MAX1452AAE [MAXIM]
Low-Cost Precision Sensor Signal Conditioner; 低成本，精密的传感器信号调理器
| 型号： | MAX1452AAE |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Low-Cost Precision Sensor Signal Conditioner |
| 文件： | 总24页 (文件大小：282K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1829; Rev 1; 6/01
Low-Cost Precision Sensor
Signal Conditioner
General Description
Features
The MAX1452 is a highly integrated analog-sensor sig-
nal processor optimized for industrial and process con-
trol applications utilizing resistive element sensors.
The MAX1452 provides amplification, calibration, and
temperature compensation that enables an overall per-
formance approaching the inherent repeatability of the
sensor. The fully analog signal path introduces no
quantization noise in the output signal while enabling
digitally controlled trimming with the integrated 16-bit
DACs. Offset and span are calibrated using 16-bit
DACs, allowing sensor products to be truly inter-
changeable.
o Provides Amplification, Calibration, and
Temperature Compensation
o Accommodates Sensor Output Sensitivities
from 1mV/V to 40mV/V
o Single Pin Digital Programming
o No External Trim Components Required
o 16-Bit Offset and Span Calibration Resolution
o Fully Analog Signal Path
o On-Chip Lookup Table Supports Multipoint
The MAX1452 architecture includes a programmable
sensor excitation, a 16-step programmable-gain ampli-
fier (PGA), a 768-byte (6144 bits) internal EEPROM,
four 16-bit DACs, an uncommitted op amp, and an on-
chip temperature sensor. In addition to offset and span
compensation. The MAX1452 provides a unique tem-
perature compensation strategy for offset TC and
FSOTC that was developed to provide a remarkable
degree of flexibility while minimizing testing costs.
Calibration Temperature Correction
o Supports Both Current and Voltage Bridge
Excitation
o Fast 3.2kHz Frequency Response
o On-Chip Uncommitted Op Amp
o Secure-Lock™ Prevents Data Corruption
o Low 2mA Current Consumption
The MAX1452 is packaged for the commercial, industri-
al, and automotive temperature ranges in 16-pin SSOP
packages.
Ordering Information
Customization
PART
TEMP. RANGE
PIN-PACKAGE
16 SSOP
16 SSOP
16 SSOP
Dice*
Maxim can customize the MAX1452 for high-volume
dedicated applications. Using our dedicated cell library
of more than 2000 sensor-specific functional blocks,
Maxim can quickly provide a modified MAX1452 solu-
tion. Contact Maxim for further information.
MAX1452CAE
MAX1452EAE
MAX1452AAE
MAX1452C/D
0°C to +70°C
-40°C to +85°C
-40°C to +125°C
0°C to +70°C
*Dice are tested at T = +25°C, DC parameters only.
A
Applications
Pressure Sensors
A detailed block diagram appears at the end of data sheet.
Transducers and Transmitters
Strain Gauges
Pressure Calibrators and Controllers
Resistive Elements Sensors
Accelerometers
Pin Configuration
TOP VIEW
ISRC
OUT
1
2
3
4
5
6
7
8
16 FSOTC
15 AMP+
14 AMP-
Humidity Sensors
V
SS
Outputs Supported
4–20mA
0 to +5V (Rail-to-Rail®)
+0.5V to +4.5V Ratiometric
+2.5V to 2.5V
INM
BDR
INP
13 AMPOUT
12 CLK1M
11 DIO
MAX1452
(NOT TO SCALE)
V
10 UNLOCK
DD
TEST
9
V
DDF
Rail-to-Rail is a trademark of Nippon Motorola Ltd.
Secure-Lock is a trademark of Maxim Integrated Products.
SSOP
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Low-Cost Precision Sensor
Signal Conditioner
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, V
to V .........................................-0.3V, +6V
Operating Temperature:
DD
SS
All Other Pins ...................................(V - 0.3V) to (V
Short-Circuit Duration, FSOTC, OUT, BDR,
AMPOUT .................................................................Continuous
+ 0.3V)
MAX1452CAE/MAX1452C/D ...............................0°C to +70°C
MAX1452EAE ...................................................-40°C to +85°C
MAX1452AAE .................................................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature.........................................-65°C to +150°C
Lead Temperature (soldering, 10s) ................................ +300°C
SS
DD
Continuous Power Dissipation (T = +70°C)
A
16-Pin SSOP (derate 8.00mW/°C above +70°C) ..........640mW
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
= +5V, V = 0, T = +25°C, unless otherwise noted.)
