TI ADS1110A2IDBVR 16-bit analog-to-digital converter with onboard reference Datasheet

ADS1110
SBAS276A − MARCH 2003 − REVISED NOVEMBER 2003
16-Bit ANALOG-TO-DIGITAL CONVERTER
with Onboard Reference
FEATURES
DESCRIPTION
D COMPLETE DATA ACQUISITION SYSTEM IN
The ADS1110 is a precision, continuously self−calibrating
Analog-to-Digital (A/D) converter with differential inputs and
up to 16 bits of resolution in a small SOT23-6 package. The
onboard 2.048V reference provides an input range of
±2.048V differentially. The ADS1110 uses an I2C-compatible
serial interface and operates from a single power supply
ranging from 2.7V to 5.5V.
A TINY SOT23-6 PACKAGE
D ONBOARD REFERENCE:
Accuracy: 2.048V ±0.05%
Drift: 5ppm/°C
D
D
D
D
D
D
D
ONBOARD PGA
ONBOARD OSCILLATOR
16-BITS NO MISSING CODES
INL: 0.01% of FSR max
CONTINUOUS SELF-CALIBRATION
SINGLE-CYCLE CONVERSION
PROGRAMMABLE DATA RATE: 15SPS TO
240SPS
D I2CINTERFACE—EIGHT AVAILABLE
ADDRESSES
D POWER SUPPLY: 2.7V to 5.5V
D LOW CURRENT CONSUMPTION: 240µA
The ADS1110 can perform conversions at rates of 15, 30, 60,
or 240 samples per second. The onboard programmable
gain amplifier (PGA), which offers gains of up to 8, allows
smaller signals to be measured with high resolution. In
single-conversion mode, the ADS1110 automatically powers
down after a conversion, greatly reducing current
consumption during idle periods.
The ADS1110 is designed for applications requiring
high-resolution measurement, where space and power
consumption are major considerations. Typical applications
include portable instrumentation, industrial process control,
and smart transmitters.
APPLICATIONS
D
D
D
D
D
D
PORTABLE INSTRUMENTATION
INDUSTRIAL PROCESS CONTROL
SMART TRANSMITTERS
CONSUMER GOODS
FACTORY AUTOMATION
TEMPERATURE MEASUREMENT
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments
semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
Copyright  2003, Texas Instruments Incorporated
! ! www.ti.com
ADS1110
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ABSOLUTE MAXIMUM RATINGS(1)
VDD to GND
Input Current
100mA, Momentary
−0.3V to +6V
Input Current
10mA, Continuous
Voltage to GND, VIN+, VIN−
−0.3V to VDD + 0.3V
Voltage to GND, SDA, SCL
−0.5V to 6V
Maximum Junction Temperature
+150°C
Operating Temperature Range
−40°C to +125°C
Storage Temperature Range
−60°C to +150°C
This integrated circuit can be damaged by ESD.
Texas Instruments recommends that all
integrated circuits be handled with appropriate
precautions. Failure to observe proper handling and
installation procedures can cause damage.
ESD damage can range from subtle performance degradation
to complete device failure. Precision integrated circuits may
be more susceptible to damage because very small
parametric changes could cause the device not to meet its
published specifications.
Lead Temperature (soldering, 10s)
+300°C
(1) Stresses above those listed under “Absolute Maximum Ratings”
may cause permanent damage to the device. Exposure to
absolute maximum conditions for extended periods may affect
device reliability.
PACKAGE/ORDERING INFORMATION
PRODUCT
I2C
ADDRESS
PACKAGE−LEAD
PACKAGE
DESIGNATOR(1)
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
MARKING
ADS1110
1001 000
SOT23-6
DBV
−40°C to +85°C
ED0
ADS1110
1001 001
SOT23-6
DBV
−40°C to +85°C
ED1
ADS1110
1001 010
SOT23-6
DBV
−40°C to +85°C
ED2
ADS1110
1001 011
SOT23-6
DBV
−40°C to +85°C
ED3
ADS1110
1001 100
SOT23-6
DBV
−40°C to +85°C
ED4
ADS1110
1001 101
SOT23-6
DBV
−40°C to +85°C
ED5
ADS1110
1001 110
SOT23-6
DBV
−40°C to +85°C
ED6
ADS1110
1001 111
SOT23-6
DBV
−40°C to +85°C
ED7
(1) For the most current specification and package information, refer to our web site at www.ti.com.
