TI1 ADS1201U High dynamic range delta-sigma modulator Datasheet

®
ADS
ADS1201
120
1
High Dynamic Range
DELTA-SIGMA MODULATOR
FEATURES
DESCRIPTION
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The ADS1201 is a precision, 130dB dynamic range,
delta-sigma (∆Σ) modulator operating from a single
+5V supply. The differential inputs are ideal for direct
connection to transducers or low level signals. With
the appropriate digital filter and modulator rate, the
device can be used to achieve 24-bit analog-to-digital
(A/D) conversion with no missing codes. Effective
resolution of 20 bits can be maintained with a digital
filter bandwidth of 1kHz at a modulator rate of 320kHz.
130dB DYNAMIC RANGE
FULLY DIFFERENTIAL INPUT
TWO-WIRE INTERFACE
INTERNAL/EXTERNAL REFERENCE
ON-CHIP SWITCHES FOR CALIBRATION
APPLICATIONS
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INDUSTRIAL PROCESS CONTROL
INSTRUMENTATION
SMART TRANSMITTERS
PORTABLE INSTRUMENTS
WEIGH SCALES
PRESSURE TRANSDUCERS
AVDD
AGND
The ADS1201 is designed for use in high resolution
measurement applications including smart transmitters, industrial process control, weigh scales, chromatography, and portable instrumentation. It is available
in a 16-lead SOIC package.
REF IN
REF OUT
VBIAS
+2.5V
Reference
Bias
Generator
BIASEN
REFEN
AINP
AINN
Second-Order
∆Σ
Modulator
CAL GAIN/OFFSET
MOUT
MCLK
DVDD
DGND
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111
Twx: 910-952-1111 • Internet: http://www.burr-brown.com/ • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
©
SBAS081
1997 Burr-Brown Corporation
PDS-1417C
Printed in U.S.A. October, 1999
SPECIFICATIONS
At TA = +25°C, AVDD = DVDD = +5V, MCLK = 320kHz, REFEN LOW, BIASEN LOW, and external +2.5V reference, unless otherwise specified.
ADS1201U
PARAMETER
CONDITIONS
MIN
ANALOG INPUT
Absolute Input Voltage Range
0
–10
–5
–20
With VBIAS(1)
Differential Input Voltage Range
With VBIAS(1)
Input Impedance
Input Capacitance
Input Leakage Current
TYP
See Note 2
250(4)
8
5
At TMIN to TMAX
SYSTEM PERFORMANCE
Dynamic Range
Integral Linearity Error
10Hz
60Hz
1kHz
60Hz
1kHz
Offset Error(2)
Offset Drift(3)
Gain Error(2)
Gain Error Drift(3)
Common-Mode Rejection
Power Supply Rejection
REFERENCE
Internal Reference (REFOUT)
Drift
Noise
Load Current
Output Impedance
External Reference (REFIN)
Load Current
VBIAS Output
Drift
Load Current
DIGITAL INPUT/OUTPUT
Logic Family
Logic Levels:
VIH (MCLK)
VIL (MCLK)
VOH (MOUT)
VOL (MOUT)
MCLK Frequency
POWER SUPPLY REQUIREMENTS
Power Supply Voltage
Supply Current
Analog Current
Digital Current
Additional Analog Current
REFOUT Enabled
VBIAS Enabled
Total Power Dissipation
Bandwidth(5)
Bandwidth(5)
Bandwidth(5)
Bandwidth(5)
Bandwidth(5)
115(6)
MAX
UNITS
+5
+10
+5
+20
V
V
V
V
kΩ
pF
pA
nA
50
1
130(6)
120(6)
115(6)
±0.0015
±0.0015
At DC
80
2.4
Source or Sink
See Note 7
1
See Note 7
1
100
80
2.5
25
50
–1
2.6
1
2
2.0
Using Internal Reference
3.15
3.3
50
3.0
2.5
3.45
10
dB
dB
dB
%FSR
%FSR
µV
µV/°C
ppm
µV/°C
dB
dB
V
ppm/°C
µVp-p
mA
Ω
V
µA
V
ppm/°C
mA
TTL Compatible CMOS
IOH
IOL
IIH = +5µA
IIL = +5µA
= 2 TTL Loads
= 2 TTL Loads
2.0
–0.3
2.4
Specified Performance
0.02
0.4
1
V
V
V
V
MHz
4.75
5.25
V
No Load
No Load
REFOUT, V BIAS Disabled
TEMPERATURE RANGE
Specified Performance
–40
DVDD +0.3
0.8
4.6
0.4
mA
mA
1.6
1
25
40
mA
mA
mW
+85
°C
NOTES: (1) This range is set with external resistors and VBIAS (as described in the text). Other ranges are possible. (2) After the on-chip offset and gain