SS A
DD
PARAMETER
SYMBOL
CONDITIONS
MIN
4.5
TYP
MAX
UNITS
GENERAL CHARACTERISTICS
Supply Voltage
V
5.0
2.0
1
5.5
2.5
V
DD
Supply Current
I
(Note 1)
mA
MHz
DD
Oscillator Frequency
ANALOG INPUT
f
0.85
1.15
OSC
Input Impedance
R
1
MΩ
IN
Input Referred Offset Tempco
(Notes 2, 3)
± 1
µV/°C
Input Referred Adjustable
Offset Range
Offset TC = 0 at minimum gain (Note 4)
Percent of +4V span, V = +0.5V to 4.5V
± 150
0.01
90
mV
%
Amplifier Gain Nonlinearity
OUT
Specified for common-mode voltages
between V and V (Note 2)
Common-Mode Rejection Ratio
CMRR
dB
SS
DD
Input Referred Adjustable FSO
Range
(Note 5)
1-40
mV/V
V/V
ANALOG OUTPUT
39-
240
Differential Signal-Gain Range
Selectable in 16 steps
Configuration [5:2] 0000bin
Configuration [5:2] 0001bin
Configuration [5:2] 0010bin
Configuration [5:2] 0100bin
Configuration [5:2] 1000bin
34
47
39
52
46
59
Differential Signal Gain
58
65
74
V/V
V
82
91
102
157
133
143
Maximum Output Voltage Swing
No load from each supply
0.02
Output Voltage Low
I
I
= 1mA sinking, T = T
to T
MAX
0.100
4.87
0.1
0.20
1.20
V
V
OUT
A
MIN
Output Voltage High
Output Impedance at DC
= 1mA sourcing, T = T
to T
MAX
4.75
0.90
OUT
A
MIN
Ω
∆V
∆Offset
/
OUT
Output Offset Ratio
1.05
V/V
2
_______________________________________________________________________________________
Low-Cost Precision Sensor
Signal Conditioner
ELECTRICAL CHARACTERISTICS (continued)
(V
= +5V, V = 0, T = +25°C, unless otherwise noted.)
SS A
DD
PARAMETER
SYMBOL
∆V
∆Offset TC
CONDITIONS
MIN
TYP
MAX
UNITS
/
OUT
Output Offset TC Ratio
0.9
1
1.2
V/V
Step Response and IC
(63% Final Value)
150
1
µs
Maximum Capacitive Load
µF
DC to 1kHz (gain = minimum, source
Output Noise
0.5
mV
RMS
impedance = 5kΩ V
filter)
DDF
BRIDGE DRIVE
Bridge Current
I
R = 1.7kΩ
0.1
10
0.5
12
2
mA
BDR
L
Current Mirror Ratio
AA
R
= internal
14
A/A
hex
ISOURCE
V
Range (Span Code)
T
= T
to T
MAX
4000
C000
SPAN
A
MIN
DIGITAL–TO–ANALOG CONVERTERS
DAC Resolution
16
76
bits
∆V
∆Code
/
OUT
ODAC Bit Weight
DAC reference = V
DAC reference = V
DAC reference = V
DAC reference = V
= +5.0V
µV/bit
DD
∆V
∆Code
/
OUT
OTCDAC Bit Weight
FSODAC Bit Weight
FSOTCDAC Bit Weight
= +2.5V
38
76
38
µV/bit
µV/bit
µV/bit
BDR
∆V
∆Code
/
OUT
= +5.0V
DD
∆V
∆Code
/
OUT
= +2.5V
BDR
COARSE OFFSET DAC
IRODAC Resolution
Including sign
4
9
bits
∆V
∆Code
/
Input referred, DAC reference =
V = +5.0V (Note 6)
DD
OUT
IRODAC Bit Weight
mV/bit
FSOTC BUFFER
V
+
0.1
SS
Minimum Output Voltage Swing
No load
No load
V
Maximum Output Voltage Swing
V
DD
- 1.0
V
Current Drive
V
= +2.5V
-40
+40
µA
FSOTC
INTERNAL RESISTORS
Current-Source Reference
Resistor
R
75
kΩ
ISRC
Current-Source Reference
Resistor Temperature Coefficient
∆R
1300
75
ppm/°C
kΩ
ISRC
FSOTC Resistor
R
FTC
FSOTC Resistor Temperature
Coefficient
∆R
1300
ppm/°C
FTC
_______________________________________________________________________________________
3
Low-Cost Precision Sensor
Signal Conditioner
ELECTRICAL CHARACTERISTICS (continued)
(V
= +5V, V = 0, T = +25°C, unless otherwise noted.)