Top View
2
SOT23
ORDERING
NUMBER
TRANSPORT
MEDIA, QUANTITY
ADS1110A0IDBVT
Tape and Reel, 250
ADS1110A0IDBVR
Tape and Reel, 3000
ADS1110A1IDBVT
Tape and Reel, 250
ADS1110A1IDBVR
Tape and Reel, 3000
ADS1110A2IDBVT
Tape and Reel, 250
ADS1110A2IDBVR
Tape and Reel, 3000
ADS1110A3IDBVT
Tape and Reel, 250
ADS1110A3IDBVR
Tape and Reel, 3000
ADS1110A4IDBVT
Tape and Reel, 250
ADS1110A4IDBVR
Tape and Reel, 3000
ADS1110A5IDBVT
Tape and Reel, 250
ADS1110A5IDBVR
Tape and Reel, 3000
ADS1110A6IDBVT
Tape and Reel, 250
ADS1110A6IDBVR
Tape and Reel, 3000
ADS1110A7IDBVT
Tape and Reel, 250
ADS1110A7IDBVR
Tape and Reel, 3000
ADS1110
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SBAS276A − MARCH 2003 − REVISED NOVEMBER 2003
ELECTRICAL CHARACTERISTICS
All specifications at −40°C to +85°C, VDD = 5V, and all PGAs, unless otherwise noted.
ADS1110
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
ANALOG INPUT
Full-Scale Input Voltage
Analog Input Voltage
(VIN+) − (VIN−)
VIN+ to GND or VIN− to GND
±2.048/PGA
GND − 0.2
Differential Input Impedance
Common-Mode Input Impedance
PGA = 1
PGA = 2
PGA = 4
PGA = 8
V
VDD + 0.2
V
2.8/PGA
MΩ
3.5
3.5
1.8
0.9
MΩ
MΩ
MΩ
MΩ
SYSTEM PERFORMANCE
Resolution and No Missing Codes
DR = 00
DR = 01
DR = 10
DR = 11
12
14
15
16
Data Rate
DR = 00
DR = 01
DR = 10
DR = 11
180
45
22
11
Output Noise
240
60
30
15
12
14
15
16
Bits
Bits
Bits
Bits
308
77
39
20
SPS
SPS
SPS
SPS
See Typical Characteristic Curves
Integral Nonlinearity
DR = 11, PGA = 1, End Point Fit(1)
±0.004
±0.010
% of FSR(2)
Offset Error
PGA = 1
PGA = 2
PGA = 4
PGA = 8
1.2
0.7
0.5
0.4
8
4
2.5
1.5
mV
mV
mV
mV
Offset Drift
PGA = 1
PGA = 2
PGA = 4
PGA = 8
1.2
0.6
0.3
0.3
µV/°C
µV/°C
µV/°C
µV/°C
Offset vs VDD
PGA = 1
PGA = 2
PGA = 4
PGA = 8
800
400
200
150
µV/V
µV/V
µV/V
µV/V
Gain Error(3)
PGA Gain Error Match(3)
Gain Error Drift(3)
Match Between Any Two PGA Gains
Gain vs VDD
Common-Mode Rejection
At DC and PGA = 8
At DC and PGA = 1
95
%
0.05
0.40
0.02
0.10
%
5
40
ppm/°C
80
ppm/V
105
100
dB
dB
DIGITAL INPUT/OUTPUT
Logic Level
VIH
VIL
VOL
IOL = 3mA
0.7 • VDD
GND − 0.5
GND
Input Leakage
IH
IL
VIH = 5.5V
VIL = GND
−10
Power-Supply Voltage
VDD
2.7
5.5
V
Supply Current
Power Down
Active Mode
0.05
240
2
350
µA
µA
Power Dissipation
VDD = 5.0V
VDD = 3.0V
1.2
0.675
1.75
mW
mW
6
0.3 • VDD
0.4
V
V
V
10
µA
µA
POWER-SUPPLY REQUIREMENTS
(1) 99% of full-scale.
(2) FSR = full-scale range = 2 × 2.048V/PGA = 4.096V/PGA.
(3) Includes all errors from onboard PGA and reference.
3
ADS1110
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TYPICAL CHARACTERISTICS
At TA = 25°C and VDD = 5V, unless otherwise noted.
