NSC ADC1034

ADC1031/ADC1034/ADC1038 10-Bit Serial
I/O A/D Converters with Analog Multiplexer
and Track/Hold Function
General Description
Features
The ADC1031, ADC1034 and ADC1038 are 10-bit successive approximation A/D converters with serial I/O. The serial input, for the ADC1034 and ADC1038, controls a singleended analog multiplexer that selects one of 4 input channels (ADC1034) or one of 8 input channels (ADC1038). The
ADC1034 and ADC1038 serial output data can be configured into a left- or right-justified format.
An input track/hold is implemented by a capacitive reference ladder and sampled-data comparator. This allows the
analog input to vary during the A/D conversion cycle.
Separate serial I/O and conversion clock inputs are provided to facilitate the interface to various microprocessors.
Y
Y
Y
Y
Y
Y
Y
Y
Key Specifications
Y
Applications
Y
Y
Y
Y
Y
Engine control
Process control
Instrumentation
Test equipment
Serial I/O (MICROWIRETM compatible)
Separate asynchronous converter clock and serial data
I/O clock
Analog input track/hold function
Ratiometric or absolute voltage referencing
No zero or full scale adjustment required
0V to 5V analog input range with single 5V power
supply
TTL/MOS input/output compatible
No missing codes
Y
Y
Y
Y
Resolution
10 bits
g 1 LSB (max)
Total unadjusted error
Single supply
5V g 5%
Power dissipation
20 mW (max)
Max. conversion time (fC e 3 MHz)
13.7 ms (max)
Serial data exchange time (fS e 1 MHz)
10 ms (max)
TRI-STATEÉ is a registered trademark of National Semiconductor Corporation.
MICROWIRETM is a trademark of National Semiconductor Corporation.
Connection Diagrams
Dual-In-Line and SO Packages
TL/H/10556–4
Top View
ADC1031 In NS Package N08E
TL/H/10556 – 3
Top View
TL/H/10556 – 2
ADC1034 In NS Packages
J16A, M16B or N16E
Top View
ADC1038 In NS Packages
J20A, M20B or N20A
Ordering Information
Industrial b40§ C s TA s a 85§ C
ADC1031CIN
N08E
ADC1034CIN
N16E
ADC1034CIWM
M16B
ADC1038CIN
N20A
ADC1038CIWM
M20B
Military b55§ C s TA s a 125§ C
C1995 National Semiconductor Corporation
Package
Package
ADC1034CMJ
J16A
ADC1038CMJ
J20A
TL/H/10556
RRD-B30M75/Printed in U. S. A.
ADC1031/ADC1034/ADC1038 10-Bit Serial I/O A/D Converters
with Analog Multiplexer and Track/Hold Function
January 1995
Absolute Maximum Ratings (Notes 1 & 3)
Operating Ratings (Notes 2 & 3)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Temperature Range
ADC1031CIN,
ADC1034CIN,
ADC1034CIWM,
ADC1038CIN,
ADC1038CIWM
ADC1034CMJ, ADC1038CMJ
Supply Voltage (VCC)
6.5V
Voltage at Inputs and Outputs
Input Current at Any Pin (Note 4)
Package Input Current (Note 4)
Package Dissipation
at TA e 25§ C (Note 5)
ESD Susceptability (Note 6)
Soldering Information
N Package (10 sec.)
J Package (10 sec.)
SO Package (Note 7):
Vapor Phase (60 sec.)
Infrared (15 sec.)
b 0.3V to VCC a 0.3V
g 5 mA
g 20 mA
Supply Voltage (VCC)
Reference Voltage
(VREF e VREF a b VREFb)
500 mW
2000V
TMIN s TA s TMAX
b 40§ C s TA s a 85§ C
b 55§ C s TA s a 125§ C
4.75 VDC to 5.25 VDC
2.0 VDC to VCC a 0.05V
260§ C
300§ C
215§ C
220§ C
b 65§ C to a 150§ C
Storage Temperature
Electrical Characteristics
The following specifications apply for VCC e a 5.0V, VREF e a 4.6V, fS e 700 kHz, and fC e 3 MHz unless otherwise
specified. Boldface limits apply for TA e TJ e TMIN to TMAX; all other limits TA e TJ e 25§ C.
