TI ADS1218 8-channel, 24-bit analog-to-digital converter with flash memory Datasheet

 ADS1218
SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
8-Channel, 24-Bit
ANALOG-TO-DIGITAL CONVERTER with FLASH Memory
FEATURES
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24 BITS NO MISSING CODES
0.0015% INL
22 BITS EFFECTIVE RESOLUTION (PGA = 1),
19 BITS (PGA = 128)
4K BYTES OF FLASH MEMORY
PROGRAMMABLE FROM 2.7V TO 5.25V
PGA FROM 1 TO 128
SINGLE CYCLE SETTLING MODE
PROGRAMMABLE DATA OUTPUT RATES UP
TO 1kHz
PRECISION ON-CHIP 1.25V/2.5V REFERENCE:
ACCURACY: 0.2%
DRIFT: 5ppm/°C
EXTERNAL DIFFERENTIAL REFERENCE OF
0.1V TO 2.5V
ON-CHIP CALIBRATION
PIN-COMPATIBLE WITH ADS1216
SPI™ COMPATIBLE
2.7V TO 5.25V
< 1mW POWER CONSUMPTION
The eight input channels are multiplexed. Internal
buffering can be selected to provide a very high input
impedance for direct connection to transducers or
low-level voltage signals. Burnout current sources are
provided that allow for the detection of an open or
shorted sensor. An 8-bit Digital-to-Analog (D/A)
converter provides an offset correction with a range
of 50% of the FSR (Full-Scale Range).
The PGA (Programmable Gain Amplifier) provides
selectable gains of 1 to 128 with an effective
resolution of 19 bits at a gain of 128. The A/D
conversion is accomplished with a second-order
delta-sigma modulator and programmable sinc filter.
The reference input is differential and can be used for
ratiometric conversion. The on-board current DACs
(Digital-to-Analog Converters) operate independently
with the maximum current set by an external resistor.
The serial interface is SPI-compatible. Eight bits of
digital I/O are also provided that can be used for input
or output. The ADS1218 is designed for
high-resolution measurement applications in smart
transmitters, industrial process control, weight scales,
chromatography, and portable instrumentation.
AGND
AVDD
RDAC
IDAC2
8−Bit
IDAC
IDAC1
8−Bit
IDAC
APPLICATIONS
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INDUSTRIAL PROCESS CONTROL
LIQUID/GAS CHROMATOGRAPHY
BLOOD ANALYSIS
SMART TRANSMITTERS
PORTABLE INSTRUMENTATION
WEIGHT SCALES
PRESSURE TRANSDUCERS
VREFOUT
VRCAP
VREF+
VREF−
XIN
XOUT
Clock Generator
1.25V or
2.5V
Reference
Offset
DAC
AIN0
AIN1
Registers
AIN2
Program−
AIN3
MUX
BUF
+
PGA
AIN4
2nd−Order
Modulator
mable
Controller
RAM
Digital
F ilter
AIN5
4K Bytes
FLASH
AIN7
AINCOM
POL
DESCRIPTION
The ADS1218 is a precision, wide dynamic range,
delta-sigma, Analog-to-Digital (A/D) converter with
24-bit resolution and Flash memory operating from
2.7V to 5.25V supplies. The delta-sigma, A/D
converter provides up to 24 bits of no missing code
performance and effective resolution of 22 bits.
WREN
AIN6
Serial Interface
Digital I/O
Interface
SCLK
DIN
DOUT
CS
DVDD
DGND
BUFEN
D0
... D7
PDWN
DSYNC
RESET
DRDY
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.
SPI is a trademark of Motorola.
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 the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2001–2005, Texas Instruments Incorporated
ADS1218
www.ti.com
SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
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.
ORDERING INFORMATION
For the most current package and ordering information, see the Package Option Addendum at the end of this
document, or see the TI web site at www.ti.com.
ABSOLUTE MAXIMUM RATINGS (1)
AVDD to AGND
DVDD to DGND
Input Current
Input Current
AIN
–0.3V to +6V
–0.3V to +6V
100mA, Momentary
10mA, Continuous
GND – 0.5V to AVDD + 0.5V
AVDD to DVDD
AGND to DGND
–6V to +6V
–0.3V to +0.3V
Digital Input Voltage to GND
–0.3V to DVDD + 0.3V
Digital Output Voltage to GND
–0.3V to DVDD + 0.3V
Maximum Junction Temperature
Operating Temperature Range
Storage Temperature Range
Lead Temperature (soldering, 10s)
(1)
2
+150°C
–40°C to +85°C
–60°C to +100°C
+300°C
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.
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
ELECTRICAL CHARACTERISTICS: AVDD = 5V
All specifications TMIN to TMAX, AVDD = +5V, DVDD = +2.7V to 5.25V, fMOD = 19.2kHz, fOSC = 2.4576MHz, PGA = 1, Buffer On,
RDAC = 150kΩ, VREF ≡ (REF IN+) – (REF IN–) = +2.5V, and fDATA = 10Hz, unless otherwise specified.
ADS1218
PARAMETER
CONDITIONS
MIN
TYP
Buffer Off
AGND – 0.1
Buffer On
AGND + 0.05
MAX
UNIT
AVDD + 0.1
V
AVDD – 1.5
V
ANALOG INPUT (AIN0 – AIN7, AINCOM)
Analog Input Range
Full-Scale Input Voltage Range
(In+) – (In–), See Block Diagram
±VREF/PGA
V
Differential Input Impedance
Buffer Off
5/PGA
MΩ
Input Current
Buffer On
0.5
nA
Fast Settling Filter
–3dB
0.469 × fDATA
Hz
Sinc2 Filter
–3dB
0.318 × fDATA
Hz
Sinc3 Filter
–3dB
0.262 × fDATA
Bandwidth
Programmable Gain Amplifier
User-Selectable Gain Ranges
1
Input Capacitance
Input Leakage Current
Modulator Off, T = +25°C
Burnout Current Sources
Hz
128
9
pF
5
pA
2
µA
OFFSET DAC
Offset DAC Range
±VREF/(2 × PGA)
Offset DAC Monotonicity
V
8
Offset DAC Gain Error
Offset DAC Gain Error Drift
Bits
±10
%
1
ppm/°C
SYSTEM PERFORMANCE
Resolution
24
No Missing Codes
Integral Nonlinearity
Offset Error (1)
24
Bits
End Point Fit
±0.0015
% of FS
Before Calibration
Offset Drift (1)
Gain Error
After Calibration
Gain Error Drift (1)
Common-Mode Rejection
Normal-Mode Rejection
at DC
7.5
ppm of FS
0.02
ppm of FS/°C
0.005
%
0.5
ppm/°C
100
dB
fCM = 60Hz, fDATA = 10Hz
130
dB
fCM = 50Hz, fDATA = 50Hz
120
dB
fCM = 60Hz, fDATA = 60Hz
120
dB
fSIG = 50Hz, fDATA = 50Hz
100
dB
fSIG = 60Hz, fDATA = 60Hz
100
dB
Output Noise
Power-Supply Rejection
Bits
sinc3
See Typical Characteristics
at DC, dB = –20 log(∆VOUT/∆VDD) (2)
80
95
dB
VOLTAGE REFERENCE INPUT
Reference Input Range
VREF
REF IN+, REF IN–
0
VREF ≡ (REF IN+) – (REF IN–)
0.1
AVDD
2.5
2.6
V
V
Common-Mode Rejection
at DC
120
dB
Common-Mode Rejection
fVREFCM = 60Hz, fDATA = 60Hz
120
dB
VREF = 2.5V
1.3
µA
Bias Current (3)
(1)
(2)
(3)
Calibration can minimize these errors.
∆VOUT is change in digital result.
12pF switched capacitor at fSAMP clock frequency.
3
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
ELECTRICAL CHARACTERISTICS: AVDD = 5V (continued)
All specifications TMIN to TMAX, AVDD = +5V, DVDD = +2.7V to 5.25V, fMOD = 19.2kHz, fOSC = 2.4576MHz, PGA = 1, Buffer On,
RDAC = 150kΩ, VREF ≡ (REF IN+) – (REF IN–) = +2.5V, and fDATA = 10Hz, unless otherwise specified.
ADS1218
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
REF HI = 1 at +25°C
2.495
2.50
2.505
V
ON-CHIP VOLTAGE REFERENCE
Output Voltage
REF HI = 0
Short-Circuit Current Source
Short-Circuit Current Sink
Short-Circuit Duration
1.25
V
8
mA
50
µA
Sink or Source
Indefinite
5
ppm/°C
BW = 0.1Hz to 100Hz
10
µVPP
Sourcing 100µA
3
Ω
50
µs
RDAC = 150kΩ, Range = 1
0.5
mA
RDAC = 150kΩ, Range = 2
1
mA
RDAC = 150kΩ, Range = 3
2
mA
RDAC = 15kΩ, Range = 3
20
mA
Maximum Short-Circuit Current Duration
RDAC = 10kΩ
Indefinite
Monotonicity
RDAC = 150kΩ
Drift
Noise
Output Impedance
Startup Time
IDAC
Full-Scale Output Current
RDAC = 0Ω
Compliance Voltage
10
8
Bits
0
Output Impedance
Minutes
AVDD – 1
V
See Typical Characteristics
PSRR
VOUT = AVDD/2
400
Absolute Error
Individual IDAC
5
ppm/V
%
Absolute Drift
Individual IDAC
75
ppm/°C
Mismatch Error
Between IDACs, Same Range and Code
0.25
%
Mismatch Drift
Between IDACs, Same Range and Code
15
ppm/°C
POWER-SUPPLY REQUIREMENTS
Power-Supply Voltage
Analog Current (IADC + IVREF + IDAC)
ADC Current (IADC)
AVDD
4.75
1
Digital Current
Power Dissipation
V
nA
PGA = 1, Buffer Off
175
275
µA
PGA = 128, Buffer Off
500
750
µA
PGA = 1, Buffer On
250
350
µA
PGA = 128, Buffer On
900
1375
µA
250
375
µA
Excludes Load Current
480
675
µA
Normal Mode, DVDD = 5V
180
275
µA
SLEEP Mode, DVDD = 5V
150
µA
Read Data Continuous Mode, DVDD = 5V
230
µA
PDWN = Low
1
nA
PGA = 1, Buffer Off, REFEN = 0,
IDACS Off, DVDD = 5V
1.8
VREF Current (IVREF)
IDAC Current (IDAC)
5.25
PDWN = 0, or SLEEP
2.8
mW
TEMPERATURE RANGE
Operating
–40
+85
°C
Storage
–60
+100
°C
4
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
ELECTRICAL CHARACTERISTICS: AVDD = 3V
All specifications TMIN to TMAX, AVDD = +3V, DVDD = +2.7V to 5.25V, fMOD = 19.2kHz, fOSC = 2.4576MHz, PGA = 1, Buffer On,
RDAC = 75kΩ, VREF ≡ (REF IN+) – (REF IN–) = +1.25V, and fDATA = 10Hz, unless otherwise specified.