SS A
DD
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
TEMPERATURE-TO-DIGITAL CONVERTER
Temperature ADC Resolution
Offset
8
3
bits
LSB
°C/bit
LSB
hex
Gain
1.45
0.5
00
Nonlinearity
Lowest Digital Output
Highest Digital Output
UNCOMMITTED OP AMP
Open Loop Gain
AF
hex
R = 100kΩ
L
90
dB
V
Input Common-Mode Range
V
V
DD
SS
V
0.02
+
V
0.02
-
DD
SS
Output Swing
No load, T = T
to T
MIN
V
A
MIN
MAX
to T
Output Voltage High
Output Voltage Low
Offset
1mA source, T = T
4.85
4.90
0.05
V
V
A
MAX
1mA sink, T = T
to T
MAX
0.15
+20
A
MIN
V
= +2.5V, unity gain buffer
-20
mV
MHz
IN+
Unity Gain Bandwidth
EEPROM
2
Maximum Erase/Write Cycles
Minimum Erase Time
(Note 7)
(Note 8)
10k
6
Cycles
ms
Note 1: Excludes sensor or load current.
Note 2: All electronics temperature errors are compensated together with sensors errors.
Note 3: The sensor and the MAX1452 must be at the same temperature during calibration and use.
Note 4: This is the maximum allowable sensor offset.
Note 5: This is the sensor's sensitivity normalized to its drive voltage, assuming a desired full span output of +4V and a bridge volt-
age of +2.5V.
Note 6: Bit weight is ratiometric to V
.
DD
Note 7: Programming of the EEPROM at room temperature is recommended.
Note 8: Allow a minimum of 6ms elapsed time before sending any command.
4
_______________________________________________________________________________________
Low-Cost Precision Sensor
Signal Conditioner
Typical Operating Characteristics
(V
= +5V, T = +25°C, unless otherwise noted.)
DD
A
AMPLIFIER GAIN NONLINEARITY
OFFSET DAC DNL
5.0
5.0
ODAC = 6800hex
OTCDAC = 0
FSODAC = 4000hex
2.5
0
FSOTCDAC = 8000hex
IRO = 2hex
PGA = 0
2.5
0
-2.5
-5.0
-2.5
-5.0
-50
-25
0
25
50
0
10k 20k 30k 40k 50k 60k 70k
DAC CODE
INPUT VOLTAGE [INP-INM] (mV)
OUTPUT NOISE
OUT
10mV/div
400µs/div
C = 4.7µF, R
= 1kΩ
LOAD
Pin Description
PIN
NAME
FUNCTION
1
ISRC
OUT
Bridge Drive Current Mode Setting
High ESD and Scan Path Output Signal. May need a 0.1µF capacitor, in noisy environments.
OUT may be parallel connected to DIO.
2
3
4
5
6
7
8
V
Negative Supply Voltage
SS
INM
BDR
INP
Bridge Negative Input. Can be swapped to INP by configuration register.
Bridge Drive
Bridge Positive Input. Can be swapped to INM by configuration register.
V
Positive Supply Voltage. Connect a 0.1µF capacitor from V
to V
.
SS
DD
DD
TEST
Internally Connected. Connect to V
.