Symbol
Parameter
Conditions
Typical
(Note 8)
Limit
(Note 9)
Units
(Limits)
g1
LSB (max)
10
Bits (min)
5
11
kX
kX (min)
kX (max)
(VCC a 0.05)
V (max)
(VCC a 0.05)
(GND b 0.05)
V (max)
V (min)
CONVERTER AND MULTIPLEXER CHARACTERISTICS
Total Unadjusted
Error
CIN, CIWM, CMJ
(Note 10)
Differential Linearity
RREF
Reference Input Resistance
8
VREF
Reference Voltage
VIN
Analog Input Voltage
(Note 11)
On Channel Leakage Current
On Channel e 5 VDC,
Off Channel e 0 VDC
5.0
200
500
nA (max)
nA (max)
(Note 12)
On Channel e 0 VDC,
Off Channel e 5 VDC
5.0
b 200
b 500
nA (max)
nA (max)
Off Channel Leakage Current
On Channel e 5 VDC,
Off Channel e 0 VDC
5.0
b 200
b 500
nA (max)
nA (max)
(Note 12)
On Channel e 0 VDC,
Off Channel e 5 VDC
5.0
200
500
nA (max)
nA (max)
g 1/4
LSB (max)
g 1/4
LSB (max)
Power Supply
Sensitivity
Zero Error
4.75 VDC s VCC s 5.25 VDC
Full Scale Error
2
Electrical Characteristics (Continued)
The following specifications apply for VCC e a 5.0V, VREF e a 4.6V, fS e 700 kHz, and fC e 3 MHz unless otherwise
specified. Boldface limits apply for TA e TJ e TMIN to TMAX; all other limits TA e TJ e 25§ C.
Symbol
Parameter
Conditions
Typical
(Note 8)
Limit
(Note 9)
Units
(Limits)
DIGITAL AND DC CHARACTERISTICS
VIN(1)
Logical ‘‘1’’ Input Voltage
VCC e 5.25 VDC
2.0
V (min)
VIN(0)
Logical ‘‘0’’ Input Voltage
VCC e 4.75 VDC
0.8
V (max)
IIN(1)
Logical ‘‘1’’ Input Current
VIN e 5.0 VDC
IIN(0)
Logical ‘‘0’’ Input Current
VIN e 0 VDC
VOUT(1)
Logical ‘‘1’’ Output Voltage
VCC e 4.75 VDC
IOUT e b360 mA
IOUT e b10 mA
VOUT(0)
Logical ‘‘0’’ Output Voltage
IOUT
TRI-STATE Output Current
0.005
2.5
mA (max)
b 0.005
b 2.5
mA (max)
2.4
4.5
V (min)
V (min)
0.4
V (max)
VCC e 4.75 VDC
IOUT e 1.6 mA
VOUT e 0V
b 0.01
b3
mA (max)
VOUT e 5V
0.01
3
mA (max)
ISOURCE Output Source Current
VOUT e 0V
b 14
b 6.5
mA (min)
ISINK
Output Sink Current
VOUT e VCC
16
8.0
mA (min)
ICC
Supply Current
CS e HIGH, VREF Open
1.5
3
mA (max)
0.7
4.0
3.0
MHz (min)
MHz (max)
AC CHARACTERISTICS
fC
fS
Conversion Clock (CCLK)
Frequency
Serial Data Clock (SCLK)
fC e 3 MHz, R/L e ‘‘0’’
183
kHz (min)
Frequency (Note 13)
fC e 3 MHz, R/L e ‘‘1’’
622
kHz (min)
fC e 3 MHz, R/L e ‘‘0’’ or R/L e ‘‘1’’
1.0
MHz (max)
TC
Conversion Time
Not Including MUX Addressing and
Analog Input Sampling Times
41 (1/fC)
a 200 ns
(max)
tCA
Analog Sampling Time
After Address is Latched,CS e Low
4.5 (1/fS)
a 200 ns
(max)
tACC
Access Time Delay from CS or OE
Falling Edge to DO Data Valid
OE e ‘‘0’’
100
200
ns (max)
tSET-UP
Set-up Time of CS Falling
Edge to SCLK Rising Edge
75
150
ns (min)
t1H, t0H
Delay from OE or CS Rising
Edge to DO TRI-STATE
100
120
ns (max)
tHDI