ADS1218
PARAMETER
CONDITIONS
MIN
TYP
Buffer Off
AGND – 0.1
Buffer On
AGND + 0.05
MAX
UNIT
AVDD + 0.1
V
AVDD – 1.5
V
ANALOG INPUT (AIN0 – AIN7, AINCOM)
Analog Input Range
Full-Scale Input Voltage Range
(In+) – (In–), See Block Diagram
±VREF/PGA
V
Input Impedance
Buffer Off
5/PGA
MΩ
Input Current
Buffer On
0.5
nA
Fast Settling Filter
–3dB
0.469 × fDATA
Hz
Sinc2 Filter
–3dB
0.318 × fDATA
Hz
Sinc3 Filter
–3dB
0.262 × fDATA
Bandwidth
Programmable Gain Amplifier
User-Selectable Gain Ranges
1
Input Capacitance
Input Leakage Current
Modulator Off, T = +25°C
Burnout Current Sources
Hz
128
9
pF
5
pA
2
µA
OFFSET DAC
Offset DAC Range
±VREF/(2 × PGA)
Offset DAC Monotonicity
V
8
Offset DAC Gain Error
Offset DAC Gain Error Drift
Bits
±10
%
2
ppm/°C
SYSTEM PERFORMANCE
Resolution
24
Bits
No Missing Codes
Integral Nonlinearity
Offset Error (1)
End Point Fit
Before Calibration
Offset Drift (1)
Gain Error
After Calibration
Gain Error Drift (1)
Common-Mode Rejection
Normal-Mode Rejection
at DC
Bits
±0.0015
% of FS
15
ppm of FS
0.04
ppm of FS/°C
0.010
%
1.0
ppm/°C
100
dB
fCM = 60Hz, fDATA = 10Hz
130
dB
fCM = 50Hz, fDATA = 50Hz
120
dB
fCM = 60Hz, fDATA = 60Hz
120
dB
fSIG = 50Hz, fDATA = 50Hz
100
dB
100
dB
fSIG = 60Hz, fDATA = 60Hz
Output Noise
Power-Supply Rejection
24
See Typical Characteristics
at DC, dB = –20 log(∆VOUT/∆VDD) (2)
75
90
dB
VOLTAGE REFERENCE INPUT
Reference Input Range
VREF
REF IN+, REF IN–
0
AVDD
VREF ≡ (REF IN+) – (REF IN–)
0.1
1.25
Common-Mode Rejection
at DC
Common-Mode Rejection
Bias Current (3)
(1)
(2)
(3)
V
V
120
dB
fVREFCM = 60Hz, fDATA = 60Hz
120
dB
VREF = 1.25V
0.65
µA
Calibration can minimize these errors.
∆VOUT is change in digital result.
12pF switched capacitor at fSAMP clock frequency.
5
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
ELECTRICAL CHARACTERISTICS: AVDD = 3V (continued)
All specifications TMIN to TMAX, AVDD = +3V, DVDD = +2.7V to 5.25V, fMOD = 19.2kHz, fOSC = 2.4576MHz, PGA = 1, Buffer On,
RDAC = 75kΩ, VREF ≡ (REF IN+) – (REF IN–) = +1.25V, and fDATA = 10Hz, unless otherwise specified.
ADS1218
PARAMETER
CONDITIONS
MIN
TYP
MAX
REF HI = 0 at +25°C
1.245
1.25
1.255
UNIT
ON-CHIP VOLTAGE REFERENCE
Output Voltage
V
Short-Circuit Current Source
3
mA
Short-Circuit Current Sink
50
µA
Short-Circuit Duration
Sink or Source
Indefinite
5
ppm/°C
BW = 0.1Hz to 100Hz
10
µVPP
Sourcing 100µA
3
Ω
50
µs
RDAC = 75kΩ, Range = 1
0.5
mA
RDAC = 75kΩ, Range = 2
1
mA
RDAC = 75kΩ, Range = 3
2
mA
RDAC = 15kΩ, Range = 3
20
mA
Maximum Short-Circuit Current Duration
RDAC = 10kΩ
Indefinite
Monotonicity
RDAC = 75kΩ
Drift
Noise
Output Impedance
Startup Time
IDAC
Full-Scale Output Current
RDAC = 0Ω
Compliance Voltage
10
8
Bits
0
Output Impedance
Minutes
AVDD – 1
V
See Typical Characteristics
PSRR
VOUT = AVDD/2
600
Absolute Error
Individual IDAC
5
ppm/V
%
Absolute Drift
Individual IDAC
75
ppm/°C
Mismatch Error
Between IDACs, Same Range and Code
0.25
%
Mismatch Drift
Between IDACs, Same Range and Code
15
ppm/°C
POWER-SUPPLY REQUIREMENTS
Power-Supply Voltage
Analog Current (IADC + IVREF + IDAC)
ADC Current (IADC)
AVDD
2.7
1
Digital Current
Power Dissipation
V
nA
PGA = 1, Buffer Off
160
250
µA
PGA = 128, Buffer Off
450
700
µA
PGA = 1, Buffer On
230
325
µA
PGA = 128, Buffer On
850
1325
µA
250
375
µA
Excludes Load Current
480
675
µA
Normal Mode, DVDD = 3V
90
200
µA
SLEEP Mode, DVDD = 3V
75
µA
Read Data Continuous Mode, DVDD = 3V
113
µA
PDWN = 0
1
nA
PGA = 1, Buffer Off, REFEN = 0,
IDACS Off, DVDD = 3V
0.8
VREF Current (IVREF)
IDAC Current (IDAC)
3.3
PDWN = 0, or SLEEP
1.4
mW
TEMPERATURE RANGE
Operating
–40
+85
°C
Storage
–60
+100
°C
6
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
DIGITAL CHARACTERISTICS: TMIN to TMAX, DVDD = 2.7V to 5.25V
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
Digital Input/Output
Logic Family
CMOS
Logic Level
VIH
0.8 × DVDD
DVDD
V
VIL
DGND
0.2 × DVDD
V
VOH
IOH = 1mA
DVDD – 0.4
VOL
IOL = 1mA
DGND
V
DGND + 0.4
V
10
µA
Input Leakage
IIH
VI = DVDD
IIL
VI = 0
–10
1
5
MHz
1/fOSC
200
1000
ns
Master Clock Rate: fOSC
(1)
Master Clock Period: tOSC (1)
(1)
µA
For the Write RAM to Flash operation (WR2F), the SPEED bit in the SETUP register must be set appropriately and the device operating
frequency must be: 2.3MHz < fOSC < 4.13MHz.
FLASH CHARACTERISTICS: TMIN to TMAX, DVDD = 2.7V to 5.25V, unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
Operating Current
Page Write
Page Read
DVDD = 5V, During WR2F Command
17
mA
DVDD = 3V, During WR2F Command
9
mA
DVDD = 5V, During RF2R Command
8
mA
DVDD = 3V, During RF2R Command
Endurance
Data Retention
DVDD for Erase/Write
at +25°C
2
mA
100,000
Write Cycles
100
2.7
Years
5.25
V
7
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
PIN CONFIGURATION
XIN
31
XOUT
32
PDWN
DRDY
33
POL
CS
34
DSYNC
SCLK
35
TQFP
DGND
DIN
36
DVDD
DOUT
Top View
30
29
28
27
26
25
D0 37
24 RESET
D1 38
23 BUFEN
D2 39
22 DGND
D3 40
21 DGND
D4 41
20 DGND
19 DGND
D5 42
ADS1218
D6 43
18 WREN
D7 44
17 RDAC
5
6
7
8
9
10
11
12
AGND
4
AINCOM
3
AIN7
2
AIN4
1
AIN6
13 AVDD
AIN5
VREF− 48
AIN3
14 VRCAP
AIN2
VREF+ 47
AIN1
15 IDAC1
AIN0
VREFOUT 46
AGND
16 IDAC2
AVDD
AGND 45
PIN DESCRIPTIONS
PIN
NUMBER
NAME
DESCRIPTION
1
AVDD
2
3
4
8
PIN
NUMBER
NAME
DESCRIPTION
Analog Power Supply
24
RESET
Active Low, resets the entire chip.
AGND
Analog Ground
25
XIN
AIN0
Analog Input 0
26
XOUT
AIN1
Analog Input 1
27
PDWN
Clock Input
Clock Output, used with crystal or resonator.
Active Low. Power Down. The power-down
function shuts down the analog and digital
circuits.
5
AIN2
Analog Input 2
6
AIN3
Analog Input 3
28
POL
7
AIN4
Analog Input 4
29
DSYNC
Active Low, Synchronization Control
8
AIN5
Analog Input 5
30
DGND
Digital Ground
9
AIN6
Analog Input 6
31
DVDD
Digital Power Supply
10
AIN7
Analog Input 7
32
DRDY
Active Low, Data Ready
11
AINCOM
Analog Input Common
33
CS
Active Low, Chip Select
12
AGND
Analog Ground
34
SCLK
13
AVDD
Analog Power Supply
35
DIN
14
VRCAP
VREF Bypass CAP
36
DOUT
Serial Data Output
15
IDAC1
Current DAC1 Output
37–44
D0-D7
Digital I/O 0–7
16
IDAC2
Current DAC2 Output
45
AGND
Analog Ground
17
RDAC
Current DAC Resistor
46
VREFOUT
Serial Clock Polarity
Serial Clock, Schmitt Trigger
Serial Data Input, Schmitt Trigger
Voltage Reference Output
18
WREN
Active High, Flash Write Enable
47
VREF+
Positive Differential Reference Input
19–22
DGND
Digital Ground
48
VREF–
Negative Differential Reference Input
23
BUFEN
Buffer Enable
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
TIMING SPECIFICATIONS
CS
t3
t1
t2
t10
SCLK
(POL = 0)
SCLK
(POL = 1)
t4
DIN
MSB
t2
t6
t5
t 11
LSB
(Command or Command and Data)
DOUT
t7
t8
t9
MSB(1)
LSB(1)
NOTE: (1) Bit Order = 0.