calibration functions have been employed. (3) Re-calibration can reduce these errors. (4) Input impedance changes with MCLK. (5) Assume brick wall digital
filter is used. (6) 20 Log (full scale/r ms noise). (7) After calibration, these errors will be of the order of the effective resolution.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
®
ADS1201
2
ELECTROSTATIC
DISCHARGE SENSITIVITY
ABSOLUTE MAXIMUM RATINGS
Analog Input: Current ................................................ ±100mA, Momentary
±10mA, Continuous
Voltage ................................... AGND –0.3V to AVDD +0.3V
AVDD to DVDD ........................................................................... –0.3V to 6V
AVDD to AGND ......................................................................... –0.3V to 6V
DVDD to DGND ......................................................................... –0.3V to 6V
AGND to DGND ................................................................................ ±0.3V
REFIN Voltage to AGND ............................................ –0.3V to AVDD +0.3V
Digital Input Voltage to DGND .................................. –0.3V to DVDD +0.3V
Digital Output Voltage to DGND ............................... –0.3V to DVDD +0.3V
Lead Temperature (soldering, 10s) .............................................. +300°C
Internal Power Dissipation ............................................................. 500mW
This integrated circuit can be damaged by ESD. Burr-Brown
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.
NOTE: (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.
PIN DESCRIPTIONS
PIN CONFIGURATION
Top View
SOIC
AVDD
1
16 REFEN
REFOUT
2
15 MOUT
REFIN
3
14 MCLK
NIC
4
ADS1201
PIN NO
NAME
DESCRIPTION
1
2
AVDD
REFOUT
3
4
5
6
7
8
REFIN
NIC
AINP
AINN
AGND
VBIAS
9
BIASEN
10
GAIN/OFFSET
11
CAL
12
13
14
DGND
DVDD
MCLK
15
16
MOUT
REFEN
Analog Input: Analog Supply, +5V nominal.
Analog Output: Internal Reference Voltage Output:
+2.5V nominal.
Analog Input: Reference Voltage Input.
Not Internally Connected.
Analog Input: Noninverting Input.
Analog Input: Inverting Input.
Analog Input: Analog Ground.
Analog Output: Bias Voltage Output, nominally
+3.3V (with +2.5V reference).
Digital Input: Bias Voltage Enable Input (HIGH =
enabled, LOW = disabled).
Digital Input: Gain/Offset Calibration Select Input
(with CAL LOW; HIGH = gain configuration,
LOW = offset configuration).
Digital Input: Calibration Control Input (HIGH =
normal operation, LOW = gain or offset
calibration configuration).
Digital Input: Digital Ground.
Digital Input: Digital Supply, +5V nominal.
Digital Input: Modulator Clock Input. CMOS
compatible.
Digital Output: Modulator Output.
Digital Input: REFOUT Voltage Enable Input
(HIGH = enabled, LOW = disabled).
13 DVDD
AINP
5
12 DGND
AINN
6
11 CAL
AGND
7
10 GAIN/OFFSET
VBIAS
8
9
BIASEN
PACKAGE/ORDERING INFORMATION
PRODUCT
PACKAGE
PACKAGE
DRAWING
NUMBER
ADS1201U
SOL-16
211
–40°C to +85°C
ADS1201U
ADS1201U
Rails
"
"
"
"
ADS1201U/1K
Tape and Reel
"
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
MARKING
ORDERING
NUMBER(1)
TRANSPORT
MEDIA
NOTE: (1) Models with a slash (/) are available only in Tape and Reel in the quantities indicated (e.g., /1K indicates 1000 devices per reel). Ordering 1000 pieces
of “ADS1201U/1K” will get a single 1000-piece Tape and Reel.