SS
_______________________________________________________________________________________
5
Low-Cost Precision Sensor
Signal Conditioner
Pin Description (continued)
PIN
NAME
FUNCTION
Positive Supply Voltage for EEPROM. Connect a 0.1µF capacitor from V
to V . Connect V
DDF
DDF
.
SS
9
V
DDF
to V
or for improved noise performance connect a 1kΩ resistor to V
DD
DD
10
11
12
13
14
15
16
UNLOCK
DIO
Secure-Lock Disable. Allows communication to the device.
Digital Input Output. DIO allows communication with the device.
1MHz Clock Output. The clock can be shut off by a configuration bit.
Uncommitted Amplifier Output
CLK1M
AMPOUT
AMP-
Uncommitted Amplifier Negative Input
AMP+
Uncommitted Amplifier Positive Input
FSOTC
Full Span TC Buffered Output
The single pin, serial Digital Input-Output (DIO) commu-
nication architecture and the ability to timeshare its
activity with the sensor’s output signal enables output
sensing and calibration programming on a single line
by parallel connecting OUT and DIO. The MAX1452
provides a Secure-Lock feature that allows the cus-
tomer to prevent modification of sensor coefficients and
the 52-byte user definable EEPROM data after the sen-
sor has been calibrated. The Secure-Lock feature also
provides a hardware override to enable factory rework
and recalibration by assertion of logic high on the
UNLOCK pin.
Detailed Description
The MAX1452 provides amplification, calibration, and
temperature compensation to enable an overall perfor-
mance approaching the inherent repeatability of the
sensor. The fully analog signal-path introduces no
quantization noise in the output signal while enabling
digitally controlled trimming with the integrated 16-bit
DACs. Offset and span can be calibrated to within
0.02% of span.
The MAX1452 architecture includes a programmable
sensor excitation, a 16-step programmable-gain ampli-
fier (PGA), a 768-byte (6144 bits) internal EEPROM, four
16-bit DACs, an uncommitted op amp, and an on-chip
temperature sensor.The MAX1452 also provides a
unique temperature compensation strategy for offset
TC and FSOTC that was developed to provide a
remarkable degree of flexibility while minimizing testing
costs.
The MAX1452 allows complete calibration and sensor
verification to be performed at a single test station.
Once calibration coefficients have been stored in the
ASIC, the customer can choose to retest in order to ver-
ify performance as part of a regular QA audit or to gen-
erate final test data on individual sensors.
The MAX1452’s low current consumption and the inte-
grated uncommitted op amp enables a 4–20mA output
signal format in a sensor that is completely powered
from a 2-wire current loop. Frequency response can be
user-adjusted to values lower than the 3.2kHz band-
width by using the uncommitted op amp and simple
passive components.
The customer can select from one to 114 temperature
points to compensate their sensor. This allows the lati-
tude to compensate a sensor with a simple first order
linear correction or match an unusual temperature
curve. Programming up to 114 independent 16-bit EEP-
ROM locations corrects performance in 1.5°C tempera-
ture increments over a range of -40°C to +125°C. For
sensors that exhibit a characteristic temperature perfor-
mance, a select number of calibration points can be
used with a number of preset values that define the
temperature curve. In cases where the sensor is at a
different temperature than the ASIC, the MAX1452 uses
the sensor bridge itself to provide additional tempera-
ture correction.
The MAX1452 (Figure 1) provides an analog amplifica-
tion path for the sensor signal. It also uses an analog
architecture for first-order temperature correction. A
digitally controlled analog path is then used for nonlin-
ear temperature correction. Calibration and correction
is achieved by varying the offset and gain of a pro-
grammable-gain-amplifier (PGA) and by varying the
sensor bridge excitation current or voltage. The PGA
6
_______________________________________________________________________________________
Low-Cost Precision Sensor
Signal Conditioner
Offset Correction
Initial offset correction is accomplished at the input
stage of the signal gain amplifiers by a coarse offset
setting. Final offset correction occurs through the use of
a temperature indexed lookup table with 176 16-bit
entries. The on-chip temperature sensor provides a
unique 16-bit offset trim value from the table with an
indexing resolution of approximately 1.5°C from -40°C
to +125°C. Every millisecond, the on-chip temperature
sensor provides indexing into the offset lookup table in
EEPROM and the resulting value transferred to the off-
set DAC register. The resulting voltage is fed into a
summing junction at the PGA output, compensating the
sensor offset with a resolution of 76µV ( 0.0019%
FSO). If the offset TC DAC is set to zero then the maxi-
mum temperature error is equivalent to one degree of
temperature drift of the sensor, given the Offset DAC
has corrected the sensor at every 1.5°C. The tempera-
ture indexing boundaries are outside of the specified
Absolute Maximum Ratings. The minimum indexing
value is 00hex corresponding to approximately -69°C.