TIMING SPECIFICATION TABLE
SPEC
DESCRIPTION
t1
SCLK Period
t2
SCLK Pulse Width, High and Low
t3
MIN
MAX
4
3
DRDY Periods
200
ns
CS Low to first SCLK Edge; Setup Time
0
ns
t4
DIN Valid to SCLK Edge; Setup Time
50
ns
t5
Valid DIN to SCLK Edge; Hold Time
50
ns
t6
Delay between last SCLK edge for DIN and first SCLK edge for DOUT:
RDATA, RDATAC, RREG, WREG, RRAM
50
tOSC Periods
CSREG, CSRAMX, CSRAM
200
tOSC Periods
CSARAM, CSARAMX
1100
tOSC Periods
t7 (1)
SCLK Edge to Valid New DOUT
t8 (1)
SCLK Edge to DOUT, Hold Time
0
t9
Last SCLK Edge to DOUT Tri-State
NOTE: DOUT goes tri-state immediately when CS goes High.
6
t10
CS Low time after final SCLK edge
0
ns
t11
Final SCLK edge of one op code until first edge SCLK of next command:
4
tOSC Periods
RREG, WREG, RRAM, WRAM, CSRAMX, CSARAMX, CSRAM, CSARAM,
CSREG, SLEEP, RDATA, RDATAC, STOPC
DSYNC
50
ns
10
tOSC Periods
ns
16
tOSC Periods
33,000
tOSC Periods
CREG, CRAM
220
tOSC Periods
RF2R
1090
tOSC Periods
CREGA
1600
tOSC Periods
CSFL
WR2F
76,850 (SPEED = 0)
101,050 (SPEED = 1)
SELFGCAL, SELFOCAL, SYSOCAL, SYSGCAL
SELFCAL
RESET (Command, SCLK, or Pin)
(1)
UNIT
tOSC Periods
tOSC Periods
4
tOSC Periods
7
DRDY Periods
14
DRDY Periods
2640
tOSC Periods
Load = 20pF | | 10kΩ to DGND.
9
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
ADS1218
Resets On Falling Edge
SCLK Reset Waveform
t 13
t13
SCLK
t12
t 14
t16
t15
t17
RESET, DSYNC, PDWN
DRDY
TIMING SPECIFICATION TABLE
SPEC
10
DESCRIPTION
MIN
MAX
UNIT
t12
SCLK Reset, First High Pulse
300
500
tOSC Periods
t13
SCLK Reset, Low Pulse
t14
SCLK Reset, Second High Pulse
550
750
tOSC Periods
t15
SCLK Reset, Third High Pulse
1050
1250
tOSC Periods
t16
Pulse Width
4
tOSC Periods
t17
Data Not Valid During this Update Period
4
tOSC Periods
5
tOSC Periods
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
TYPICAL CHARACTERISTICS
AVDD = +5V, DVDD = +5V, fOSC = 2.4576MHz, PGA = 1, RDAC = 150kΩ, VREF ≡ (REF IN+) – (REF IN–) = +2.5V, and
fDATA = 10Hz, unless otherwise specified.
EFFECTIVE NUMBER OF BITS
vs DECIMATION RATIO
EFFECTIVE NUMBER OF BITS
vs DECIMATION RATIO
22
22
PGA1
PGA2
PGA4
PGA1 PGA2
PGA8
20
20
19
19
18
PGA16
PGA32
PGA64
PGA128
17
16
15
PGA8
18
17
16
PGA32
PGA16
PGA64
PGA128
15
14
14
Sinc3 Filter
13
Sinc3 Filter, Buffer ON
13
12
12
0
500
1000
1500
Decimation Ratio =
2000
0
500
f MOD
1000
Decimation Ratio =
fDATA
1500
fMOD
2000
fDATA
Figure 1.
Figure 2.
EFFECTIVE NUMBER OF BITS
vs DECIMATION RATIO
EFFECTIVE NUMBER OF BITS
vs DECIMATION RATIO
22
22
PGA1
21
PGA2
PGA4
PGA1 PGA2
PGA8
20
20
19
19
18
17
PGA16
PGA64
PGA32
PGA4
PGA128
16
18
17
16
15
15
14
Sinc3 Filter,
13
PGA32
14
VREF = 1.25V, Buffer OFF
1000
Decimation Ratio =
Figure 3.
1500
fMOD
f DATA
2000
PGA128
Sinc3 Filter, VREF = 1.25V, Buffer ON
12
500
PGA64
PGA16
13
12
0
PGA8
21
ENOB (rms)
ENOB (rms)
PGA4
21
ENOB (rms)
ENOB (rms)
21
0
500
1000
Decimation Ratio =
1500
fMOD
2000
fDATA
Figure 4.
11
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
TYPICAL CHARACTERISTICS (continued)
AVDD = +5V, DVDD = +5V, fOSC = 2.4576MHz, PGA = 1, RDAC = 150kΩ, VREF ≡ (REF IN+) – (REF IN–) = +2.5V, and
fDATA = 10Hz, unless otherwise specified.
EFFECTIVE NUMBER OF BITS
vs DECIMATION RATIO
FAST SETTLING FILTER
EFFECTIVE NUMBER OF BITS vs DECIMATION RATIO
22
22
PGA1
PGA2
PGA4
PGA8
21
20
20
19
19
ENOB (rms)
ENOB (rms)
21
18
17
PGA32
16
PGA64
PGA128
PGA16
15
18
17
16
15
14
14
Sinc2 Filter
13
Fast Settling Filter
13
12
12
0
500
1000
1500
Decimation Ratio =
2000
0
500
1000
fMOD
Decimation Ratio =
fDATA
Figure 5.
NOISE vs INPUT SIGNAL
0.5
CMRR (dB)
Noise (rms, ppm of FS)
0.6
0.4
0.3
0.2
0.1
−0.5
0.5
1.5
130
120
110
100
90
80
70
60
50
40
30
20
10
0
2.5
1
10
VIN (V)
100
10k
100k
Figure 8.
PSRR vs FREQUENCY
OFFSET vs TEMPERATURE
50
120
110
PGA16
PGA1
100
0
Offset (ppm of FS)
90
80
PSRR (dB)
1k
Frequency of CM Signal (Hz)
Figure 7.
70
60
50
40
30
−50
PGA64
−100
PGA128
−150
20
10
−200
0
1
10
100
1k
10k
Frequency of Power Supply (Hz)
Figure 9.
12
fDATA
CMRR vs FREQUENCY
0.7
−1.5
2000
Figure 6.
0.8
0
−2.5
1500
fMOD
100k
−50
−30
−10
10
30
Temperature (C)
Figure 10.
50
70
90
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
TYPICAL CHARACTERISTICS (continued)
AVDD = +5V, DVDD = +5V, fOSC = 2.4576MHz, PGA = 1, RDAC = 150kΩ, VREF ≡ (REF IN+) – (REF IN–) = +2.5V, and
fDATA = 10Hz, unless otherwise specified.
GAIN vs TEMPERATURE
INTEGRAL NONLINEARITY vs INPUT SIGNAL
1.00010
10
8
1.00002
0.99998
0.99994
4
+85 C
2
0
−2
−4
+25 C
−6
0.99990
0.99986
− 40 C
6
INL (ppm of FS)
Gain (Normalized)
1.00006
−8
−50
−30
−10
10
30
50
70
−10
−2.5
90
−2
−1.5
−1
−0.5
Figure 11.
0.5
1
1.5
2
2.5
64
128
Figure 12.
CURRENT vs TEMPERATURE
ADC CURRENT vs PGA
900
250
IDIGITAL
AVDD = 5V, Buffer = ON
800
Buffer = OFF
200
700
IANALOG
600
150
I ADC (µA)
Current (µA)
0
VIN (V)
Temperature ( C)
IANALOG
I DIGITAL
100
500
AVDD = 3V, Buffer = ON
400
Buffer = OFF
300
200
50
100
0
−50
−30
0
−10
10
30
50
70
90
0
1
Current (µA)
HISTOGRAM OF OUTPUT DATA
Normal
fOSC = 4.91MHz
4000
Normal
fOSC = 2.45MHz
200
150
100
Power
Down
SLEEP
fOSC = 2.45MHz
3500
3000
2500
2000
1500
1000
500
0
0
3.0
4.0
VDD (V)
Figure 15.
32
4500
Number of Occurrences
SLEEP
fOSC = 4.91MHz
50
16
Figure 14.
SPEED = 0
250
8
Figure 13.
DIGITAL CURRENT
300
4
PGA Setting
400
350
2
Temperature (C)
5.0
−2
−1.5
−1
−0.5
0
0.5
1
1.5
2
ppm of FS
Figure 16.
13
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
TYPICAL CHARACTERISTICS (continued)
AVDD = +5V, DVDD = +5V, fOSC = 2.4576MHz, PGA = 1, RDAC = 150kΩ, VREF ≡ (REF IN+) – (REF IN–) = +2.5V, and
fDATA = 10Hz, unless otherwise specified.
VREFOUT vs LOAD CURRENT
OFFSET DAC – OFFSET vs TEMPERATURE
2.55
200
170
Offset (ppm of FSR)
VREFOUT (V)
140
2.50
110
80
50
20
−10
−40
−70
2.45
−0.5
−100
0
0.5
1.0
1.5
2.0
2.5
−50
−30
−10
10
30
50
VREFOUT Current Load (mA)
Temperature (C)
Figure 17.
Figure 18.
OFFSET DAC – GAIN vs TEMPERATURE
70
90
IDAC ROUT vs VOUT
1.00020
1.000
1.00016
+85C
1.000
1.00008
IOUT (Normalized)
Normalized Gain
1.00012
1.00004
1.00000
0.99996
0.99992
0.99988
+25 C
0.999
0.999
0.99984
−40C
0.99980
0.99976
−50
−30
−10
0.998
10
30
50
70
90
0
1
2
3
Temperature (C)
VDD − VOUT (V)
Figure 19.
Figure 20.