4
ADS1110
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TYPICAL CHARACTERISTICS (continued)
At TA = 25°C and VDD = 5V, unless otherwise noted.
5
ADS1110
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TYPICAL CHARACTERISTICS (continued)
At TA = 25°C and VDD = 5V, unless otherwise noted.
THEORY OF OPERATION
The ADS1110 is a fully differential, 16-bit, self-calibrating,
delta-sigma A/D converter. Extremely easy to design with
and configure, the ADS1110 allows precise measurements to be obtained with a minimum of effort.
mance of the onboard reference as well as the performance of the A/D converter core. There are no separate
specifications for the onboard reference itself.
The ADS1110 consists of a delta-sigma A/D converter
core with adjustable gain, a 2.048V reference, a clock oscillator, and an I2C interface. Each of these blocks are described in detail in the sections that follow.
OUTPUT CODE CALCULATION
ANALOG-TO-DIGITAL CONVERTER
The ADS1110 A/D converter core consists of a differential
switched-capacitor delta-sigma modulator followed by a
digital filter. The modulator measures the voltage difference between the positive and negative analog inputs and
compares it to a reference voltage, which, in the ADS1110,
is 2.048V. The digital filter receives a high-speed bitstream
from the modulator and outputs a code, which is a number
proportional to the input voltage.
The output code is a scalar value that is, except for clipping, proportional to the voltage difference between the
two analog inputs. The output code is confined to a finite
range of numbers; this range depends on the number of
bits needed to represent the code. The number of bits
needed to represent the output code for the ADS1110 depends on the data rate, as shown in Table 1.
DATA RATE
NUMBER OF
BITS
MINIMUM
CODE
MAXIMUM
CODE
15SPS
16
−32,768
32,767
30SPS
15
−16,384
16,383
60SPS
14
−8192
8191
240SPS
12
−2048
2047
Table 1. Minimum and Maximum Codes
VOLTAGE REFERENCE
The ADS1110 contains an onboard 2.048V voltage reference. This reference is always used as the A/D converter’s
voltage reference; an external reference cannot be connected. The ADS1110’s voltage reference is internal only,
and cannot be measured directly or used by external circuitry.
The onboard reference’s specifications are part of the
ADS1110’s overall gain and drift specifications. The converter’s drift and gain error specifications reflect the perfor6
For a minimum output code of Min Code, gain setting of
PGA, and positive and negative input voltages of VIN+ and
VIN−, the output code is given by the expression:
Output Code + −1
Min Code
PGA
(V IN)) * (V IN*)
2.048V
In the previous expression, it is important to note that the
negated minimum output code is used. The ADS1110
outputs codes in binary two’s complement format, so the
absolute values of the minima and maxima are not the
same; the maximum n−bit code is 2n−1 − 1, while the
minimum n−bit code is −1 × 2n−1.
ADS1110
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For example, the ideal expression for output codes with a
data rate of 16SPS and PGA = 2 is:
Output Code + 16384
2
(VIN)) * (VIN*)
2.048V
The ADS1110 outputs all codes right-justified and
sign-extended. This makes it possible to perform
averaging on the higher data rate codes using only a 16-bit
accumulator.
Table 2 shows the output codes for various input levels.
SELF-CALIBRATION
The previous expressions for the ADS1110’s output code
do not account for the gain and offset errors in the
modulator. To compensate for these, the ADS1110
incorporates self-calibration circuitry.
The self-calibration system operates continuously and
requires no user intervention. No adjustments can be
made to the self-calibration system, and none need to be
made. The self-calibration system cannot be deactivated.
The offset and gain error figures shown in the Electrical
Characteristics include the effects of calibration.
generated by the onboard clock oscillator, so its frequency,
nominally 275kHz, is dependent on supply voltage and
temperature.
The common-mode and differential input impedances are
different. For a gain setting of PGA, the differential input
impedance is typically:
2.8MΩ/PGA
The common-mode impedance also depends on the PGA
setting. See the Electrical Characteristics for details.
The typical value of the input impedance often cannot be
neglected. Unless the input source has a low impedance,
the ADS1110’s input impedance may affect the
measurement accuracy. For sources with high output
impedance, buffering may be necessary. Bear in mind,
however, that active buffers introduce noise, and also
introduce offset and gain errors. All of these factors should
be considered in high-accuracy applications.
Because the clock oscillator frequency drifts slightly with
temperature, the input impedances will also drift. For many
applications, this input impedance drift can be neglected,
and the expression given above for typical input
impedance can be used.