All temperatures below this value will output the coeffi-
cient value at index 00hex. The maximum indexing
value is AFhex, which is the highest lookup table entry.
V
DD
V
DD
BIAS
GENERATOR
IRO
DAC
MAX1452
CLK1M
TEST
OSCILLATOR
INP
PGA
OUT
∑
INM
CURRENT
SOURCE
ANAMUX
ISRC
BDR
A = 1
FSOTC
TEMP
SENSOR
176
8-BIT ADC
TEMPERATURE
LOOK UP
POINTS FOR
OFFSET AND
SPAN.
VDDF
DIO
INTERNAL
EEPROM
6144 BITS
UNLOCK
416 BITS
FOR USER
V
DD
BDR
OP-AMP
AMP+
AMP-
AMPOUT
All temperatures higher than approximately 184°C will
output the highest lookup table index value. No index-
ing wrap-around errors are produced.
V
SS
FSO Correction
Two functional blocks control the FSO gain calibration.
First, a coarse gain is set by digitally selecting the gain
of the PGA. Second, FSO DAC sets the sensor bridge
current or voltage with the digital input obtained from a
temperature-indexed reference to the FSO lookup table
in EEPROM. FSO correction occurs through the use of
a temperature indexed lookup table with 176 16-bit
entries. The on-chip temperature sensor provides a
unique FSO trim from the table with an indexing resolu-
tion approaching one 16-bit value at every 1.5°C from
-40°C to +125°C. The temperature indexing boundaries
are outside of the specified Absolute Maximum
Ratings. The minimum indexing value is 00hex corre-
sponding to approximately -69°C. All temperatures
below this value will output the coefficient value at
index 00hex. The maximum indexing value is AFhex,
which is the highest lookup table entry. All tempera-
tures higher than approximately 184°C will output the
highest lookup table index value. No indexing wrap-
around errors are produced.
Figure 1. Functional Diagram
utilizes a switched capacitor CMOS technology, with an
input referred offset trimming range of more than
150mV with an approximate 3µV resolution (16 bits).
The PGA provides gain values from 39V/V to 240V/V in
16 steps.
The MAX1452 uses four 16-bit DACs with calibration
coefficients stored by the user in an internal 768 x 8
EEPROM (6144 bits). This memory contains the follow-
ing information, as 16-bit wide words:
•
•
•
•
•
Configuration Register
Offset Calibration Coefficient Table
Offset Temperature Coefficient Register
FSO (Full-Span Output) Calibration Table
FSO Temperature Error Correction Coefficient
Register
Linear and Nonlinear Temperature
Compensation
Writing 16-bit calibration coefficients into the offset TC
and FSOTC registers compensates first-order tempera-
•
52 bytes (416 bits) uncommitted for customer pro-
gramming of manufacturing data (e.g., serial num-
ber and date)
_______________________________________________________________________________________
7
Low-Cost Precision Sensor
Signal Conditioner
ture errors. The piezoresistive sensor is powered by a
current source resulting in a temperature-dependent
bridge voltage due to the sensor's temperature resis-
tance coefficient (TCR). The reference inputs of the off-
set TC DAC and FSOTC DAC are connected to the
bridge voltage. The DAC output voltages will track the
bridge voltage as it varies with temperature, and by
varying the offset TC and FSOTC digital code a portion
of the bridge voltage, which is temperature dependent,
is used to compensate the first order temperature
errors.
For high accuracy applications (errors less than
0.25%), the first-order offset and FSOTC should be
compensated with the offset TC and FSOTC DACs, and
the residual higher order terms with the lookup table.