IDAC NORMALIZED vs TEMPERATURE
4
5
IDAC MATCHING vs TEMPERATURE
3000
1.01
2000
1000
IDAC Match (ppm)
IOUT (Normalized)
1.005
1
0.995
0
−1000
−2000
−3000
−4000
0.99
−5000
0.985
−50
−30
−10
−6000
10
30
Temperature ( C)
Figure 21.
14
50
70
90
−50
−30
−10
10
30
Temperature (C)
Figure 22.
50
70
90
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
TYPICAL CHARACTERISTICS (continued)
AVDD = +5V, DVDD = +5V, fOSC = 2.4576MHz, PGA = 1, RDAC = 150kΩ, VREF ≡ (REF IN+) – (REF IN–) = +2.5V, and
fDATA = 10Hz, unless otherwise specified.
IDAC INTEGRAL NONLINEARITY
RANGE = 1, RDAC = 150kΩ, VREF = 2.5V
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
INL (LSB)
DNL (LSB)
IDAC DIFFERENTIAL NONLINEARITY
RANGE = 1, RDAC = 150kΩ, VREF = 2.5V
0.1
0
−0.1
0.1
0
−0.1
−0.2
−0.2
−0.3
−0.3
−0.4
−0.4
−0.5
−0.5
0
32
64
96
128
160
192
224
255
0
32
64
96
128
160
IDAC Code
IDAC Code
Figure 23.
Figure 24.
192
224
255
15
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
OVERVIEW
INPUT MULTIPLEXER
The input multiplexer provides for any combination of
differential inputs to be selected on any of the input
channels, as shown in Figure 25. For example, if
channel 1 is selected as the positive differential input
channel, any other channel can be selected as the
negative differential input channel. With this method,
it is possible to have up to eight fully differential input
channels.
In addition, current sources are supplied that will
source or sink current to detect open or short circuits
on the input pins.
AVDD
Burnout Current Source On
AIN2
BURNOUT CURRENT SOURCES
INPUT BUFFER
The input impedance of the ADS1218 without the
buffer is 5MΩ/PGA. With the buffer enabled, the input
voltage range is reduced and the analog
power-supply current is higher. The buffer is
controlled by ANDing the state of the BUFEN pin with
the state of the BUFFER bit in the ACR register. See
Application Report Input Currents for High-Resolution
ADCs (SBAA090) for more information.
AIN3
AIN4
AIN5
Burnout Current Source On
AIN6
AGND
IDAC1
AIN7
AINCOM
Figure 25. Input Multiplexer Configuration
TEMPERATURE SENSOR
An on-chip diode provides temperature sensing
capability. When the configuration register for the
input MUX is set to all 1s, the diode is connected to
the input of the A/D converter. All other channels are
16
In this mode, the output of IDAC1 is also connected
to the output pin, so some current may flow into an
external load from IDAC1, rather than the diode. See
Application Report Measuring Temperature with the
ADS1256, ADS1217, or ADS1218 (SBAA073) for
more information.
When the Burnout bit is set in the ACR configuration
register, two current sources are enabled. The current
source on the positive input channel sources
approximately 2µA of current. The current source on
the negative input channel sinks approximately 2µA.
This allows for the detection of an open circuit
(full-scale reading) or short circuit (0V differential
reading) on the selected input differential pair.
AIN0
AIN1
open. The anode of the diode is connected to the
positive input of the A/D converter, and the cathode
of the diode is connected to negative input of the A/D
converter. The output of IDAC1 is connected to the
anode to bias the diode and the cathode of the diode
is also connected to ground to complete the circuit.
IDAC1 AND IDAC2
The ADS1218 has two 8-bit current output DACs that
can be controlled independently. The output current is
set with RDAC, the range select bits in the ACR
register, and the 8-bit digital value in the IDAC
register.
The output current = VREF/(8RDAC)(2RANGE–1)(DAC
CODE). With VREFOUT = 2.5V and RDAC = 150kΩ to
AGND the full-scale output can be selected to be
0.5mA, 1mA, or 2mA. The compliance voltage range
is 0V to within 1V of AVDD. When the internal voltage
reference of the ADS1218 is used, it is the reference
for the IDAC. An external reference may be used for
the IDACs by disabling the internal reference and
tying the external reference input to the VREFOUT pin.
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
PGA
VRCAP PIN
The Programmable Gain Amplifier (PGA) can be set
to gains of 1, 2, 4, 8, 16, 32, 64, or 128. Using the
PGA can improve the effective resolution of the A/D
converter. For instance, with a PGA of 1 on a 5V
full-scale range, the A/D converter can resolve to
1µV. With a PGA of 128, on a 40mV full-scale range,
the A/D converter can resolve to 75nV.
This pin provides a bypass cap for noise filtering on
internal VREF circuitry only. As this is a sensitive pin,
place the capacitor as close as possible and avoid
any resistive loading. The recommended capacitor is
a 1000pF ceramic cap. If an external VREF is used,
this pin can be left unconnected.
CLOCK GENERATOR
PGA OFFSET DAC
The input to the PGA can be shifted by half the
full-scale input range of the PGA by using the ODAC
register. The ODAC (Offset DAC) register is an 8-bit
value; the MSB is the sign and the seven LSBs
provide the magnitude of the offset. Using the ODAC
register does not reduce the performance of the A/D
converter. See Application Report The Offset DAC
(SBAA077) for more information.
The clock source for the ADS1218 can be provided
from a crystal, oscillator, or external clock. When the
clock source is a crystal, external capacitors must be
provided to ensure startup and a stable clock
frequency; see Figure 26 and Table 1.
XIN
C1
Crystal
MODULATOR
XOUT
C2
The modulator is a single-loop second-order system.
The modulator runs at a clock speed (fMOD) that is
derived from the external clock (fOSC). The frequency
division is determined by the SPEED bit in the
SETUP register.
Figure 26. Crystal Connection
Table 1. Typical Clock Sources
SPEED BIT
fMOD
0
fOSC/128
CLOCK
SOURCE
FREQUENCY
C1
C2
PART NUMBER
1
fOSC/256
Crystal
2.4576
0-20pF
0-20pF
ECS, ECSD 2.45 - 32
Crystal
4.9152
0-20pF
0-20pF
ECS, ECSL 4.91
VOLTAGE REFERENCE INPUT
Crystal
4.9152
0-20pF
0-20pF
ECS, ECSD 4.91
The ADS1218 uses a differential voltage reference
input. The input signal is measured against the
differential voltage VREF ≡ (VREF+) – (VREF–). For
AVDD = 5V, VREF is typically 2.5V. For AVDD = 3V,
VREF is typically 1.25V. Due to the sampling nature of
the modulator, the reference input current increases
with higher modulator clock frequency (fMOD) and
higher PGA settings.
Crystal
4.9152
0-20pF
0-20pF
CTS, MP 042 4M9182
ON-CHIP VOLTAGE REFERENCE
A selectable voltage reference (1.25V or 2.5V) is
available for supplying the voltage reference input. To
use, connect VREF– to AGND and VREF+ to VREFOUT.
The enabling and voltage selection are controlled
through bits REF EN and REF HI in the setup
register. The 2.5V reference requires AVDD = 5V.
When using the on-chip voltage reference, the
VREFOUT pin should be bypassed with a 0.1µF
capacitor to AGND.
CALIBRATION
The offset and gain errors in the ADS1218, or the
complete system, can be reduced with calibration.
Internal calibration of the ADS1218 is called self
calibration. This is handled with three commands.
One command does both offset and gain calibration.
There is also a gain calibration command and an
offset calibration command. Each calibration process
takes seven tDATA periods to complete. It takes 14
tDATA periods to complete both an offset and gain
calibration. Self-gain calibration is optimized for PGA
gains less than 8. When using higher gains, system
gain calibration is recommended.
For system calibration, the appropriate signal must be
applied to the inputs. The system offset command
requires a zero differential input signal. It then
computes an offset that will nullify offset in the
system. The system gain command requires a
positive full-scale differential input signal. It then
computes a value to nullify gain errors in the system.
Each of these calibrations will take seven tDATA
periods to complete.
17
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
Calibration must be performed after power on, a
change in decimation ratio, or a change of the PGA.
For operation with a reference voltage greater than
(AVDD– 1.5V), the buffer must also be turned off
during calibration.
At the completion of calibration, the DRDY signal
goes low, which indicates the calibration is finished
and valid data is available. See Application Report
Calibration Routine and Register Value Generation
for the ADS121x Series (SBAA099) for more
information.
DIGITAL FILTER
The Digital Filter can use either the fast settling,
sinc2, or sinc3 filter, as shown in Figure 27. In
addition, the Auto mode changes the sinc filter after
the input channel or PGA is changed. When
switching to a new channel, it will use the fast settling
filter for the next two conversions, the first of which
should be discarded. It will then use the sinc2
followed by the sinc3 filter. This combines the
low-noise advantage of the sinc3 filter with the quick
response of the fast settling time filter. See Figure 28
for the frequency response of each filter.
When using the fast setting filter, select a decimation
value set by the DEC0 and M/DEC1 registers that is
evenly divisible by four for the best gain accuracy.
For example, choose 260 rather than 261.
18
Adjustable Digital Filter
Sinc3
Modulator
Output
Sinc2
Data Out
Fast Settling
FILTER SETTLING TIME
FILTER
SETTLING TIME
(Conversion Cycles)
Sinc3
Sinc2
Fast
3(1)
2(1)
1(1)
NOTE: (1) With Synchronized Channel Changes.
AUTO MODE FILTER SELECTION
CONVERSION CYCLE
1
Discard
2
3
4
Fast
Sinc2
Sinc3
Figure 27. Filter Step Responses
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
SINC2 FILTER RESPONSE(1)
(−3dB = 0.318 • f DATA = 19.11Hz)
0
0
−20
−20
−40
−40
Gain (dB)
Gain (dB)
SINC3 FILTER RESPONSE(1)
(−3dB = 0.262 • fDATA = 15.76Hz)
−60
−80
−60
−80
−100
−100
−120
−120
0
30
60
90
120
150 180
210 240 270 300
0
30
60
90
Frequency (Hz)
120
150 180 210 240 270 300
Frequency (Hz)
FAST SETTLING FILTER RESPONSE(1)
(−3dB = 0.469 • fDATA = 28.125Hz)
0
−20
Gain (dB)
−40
−60
−80
−100
−120
0
30
60
90
120
150 180
210 240 270 300
Frequency (Hz)
NOTE: (1) fDATA = 60Hz.