®
3
ADS1201
TYPICAL PERFORMANCE CURVES
At TA = +25°C, AVDD = DVDD = +5V, MCLK = 320kHz, REFEN LOW, BIASEN LOW, and external +2.5V reference, unless otherwise specified.
rms NOISE
LINEARITY
1.2
1.5
1.0
1
0.5
0
(ppm)
(ppm)
0.8
0.6
–0.5
–1.0
–1.5
0.4
–2.0
–2.5
0.2
–3.0
0
–3.5
–5
–4
–3
–2
–1
0
1
2
3
4
5
–5
–4
–3
–2
–1
VDIN (V)
0
1
2
3
4
5
VDIN (V)
PSRR vs FREQUENCY
CMRR vs FREQUENCY
70
110
105
PSRR (dB)
CMRR (dB)
68
66
64
100
62
95
60
0.1
1
10
100
0.1
1000
1.0
10
TYPICAL SINK CURRENT
1k
10k
100k
TYPICAL SOURCE CURRENT
30
30
25
25
20
20
IOUT (mA)
IOUT (mA)
100
Frequency (Hz)
Frequency (Hz)
15
15
10
10
5
5
0
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0
VOL (V)
1.0
1.5
2.0
2.5
VOL (V)
®
ADS1201
0.5
4
3.0
3.5
4.0
4.5
5.0
TYPICAL PERFORMANCE CURVES
(Cont.)
At TA = +25°C, AVDD = DVDD = +5V, MCLK = 320kHz, REFEN LOW, BIASEN LOW, and external +2.5V reference, unless otherwise specified.
CMRR vs VDIN
110
CMRR (dB)
105
100
95
90
85
80
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
VDIN (V)
GENERAL DESCRIPTION
THEORY OF OPERATION
The ADS1201 is a single channel, second-order, CMOS
analog modulator designed for high resolution conversions
from dc to 1000Hz. The output of the converter (MOUT)
provides a stream of digital ones and zeros. The time
average of this serial output is proportional to the analog
input voltage. The combination of an ADS1201 and a
processor that is programmed to implement a digital filter
results in a high resolution A/D converter system. This
system allows flexibility with the digital filter design and is
capable of A/D conversion results that have a dynamic range
that exceeds 130dB (see Figure 1).
The differential analog input of the ADS1201 is implemented with a switched capacitor circuit. This switched
capacitor circuit implements a 2nd-order modulator stage
which digitizes the input signal into a binary output stream.
The input stage of the converter can be configured to sample
an analog signal or to perform a calibration which quantifies
offset and gain errors. The sample clock (MCLK) provides
the switched capacitor network and modulator clock signal
for the A/D conversion process, as well as the output data
framing clock. Different frequencies for this clock allows
for a variety of performance solutions in resolution and
signal bandwidth. The analog input signal is continuously
sampled by the A/D converter and compared to an internal
or external voltage reference. A digital stream appears at the
output of the converter. This digital stream accurately represents the analog input voltage over time.
Analog Supply
1
AVDD
REFEN 16
2
REFOUT
MOUT 15
3
REFIN
MCLK 14
4
NIC
5
AINP
DGND 12
6
AINN
CAL 11
7
AGND
8
VBIAS
10µF
Digital
Supply
0.1µF
DVDD 13
ADS1201
200Ω
0.1µF
Processor
200Ω
47pF
GAIN/OFFSET 10
47pF
BIASEN
9
FIGURE 1. Connection Diagram for the ADS1201 Delta-Sigma Modulator Including External Processor.
®
5
ADS1201
1-Bit Data
Stream
Switched
Capacitor
Analog
Input
Processor
for
Filtering
2nd-Order
Charge-Balancing
A/D Converter
Analog
Inputs
Programmable Gain Amp
2nd-Order Modulator
VIN+
VREF
1-Bit DAC
VIN–
FIGURE 2. Block Diagram of the ADS1201.