ALIASING
CLOCK OSCILLATOR
The ADS1110 features an onboard clock oscillator, which
drives the operation of the modulator and digital filter. The
Typical Characteristics show variations in data rate over
supply voltage and temperature.
It is not possible to operate the ADS1110 with an external
system clock.
INPUT IMPEDANCE
The ADS1110 uses a switched-capacitor input stage. To
external circuitry, it looks roughly like a resistance. The
resistance value depends on the capacitor values and the
rate at which they are switched. The switching frequency
is the same as the modulator frequency; the capacitor
values depend on the PGA setting. The switching clock is
If frequencies are input to the ADS1110 that exceed half
the data rate, aliasing will occur. To prevent aliasing, the
input signal must be bandlimited. Some signals are
inherently bandlimited. For example, a thermocouple’s
output, which has a limited rate of change, may
nevertheless contain noise and interference components.
These can fold back into the sampling band just as any
other signal can.
The ADS1110’s digital filter provides some attenuation of
high-frequency noise, but the digital filter’s Sinc1
frequency response cannot completely replace an
anti-aliasing filter. For a few applications, some external
filtering may be needed; in such applications, a simple RC
filter will suffice.
When designing an input filter circuit, remember to take
into account the interaction between the filter network and
the input impedance of the ADS1110.
DIFFERENTIAL INPUT SIGNAL
DATA RATE
−2.048V(1)
−1LSB
ZERO
+1LSB
+2.048V
15SPS
8000H
C000H
FFFFH
0000H
0000H
0001H
0001H
7FFFH
E000H
F800H
FFFFH
0000H
0000H
0001H
0001H
1FFFH
30SPS
60SPS
240SPS
FFFFH
FFFFH
3FFFH
07FFH
(1) Differential input only; do not drive the ADS1110’s inputs below −200mV.
Table 2. Output Codes for Different Input Signals
7
ADS1110
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USING THE ADS1110
OPERATING MODES
The ADS1110 operates in one of two modes: continuous
conversion or single conversion.
In continuous conversion mode, the ADS1110 continuously performs conversions. Once a conversion has been
completed, the ADS1110 places the result in the output
register and immediately begins another conversion.
In single conversion mode, the ADS1110 waits until the
ST/DRDY bit in the conversion register is set to 1. When
this happens, the ADS1110 powers up and performs a
single conversion. After the conversion completes, the
ADS1110 places the result in the output register, resets the
ST/DRDY bit to 0, and powers down. Writing a 1 to
ST/DRDY while a conversion is in progress has no effect.
When switched from continuous conversion mode to
single conversion mode, the ADS1110 completes the
current conversion, resets the ST/DRDY bit to 0, and
powers down.
RESET AND POWER−UP
When the ADS1110 powers up, it automatically performs
a reset. As part of the reset, the ADS1110 sets all of the bits
in the configuration register to their default settings.
The ADS1110 responds to the I2C General Call Reset
command. When the ADS1110 receives a General Call
Reset, it performs an internal reset, exactly as though it
had just been powered on.
I2C INTERFACE
The ADS1110 communicates through an I2C
(inter-integrated circuit) interface. I2C is a two-wire
open-drain interface supporting multiple devices and
masters on a single bus. Devices on the I2C bus only drive
the bus lines LOW by connecting them to ground; they
never drive the bus lines HIGH. Instead, the bus wires are
pulled HIGH by pull-up resistors, so the bus wires are
HIGH when no device is driving them LOW. This way, two
devices cannot conflict; if two devices drive the bus
simultaneously, there is no driver contention.
Communication on the I2C bus always takes place
between two devices, one acting as the master and the
other acting as the slave. Both masters and slaves can
read and write, but slaves can only do so under the
direction of the master. Some I2C devices can act as
masters or slaves, but the ADS1110 can only act as a slave
device.
8
An I2C bus consists of two lines, SDA and SCL. SDA
carries data; SCL provides the clock. All data is
transmitted across the I2C bus in groups of eight bits. To
send a bit on the I2C bus, the SDA line is driven to the
appropriate level while SCL is LOW (a LOW on SDA
indicates the bit is zero; a HIGH indicates the bit is one).
Once the SDA line has settled, the SCL line is brought
HIGH, then LOW. This pulse on SCL clocks the SDA bit
into the receiver’s shift register.