DI Hold Time from SCLK Rising Edge
0
50
ns (min)
tSDI
DI Set-up Time to SCLK Rising Edge
50
100
ns (min)
RL e 3 kX, CL e 100 pF
3
2
Electrical Characteristics (Continued)
The following specifications apply for VCC e a 5.0V, VREF e a 4.6V, fS e 700 kHz, and fC e 3 MHz unless otherwise
specified. Boldface limits apply for TA e TJ e TMIN to TMAX; all other limits TA e TJ e 25§ C.
Symbol
Parameter
Conditions
Typical
(Note 8)
Limit
(Note 9)
Units
(Limits)
AC CHARACTERISTICS (Continued)
tHDO
DO Hold Time from SCLK Falling Edge
RL e 30 kX, CL e 100 pF
70
10
ns (min)
tDDO
Delay from SCLK Falling
Edge to DO Data Valid
RL e 30 kX, CL e 100 pF
150
250
ns (max)
tRDO
DO Rise Time
RL e 30 kX,
CL e 100 pF
TRI-STATE to High
35
75
ns (max)
Low to High
75
150
ns (max)
tFDO
DO Fall Time
RL e 30 kX,
CL e 100 pF
TRI-STATE to Low
35
75
ns (max)
High to Low
75
150
ns (max)
CIN
Input Capacitance
Analog Inputs (CH0 – CH7)
50
pF
All Other Inputs
7.5
pF
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.
Note 2: Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications
and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics
may degrade when the device is not operated under the listed test conditions.
Note 3: All voltages are measured with respect to AGND and DGND, unless otherwise specified.
Note 4: When the input voltage (VIN) at any pin exceeds the power supplies (VIN k DGND, or VIN l VCC) the current at that pin should be limited to 5 mA. The
20 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 5 mA to four pins.
Note 5: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax, iJA and the ambient temperature, TA. The maximum
allowable power dissipation at any temperature is PD e (TJmax b TA)/iJA or the number given in the Absolute Maximum Ratings, whichever is lower. For this
device, TJmax e 125§ C. The typical thermal resistance (iJA) of these parts when board mounted follow: ADC1031 with CIN suffixes 71§ C/W, ADC1034 with CMJ
suffixes 52§ C/W, ADC1034 with CIN suffixes 54§ C/W, ADC1034 with CIWM suffixes 70§ C/W, ADC1038 with CMJ suffixes 53§ C/W, ADC1038 with CIN suffixes
46§ C/W, ADC1038 with CIWM suffixes 64§ C/W.
Note 6: Human body model, 100 pF capacitor discharged through a 1.5 kX resistor.
Note 7: See AN450 ‘‘Surface Mounting Methods and Their Effect on Product Reliability’’ or Linear Databook section ‘‘Surface Mount’’ for other methods of
soldering surface mount devices.
Note 8: Typicals are at TJ e 25§ C and represent most likely parametric norm.
Note 9: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 10: Total unadjusted error includes offset, full-scale, linearity, multiplexer, and hold step errors.