ANALOG INPUT STAGE
out of the analog inputs exceed 10mA. In addition, the
linearity of the device is guaranteed only when the analog
voltage applied to either input resides within the range
defined by AGND = > –30mV and < = AVDD + 30mV. If
either of the inputs exceed these limits, the input protection
diodes on the front end of the converter will begin to turn on.
This will induce leakage paths resulting in nonlinearities in
the conversion process.
Analog Input
The input design topology of the ADS1201 is based on a
fully differential switched capacitor architecture. This input
stage provides the mechanism to achieve low system noise,
high common-mode rejection (100dB) and excellent power
supply rejection. The input impedance of the analog input is
dependent on the input capacitor and modulator clock frequency (MCLK), which is also the sampling frequency of
the converter. Figure 3 shows the basic input structure of the
ADS1201. The relationship between the input impedance of
the ADS1201 and the modulator clock frequency is:
A IN Input Im pedance(Ω) =
For this reason, the 0V to 5V input range must be used with
caution. Should AVDD be 4.75V, the analog input signal
would swing outside the guaranteed specifications of the
device. Designs utilizing this mode of operation should
consider limiting the span to a slightly smaller range. Common-mode voltages are also a significant concern and must
be carefully analyzed.
1E12
12 • fMCLK
The input impedance becomes a consideration in designs
where the source impedance of the input signal is significant. In this case, it is possible for a portion of the signal to
be lost across this external source impedance. The importance of this effect depends on the desired system performance.
Modulator
There are two restrictions on the analog input signal to the
ADS1201. Under no conditions should the current into or
The modulator topology is fundamentally a 2nd-order, chargebalancing A/D converter, as the one conceptualized in Figure 4. The analog input voltage and the output of the 1-bit
DAC is differentiated, providing an analog voltage at X2 and
X3. The voltage at X2 and X3 are presented to their individual integrators. The output of these integrators progress
in a negative or positive direction. When the value of the
signal at X4 equals the comparator reference voltage, the
output of the comparator switches from negative to positive
or positive to negative, depending on its original state. When
the output value of the comparator switches from a HIGH to
LOW or vise versa, the 1-bit DAC responds on the next
clock pulse by changing its analog output voltage at X6,
causing the integrators to progress in the opposite direction.
The feedback of the modulator to the front end of the
integrators force the value of the integrator output to track
the average of the input.
RSW
8kΩ (typ)
The modulator sampling frequency (MCLK) can be operated over a range of 20kHz to 1MHz. The frequency of
MCLK can be increased to improve the performance of the
converter or adjusted to comply with the clock requirements
of the application.
High
Impedance
> 1GΩ
AIN+
CINT
12pF (typ)
Switching Frequency
= MCLK
RSW
8kΩ (typ)
AIN–
VCM
CINT
12pF (typ)
High
Impedance
> 1GΩ
FIGURE 3. Input Impedance of the ADS1201.
®
ADS1201
6
REFERENCE CIRCUIT
ence is used, the correct connection configuration is shown
in Figure 5a. The capacitor in this circuit is absolutely
required if low noise performance is desired.
There are two reference circuits included in the ADS1201
converter: VREF (REFIN, REFOUT) and VBIAS. The circuitry
for VREF is configured to allow the user to utilize the internal
reference on the chip or provide an external reference to the
converter (see Figure 5). The second reference, VBIAS, is
derived from VREF, whether it is internal or external. VBIAS
is exclusively an output reference. This ratiometric relationship between VREF and VBIAS reduces system errors when
two separate bias voltages are required in the application.
An external reference can be used to reduce the noise in the
conversion process. If an external reference is used, care
should be taken to insure that the selected reference has low
noise performance. The appropriate connection circuit of an
external reference is shown in Figure 5b. The reference must
be configured with appropriate capacitors to reduce the high
frequency noise that may be contributed by the reference.
The input impedance of REFIN changes with the modulator
clock frequency. The relationship is:
REFERENCE INPUT (REFIN)
The reference input (REFIN) of the ADS1201 can be configured so that the 2.5V (nominal) internal or external reference
can be used in the conversion process. If the internal refer-
Typical REFIN Input Im pedance =
1E12
50 • fMCLK
fMCLK
X2
X(t)
X3
Integrator 1
X4
Integrator 2
MOUT
fS
VREF
Comparator
X6
D/A Converter
FIGURE 4. Block Diagram of a Second-Order Modulator.