The I2C bus is bidirectional: the SDA line is used both for
transmitting and receiving data. When a master reads from
a slave, the slave drives the data line; when a master
sends to a slave, the master drives the data line. The
master always drives the clock line. The ADS1110 never
drives SCL, because it cannot act as a master. On the
ADS1110, SCL is an input only.
Most of the time the bus is idle, no communication is taking
place, and both lines are HIGH. When communication is
taking place, the bus is active. Only master devices can
start a communication. They do this by causing a START
condition on the bus. Normally, the data line is only allowed
to change state while the clock line is LOW. If the data line
changes state while the clock line is HIGH, it is either a
START condition or its counterpart, a STOP condition. A
START condition is when the clock line is HIGH and the
data line goes from HIGH to LOW. A STOP condition is
when the clock line is HIGH and the data line goes from
LOW to HIGH.
After the master issues a START condition, it sends a byte
that indicates which slave device it wants to communicate
with. This byte is called the address byte. Each device on
an I2C bus has a unique 7-bit address to which it responds.
(Slaves can also have 10-bit addresses; see the I2C
specification for details.) The master sends an address in
the address byte, together with a bit that indicates whether
it wishes to read from or write to the slave device.
Every byte transmitted on the I2C bus, whether it is
address or data, is acknowledged with an acknowledge
bit. When a master has finished sending a byte (eight data
bits) to a slave, it stops driving SDA and waits for the slave
to acknowledge the byte. The slave acknowledges the
byte by pulling SDA LOW. The master then sends a clock
pulse to clock the acknowledge bit. Similarly, when a
master has finished reading a byte, it pulls SDA LOW to
acknowledge this to the slave. It then sends a clock pulse
to clock the bit. (Remember that the master always drives
the clock line.)
A not-acknowledge is performed by simply leaving SDA
HIGH during an acknowledge cycle. If a device is not
present on the bus, and the master attempts to address it,
it will receive a not−acknowledge because no device is
present at that address to pull the line LOW.
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When a master has finished communicating with a slave,
it may issue a STOP condition. When a STOP condition is
issued, the bus becomes idle again. A master may also
issue another START condition. When a START condition
is issued while the bus is active, it is called a repeated
START condition.
Each variant of the ADS1110 is marked with EDx, where
x identifies the address variant. For example, the
ADS1110A0 is marked ED0, and the ADS1110A3 is
marked ED3. See the Package/Ordering Information table
for a complete listing.
A timing diagram for an ADS1110 I2C transaction is shown
in Figure 1. The parameters for this diagram are given in
Table 3.
I2C GENERAL CALL
The ADS1110 responds to a General Call Reset, which is
an address byte of 00h followed by a data byte of 06H. The
ADS1110 acknowledges both bytes.
ADS1110 I2C ADDRESSES
The ADS1110 I2C address is 1001aaa, where aaa are bits
set at the factory. The ADS1110 is available in eight
different versions, each having a different I2C address. For
example, the ADS1110A0 has address 1001000, and the
ADS1110A3 has address 1001011. See the Ordering
Information table for a complete listing.
On receiving a General Call Reset, the ADS1110 performs
a full internal reset, just as though it had been powered off
and then on. If a conversion is in process, it is interrupted;
the output register is set to zero, and the configuration
register is set to its default setting.
The ADS1110 always acknowledges the General Call
address byte of 00H, but it does not acknowledge any
General Call data bytes other than 04H or 06H.
The I2C address is the only difference between the eight
variants. In all other respects, they operate identically.
Figure 1. I2C Timing Diagram
FAST MODE
MIN
PARAMETER
SCLK operating frequency
HIGH-SPEED MODE
MAX
MIN
0.4
MAX
UNITS
3.4
MHz
t(SCLK)
t(BUF)
600
160
ns
Hold time after repeated START condition.
After this period, the first clock is generated.
t(HDSTA)
600
160
ns
Repeated START condition setup time
t(SUSTA)
t(SUSTO)
t(HDDAT)
600
160
ns
600
160
ns
0
0
ns
t(SUDAT)
t(LOW)
100
10
ns
1300
160
ns
600
60
Bus free time between START and STOP condition
Stop condition setup time
Data hold time
Data setup time
SCLK clock LOW period
SCLK clock HIGH period
Clock/data fall time
Clock/data rise time
t(HIGH)
tF
tR
ns
300
160
ns
300
160
ns
Table 3. Timing Diagram Definitions
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I2C DATA RATES
For more information on High-speed mode, consult the I2C
specification.