The offset and FSO compensation DACs provide
unique compensation values for approximately 1.5°C of
temperature change as the temperature indexes the
address pointer through the coefficient lookup table.
Changing the offset does not effect the FSO, however
changing the FSO will affect the offset due to nature of
the bridge. The temperature is measured on both the
MAX1452 die and at the bridge sensor. It is recom-
mended to compensate the first-order temperature
errors using the bridge sensor temperature.
The internal feedback resistors (R
and R
) for
STC
ISRC
FSO temperature compensation are optimized to 75kΩ
for silicon piezoresistive sensors. However, since the
required feedback resistor values are sensor depen-
dent, external resistors may also be used. The internal
resistors selection bit in the configuration register
selects between internal and external feedback resis-
tors.
Typical Ratiometric
Operating Circuit
Ratiometric output configuration provides an output that
is proportional to the power supply voltage. This output
can then be applied to a ratiometric ADC to produce a
digital value independent of supply voltage.
Ratiometricity is an important consideration for battery-
operated instruments, automotive, and some industrial
applications.
To calculate the required offset TC and FSOTC com-
pensation coefficients, two test-temperatures are need-
ed. After taking at least two measurements at each
temperature, calibration software (in a host computer)
calculates the correction coefficients and writes them to
the internal EEPROM.
The MAX1452 provides a high-performance ratiometric
output with a minimum number of external components
(Figure 2). These external components include the fol-
lowing:
With coefficients ranging from 0000hex to FFFFhex and
a +5V reference, each DAC has a resolution of 76µV.
Two of the DACs (offset TC and FSOTC) utilize the sen-
sor bridge voltage as a reference. Since the sensor
bridge voltage is approximately set to +2.5V the FSOTC
and offset TC exhibit a step size of less than 38µV.
•
•
•
One supply bypass capacitor.
One optional output EMI suppression capacitor.
Two optional resistors, RISRC and RSTC, for special
sensor bridge types.
+5V V
OUT
DD
7
V
DD
5
6
9
BDR
INP
V
DDF
OUT
2
MAX1452
16
FSOTC
4
SENSOR
INM
RSTC
1
ISRC
0.1µF
0.1µF
RISRC
TEST
V
SS
8
3
GND
Figure 2. Basic Ratiometric Output Configuration
8
_______________________________________________________________________________________
Low-Cost Precision Sensor
Signal Conditioner
2N4392
G
1
VPWR
+12V TO +40V
IN
D
S
MAX6105
2
5V
GND
3
7
1kΩ
V
DD
5
6
9
2
BDR
INP
V
DDF
OUT
OUT
MAX1452
16
FSOTC
4
SENSOR
INM
RSTC
1
ISRC
0.1µF
0.1µF
0.1µF
0.1µF
RISRC
TEST
V
SS
8
3
GND
Figure 3. Basic Nonratiometric Output Configuration
Internal Calibration Registers (ICRs)
Typical Nonratiometric
Operating Circuit
(12VDC < VPWR < 40VDC)
The MAX1452 has five 16-bit internal calibration regis-
ters that are loaded from EEPROM, or loaded from the
serial digital interface.
Nonratiometric output configuration enables the sensor
power to vary over a wide range. A high performance
voltage reference, such as the MAX6105, is incorporat-
ed in the circuit to provide a stable supply and refer-
ence for MAX1452 operation. A typical example is
shown in Figure 3. Nonratiometric operation is valuable
when wide ranges of input voltage are to be expected
and the system A/D or readout device does not enable
ratiometric operation.
Data can be loaded into the internal calibration regis-
ters under three different circumstances.
Normal Operation, Power-On Initialization Sequence
•
The MAX1452 has been calibrated, the Secure-
Lock byte is set (CL[7:0] = FFhex) and UNLOCK is
low.
•
•
•
Power is applied to the device.
The power-on reset functions have completed.
Typical 2-Wire, Loop Powered,
4–20mA Operating Circuit
Registers CONFIG, OTCDAC, and FSOTCDAC are
refreshed from EEPROM.
•
Registers ODAC, and FSODAC are refreshed from
the temperature indexed EEPROM locations.