+5V
1
AVDD
REFEN 16
2
REFOUT
MOUT 15
3
MCLK 14
REFIN
External
VREF
1µF
4
DVDD 13
NIC
1
AVDD
REFEN 16
2
REFOUT
MOUT 15
3
REFIN
MCLK 14
4
NIC
1µF
ADS1201
DVDD 13
ADS1201
5
AINP
DGND 12
5
AINP
DGND 12
6
AINN
CAL 11
6
AINN
CAL 11
7
AGND
GAIN/OFFSET 10
7
AGND
8
VBIAS
9
8
VBIAS
BIASEN
(a) Internal Reference
GAIN/OFFSET 10
BIASEN
9
(b) External Reference
FIGURE 5. Two Voltage Reference Connection Alternatives for the ADS1201.
®
7
ADS1201
The reference input voltage can vary between 2V and 3V.
Higher reference voltages will cause the full-scale range to
increase while the internal circuit noise of the converter
remains approximately the same. This will increase the LSB
weight but not the internal noise, resulting in increased
signal-to-noise ratio. Likewise, lower reference voltages
will decrease the signal-to-noise ratio.
reference are given in the Specifications table. Note that this
reference is not designed to sink or to source more than 1mA
of current. In addition, loading the reference with a dynamic
or variable load is not recommended. This can result in
small changes in reference voltage as the load changes.
The internal reference, which generates +2.5V, can be disabled when an external reference is used. This internal
reference is disabled with the REFEN pin. When the reference is disabled, the supply current (AVDD) of the converter
will reduce by approximately 1.6mA.
The VBIAS output voltage is dependent on the reference
input (REFIN) voltage and is approximately 1.33 times as
great. The output of VBIAS is used to bias input signals of
greater than 5V. If a resistor network is used in combination
with the VBIAS output, the signal range can be scaled and
level shifted to match the input range of the ADS1201.
Figure 6 shows a connection diagram which will allow the
ADS1201 to accept a ±10V input signal (20V full-scale
range). If BIASEN is HIGH, the voltage at VBIAS will be
3.3V (assumes a 2.5V nominal VREF).
VOLTAGE BIAS OUTPUT (VBIAS)
REFERENCE OUTPUT (VREFOUT)
The ADS1201 contains an internal +2.5V reference. When
using this feature, REFEN must be HIGH (see Figure 5).
Tolerances, drift, noise, and other specifications for this
REFEN
REFOUT
LOW
High Impedance
HIGH
2.5V (nominal)
TABLE I. Reference Enable.
0.1µF
1
AVDD
REFEN 16
2
REFOUT
MOUT 15
Serial Data Out
3
REFIN
MCLK 14
Clock In
4
NIC
1µF
R1
3kΩ
VIN+
DVDD 13
ADS1201
R2
3kΩ
VIN–
R3
1kΩ
R4
1kΩ
0.1µF
5
AINP
DGND 12
6
AINN
CAL 11
7
AGND
8
VBIAS
GAIN/OFFSET 10
BIASEN
9
FIGURE 6. ±10V Bipolar Input Configuration Using VBIAS.
t1
t2
t3
t4
Clock Period
3125
ns
t2
Clock HIGH
1562.5
ns
t3
Clock LOW
1562.5
ns
t4
Clock Rise Time
6
ns
t5
Clock Fall Time
6
t6
DOUT Valid after Clock Rising Edge
t6
MOUT
Data Valid
Data Valid
Data Valid
Data Valid
FIGURE 7. Timing Diagram for the Digital Interface of the ADS1201.
®
ADS1201
8
TYP
UNITS
DESCRIPTION
t1
MCLK
MIN
MAX
SYMBOL
t5
ns
400
ns
BIASEN
VBIAS
LOW
High Impedance
HIGH
1.33V • VREF
An input differential signal of 0V will ideally produce a
stream of ones and zeros that are HIGH 50% of the time and
LOW 50% of the time. A differential input of 5V will
produce a stream of ones and zeros that are HIGH 90% of
the time. A differential input of –5V will produce a stream
of ones and zeros that are HIGH 10% of the time. The input
voltage versus the output modulator signal is shown in
Figure 8.