The I2C bus operates in one of three speed modes:
Standard, which allows a clock frequency of up to 100kHz;
Fast, which allows a clock frequency of up to 400kHz; and
High-speed mode (also called Hs mode), which allows a
clock frequency of up to 3.4MHz. The ADS1110 is fully
compatible with all three modes.
REGISTERS
The ADS1110 has two registers that are accessible via its
I2C port. The output register contains the result of the last
conversion; the configuration register allows the user to
change the ADS1110 operating mode and query the status
of the device.
No special action needs to be taken to use the ADS1110
in Standard or Fast modes, but High-speed mode must be
activated. To activate High-speed mode, send a special
address byte of 00001xxx following the START condition,
where xxx are bits unique to the Hs-capable master. This
byte is called the Hs master code. (Note that this is different
from normal address bytes: the low bit does not indicate
read/write status.) The ADS1110 will not acknowledge this
byte; the I2C specification prohibits acknowledgment of
the Hs master code. On receiving a master code, the
ADS1110 will switch on its Hs mode filters, and
communicate at up to 3.4MHz. The ADS1110 will switch
out of Hs mode with the next STOP condition.
OUTPUT REGISTER
The 16-bit output register contains the result of the last
conversion in binary two’s complement format. Following
reset or power−up, the output register is cleared to zero;
it remains zero until the first conversion is completed.
The output register’s format is shown in Table 4.
BIT
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
NAME
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
Table 4. Output Register
10
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CONFIGURATION REGISTER
The 8-bit configuration register can be used to control the
ADS1110’s operating mode, data rate, and PGA settings.
The configuration register format is shown in Table 5. The
default setting is 8CH.
BIT
7
6
5
4
3
2
1
0
NAME
ST/DRDY
0
0
SC
DR1
DR0
PGA1
PGA0
DEFAULT
1
0
0
0
1
1
0
0
Table 5. Configuration Register
Bit 7: ST/DRDY
The meaning of the ST/DRDY bit depends on whether it is
being written to or read from.
In single conversion mode, writing a 1 to the ST/DRDY bit
causes a conversion to start, and writing a 0 has no effect.
In continuous conversion mode, the ADS1110 ignores the
value written to ST/DRDY.
When read, ST/DRDY indicates whether the data in the
output register is new data. If ST/DRDY is 0, the data just
read from the output register is new, and has not been read
before. If ST/DRDY is 1, the data just read from the output
register has been read before.
The ADS1110 sets ST/DRDY to 0 when it writes data into
the output register. It sets ST/DRDY to 1 after any of the
bits in the configuration register have been read. (Note that
the read value of the bit is independent of the value written
to this bit.)
In continuous-conversion mode, use ST/DRDY to
determine when new conversion data is ready. If
ST/DRDY is 1, the data in the output register has already
been read, and is not new. If it is 0, the data in the output
register is new, and has not yet been read.
In single-conversion mode, use ST/DRDY to determine
when a conversion has completed. If ST/DRDY is 1, the
output register data is old, and the conversion is still in
process; if it is 0, the output register data is the result of the
new conversion.
Note that the output register is returned from the ADS1110
before the configuration register. The state of the
ST/DRDY bit applies to the data just read from the output
register, and not to the data from the next read operation.
Bits 6−5: Reserved
Bits 6 and 5 must be set to zero.
Bit 4: SC
SC controls whether the ADS1110 is in continuous
conversion or single conversion mode. When SC is 1, the
ADS1110 is in single conversion mode; when SC is 0, the
ADS1110 is in continuous conversion mode. The default
setting is 0.
Bits 3−2: DR
Bits 3 and 2 control the ADS1110’s data rate, as shown in
Table 6.
DR1
DR0
DATA RATE
0
0
240SPS
0
1
60SPS
1
1(1)
0
1(1)
30SPS
15SPS(1)
(1) Default setting.
Table 6. DR Bits
Bits 1−0: PGA
Bits 1 and 0 control the ADS1110’s gain setting, as shown
in Table 7.
PGA1
0(1)
PGA0
0(1)
GAIN
1(1)
0
1
2
1
0
4
1
1
8
(1) Default setting.