Note 11: Two on-chip diodes are tied to each analog input. They will forward-conduct for analog input voltages one diode drop below ground or one diode drop
greater than VCC supply. Be careful during testing at low VCC levels (4.5V), as high level analog inputs (5V) can cause an input diode to conduct, especially at
elevated temperatures, which will cause errors for analog inputs near full-scale. The spec allows 50 mV forward bias of either diode; this means that as long as the
analog VIN does not exceed the supply voltage by more than 50 mV, the output code will be correct. Exceeding this range on an unselected channel will corrupt the
reading of a selected channel. To achieve an absolute 0 VDC to 5 VDC input voltage range will therefore require a minimum supply voltage of 4.950 VDC over
temperature variations, initial tolerance and loading.
Note 12: Channel leakage current is measured after the channel selection.
Note 13: In order to synchronize the serial data exchange properly, SARS needs to go low after completion of the serial I/O data exchange. If this does not occur
the output shift register will be reset and the correct output data lost. The minimum limit for SCLK will depend on CCLK frequency and whether right-justified or leftjustified, and can be determined by the following equations:
fS l (8.5/41) (fC) with right-justification (R/L e ‘‘1’’) and fS l (2.5/41) (fC) with left-justification (R/L e ‘‘0’’).
4
Typical Performance Characteristics
Power Supply Current
(ICC) vs CCLK
Power Supply Current (ICC)
vs Ambient Temperature
Reference Current (IREF)
vs Ambient Temperature
Linearity Error vs
CCLK Frequency
Linearity Error vs
Ambient Temperature
Linearity Error vs
Reference Voltage
Zero Error vs
Reference Voltage
TL/H/10556 – 5
5
Test Circuits
t1H, t0H
DO except ‘‘TRI-STATE’’
Leakage Current
TL/H/10556–6
TL/H/10556 – 7
TL/H/10556 – 8
Timing Diagrams
DO High to Low State
DO Low to High State
TL/H/10556–9
DO ‘‘TRI-STATE’’ Rise
and Fall Times
TL/H/10556 – 10
TL/H/10556 – 11
DO Data Output Timing
DI Data Input Timing
TL/H/10556–12
TL/H/10556 – 13
6
Timing Diagrams (Continued)
ADC1031 CS High during Conversion
TL/H/10556 – 14
ADC1038/ADC1034 CS High during Conversion
TL/H/10556 – 15
CCLK continuously enabled
7
Timing Diagrams (Continued)
ADC1038/ADC1034 CS Low Continuously
TL/H/10556 – 16
CCLK continuously enabled
Multiplexer Address/Channel Assignment Tables
ADC1038
MUX Address
ADC1034
A2
A1
A0
Analog
Channel
Selected
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
MUX Address
A2
A1
A0
Analog
Channel
Selected
X
X
X
X
0
0
1
1
0
1
0
1
CH0
CH1
CH2
CH3
Note: ‘‘X’’ e don’t care
8
TL/H/10556 – 17
ADC1038 Functional Block Diagram
9
1.0 Pin Descriptions
CCLK
The clock applied to this input controls the successive approximation conversion time interval.
The clock frequency applied to this input can be
between 700 kHz and 4 MHz.
SCLK
The serial data clock input. The clock applied to
this input controls the rate at which the serial
data exchange occurs and the analog sampling
time available to acquire an analog input voltage.
The rising edge loads the information on the DI
pin into the multiplexer address shift register (address register). This address controls which
channel of the analog input multiplexer (MUX) is
selected.
The falling edge shifts the data resulting from the
previous A/D conversion out on DO. CS and OE
enable or disable the above functions.
The serial data input pin. The data applied to this
pin is shifted by SCLK into the multiplexer address register. The first 3 bits of data (A0–A2)
are the MUX channel address (see the Multiplexer Address/Channel Assignment tables). The
fourth bit (R/L) determines the data format of the
conversion result in the conversion to be started.
