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ADS1110
SBAS276 - MARCH 2003
16-Bit ANALOG-TO-DIGITAL CONVERTER with Onboard Reference
FEATURES
D COMPLETE DATA ACQUISITION SYSTEM IN
A TINY SOT23-6 PACKAGE
DESCRIPTION
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. 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.
D ONBOARD REFERENCE:
Accuracy: 2.048V 0.05% Drift: 5ppm/C 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 ADDRESSES
D D D D D D D
D I2CINTERFACE--EIGHT AVAILABLE D POWER SUPPLY: 2.7V to 5.5V D LOW CURRENT CONSUMPTION: 240A
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.
PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters.
Copyright 2003, Texas Instruments Incorporated
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ABSOLUTE MAXIMUM RATINGS(1)
VDD to GND Input Current Input Current Voltage to GND, VIN+, VIN- Voltage to GND, SDA, SCL Maximum Junction Temperature Operating Temperature Range Storage Temperature Range -0.3V to +6V 100mA, Momentary 10mA, Continuous -0.3V to VDD + 0.3V -0.5V to 6V +150C -40C to +105C -60C to +150C
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) +300C (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 1001 000 1001 001 1001 010 1001 011 1001 100 1001 101 1001 110 1001 111 PACKAGE-LEAD PACKAGE DESIGNATOR(1) DBV DBV DBV DBV DBV DBV DBV DBV SPECIFIED TEMPERATURE RANGE -40C to +85C 40C -40C to +85C 40C -40C to +85C 40C -40C to +85C 40C -40C to +85C 40C -40C to +85C 40C -40C to +85C 40C -40C to +85C 40C PACKAGE MARKING ED0 ED1 ED2 ED3 ED4 ED5 ED6 ED7 ORDERING NUMBER ADS1110A0IDBVT ADS1110 ADS1110 ADS1110 ADS1110 ADS1110 ADS1110 ADS1110 ADS1110 SOT23-6 SOT23 6 SOT23-6 SOT23 6 SOT23-6 SOT23 6 SOT23-6 SOT23 6 SOT23-6 SOT23 6 SOT23-6 SOT23 6 SOT23-6 SOT23 6 SOT23-6 SOT23 6 ADS1110A0IDBVR ADS1110A1IDBVT ADS1110A1IDBVR ADS1110A2IDBVT ADS1110A2IDBVR ADS1110A3IDBVT ADS1110A3IDBVR ADS1110A4IDBVT ADS1110A4IDBVR ADS1110A5IDBVT ADS1110A5IDBVR ADS1110A6IDBVT ADS1110A6IDBVR ADS1110A7IDBVT ADS1110A7IDBVR TRANSPORT MEDIA, QUANTITY Tape and Reel, 250 Tape and Reel, 3000 Tape and Reel, 250 Tape and Reel, 3000 Tape and Reel, 250 Tape and Reel, 3000 Tape and Reel, 250 Tape and Reel, 3000 Tape and Reel, 250 Tape and Reel, 3000 Tape and Reel, 250 Tape and Reel, 3000 Tape and Reel, 250 Tape and Reel, 3000 Tape and Reel, 250 Tape and Reel, 3000
(1) For the most current specification and package information, refer to our web site at www.ti.com.
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ELECTRICAL CHARACTERISTICS
All specifications at -40C to +85C, VDD = 5V, and all PGAs, unless otherwise noted.
ADS1110 PARAMETER ANALOG INPUT Full-Scale Input Voltage Analog Input Voltage Differential Input Impedance Common-Mode Input Impedance PGA = 1 PGA = 2 PGA = 4 PGA = 8 DR = 00 DR = 01 DR = 10 DR = 11 DR = 00 DR = 01 DR = 10 DR = 11 DR = 11, PGA = 1, End Point Fit(1) PGA = 1 PGA = 2 PGA = 4 PGA = 8 PGA = 1 PGA = 2 PGA = 4 PGA = 8 PGA = 1 PGA = 2 PGA = 4 PGA = 8 Match Between Any Two PGA Gains 12 14 15 16 180 45 22 11 240 60 30 15 0.004 1.2 0.7 0.5 0.4 1.2 0.6 0.3 0.3 800 400 200 150 0.05 0.02 5 80 At DC and PGA = 8 At DC and PGA = 1 95 105 100 0.40 0.10 40 (VIN+) - (VIN-) VIN+ to GND or VIN- to GND CONDITIONS MIN TYP MAX UNIT V VDD + 0.2 2.8/PGA 3.5 3.5 1.8 0.9 12 14 15 16 308 77 39 20 0.010 8 4 2.5 1.5 V M M M M M Bits Bits Bits Bits SPS SPS SPS SPS
% of FSR(2)
2.048/PGA
GND - 0.2
SYSTEM PERFORMANCE Resolution and No Missing Codes
Data Rate
Output Noise Integral Nonlinearity Offset Error
See Typical Characteristic Curves mV mV mV mV V/C V/C V/C V/C V/V V/V V/V V/V % % ppm/C ppm/V dB dB
Offset Drift
Offset vs VDD
Gain Error(3) PGA Gain Error Match(3) Gain Error Drift(3) Gain vs VDD Common Mode Common-Mode Rejection DIGITAL INPUT/OUTPUT Logic Level VIH VIL VOL Input Leakage IH IL POWER-SUPPLY REQUIREMENTS Power-Supply Voltage Su ly Supply Current Power Dissi ation Dissipation VDD Power Down Active Mode VDD = 5.0V VDD = 3.0V 2.7 0.7 * VDD GND - 0.5 GND
IOL = 3mA VIH = 5.5V VIL = GND
6 0.3 * VDD 0.4 10
V V V A A V A A mW mW
-10 5.5 0.05 240 1.2 0.675 2 350 1.75
(1) 99% of full-scale. (2) FSR = full-scale range = 2 x 2.048V/PGA = 4.096V/PGA. (3) Includes all errors from onboard PGA and reference.