Table 7. PGA Bits
11
ADS1110
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READING FROM THE ADS1110
To read the output register and the configuration register
from the ADS1110, address the ADS1110 for reading, then
read three bytes. The first two bytes will be the output
register’s contents, and the third will be the configuration
register’s contents.
It is not required to read the configuration register byte. It
is permissible to read fewer than three bytes during a read
operation.
Reading more than three bytes from the ADS1110 has no
effect. All bytes following the third will be FFH.
It is possible to ignore the ST/DRDY bit and read data from
the ADS1110’s output register at any time, without regard
to whether a new conversion is complete. If the output
Figure 2. Timing Diagram for Reading From the ADS1110
Figure 3. Timing Diagram for Writing To the ADS1110
12
register is read more than once during a conversion cycle,
it will return the same data each time. New data will be
returned only when the output register has been updated.
A timing diagram of a typical ADS1110 read operation is
shown in Figure 2.
WRITING TO THE ADS1110
To write to the configuration register, address the ADS1110
for writing, and send one byte. The byte will be written to
the configuration register. Note that the output register
cannot be written to.
Writing more than one byte to the ADS1110 has no effect.
The ADS1110 will ignore any bytes sent to it after the first
one, and it will only acknowledge the first byte.
A timing diagram of a typical ADS1110 write operation is
shown in Figure 3.
ADS1110
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APPLICATIONS INFORMATION
The sections that follow give example circuits and tips for
using the ADS1110 in various situations.
BASIC CONNECTIONS
For many applications, connecting the ADS1110 is
extremely simple. A basic connection diagram for the
ADS1110 is shown in Figure 4.
Pull-up resistors are necessary on both the SDA and SCL
lines because I2C bus drivers are open-drain. The size of
these resistors depends on the bus operating speed and
capacitance of the bus lines. Higher-value resistors
consume less power, but increase the transition times on
the bus, limiting the bus speed. Lower-value resistors
allow higher speed at the expense of higher power
consumption. Long bus lines have higher capacitance and
require smaller pull-up resistors to compensate. The
resistors should not be too small; if they are, the bus drivers
may not be able to pull the bus lines low.
CONNECTING MULTIPLE DEVICES
Connecting multiple ADS1110s to a single bus is trivial.
The ADS1110 is available in eight different versions, each
of which has a different I2C address. An example showing
three ADS1110s connected on a single bus is shown in
Figure 5. Up to eight ADS1110s (provided their addresses
are different) can be connected to a single bus.
Figure 4. Typical Connections of the ADS1110
The fully differential voltage input of the ADS1110 is ideal
for connection to differential sources with moderately low
source impedance, such as bridge sensors and
thermistors. Although the ADS1110 can read bipolar
differential signals, it cannot accept negative voltages on
either input. It may be helpful to think of the ADS1110
positive voltage input as non−inverting, and of the negative
input as inverting.
When the ADS1110 is converting, it draws current in short
spikes. The 0.1µF bypass capacitor supplies the
momentary bursts of extra current needed from the supply.
The ADS1110 interfaces directly to standard mode, fast
mode, and high−speed mode I2C controllers. Any
microcontroller’s I2C peripheral, including master-only
and non-multiple-master I2C peripherals, will work with the
ADS1110.
The
ADS1110
does
not
perform
clock-stretching (i.e., it never pulls the clock line low), so
it is not necessary to provide for this unless
clock-stretching devices are on the same I2C bus.
Figure 5. Connecting Multiple ADS1110s
Note that only one set of pull-up resistors is needed per
bus. The pull-up resistor values may need to be lowered
slightly to compensate for the additional bus capacitance
presented by multiple devices and increased line length.
13
ADS1110
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SBAS276A − MARCH 2003 − REVISED NOVEMBER 2003
Figure 6 shows a circuit with several different devices
connected to a single I2C bus. A Texas Instruments
TMP100 temperature sensor and a Texas Instruments
DAC8574 4-channel 16-bit digital-to-analog converter
share the bus with two ADS1110s.
Figure 7. Using GPIO with a Single ADS1110
Bit-banging I2C with GPIO pins can be done by setting the
GPIO line to zero and toggling it between input and output
modes to apply the proper bus states. To drive the line low,
the pin is set to output a zero; to let the line go high, the pin
is set to input. When the pin is set to input, the state of the
pin can be read; if another device is pulling the line low, this
will read as a zero in the port’s input register.