When R/L is low the output data format is leftjustified; when high it is right-justified. When rightjustified, six leading ‘‘0’’s are output on DO before the MSB information; thus the complete conversion result is shifted out in 16 clock periods.
The data output pin. The A/D conversion result
(D0 – D9) is output on this pin. This result can be
left- or right-justified depending on the value of
R/L bit shifted in on DI.
This pin is an output and indicates the status of
the internal successive approximation register
(SAR). When high, it signals that the A/D conversion is in progress. This pin is set high after the
analog input sampling time (tCA) and remains
high for 41 CCLK periods. When SARS goes low,
the output shift register has been loaded with the
conversion result and another A/D conversion
sequence can be started.
DI
DO
SARS
CS
OE
CH0 –
CH7
VREF a
VREFb
VCC
DGND,
AGND
GND
The positive analog voltage reference for the analog inputs. In order to maintain accuracy the
voltage range of VREF (VREF e VREF a b
VREFb) is 2.5 VDC to 5.0 VDC and the voltage at
VREF a cannot exceed VCC a 50 mV. In the
ADC1031 VREFb is always GND.
The negative voltage reference for the analog inputs. In order to maintain accuracy the voltage at
this pin must not go below DGND and AGND by
more than 50 mV or exceed 40% of VCC (for VCC
e 5V, VREF b (max) e 2V). In the ADC1031
VREFb is internally connected to the GND pin.
The power supply pin. The operating voltage
range of VCC is 4.75 VDC to 5.25 VDC. VCC
should be bypassed with 10 mF and 0.1 mF capacitors to digital ground for proper operation of
the A/D converter.
The digital and analog ground pins for the
ADC1034 and the ADC1038. In order to maintain
accuracy the voltage difference between these
two pins must not exceed 300 mV.
The digital and analog ground pin for the
ADC1031.
2.0 Functional Description
2.1 DIGITAL INTERFACE
The ADC1034 and ADC1038 implement their serial interface via seven digital control lines. There are two clock inputs for the ADC1034/ADC1038. The SCLK controls the
rate at which the serial data exchange occurs and the duration of the analog sampling time window. The CCLK controls
the conversion time and must be continuously enabled. A
low on CS enables the rising edge of SCLK to shift in the
serial multiplexer addressing data on the DI pin. The first
three bits of this data select the analog input channel for the
ADC1038 and the ADC1034 (see the Channel Addressing
Tables). The following bit, R/L, selects the output data format (right-justified or left-justified) for the conversion to be
started. With CS and OE low the DO pin is active (out of
TRI-STATE) and the falling edge of SCLK shifts out the data
from the previous analog conversion. When the first conversion is started the data shifted out on DO is erroneous as it
depends on the state of the Parallel Load 16-Bit Shift Register on power up, which is unpredictable.
The ADC1031 implements its serial interface with only four
control pins since it has only one analog input and comes in
an eight pin mini-dip package. The SCLK, CCLK, CS and DO
pins are available for the serial interface. The output data
format cannot be selected and defaults to a left-justified
format. The state of DO is controlled by CS only.
The chip select pin. When a low is applied to this
pin, the rising edge of SCLK shifts the data on DI
into the address register. In the ADC1031 this pin
also functions as the OE pin.
The output enable pin. When OE and CS are
both low the falling edge of SCLK shifts out the
previous A/D conversion data on the DO pin.
The analog inputs of the MUX. A channel input is
selected by the address information at the DI pin,
which is loaded on the rising edge of SCLK into
the address register.
Source impedances (RS) driving these inputs
should be kept below 1 kX. If RS is greater than
1 kX, the sampled data comparator will not have
enough time to acquire the correct value of the
applied input voltage.
The voltage applied to these inputs should not
exceed VCC or go below DGND or AGND by
more than 50 mV. Exceeding this range on an
unselected channel will corrupt the reading of a
selected channel.