Figure 28. Filter Frequency Responses
DIGITAL I/O INTERFACE
SERIAL PERIPHERAL INTERFACE
The ADS1218 has eight pins dedicated for digital I/O.
The default power-up condition for the digital I/O pins
are as inputs. All of the digital I/O pins are individually
configurable as inputs or outputs. They are
configured through the DIR control register. The DIR
register defines whether the pin is an input or output,
and the DIO register defines the state of the digital
output. When the digital I/O are configured as inputs,
DIO is used to read the state of the pin. If the digital
I/O are not used, either 1) configure as outputs; or 2)
leave as inputs and tie to ground; this prevents
excess power dissipation.
The Serial Peripheral Interface (SPI) allows a
controller to communicate synchronously with the
ADS1218. The ADS1218 operates in slave-only
mode.
Chip Select (CS)
The chip select (CS) input of the ADS1218 must be
externally asserted before a master device can
exchange data with the ADS1218. CS must be low
for the duration of the transaction. CS can be tied
low.
19
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
Serial Clock (SCLK)
REGISTER BANK
SCLK, a Schmitt Trigger input, clocks data transfer
on the DIN input and DOUT output. When transferring
data to or from the ADS1218, multiple bits of data
may be transferred back-to-back with no delay in
SCLKs or toggling of CS. Make sure to avoid glitches
on SCLK because they can cause extra shifting of the
data.
The operation of the device is set up through
individual registers. The set of the 16 registers
required to configure the device is referred to as a
Register Bank, as shown in Figure 29.
Configuration
Register Bank
16 bytes
SETUP
MUX
ACR
IDAC1
IDAC2
ODAC
DIO
DIR
DEC0
M/DEC1
OCR0
OCR1
OCR2
FSR0
FSR1
FSR2
Polarity (POL)
The serial clock polarity is specified by the POL input.
When SCLK is active high, set POL high. When
SCLK is active low, set POL low.
DATA READY
The DRDY output is used as a status signal to
indicate when data is ready to be read from the
ADS1218. DRDY goes low when new data is
available. It is reset high when a read operation from
the data register is complete. It also goes high prior
to the updating of the output register to indicate when
not to read from the device to ensure that a data read
is not attempted while the register is being updated.
RAM
128 Bytes
Bank 0
16 bytes
Bank 2
16 bytes
DSYNC OPERATION
FLASH
4k Bytes
Page 0
128 bytes
Bank 7
16 bytes
DSYNC is used to provide for synchronization of the
A/D
conversion
with
an
external
event.
Synchronization can be achieved either through the
DSYNC pin or the DSYNC command. When the
DSYNC pin is used, the filter counter is reset on the
falling edge of DSYNC. The modulator is held in reset
until DSYNC is taken high. Synchronization occurs on
the next rising edge of the system clock after DSYNC
is taken high.
Page 31
128 bytes
MEMORY
Three types of memory are used on the ADS1218:
registers, RAM, and Flash. 16 registers directly
control the various functions (PGA, DAC value,
Decimation Ratio, etc.) and can be directly read or
written to. Collectively, the registers contain all the
information needed to configure the part, such as
data format, mux settings, calibration settings,
decimation ratio, etc. Additional registers, such as
conversion data, are accessed through dedicated
instructions.
The on-chip Flash can be used to store non-volatile
data. The Flash data is separate from the
configuration registers and therefore can be used for
any purpose, in addition to device configuration. The
Flash page data is read and written in 128 byte
blocks through the RAM banks; for example, all RAM
banks map to a single page of Flash, as shown in
Figure 29.
20
Figure 29. Memory Organization
RAM
Reads and Writes to Registers and RAM occur on a
byte basis. However, copies between registers and
RAM occurs on a bank basis. The RAM is
independent of the Registers; for example, the RAM
can be used as general-purpose RAM.
The ADS1218 supports any combination of eight
analog inputs. With this flexibility, the device could
easily support eight unique configurations—one per
input channel. In order to facilitate this type of usage,
eight separate register banks are available.
Therefore, each configuration could be written once
and recalled as needed without having to serially
retransmit all the configuration data. Checksum
commands are also included, which can be used to
verify the integrity of RAM.
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
The RAM provides eight banks, with a bank
consisting of 16 bytes. The total size of the RAM is
128 bytes. Copies between the registers and RAM
are performed on a bank basis. Also, the RAM can
be directly read or written through the serial interface
on power-up. The banks allow separate storage of
settings for each input.
The RAM address space is linear; therefore,
accessing RAM is done using an auto-incrementing
pointer. Access to RAM in the entire memory map
can be done consecutively without having to address
each bank individually. For example, if you were
currently accessing bank 0 at offset 0xF (the last
location of bank 0), the next access would be bank 1
and offset 0x0. Any access after bank 7 and offset
0xF will wrap around to bank 0 and Offset 0x0.
Although the Register Bank memory is linear, the
concept of addressing the device can also be thought
of in terms of bank and offset addressing. Looking at
linear and bank addressing syntax, we have the
following comparison: in the linear memory map, the
address 0x14 is equivalent to bank 1 and offset 0x4.
Simply stated, the most significant four bits represent
the bank, and the least significant four bits represent
the offset. The offset is equivalent to the register
address for that bank of memory.
FLASH
Reads and Writes to Flash occur on a Page basis.
Therefore, the entire contents of RAM is used for
both Read and Write operations. The Flash is
independent of the Registers; for example, the Flash
can be used as general-purpose Flash.
Upon power-up or reset, the contents of Flash Page 0
are loaded into RAM. Subsequently, the contents of
RAM Bank 0 are loaded into the configuration
register. Therefore, the user can customize the
power-up configuration for the device. Care should be
taken to ensure that data for Flash Page 0 is written
correctly, in order to prevent unexpected operation
upon power-up.
The ADS1218 supports any combination of eight
analog inputs and the Flash memory supports up to
32 unique Page configurations. With this flexibility,
the device could support 32 unique configurations for
each of the eight analog input channels. For instance,
the on-chip temperature sensor could be used to
monitor temperature, then different calibration
coefficients could be recalled for each of the eight
analog input channels based on the change in
temperature. This would enable the user to recall
calibration coefficients for every 4°C change in
temperature over the industrial temperature range,
which could be used to correct for drift errors.
Checksum commands are also included, which can
be used to verify the integrity of Flash.
The following two commands can be used to
manipulate the Flash. First, the contents of Flash can
be written to with the WR2F (write RAM to Flash)
command. This command first erases the designated
Flash page and then writes the entire content of RAM
(all banks) into the designated Flash page. Second,
the contents of Flash can be read with the RF2R
(read Flash to RAM) command. This command reads
the designated Flash page into the entire contents of
RAM (all banks). In order to ensure maximum
endurance and data retention, the SPEED bit in the
SETUP register must be set for the appropriate fOSC
frequency.
Writing to or erasing Flash can be disabled either
through the WREN pin or the WREN register bit. If
the WREN pin is low OR the WREN bit is cleared,
then the WR2F command has no effect. This protects
the integrity of the Flash data from being
inadvertently corrupted.
Accessing the Flash data either through read, write,
or erase may affect the accuracy of the conversion
result. Therefore, the conversion result should be
discarded when accesses to Flash are done.
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
REGISTER MAP
Table 2. Registers
ADDRESS
REGISTER
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
00H
SETUP
ID
ID
ID
SPEED
REF EN
REF HI
BUF EN
BIT ORDER
01H
MUX
PSEL3
PSEL2
PSEL1
PSEL0
NSEL3
NSEL2
NSEL1
NSEL0
02H
ACR
BOCS
IDAC2R1
IDAC2R0
IDAC1R1
IDAC1R0
PGA2
PGA1
PGA0
03H
IDAC1
IDAC1_7
IDAC1_6
IDAC1_5
IDAC1_4
IDAC1_3
IDAC1_2
IDAC1_1
IDAC1_0
04H
IDAC2
IDAC2_7
IDAC2_6
IDAC2_5
IDAC2_4
IDAC2_3
IDAC2_2
IDAC2_1
IDAC2_0
05H
ODAC
SIGN
OSET_6
OSET_5
OSET_4
OSET_3
OSET_2
OSET_1
OSET_0
06H
DIO
DIO_7
DIO_6
DIO_5
DIO_4
DIO_3
DIO_2
DIO_1
DIO_0
07H
DIR
DIR_7
DIR_6
DIR_5
DIR_4
DIR_3
DIR_2
DIR_1
DIR_0
08H
DEC0
DEC07
DEC06
DEC05
DEC04
DEC03
DEC02
DEC01
DEC00
09H
M/DEC1
DRDY
U/B
SMODE1
SMODE0
WREN
DEC10
DEC9
DEC8
0AH
OCR0
OCR07
OCR06
OCR05
OCR04
OCR03
OCR02
OCR01
OCR00
0BH
OCR1
OCR15
OCR14
OCR13
OCR12
OCR11
OCR10
OCR09
OCR08
0CH
OCR2
OCR23
OCR22
OCR21
OCR20
OCR19
OCR18
OCR17
OCR16
0DH
FSR0
FSR07
FSR06
FSR05
FSR04
FSR03
FSR02
FSR01
FSR00
0EH
FSR1
FSR15
FSR14
FSR13
FSR12
FSR11
FSR10
FSR09
FSR08
0FH
FSR2
FSR23
FSR22
FSR21
FSR20
FSR19
FSR18
FSR17
FSR16
DETAILED REGISTER DEFINITIONS
SETUP (Address 00H) Setup Register
Reset value is set by Flash memory page 0. Factory programmed to iii01110.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
ID
ID
ID
SPEED
REF EN
REF HI
BUF EN
BIT ORDER
bits 7-5 Factory Programmed Bits
bit 4
SPEED: Modulator Clock Speed
0 : fMOD = fOSC/128
1 : fMOD = fOSC/256
NOTE: When writing to Flash memory using the WR2F command, SPEED must be set as follows:
2.30MHz < fOSC < 3.12MHz → SPEED = 0
3.13MHz < fOSC < 4.12MHz → SPEED = 1
bit 3
REF EN: Internal Voltage Reference Enable
0 = Internal Voltage Reference Disabled
1 = Internal Voltage Reference Enabled
bit 2
REF HI: Internal Reference Voltage Select
0 = Internal Reference Voltage = 1.25V
1 = Internal Reference Voltage = 2.5V
bit 1
BUF EN: Buffer Enable
0 = Buffer Disabled
1 = Buffer Enabled
bit 0
BIT ORDER: Set Order Bits are Transmitted
0 = Most Significant Bit Transmitted First
1 = Least Significant Bit Transmitted First Data is always shifted into the part most significant bit first.