Note that no pull-up resistor is shown on the SCL line. In
this simple case, the resistor is not needed; the
microcontroller can simply leave the line on output, and set
it to one or zero as appropriate. It can do this because the
ADS1110 never drives its clock line low. This technique
can also be used with multiple devices, and has the
advantage of lower current consumption due to the
absence of a resistive pull-up.
Figure 6. Connecting Multiple Device Types
The TMP100 and DAC8574 devices detect their I2C bus
addresses based on the states of pins. In the example, the
TMP100 has the address 1001011, and the DAC8574 has
the address 1001100. Consult the DAC8574 and TMP100
data sheets, located at www.ti.com, for details.
USING GPIO PORTS FOR I2C
Most microcontrollers have programmable input/output
pins that can be set in software to act as inputs or outputs.
If an I2C controller is not available, the ADS1110 can be
connected to GPIO pins and the I2C bus protocol
simulated, or “bit-banged”, in software. An example of this
for a single ADS1110 is shown in Figure 7.
14
If there are any devices on the bus that may drive their
clock lines low, the above method should not be used; the
SCL line should be high-Z or zero and a pull-up resistor
provided as usual. Note also that this cannot be done on
the SDA line in any case, because the ADS1110 does drive
the SDA line low from time to time, as all I2C devices do.
Some microcontrollers have selectable strong pull-up
circuits built in to their GPIO ports. In some cases, these
can be switched on and used in place of an external pull-up
resistor. Weak pull-ups are also provided on some
microcontrollers, but usually these are too weak for I2C
communication. If there is any doubt about the matter, test
the circuit before committing it to production.
ADS1110
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SBAS276A − MARCH 2003 − REVISED NOVEMBER 2003
SINGLE-ENDED INPUTS
Although the ADS1110 has a fully differential input, it can
easily measure single-ended signals. A simple
single-ended connection scheme is shown in Figure 8.
The ADS1110 is configured for single-ended
measurement by grounding either of its input pins, usually
VIN−, and applying the input signal to VIN+. The
single-ended signal can range from 0V to 2.048V. The
ADS1110 loses no linearity anywhere in its input range.
Negative voltages cannot be applied to this circuit
because the ADS1110 inputs can only accept positive
voltages.
Figure 9. Low-Side Current Measurement
It is suggested that the ADS1110 be operated at a gain of
8. The gain of the OPA335 can then be set lower. For a gain
of 8, the op amp should be set up to give a maximum output
voltage of no greater than 0.256V. If the shunt resistor is
sized to provide a maximum voltage drop of 50mV at
full-scale current, the full-scale input to the ADS1110 is
0.2V.
Figure 8. Measuring Single-Ended Inputs
The ADS1110 input range is bipolar differential with
respect to the reference, i.e. 2.048V. The single-ended
circuit shown in Figure 8 covers only half the ADS1110
input scale because it does not produce differentially
negative inputs; therefore, one bit of resolution is lost.
LOW-SIDE CURRENT MONITOR
Figure 9 shows a circuit for a low-side shunt-type current
monitor. The circuit reads the voltage across a shunt
resistor, which is sized as small as possible while still
giving a readable output voltage. This voltage is amplified
by an OPA335 low-drift op amp and the result is read by the
ADS1110.
ADVICE
The ADS1110 is fabricated in a small-geometry
low-voltage process. The analog inputs feature protection
diodes to the supply rails. However, the current-handling
ability of these diodes is limited, and the ADS1110 can be
permanently damaged by analog input voltages that
remain more than approximately 300mV beyond the rails
for extended periods. One way to protect against
overvoltage is to place current-limiting resistors on the
input lines. The ADS1110 analog inputs can withstand
momentary currents of as large as 10mA.
The previous paragraph does not apply to the I2C ports,
which can both be driven to 6V regardless of the supply.
If the ADS1110 is driven by an op amp with high-voltage
supplies, such as ±12V, protection should be provided,
even if the op amp is configured so that it does not output
out-of-range voltages. Many op amps seek to one of the
supply rails immediately when power is applied, usually
before the input has stabilized; this momentary spike can
damage the ADS1110. Sometimes this damage is
incremental and results in slow, long-term failure—which
can be disastrous for permanently installed,
low-maintenance systems.
If an op amp or other front-end circuitry is used with the
ADS1110, its performance characteristics must be taken
into account. A chain is only as strong as its weakest link.
15
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