2.2 OUTPUT DATA FORMAT
When R/L is low the output data format is left-justified;
when high it is right-justified. When right-justified, six leading
‘‘0’’s are output on DO before the MSB, and the complete
conversion result is shifted out in 16 clock periods.
2.3.0 CS HIGH DURING CONVERSION
With a continuous SCLK input, CS must be used to synchronize the serial data exchange. A valid CS is recognized if it
occurs at least 100 ns (tSET-UP) before the rising edge of
SCLK, thus causing data to be input on DI. If this does not
10
An acquisition window of 4.5 SCLK cycles is available to
allow the ladder capacitance to settle to the analog input
voltage. Any change in the analog voltage before or after
the acquisition window will not effect the A/D conversion
result.
In the most simple case, the ladder’s acquisition time is determined by the Ron (9 kX) of the multiplexer switches, the
CS1 (3.5 pF) and the total ladder (CL) and stray (CS2) capacitance (48 pF). For large source resistance the analog input
can be modeled as an RC network as shown in Figure 1 .
The values shown yield an acquisition time of about 3 ms for
10 bit accuracy with a zero to a full scale change in the
reading. External source resistance and capacitance will
lengthen the acquisition time and should be accounted for.
The curve ‘‘Signal to Noise Ratio vs Output Frequency’’
(Figure 2) gives an indication of the usable bandwidth of the
ADC1031/ADC1034/ADC1038. The signal to noise ratio of
an ideal A/D is the ratio of the RMS value of the full scale
input signal amplitude to the value of the total error amplitude (including noise) caused by the transfer function of the
A/D. An ideal 10 bit A/D converter with a total unadjusted
error of 0 LSB would have a signal to noise ratio of about
62 dB, which can be derived from the equation:
S/N e 6.02(N) a 1.8
2.0 Functional Description (Continued)
occur there will be an uncertainty as to which SCLK rising
edge will clock in the first bit of data. CS must remain low
during the complete I/O exchange. Also, OE needs to be
low if data from the previous conversion needs to be accessed.
2.3.1 CS LOW CONTINUOUSLY
Another way to accomplish synchronous serial communication is to tie CS low continuously and use SARS and SCLK to
synchronize the serial data exchange. SCLK can be disabled
low during the conversion time and enabled after SARS
goes low. With CS low during the conversion time a zero will
remain on DO until the conversion is completed. Once the
conversion is complete, the falling edge of SARS will shift
out on DO the MSB before SCLK is enabled. This MSB
would be a leading zero if right-justified or D9 if left-justified.
The rest of the data will be shifted out once SCLK is enabled
as discussed previously. If CS goes high during the conversion sequence DO is put into TRI-STATE, and the conversion result is not affected so long as CS remains high until
the end of the conversion.
2.4 TYING SCLK and CCLK TOGETHER
SCLK and CCLK can be tied together. The total conversion
time will increase because the maximum clock frequency is
now 1 MHz. The timing diagrams and the serial I/O exchange time (10 SCLK cycles) remain the same, but the conversion time (TC e 41 CCLK cycles) lengthens from a minimum of 14 ms to a minimum of 41 ms. In the case where CS
is low continuously, since the applied clock cannot be disabled, SARS must be used to synchronize the data output
on DO and initiate a new conversion. The falling edge of
SARS sends the MSB information out on DO. The next rising edge of the clock shifts in MUX address bit A2 on DI.
The following clock falling edge will clock the next data bit
of information out on DO. A conversion will be started after
MUX addressing information has been loaded in (3 more
clocks) and the analog sampling time (4.5 clocks) has
elapsed. The ADC1031 does not have SARS. Therefore, CS
cannot be left low continuously on the ADC1031.
where S/N is in dB and N is the number of bits. Figure 2
shows the signal to noise ratio vs. input frequency of a typical ADC1031/4/8 with (/2 LSB total unadjusted error. The
dotted lines show signal-to-noise ratios for an ideal (noiseless) 10 bit A/D with 0 LSB error and an A/D with a 1 LSB
error.