Process Control systems benefit from a 4–20mA current
loop output format for noise immunity, long cable runs,
and 2-wire sensor operation. The loop voltages can
range from 12VDC to 40VDC and are inherently nonra-
tiometric. The low current consumption of the MAX1452
allows it to operate from loop power with a simple
4–20mA drive circuit efficiently generated using the
integrated uncommitted op amp (Figure 4).
Normal Operation, Continuous Refresh
•
The MAX1452 has been calibrated, the Secure-
Lock byte has been set (CL[7:0] = FFhex) and
UNLOCK is low.
•
•
•
Power is applied to the device.
The power-on reset functions have completed.
The temperature index timer reaches a 1ms time
period.
_______________________________________________________________________________________
9
Low-Cost Precision Sensor
Signal Conditioner
V
IN+
2N4392
G
+12V TO +40V
D
S
100Ω
1
IN
Z1
MAX6105
2
5VOUT
GND
3
7
1kΩ
V
DD
5
6
9
BDR
INP
V
DDF
16
FSOTC
0.1µF
RSTC
MAX1452
1
ISRC
OUT
0.1µF
0.1µF
4
SENSOR
INM
4.99MΩ
499kΩ
RISRC
2
0.1µF
13
AMPOUT
AMP-
2N2222A
14
15
4.99kΩ
0.1µF
AMP+
TEST
8
V
100kΩ
SS
3
47Ω
100kΩ
V
IN-
Figure 4. Basic 4–20mA Output, Loop-Powered Configuration
•
Registers CONFIG, OTCDAC, and FSOTCDAC are
refreshed from EEPROM.
Internal EEPROM
The internal EEPROM is organized as a 768 by 8-bit
memory. It is divided into 12 pages, with 64 bytes per
page. Each page can be individually erased. The mem-
ory structure is arranged as shown in Table 1. The look-
up tables for ODAC and FSODAC are also shown, with
the respective temp-index pointer. Note that the ODAC
table occupies a continuous segment, from address
000hex to address 15Fhex, whereas the FSODAC table
is divided in two parts, from 200hex to 2FFhex, and
from 1A0hex to 1FFhex. With the exception of the gen-
eral purpose user bytes, all values are 16-bit wide
words formed by two adjacent byte locations (high byte
and low byte).
•
Registers ODAC and FSODAC are refreshed from
the temperature indexed EEPROM locations.
Calibration Operation, Registers Updated by Serial
Communications
•
The MAX1452 has not had the Secure-Lock byte
set (CL[7:0] = 00hex) or UNLOCK is high.
•
•
•
Power is applied to the device.
The power-on reset functions have completed.
The registers can then be loaded from the serial
digital interface by use of serial commands. See the
section on Serial I/O and Commands.
The MAX1452 compensates for sensor offset, FSO, and
temperature errors by loading the internal calibration
registers with the compensation values. These com-
pensation values can be loaded to registers directly via
10 ______________________________________________________________________________________
Low-Cost Precision Sensor
Signal Conditioner
Table 1. EEPROM Memory Address Map
LOW-BYTE
PAGE
HIGH-BYTE
ADDRESS (hex)
TEMP-INDEX[7:0]
(hex)
CONTENTS
ADDRESS (hex)
000
03E
040
07E
080
0BE
0C0
0FE
100
13E
140
15E
160
162
164
166
168
16A
16C
17E
180
19E
1A0
1BE
1C0
1FE
200
23E
240
27E
280
2BE
2C0
2FE
001
03F
041
07F
081
0BF
0C1
0FF
101
13F
141
15F
161
163
165
167
169
16B
16D
17F
181
19F
1A1
1BF
1C1
1FF
201
23F
241
27F
281
2BF
2C1
2FF
00
1F
0
1
2
3
4
20
3F
40
5F
ODAC
Lookup Table
60
7F
80
9F
A0
AF to FF
Configuration
Reserved
OTCDAC
5
Reserved
FSOTCDAC
Control Location
52 General-Purpose
User Bytes
6
80
8F
90
7
8
9
A
B
AF to FF
00
FSODAC
Lookup Table
1F
20
3F
40
5F
60
7F
the serial digital interface during calibration or loaded
automatically from EEPROM at power-on. In this way
the device can be tested and configured during cali-
bration and test and the appropriate compensation val-
ues stored in internal EEPROM. The device will
auto-load the registers from EEPROM and be ready for
use without further configuration after each power-up.