Data is always shifted out of the part most significant byte first. This configuration bit only controls the
bit order within the byte of data that is shifted out.
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MUX (Address 01H) Multiplexer Control Register
Reset value is set by Flash memory page 0. Factory programmed to 01H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
PSEL3
PSEL2
PSEL1
PSEL0
NSEL3
NSEL2
NSEL1
NSEL0
bits 7-4
PSEL3: PSEL2: PSEL1: PSEL0: Positive Channel Select
0000 =
0001 =
0010 =
0011 =
AIN0
AIN1
AIN2
AIN3
0100
0101
0110
0111
=
=
=
=
AIN4
AIN5
AIN6
AIN7
0100
0101
0110
0111
=
=
=
=
AIN4
AIN5
AIN6
AIN7
1xxx = AINCOM (except when all bits are 1s)
1111 = Temperature Sensor Diode
bits 3-0
NSEL3: NSEL2: NSEL1: NSEL0: Negative Channel Select
0000 =
0001 =
0010 =
0011 =
AIN0
AIN1
AIN2
AIN3
1xxx = AINCOM (except when all bits are 1s)
1111 = Temperature Sensor Diode
ACR (Address 02H) Analog Control Register
Reset value is set by Flash memory page 0. Factory programmed to 00H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
BOCS
IDAC2R1
IDAC2R0
IDAC1R1
IDAC1R0
PGA2
PGA1
PGA0
bit 7
BOCS: Burnout Current Source
0 = Disabled
1 = Enabled
IDAC Current 8RV 2
REF
RANGE1
(DAC Code)
DAC
bits 6-5 IDAC2R1: IDAC2R0: Full-Scale Range Select for IDAC2
00
01
10
11
=
=
=
=
Off
Range 1
Range 2
Range 3
bits 4-3 IDAC1R1: IDAC1R0: Full-Scale Range Select for IDAC1
00
01
10
11
=
=
=
=
Off
Range 1
Range 2
Range 3
bits 2-0 PGA2: PGA1: PGA0: Programmable Gain Amplifier Gain Selection
000
001
010
011
=1
=2
=4
=8
100 =
101 =
110 =
111 =
16
32
64
128
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
IDAC1 (Address 03H) Current DAC 1
Reset value is set by Flash memory page 0. Factory programmed to 00H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
IDAC1_7
IDAC1_6
IDAC1_5
IDAC1_4
IDAC1_3
IDAC1_2
IDAC1_1
IDAC1_0
The DAC code bits set the output of DAC1 from 0 to full-scale. The value of the full-scale current is set by this Byte, VREF, RDAC, and the
DAC1 range bits in the ACR register.
IDAC2 (Address 04H) Current DAC 2
Reset value is set by Flash memory page 0. Factory programmed to 00H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
IDAC2_7
IDAC2_6
IDAC2_5
IDAC2_4
IDAC2_3
IDAC2_2
IDAC2_1
IDAC2_0
The DAC code bits set the output of DAC2 from 0 to full-scale. The value of the full-scale current is set by this Byte, VREF, RDAC, and the
DAC2 range bits in the ACR register.
ODAC (Address 05H) Offset DAC Setting
Reset value is set by Flash memory page 0. Factory programmed to 00H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
SIGN
OSET6
OSET5
OSET4
OSET3
OSET2
OSET1
OSET0
bit 7
Offset Sign
0 = Positive
1 = Negative
bits 6-0
Offset NOTE:
V REF
Code
127
2PGA
The offset must be used after calibration or the calibration will notify the effects.
DIO (Address 06H) Digital I/O
Reset value is set by Flash memory page 0. Factory programmed to 00H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
DIO7
DIO6
DIO5
DIO4
DIO3
DIO2
DIO1
DIO0
A value written to this register will appear on the digital I/O pins if the pin is configured as an output in the DIR register. Reading this
register will return the value of the digital I/O pins.
DIR (Address 07H) Direction control for digital I/O
Reset value is set by Flash memory page 0. Factory programmed to FFH.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
DIR7
DIR6
DIR5
DIR4
DIR3
DIR2
DIR1
DIR0
Each bit controls whether the Digital I/O pin is an output (= 0) or input (= 1). The default power-up state is as
inputs.
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DEC0 (Address 08H) Decimation Register (least significant 8 bits)
Reset value is set by Flash memory page 0. Factory programmed to 80H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
DEC07
DEC06
DEC05
DEC04
DEC03
DEC02
DEC01
DEC00
The decimation value is defined with 11 bits for a range of 20 to 2047. This register is the least significant 8 bits. The 3 most significant bits
are contained in the M/DEC1 register.
M/DEC1 (Address 09H) Mode and Decimation Register
Reset value is set by Flash memory page 0. Factory programmed to 07H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
DRDY
U/B
SMODE1
SMODE0
WREN
DEC10
DEC09
DEC08
bit 7
DRDY: Data Ready (Read Only)
This bit duplicates the state of the DRDY pin.
bit 6
U/B: Data Format
0 = Bipolar
1 = Unipolar
bits 5-4
U/B
ANALOG INPUT
DIGITAL OUTPUT
0
+FS
Zero
–FS
0x7FFFFF
0x000000
0x800000
1
+FS
Zero
–FS
0xFFFFFF
0x000000
0x000000
SMODE1: SMODE0: Settling Mode
00
01
10
11
bit 3
= Auto
= Fast Settling filter
= Sinc2 filter
= Sinc3 filter
WREN: Flash Write Enable
0 = Flash Writing Disabled
1 = Flash Writing Enabled
This bit and the WREN pin must both be enabled in order to write to the Flash memory.
bits 2-0
DEC10: DEC09: DEC08: Most Significant Bits of the Decimation Value
OCR0 (Address 0AH) Offset Calibration Coefficient (least significant byte)
Reset value is set by Flash memory page 0. Factory programmed to 00H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
OCR07
OCR06
OCR05
OCR04
OCR03
OCR02
OCR01
OCR00
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OCR1 (Address 0BH) Offset Calibration Coefficient (middle byte)
Reset value is set by Flash memory page 0. Factory programmed to 00H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
OCR15
OCR14
OCR13
OCR12
OCR11
OCR10
OCR09
OCR08
OCR2 (Address 0CH) Offset Calibration Coefficient (most significant byte)
Reset value is set by Flash memory page 0. Factory programmed to 00H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
OCR23
OCR22
OCR21
OCR20
OCR19
OCR18
OCR17
OCR16
FSR0 (Address 0DH) Full-Scale Register (least significant byte)
Reset value is set by Flash memory page 0. Factory programmed to 24H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
FSR07
FSR06
FSR05
FSR04
FSR03
FSR02
FSR01
FSR00
FSR1 (Address 0EH) Full-Scale Register (middle byte)
Reset value is set by Flash memory page 0. Factory programmed to 90H.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
FSR15
FSR14
FSR13
FSR12
FSR11
FSR10
FSR09
FSR08
FSR2 (Address 0FH) Full-Scale Register (most significant byte)
Reset value is set by Flash memory page 0. Factory programmed to 67H.
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bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
FSR23
FSR22
FSR21
FSR20
FSR19
FSR18
FSR17
FSR16
ADS1218
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
COMMAND DEFINITIONS
The commands listed below control the operation of
the ADS1218. Some of the commands are
stand-alone commands (e.g., RESET) while others
require additional bytes (e.g., WREG requires
command, count, and the data bytes). Commands
that output data require a minimum of four fOSC cycles
before the data is ready (e.g., RDATA).
Operands: n = count (0 to 127)
r = register (0 to 15)
x = don’t care
a = RAM bank address (0 to 7)
f = Flash memory page address (0 to 31)
Table 3. Command Summary
COMMANDS
DESCRIPTION
COMMAND BYTE (1)
2ND COMMAND BYTE
RDATA
Read Data
0000 0001 (01H)
—
RDATAC
Read Data Continuously
0000 0011 (03H)
—
STOPC
Stop Read Data Continuously
0000 1111 (0FH)
—
RREG
Read from REG Bank rrrr
0001 r r r r (1xH)
xxxx_nnnn (# of reg–1)
RRAM
Read from RAM Bank aaa
0010 0aaa (2xH)
xnnn_nnnn (# of bytes–1)
—
(1)
CREG
Copy REGs to RAM Bank aaa
0100 0aaa (4xH)
CREGA
Copy REGS to all RAM Banks
0100 1000 (48H)
—
WREG
Write to REG rrrr
0101 r r r r (5xH)
xxxx_nnnn (# of reg–1)
WRAM
Write to RAM Bank aaa
0110 0aaa (6xH)
xnnn_nnnn (# of bytes–1)
RF2R
Read Flash page to RAM
100f f f f f (8, 9xH)
—
WR2F
Write RAM to Flash page
101f f f f f (A, BxH)
—
CRAM
Copy RAM Bank aaa to REG
1100 0aaa (CxH)
—
CSRAMX
Calc RAM Bank aaa Checksum
1101 0aaa (DxH)
—
CSARAMX
Calc all RAM Bank Checksum
1101 1000 (D8H)
—
CSREG
Calc REG Checksum
1101 1111 (DFH)
—
CSRAM
Calc RAM Bank aaa Checksum
1110 0aaa (ExH)
—
CSARAM
Calc all RAM Banks Checksum
1110 1000 (E8H)
—
CSFL
Calc Flash Checksum
1110 1100 (ECH)
—
SELFCAL
Self Cal Offset and Gain
1111 0000 (F0H)
—
SELFOCAL
Self Cal Offset
1111 0001 (F1H)
—
SELFGCAL
Self Cal Gain
1111 0010 (F2H)
—
SYSOCAL
Sys Cal Offset
1111 0011 (F3H)
—
SYSGCAL
Sys Cal Gain
1111 0100 (F4H)
—
DSYNC
Sync DRDY
1111 1100 (FCH)
—
SLEEP
Put in SLEEP Mode
1111 1101 (FDH)
—
RESET
Reset to Power-Up Values
1111 1110 (FEH)
—
The data input received by the ADS1218 is always MSB first. The data out format is set by the BIT ORDER bit in ACR reg.