The sample-and-hold error specifications are included in the
error and timing specifications of the A/D. The hold step
and gain error sample/hold specs are taken into account in
the ADC1031/4/8’s total unadjusted error specification,
while the hold settling time is included in the A/D’s maximum conversion time specification. The hold droop rate can
be thought of as being zero since an unlimited amount of
time can pass between a conversion and the reading of
data. However, once the data is read it is lost and another
conversion is started.
3.2 INPUT FILTERING
Due to the sampling nature of the analog input, transients
will appear on the input pins. They are caused by the ladder
capacitance and internal stray capacitance charging current
flowing into VIN. These transients will not degrade the A/D’s
performance if they settle out within the sampling window.
This will occur if external source resistance is kept to a minimum.
3.0 Analog Considerations
3.1 THE INPUT SAMPLE AND HOLD
The ADC1031/4/8’s sample/hold capacitor is implemented
in its capacitive ladder structure. After the channel address
is received, the ladder is switched to sample the proper analog input. This sampling mode is maintained for 4.5 SCLK
cycles after the multiplexer addressing information is loaded
in. For the ADC1031/4/8, the sampling of the analog input
starts on SCLK’s 4th rising edge.
TL/H/10556 – 18
FIGURE 1. Analog Input Model
TL/H/10556 – 19
FIGURE 2. ADC1031/4/8 Signal to
Noise Ratio vs Input Frequency
11
3.0 Analog Considerations (Continued)
External Reference 2.5V Full Scale
Power Supply as Reference
Input Not Referred to GND
TL/H/10556–20
TL/H/10556 – 21
TL/H/10556 – 22
*Current path must still exist from VIN(b) to
ground
FIGURE 3. Analog Input Options
ment also facilitates ratiometric operation and in many
cases the chip power supply can be used for transducer
power as well as the VREF source.
3.3 REFERENCE AND INPUT
The two VREF inputs of the ADC1031/4/8 are fully differential and define the zero to full-scale input range of the A to D
converter. This allows the designer to easily vary the span
of the analog input since this range will be equivalent to the
voltage difference between VREF a and VREFb. By reducing VREF (VREF e VREF a b VREFb) to less than 5V, the
sensitivity of the converter can be increased (i.e., if VREF e
2V then 1 LSB e 1.95 mV). The input/reference arrange-
This reference flexibility lets the input span not only be varied but also offset from zero. The voltage at VREFb sets the
input level which produces a digital output of all zeros.
Though VIN is not itself differential, the reference design
allows nearly differential-input capability for many measurement applications. Figure 3 shows some of the configurations that are possible.
The ADC1031 has no VREFb pin. VREFb is internally tied to
GND.
Power Supply Bypassing
TL/H/10556–23
TL/H/10556 – 24
12
Protecting the Analog Inputs
TL/H/10556 – 26
Diodes are IN914
TL/H/10556 – 25
Zero-Shift and Span-Adjust (2V s VIN s 4.5V)
*1% resistors
13
TL/H/10556 – 27
14
Physical Dimensions inches (millimeters)
Order Number ADC1034CMJ
NS Package Number J16A
Order Number ADC1038CMJ
NS Package Number J20A
15
Physical Dimensions inches (millimeters) (Continued)
Order Number ADC1034CIWM
NS Package Number M16B
Order Number ADC1038CIWM
NS Package Number M20B
16
Physical Dimensions inches (millimeters) (Continued)
Order Number ADC1031CIN
NS Package Number N08E
Order Number ADC1034CIN
NS Package Number N16E
17
ADC1031/ADC1034/ADC1038 10-Bit Serial I/O A/D Converters
with Analog Multiplexer and Track/Hold Function
Physical Dimensions inches (millimeters) (Continued)
Lit. Ý 101002
Order Number ADC1038CIN
NS Package Number N20A
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