MCS6520)

PIA

ADC0802, ADC0803, ADC0804

6-20

Die Characteristics

DIE DIMENSIONS:

(101 mils x 93 mils) x 525

m x 25

METALLIZATION:

Type: Al
Thickness: 10k

PASSIVATION:

Type: Nitride over Silox
Nitride Thickness: 8k

Silox Thickness: 7k

Metallization Mask Layout

ADC0802, ADC0803, ADC0804

CLK IN

INTR

(-)

(+)

DGND

REF

AGND

V+ OR V

REF

CLK R

7 (MSB)

V+ OR V

REF

ADC0802, ADC0803, ADC0804

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