TABLE II. Bias Enable.
When enabled, the VBIAS circuitry consumes approximately
1mA with no external load. The maximum current into or
out of VBIAS should not exceed 10mA.
OFFSET and GAIN CALIBRATION
On power-up, external signals may be present before VBIAS
is enabled. This can create a situation in which a negative
voltage is applied to the analog inputs, reverse biasing the
negative input protection diode of the ADS1201. This situation should not be a problem as long as the resistors R1 and
R2 limit the current being sourced by each analog input to be
under 10mA. A potential of 0V at the analog input pin (AINP
or AINN) should be used in the calculation.
The ADS1201 offers a self-calibration function that is implemented with the GAIN/OFFSET and CALEN pins. Both
conditions provide an output stream of data, similar to
normal operation where the converter is configured to sample
an input signal at AIN.
The offset and gain errors of the ADS1201 are calibrated
independently. For best operation, the offset should be
calibrated first, followed by the gain. The calibration implementation timing diagram is shown in Figure 9. The calibration mode pins control the calibration functions of the
ADS1201.
DIGITAL OUTPUT
The timing diagram for the ADS1201 data retrieval is shown
in Figure 7. MCLK initiates the modulator process for the
ADS1201 and is used as a system clock by the ADS1201, as
well as a framing clock for data out. The modulator output
data, which is a serial stream, is available on the MOUT pin.
Typically, MOUT is read on the falling edge of MCLK.
Under any situation with MCLK, the duty cycle must be
kept constant for reliable, repeatable results.
Calibration should be performed once and then normal
operation can be resumed. Calibration of offset and gain is
recommended immediately after power-on and whenever
there is a “significant” change in the operating environment.
Significant changes in the operating environment include a
change of the MCLK frequency, MCLK duty cycle, power
Modulator Output
+FS (Analog Input)
–FS (Analog Input)
Analog Input
FIGURE 8. Analog Input versus Modulator Output of the ADS1201.
t9
t8
CAL
t8
GAIN/OFFSET
t9
t10
t11
SYMBOL
DESCRIPTION
t8
CAL and GAIN/OFFSET Rise Time
MIN
10
ns
t9
CAL and GAIN/OFFSET Fall Time
10
ns
t10
GAIN/OFFSET to CAL Setup Time
0
ns
t11
GAIN/OFFSET to CAL Hold Time
2.5 TMCLK(1)
ns
TYP
MAX
UNITS
NOTE: (1) TMCLK is the clock period of MCLK.
FIGURE 9. Timing Diagram for the Calibration Feature of the ADS1201.
®
9
ADS1201
GAIN/OFFSET
CALEN
0
1
Normal Mode
0
0
Offset Calibration, Analog inputs shorted
to ground internally.
1
0
Full-Scale Calibration, Analog inputs are
referenced to VREF internally.
The analog supply should be well regulated and low noise.
For designs requiring very high resolution from the ADS1201,
power supply rejection will be a concern. The requirements
for the digital supply are not strict. However, high frequency
noise on DVDD can capacitively couple into the analog
portion of the ADS1201. This noise can originate from
switching power supplies, microprocessors or digital signal
processors.
TABLE III. Calibration Enable.
For either supply, high frequency noise will generally be
rejected by the external digital filter at integer multiples of
MCLK. Just below and above these frequencies, noise will
alias back into the pass-band of the digital filter, affecting
the conversion result.
supply, VREF, or temperature. The amount of change which
could cause a re-calibration is dependent on the application
and effective resolution of the system.
The results of the calibration calculations are stored in two
registers in the processor chip (see Figure 1). These two
calibration results can then be used to calibrate the input
signal results with one of the following formulas:
Inputs to the ADS1201, such as AIN, REFIN, and MCLK,
should not be present before the analog and digital supplies
are on. Violating this condition could cause latch-up. If
these signals are present before the supplies are on, series
resistors should be used to limit the input current.