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RDATA
Read Data
Description: Read a single 24-bit ADC conversion result. On completion of read back, DRDY goes high.
Operands: None
Bytes: 1
Encoding: 0000 0001
Data Transfer Sequence:
DRDY
• • • (1)
0000 0001
DIN
DOUT
xxxx xxxx
xxxx xxxx
xxxx xxxx
MSB
Mid−Byte
LSB
RDATAC
Read Data Continuous
Description: Read Data Continuous mode enables the continuous output of new data on each DRDY. This
command eliminates the need to send the Read Data Command on each DRDY. This mode may be terminated
by either the STOP Read Continuous command or the RESET command.
Operands: None
Bytes: 1
Encoding: 0000 0011
Data Transfer Sequence:
Command terminated when uuuu uuuu equals STOPC or RESET.
DIN
0000 0011
• • • (1)
u u uu u u u u
uu uu u uu u
u uu u uu u u
• ••
MSB
DOUT
DRDY
Mid−Byte
LSB
• ••
DIN
u u uu u u uu
u uu u uu uu
u u uu u u uu
MSB
Mid−Byte
LSB
• ••
DOUT
NOTE: (1) For wait time, refer to timing specification.
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STOPC
Stop Continuous
Description: Ends the continuous data output mode.
Operands: None
Bytes: 1
Encoding: 0000 1111
Data Transfer Sequence:
DIN
0000 1111
RREG
Read from Registers
Description: Output the data from up to 16 registers starting with the register address specified as part of the
instruction. The number of registers read will be one plus the second byte. If the count exceeds the remaining
registers, the addresses will wrap back to the beginning.
Operands: r, n
Bytes: 2
Encoding: 0001 rrrr xxxx nnnn
Data Transfer Sequence:
Read Two Registers Starting from Register 01H (MUX)
DIN
0001 0001
0000 0001
• • • (1)
DOUT
xxxx xxxx
xxxx xxxx
MUX
ACR
NOTE: (1) For wait time, refer to timing specification.
RRAM
Read from RAM
Description: Up to 128 bytes can be read from RAM starting at the bank specified in the op code. All reads start
at the address for the beginning of the RAM bank. The number of bytes to read will be one plus the value of the
second byte.
Operands: a, n
Bytes: 2
Encoding: 0010 0aaa xnnn nnnn
Data Transfer Sequence:
Read Two RAM Locations Starting from 20H
DIN
DOUT
0010 0010
x000 0001
• • • (1)
xxxx xxxx
xxxx xxxx
RAM Data
20H
RAM Data
21H
NOTE: (1) For wait time, refer to timing specification.
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CREG
Copy Registers to RAM Bank
Description: Copy the 16 control registers to the RAM bank specified in the op code. Refer to timing
specifications for command execution time.
Operands: a
Bytes: 1
Encoding: 0100 0aaa
Data Transfer Sequence:
Copy Register Values to RAM Bank 3
DIN
1101 1111
• • • (1)
xxxx xxxx
Checksum
DOUT
NOTE: (1) For wait time, refer to timing specification.
CREGA
Copy Registers to All RAM Banks
Description: Duplicate the 16 control registers to all the RAM banks. Refer to timing specifications for command
execution time.
Operands: None
Bytes: 1
Encoding: 0100 1000
Data Transfer Sequence:
DIN
0100 1000
WREG
Write to Register
Description: Write to the registers starting with the register specified as part of the instruction. The number of
registers that will be written is one plus the value of the second byte.
Operands: r, n
Bytes: 2
Encoding: 0101 rrrr xxxx nnnn
Data Transfer Sequence:
Write Two Registers Starting from 06H (DIO)
DIN
30
0101 0110
xxxx 0001
Data for DIO Data for DIR
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WRAM
Write to RAM
Description: Write up to 128 RAM locations starting at the beginning of the RAM bank specified as part of the
instruction. The number of bytes written is RAM is one plus the value of the second byte.
Operands: a, n
Bytes: 2
Encoding: 0110 0aaa xnnn nnnn
Data Transfer Sequence:
Write to Two RAM Locations starting from 10H
DIN
0110 0001
x000 0001
Data for
10H
RF2R
Data for
11H
Read Flash Memory Page to RAM
Description: Read the selected Flash memory page to the RAM.
Operands: f
Bytes: 1
Encoding: 100f ffff
Data Transfer Sequence:
Read Flash Page 2 to RAM
DIN
1000 0010
WR2F
Write RAM to Flash Memory
Description: Write the contents of RAM to the selected Flash memory page.
Operands: f
Bytes: 1
Encoding: 101f ffff
Data Transfer Sequence:
Write RAM to Flash Memory Page 31
DIN
1011 1111
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CRAM
Copy RAM Bank to Registers
Description: Copy the selected RAM Bank to the Configuration Registers. This will overwrite all of the registers
with the data from the RAM bank.
Operands: a
Bytes: 1
Encoding: 1100 0aaa
Data Transfer Sequence:
Copy RAM Bank 0 to the Registers
DIN
1100 0000
CSRAMX
Calculate RAM Bank Checksum
Description: Calculate the checksum of the selected RAM Bank. The checksum is calculated as a sum of all the
bytes with the carry ignored. The ID, DRDY, and DIO bits are masked so they are not included in the checksum.
Operands: a
Bytes: 1
Encoding: 1101 0aaa
Data Transfer Sequence:
Calculate Checksum for RAM Bank 3
DIN
1101 0011
• • • (1)
xxxx xxxx
Checksum
DOUT
NOTE: (1) For wait time, refer to timing specification.
CSARAMX
Calculate the Checksum for all RAM Banks
Description: Calculate the checksum of all RAM Banks. The checksum is calculated as a sum of all the bytes
with the carry ignored. The ID, DRDY, and DIO bits are masked so they are not included in the checksum.
Operands: None
Bytes: 1
Encoding: 1101 1000
Data Transfer Sequence:
DIN
DOUT
1101 1000
• • • (1)
xxxx xxxx
Checksum
NOTE: (1) For wait time, refer to timing specification.
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CSREG
Calculate the Checksum of Registers
Description: Calculate the checksum of all the registers. The checksum is calculated as a sum of all the bytes
with the carry ignored. The ID, DRDY, and DIO bits are masked so they are not included in the checksum.
Operands: None
Bytes: 1
Encoding: 1101 1111
Data Transfer Sequence:
DIN
1101 1111
• • • (1)
xxxx xxxx
Checksum
DOUT
NOTE: (1) For wait time, refer to timing specification.
CSRAM
Calculate RAM Bank Checksum
Description: Calculate the checksum of the selected RAM Bank. The checksum is calculated as a sum of all the
bytes with the carry ignored. All bits are included in the checksum calculation; there is no masking of bits.
Operands: a
Bytes: 1
Encoding: 1110 0aaa
Data Transfer Sequence:
Calculate Checksum for RAM Bank 2
DIN
1110 0010
• • • (1)
DOUT
xxxx xxxx
Checksum
NOTE: (1) For wait time, refer to timing specification.
CSARAM
Calculate Checksum for all RAM Banks
Description: Calculate the checksum of all RAM Banks. The checksum is calculated as a sum of all the bytes
with the carry ignored. All bits are included in the checksum calculation; there is no masking of bits.
Operands: None
Bytes: 1
Encoding: 1110 1000
Data Transfer Sequence:
DIN
DOUT
1110 1000
• • • (1)
xxxx xxxx
Checksum
NOTE: (1) For wait time, refer to timing specification.
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SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
CSFL
Calculate Checksum for all Flash Memory Pages
Description: Calculate the checksum for all Flash memory pages. The checksum is calculated as a sum of all
the bytes with the carry ignored. All bits are included in the checksum calculation; there is no masking of bits.
Operands: None
Bytes: 1
Encoding: 1110 1100
Data Transfer Sequence:
DIN
1110 1100
SELFCAL
Offset and Gain Self Calibration
Description: Starts the process of self calibration. The Offset Control Register (OCR) and the Full-Scale
Register (FSR) are updated with new values after this operation.
Operands: None
Bytes: 1
Encoding: 1111 0000
Data Transfer Sequence:
DIN
1111 0000
SELFOCAL
Offset Self Calibration
Description: Starts the process of self-calibration for offset. The Offset Control Register (OCR) is updated after
this operation.
Operands: None
Bytes: 1
Encoding: 1111 0001
Data Transfer Sequence:
DIN
1111 0001
SELFGCAL
Gain Self Calibration
Description: Starts the process of self-calibration for gain. The Full-Scale Register (FSR) is updated with new
values after this operation.
Operands: None
Bytes: 1
Encoding: 1111 0010
Data Transfer Sequence:
DIN
34
1111 0010
ADS1218
www.ti.com
SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
SYSOCAL
System Offset Calibration
Description: Starts the system offset calibration process. For a system offset calibration, the input should be set
to 0V differential, and the ADS1218 computes the OCR register value that will compensate for offset errors. The
Offset Control Register (OCR) is updated after this operation.
Operands: None
Bytes: 1
Encoding: 1111 0011
Data Transfer Sequence:
DIN
1111 0011
SYSGCAL
System Gain Calibration
Description: Starts the system gain calibration process. For a system gain calibration, the differential input
should be set to the reference voltage and the ADS1218 computes the FSR register value that will compensate
for gain errors. The FSR is updated after this operation.
Operands: None
Bytes: 1
Encoding: 1111 0100
Data Transfer Sequence:
DIN
1111 0100
DSYNC
Sync DRDY
Description: Synchronizes the ADS1218 to the serial clock edge.
Operands: None
Bytes: 1
Encoding: 1111 1100
Data Transfer Sequence:
DIN
1111 1100
SLEEP
Sleep Mode
Description: Puts the ADS1218 into a low-power sleep mode. SCLK must be inactive while in sleep mode. To
exit this mode, issue the WAKEUP command.
Operands: None
Bytes: 1
Encoding: 1111 1101
Data Transfer Sequence:
DIN
1111 1101
35
ADS1218
www.ti.com
SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
WAKEUP
Wakeup From Sleep Mode
Description: Use this command to wake up from sleep mode.
Operands: None
Bytes: 1
Encoding: 1111 1011
Data Transfer Sequence:
DIN
1111 1011
RESET
Reset Registers
Description: Copy the contents of Flash memory page 0 to the registers. This command will also stop the Read
Continuous mode.