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TYPICAL CHARACTERISTICS
At TA = 25C and VDD = 5V, unless otherwise noted.
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TYPICAL CHARACTERISTICS (continued)
At TA = 25C and VDD = 5V, unless otherwise noted.
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TYPICAL CHARACTERISTICS (continued)
At TA = 25C 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. 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. 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.
OUTPUT CODE CALCULATION
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.
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.
DATA RATE 15SPS 30SPS 60SPS 240SPS
NUMBER OF BITS 16 15 14 12
MINIMUM CODE -32,768 -16,384 -8192 -2048
MAXIMUM CODE 32,767 16,383 8191 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 x 2n-1.
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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
(V IN)) * (V IN*) 2.048V
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:
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.
2.8M/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.
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.
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.
ALIASING
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.
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
DATA RATE 15SPS 30SPS 60SPS 240SPS
DIFFERENTIAL INPUT SIGNAL -2.048V(1) 8000H C000H E000H F800H -1LSB FFFFH FFFFH FFFFH FFFFH ZERO 0000H 0000H 0000H 0000H +1LSB 0001H 0001H 0001H 0001H +2.048V 7FFFH 3FFFH 1FFFH 07FFH
(1) Differential input only; do not drive the ADS1110's inputs below -200mV.
Table 2. Output Codes for Different Input Signals
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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.
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.
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 2-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.
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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. A timing diagram for an ADS1110 I2C transaction is shown in Figure 1. The parameters for this diagram are given in Table 3.
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.
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. 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.
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. 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 PARAMETER SCLK operating frequency Bus free time between START and STOP condition Hold time after repeated START condition. After this period, the first clock is generated. Repeated START condition setup time 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 MIN MAX 0.4 600 600 600 600 0 100 1300 600 300 300
HIGH-SPEED MODE MIN MAX 3.4 160 160 160 160 0 10 160 60 160 160 UNITS MHz ns ns ns ns ns ns ns ns ns ns
t(SCLK) t(BUF) t(HDSTA) t(SUSTA) t(SUSTO) t(HDDAT) t(SUDAT) t(LOW) t(HIGH) tF tR
Table 3. Timing Diagram Definitions
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I2C DATA RATES
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. 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.
For more information on High-speed mode, consult the I2C specification.
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.
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 NAME
15 D15
14 D14
13 D13
12 D12
11 D11
10 D10
9 D9
8 D8
7 D7
6 D6
5 D5
4 D4
3 D3
2 D2
1 D1
0 D0
Table 4. Output Register
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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 NAME DEFAULT 7 ST/DRDY 1 6 0 0 5 0 0 4 SC 0 3 DR1 1 2 DR0 1 1 PGA1 0 0 PGA0 0
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.
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.
Bits 3-2: DR
Bits 3 and 2 control the ADS1110's data rate, as shown in Table 6.
DR1 0 0 1 1(1) DR0 0 1 0 1(1) DATA RATE 240SPS 60SPS 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) 0 1 1
PGA0 0(1) 1 0 1
GAIN 1(1) 2 4 8
(1) Default setting.
Table 7. PGA Bits
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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
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.
Figure 2. Timing Diagram for Reading From the ADS1110
Figure 3. Timing Diagram for Writing To the 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 0.1F 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.
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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.
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.
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.
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ADS1110
www.ti.com SBAS276 - MARCH 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.
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.
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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.
ADS1110
www.ti.com SBAS276 - MARCH 2003
DBV (R-PDSO-G6)
PLASTIC SMALL-OUTLINE
0,95 6 4
6X
0,50 0,25
0,20 M
1,70 1,50
3,00 2,60
0,15 NOM
1 3,00 2,80
3
Gage Plane
0,25 0-8 0,55 0,35
Seating Plane 1,45 0,95 0,05 MIN 0,10
4073253-5/G 01/02
NOTES: A. B. C. D.
All linear dimensions are in millimeters. This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion. Leads 1, 2, 3 may be wider than leads 4, 5, 6 for package orientation.
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