Equivalent Calibrated Output Code = FSC (FO1 – FO2) /(FO3 – FO2)
where
FO1 = Filter output code of an applied input voltage
FO2 = Filter output code of the offset calibration
If one supply must be used to power the ADS1201, the
system’s analog supply should be used to power both AVDD
and DVDD. Experimentation may be the best way to determine the appropriate connection between AVDD and DVDD.
FO3 = Filter output code of the gain calibration
FSC = Desired full-scale output
With a simple sinc filter, the calibrated A/D conversion
would equal:
GROUNDING
Equivalent Calibrated Input Voltage = (N1 – N2) • VREF / (N3 – N2 )
where N1 = number of ones counted (or digital equivalent
after filtering) over given time (tM) with an applied input voltage
The analog and digital sections of the design should be
carefully and cleanly partitioned. Each section should have
its own ground plane with no overlap between them. AGND
should be connected to the analog ground plane as well as
all other analog grounds. DGND should be connected to the
digital ground plane and all digital signals referenced to this
plane.
N2 = number of ones counted (or digital equivalent after filtering)
during offset calibration where t12 = tM
N3 = number of ones counted (or digital equivalent after filtering)
during gain calibration where t13 = tM
A system calibration can be performed by applying two
known voltage levels to the input of the converter. In this
situation, the GAIN/OFFSET and CALEN pins are not used.
Rather, the digital output of these two known voltages are
accumulated by the processor. With this data, the processor
can determine the calibration register values that are appropriate for the application.
The ADS1201 pinout is such that the converter is cleanly
separated into an analog and digital portion. This should
allow simple layout of the analog and digital sections of the
design.
For a signal converter system, AGND and DGND of the
ADS1201 can be connected together. Do not join the ground
planes, but connect the two with a moderate signal trace
underneath the converter. For multiple converters, connect
the two ground planes at one location as central to all of the
converters as possible. In some cases, experimentation may
be required to find the best point to connect the two planes
together. Experimentation may be the best way to determine
the appropriate connection between AGND and DGND.
LAYOUT CONSIDERATIONS
POWER SUPPLIES
The ADS1201 requires the digital supply (DVDD) to be no
greater than the analog supply (AVDD). Failure to observe
this condition could cause permanent damage to the
ADS1201. The best scheme is to power the analog section of
the design and AVDD from one +5V line and the digital
section and DVDD from a separate +5V line (from the same
supply). If there are separate analog and digital power
supplies for the ADS1201, a good design approach would be
to have the analog supply come up first, followed by the
digital supply. Another approach that can be used to control
the analog and digital power supply differences is shown in
Figure 10. In this circuit, a connection has been made
between the ADS1201 supply pins via a 10Ω resistor. The
combination of this resistor and the decoupling capacitors
provides some filtering between DVDD and AVDD.
DECOUPLING
Good decoupling practices should be used for the ADS1201
and for all components in the design. All decoupling capacitors, specifically the 0.1µF ceramic capacitors, should be
placed as close as possible to the pin being decoupled. A
1µF and 10µF capacitor, in parallel with the 0.1µF ceramic
capacitor, should be used to decouple AVDD to AGND. At
a minimum, a 0.1µF ceramic capacitor should be used to
decouple DVDD to DGND, as well as for the digital supply
on each digital component.
®
ADS1201
10
+5V
10Ω
+
10µF
1
AVDD
REFEN 16
2
REFOUT
MOUT 15
3
REFIN
MCLK 14
4
NIC
0.1µF
DVDD 13
ADS1201
0.1µF
5
AINP
DGND 12
6
AINN
CAL 11
7
AGND
8
VBIAS
GAIN/OFFSET 10
BIASEN
9
FIGURE 10. Power Supply Connection Using One Power Plane and One Digital Plane.
+5V
Isolated Power
6kΩ
0.1µF
10kΩ
DSP
8
100µA
7
100µA
1µF
1
AVDD
REFEN 16
2
REFOUT
MOUT 15
3
REFIN
MCLK 14
4
NIC
2
SCLK
0.1µF
5
AINP
DGND 12
6
AINN
CAL 11
7
AGND
8
VBIAS
SDATA
REF200
5
4
+5V
DVDD 13
ADS1201
1
MDATA
Opto
Coupler
GAIN/OFFSET 10
BIASEN
+5V
Opto
Coupler
MCLK
9
3
FIGURE 11. Bridge Transducer Interface with Current Excitation.