Operands: None
Bytes: 1
Encoding: 1111 1110
Data Transfer Sequence:
DIN
1111 1110
Table 4. ADS1218 Command Map
LSB
MSB
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
0000
x (1)
rdata
x
rdatac
x
x
x
x
x
x
x
x
x
x
x
stopc
0001
rreg 0
rreg 1
rreg 2
rreg 3
rreg 4
rreg 5
rreg 6
rreg 7
rreg 8
rreg 9
rreg A
rreg B
rreg C
rreg D
rreg E
rreg F
0010
rram 0
rram 1
rram 2
rram 3
rram 4
rram 5
rram 6
rram 7
x
x
x
x
x
x
x
x
x
0011
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
0100
creg 0
creg 1
creg 2
creg 3
creg 4
creg 5
creg 6
creg 7
crega
x
x
x
x
x
x
x
0101
wreg 0
wreg 1
wreg 2
wreg 3
wreg 4
wreg 5
wreg 6
wreg 7
wreg 8
wreg 9
wreg A
wreg B
wreg C
wreg D
wreg E
wreg F
0110
wram 0 wram 1 wram 2 wram 3 wram 4 wram 5 wram 6 wram 7
x
x
x
x
x
x
x
x
0111
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
1000
rf2r 0
rf2r 1
rf2r 2
rf2r 3
rf2r 4
rf2r 5
rf2r 6
rf2r 7
rf2r 8
rf2r 9
rf2r A
rf2r B
rf2r C
rf2r D
rf2r E
rf2r F
1001
rf2r 10
rf2r 11
rf2r 12
rf2r 13
rf2r 14
rf2r 15
rf2r 16
rf2r 17
rf2r 18
rf2r 19
rf2r 1A
rf2r 1B
rf2r 1C
rf2r 1D
rf2r 1E
rf2r 1F
1010
wr2f 0
wr2f 1
wr2f 2
wr2f 3
wr2f 4
wr2f 5
wr2f 6
wr2f 7
wr2f 8
wr2f 9
wr2f A
wr2f B
wr2f C
wr2f D
wr2f E
wr2f F
1011
wr2f 10 wr2f 11 wr2f 12 wr2f 13 wr2f 14 wr2f 15 wr2f 16 wr2f 17 wr2f 18 wr2f 19
wr2f
1A
wr2f
1B
wr2f
1C
wr2f
1D
wr2f
1E
wr2f 1F
1100
cram 0
cram 1
cram 2
cram 3
cram 4
cram 5
cram 6
cram 7
x
x
x
x
x
x
x
x
1101
csramx
0
csramx
1
csramx
2
csramx
3
csramx
4
csramx
5
csramx
6
csramx
7
csramx
x
x
x
x
x
x
csreg
1110
csram
0
csram
1
csram2
csram
3
csram
4
csram
5
csram
6
csram
7
csramx
x
x
x
csfl
x
x
x
1111
self cal
self
ocal
self
gcal
sys
ocal
sys
gcal
x
x
x
x
x
x
x
dsync
sleep
reset
x
(1)
36
x = Reserved
ADS1218
www.ti.com
SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
DEFINITION OF RULES
Analog Input Voltage—the voltage at any one
analog input relative to AGND.
Analog Input Differential Voltage—given by the
following equation: (AIN+) – (AIN–). Thus, a positive
digital output is produced whenever the analog input
differential voltage is positive, while a negative digital
output is produced whenever the differential is
negative.
The data from the A/D converter is output as codes,
which then can be easily converted to other units,
such as ppm or volts. The equations and table below
show the relationship between bits or codes, ppm,
and volts.
−20 log(ppm)
ENOB 6.02
BITS rms
For example, when the converter is configured with a
2.5V reference and placed in a gain setting of 1, the
positive full-scale output is produced when the analog
input differential is 2.5V. The negative full-scale
output is produced when the differential is –2.5V. In
each case, the actual input voltages must remain
within the AGND to AVDD range.
Conversion Cycle—the term conversion cycle
usually refers to a discrete A/D conversion operation,
such as that performed by a successive
approximation converter. As used here, a conversion
cycle refers to the tDATA time period. However, each
digital output is actually based on the modulator
results from several tDATA time periods.
FILTER SETTING
MODULATOR RESULTS
Fast Settling
1 tDATA Time Period
Sinc2
2 tDATA Time Period
Sinc3
3 tDATA Time Period
Data Rate—the rate at which conversions are
completed. See definition for fDATA.
Decimation Ratio—defines the ratio between the
output of the modulator and the output Data Rate.
Valid values for the Decimation Ratio are from 20 to
2047. Larger Decimation Ratios will have lower noise.
Effective Resolution—the effective resolution of the
ADS1218 in a particular configuration can be
expressed in two different units: bits rms (referenced
to output) and Vrms (referenced to input). Computed
directly from the converter’s output data, each is a
statistical calculation. The conversion from one to the
other is shown below.
Effective number of bits (ENOB) or effective
resolution is commonly used to define the usable
resolution of the A/D converter. It is calculated from
empirical data taken directly from the device. It is
typically determined by applying a fixed known signal
source to the analog input and computing the
standard deviation of the data sample set. The rms
noise defines the ±σ interval about the sample mean.
BIPOLAR Vrms
2V REF
PGA
10
UNIPOLAR Vrms
6.02ER
20
V REF
PGA
10
6.02ER
20
24
298nV
22
1.19µV
149nV
597nV
20
4.77µV
2.39µV
18
19.1µV
9.55µV
16
76.4µV
38.2µV
14
505µV
152.7µV
12
1.22mV
610µV
fDATA—the frequency of the digital output data
produced by the ADS1218. fDATA is also referred to as
the Data Rate.
f DATA f
f
Decimation
mfactor Decimation
Ratio
Ratio
MOD
OSC
fMOD—the frequency or speed at which the modulator
of the ADS1218 is running. This depends on the
SPEED bit as shown below:
SPEED BIT
fMOD
0
fOSC/128
1
fOSC/256
fOSC—the frequency of the crystal input signal at the
XIN input of the ADS1218.
fSAMP—the frequency, or switching speed, of the input
sampling capacitor. The value is given by one of the
following equations:
PGA SETTING
SAMPLING FREQUENCY
1, 2, 4, 8
f SAMP f OSC
mfactor
8
f SAMP 2f OSC
mfactor
16
f SAMP 8f OSC
mfactor
32
f SAMP 16f OSC
mfactor
64, 128
f SAMP 16f OSC
mfactor
37
ADS1218
www.ti.com
SBAS187C – SEPTEMBER 2001 – REVISED SEPTEMBER 2005
Filter Selection—the ADS1218 uses a (sinx/x) filter
or sinc filter. There are three different sinc filters that
can be selected. A fast settling filter will settle in one
tDATA cycle. The sinc2 filter will settle in two cycles
and have lower noise. The sinc3 will achieve lowest
noise and higher number of effective bits, but
requires three cycles to settle. The ADS1218 will
operate with any one of these filters, or it can operate
in an auto mode, where it will first select the fast
settling filter after a new channel is selected for two
readings and will then switch to sinc2 for one reading,
followed by sinc3 from then on.
For example, when the converter is configured with a
2.5V reference and is placed in a gain setting of 2,
the full-scale range is: [1.25V (positive full-scale) –
(–1.25V (negative full-scale))] = 2.5V.
Full-Scale Range (FSR)—as with most A/D
converters, the full-scale range of the ADS1218 is
defined as the input, which produces the positive
full-scale digital output minus the input, which
produces the negative full-scale digital output. The
full-scale range changes with gain setting; see
Table 5.
where N is the number of bits in the digital output.
Least Significant Bit (LSB) Weight—this is the
theoretical amount of voltage that the differential
voltage at the analog input would have to change in
order to observe a change in the output data of one
least significant bit. It is computed as follows:
Full−Scale Range
LSB Weight 2N
tDATA—the inverse of fDATA, or the period between
each data output.
Table 5. Full-Scale Range versus PGA Setting
5V SUPPLY ANALOG INPUT (1)
GAIN
SETTING
(1)
(2)
38
FULL-SCALE
RANGE
DIFFERENTIAL
INPUT
VOLTAGES (2)
PGA OFFSET
RANGE
1
5V
±2.5V
±1.25V
2
2.5V
±1.25V
±0.625V
4
1.25V
±0.625V
±312.5mV
8
0.625V
±312.5mV
±156.25mV
16
312.5mV
±156.25mV
±78.125mV
34
156.25mV
±78.125mV
±39.0625mV
64
78.125mV
±39.0625mV
±19.531mV
128
39.0625mV
±19.531mV
±9.766mV
GENERAL EQUATIONS
FULL-SCALE
RANGE
DIFFERENTIAL
INPUT
VOLTAGES (2)
PGA SHIFT
RANGE
2V REF
PGA
VREF
PGA
VREF
2 PGA
With a 2.5V reference.
The ADS1218 allows common-mode voltage as long as the absolute input voltage on AIN+ or AIN– does not go below AGND or above
AVDD.
PACKAGE OPTION ADDENDUM
www.ti.com
21-May-2010
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package
Drawing
Pins
Package Qty
Eco Plan
(2)
Lead/
Ball Finish
MSL Peak Temp
(3)
ADS1218Y/250
ACTIVE
TQFP
PFB
48
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
ADS1218Y/250G4
ACTIVE
TQFP
PFB
48
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
Samples
(Requires Login)
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
12-Dec-2011
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
ADS1218Y/250
Package Package Pins
Type Drawing
TQFP
PFB
48
SPQ
250
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
177.8
16.4
Pack Materials-Page 1
9.6
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
9.6
1.5
12.0
16.0
Q2
PACKAGE MATERIALS INFORMATION
www.ti.com
12-Dec-2011
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
ADS1218Y/250
TQFP
PFB
48
250
210.0
185.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
MTQF019A – JANUARY 1995 – REVISED JANUARY 1998
PFB (S-PQFP-G48)
PLASTIC QUAD FLATPACK
0,27
0,17
0,50
36
0,08 M
25
37
24
48
13
0,13 NOM
1
12
5,50 TYP
7,20
SQ
6,80
9,20
SQ
8,80
Gage Plane
0,25
0,05 MIN
0°– 7°
1,05
0,95
Seating Plane
0,75
0,45
0,08
1,20 MAX
4073176 / B 10/96
NOTES: A. All linear dimensions are in millimeters.
B. This drawing is subject to change without notice.
C. Falls within JEDEC MS-026
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