®
11
ADS1201
+5V
+5V
Isolated Power
8
7
REF200
100µA
100µA
0.1µF
DSP
1
2
1µF
1
AVDD
REFEN 16
2
REFOUT
MOUT 15
3
REFIN
MCLK 14
4
NIC
MDATA
Opto
Coupler
+5V
DVDD 13
ADS1201
SCLK
0.1µF
5
AINP
DGND 12
6
AINN
CAL 11
7
AGND
8
VBIAS
SDATA
PT100
12.5kΩ
+5V
GAIN/OFFSET 10
Opto
Coupler
MCLK
9
BIASEN
FIGURE 12. PT100 Interface with Current Excitation.
+5V
0.1µF
10kΩ
DSP
3
2
1/2
OPA2237
1
1
AVDD
REFEN 16
2
REFOUT
MOUT 15
MDATA
3
REFIN
MCLK 14
MCLK
4
NIC
0.1µF
DVDD 13
ADS1201
RG
6
5
1/2
OPA2237
7
5
AINP
DGND 12
6
AINN
CAL 11
7
AGND
8
VBIAS
GAIN/OFFSET 10
BIASEN
FIGURE 13. Geophone Interface.
®
ADS1201
12
SCLK
0.1µF
9
SDATA
+5V
+5V
Isolated Power
0.1µF
10kΩ
DSP
3
2
1/2
OPA2237
1
10kΩ
0.1µF
16
1
AVDD
REFEN
2
REFOUT
MOUT 15
3
REFIN
MCLK 14
4
NIC
10kΩ
6
5
1/2
OPA2237
7
+5V
DVDD 13
ADS1201
RG
MDATA
Opto
Coupler
SCLK
0.1µF
5
AINP
DGND 12
6
AINN
CAL 11
7
AGND
8
VBIAS
SDATA
+5V
GAIN/OFFSET 10
BIASEN
Opto
Coupler
MCLK
9
FIGURE 14. Single-Supply, High Accuracy Thermocouple Interface.
HV+
Floating Positive
Supply
Gate Drive
0.1µF
5.1V
DSP
0.1µF
1
AVDD
REFEN 16
2
REFOUT
MOUT 15
3
REFIN
MCLK 14
4
NIC
RSENSE
Motor
AINP
6
AINN
7
AGND
8
VBIAS
+5V
DVDD 13
ADS1201
5
RSENSE
MDATA
Opto
Coupler
SCLK
0.1µF
DGND 12
SDATA
+5V
CAL 11
GAIN/OFFSET 10
BIASEN
Opto
Coupler
MCLK
9
HV–
FIGURE 15. Motor Controller Sensing Circuit.
®
13
ADS1201
PACKAGE OPTION ADDENDUM
www.ti.com
7-Oct-2008
PACKAGING INFORMATION
Orderable Device
Status (1)
Package
Type
Package
Drawing
Pins Package Eco Plan (2)
Qty
ADS1201U
ACTIVE
SOIC
DW
16
ADS1201U/1K
ACTIVE
SOIC
DW
ADS1201U/1KG4
ACTIVE
SOIC
ADS1201UG4
ACTIVE
SOIC
40
Lead/Ball Finish
MSL Peak Temp (3)
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
16
1000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
DW
16
1000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
DW
16
CU NIPDAU
Level-2-260C-1 YEAR
40
Green (RoHS &
no Sb/Br)
(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
11-Mar-2008
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
ADS1201U/1K
Package Package Pins
Type Drawing
SOIC
DW
16
SPQ
Reel
Reel
Diameter Width
(mm) W1 (mm)
1000
330.0
16.4
Pack Materials-Page 1
A0 (mm)
B0 (mm)
K0 (mm)
P1
(mm)
W
Pin1
(mm) Quadrant
10.85
10.8
2.7
12.0
16.0
Q1
PACKAGE MATERIALS INFORMATION
www.ti.com
11-Mar-2008
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
ADS1201U/1K
SOIC
DW
16
1000
346.0
346.0
33.0
Pack Materials-Page 2
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