The EEPROM is configured as an 8-bit wide array so
each of the 16-bit registers is stored as two 8-bit quan-
tities. The configuration register, FSOTCDAC and OTC-
______________________________________________________________________________________ 11
Low-Cost Precision Sensor
Signal Conditioner
DAC registers are loaded from the pre-assigned loca-
tions in the EEPROM.
terminates the baud rate synchronization sequence.
This initialization sequence on DIO should occur after a
period of 1ms after stable power is applied to the
device. This allows time for the power-on reset function
to complete and the DIO pin to be configured by
Secure-Lock or the UNLOCK pin.
The ODAC and FSODAC are loaded from the EEPROM
lookup tables using an index pointer that is a function
of temperature. An ADC converts the integrated tem-
perature sensor to an 8-bit value every 1ms. This digi-
tized value is then transferred into the temp-index
register.
Reinitialization Sequence
The MAX1452 allows for relearning the baud rate. The
reinitialization sequence is one byte transmission of
FFhex, as follows.
The typical transfer function for the temp-index is as fol-
lows:
temp-index = 0.69 ✕ Temperature (°C) + 47.58
11111111011111111111111111
where temp-index is truncated to an 8-bit integer value.
Typical values for the temp-index register are given in
Table 6.
When a serial reinitialization sequence is received, the
receive logic resets itself to its power-up state and
waits for the initialization sequence. The initialization
sequence must follow the reinitialization sequence in
order to re-establish the baud rate.
Note that the EEPROM is byte wide and the registers
that are loaded from EEPROM are 16 bits wide. Thus
each index value points to two bytes in the EEPROM.
Serial Interface Command Format
All communication commands into the MAX1452 follow
a defined format utilizing an interface register set (IRS).
The IRS is an 8-bit command that contains both an
interface register set data (IRSD) nibble (4-bit) and an
interface register set address (IRSA) nibble (4-bit). All
internal calibration registers and EEPROM locations are
accessed for read and write through this interface reg-
ister set. The IRS byte command is structured as fol-
lows:
Maxim programs all EEPROM locations to FFhex with
the exception of the oscillator frequency setting and
Secure-Lock byte. OSC[2:0] is in the Configuration
Register (Table 3). These bits should be maintained at
the factory preset values. Programming 00hex in the
Secure-Lock byte (CL[7:0] = 00hex), configures the
DIO as an asynchronous serial input for calibration and
test purposes.
Communication Protocol
The DIO serial interface is used for asynchronous serial
data communications between the MAX1452 and a
host calibration test system or computer. The MAX1452
will automatically detect the baud rate of the host com-
puter when the host transmits the initialization
sequence. Baud rates between 4800bps and
38,400bps can be detected and used regardless of the
internal oscillator frequency setting. Data format is
always 1 start bit, 8 data bits, 1 stop bit and no parity.
Communications are only allowed when Secure-Lock is
disabled (i.e., CL[7:0] = 00hex) or the UNLOCK pin is
held high.
IRS[7:0] = IRSD[3:0], IRSA[3:0]
Where:
•
IRSA[3:0] is the 4-bit interface register set address
and indicates which register receives the data nib-
ble IRSD[3:0].
•
IRSA[0] is the first bit on the serial interface after the
start bit.
•
•
IRSD[3:0] is the 4-bit interface register set data.
IRSD[0] is the fifth bit received on the serial inter-
face after the start bit.
The IRS address decoding is shown in Table 9.
Initialization Sequence
Sending the initialization sequence shown below
enables the MAX1452 to establish the baud rate that
initializes the serial port. The initialization sequence is
one byte transmission of 01hex, as follows.
Special Command Sequences
A special command register to internal logic
(CRIL[3:0]) causes execution of special command
sequences within the MAX1452. These command
sequences are listed as CRIL command codes as
shown in Table 10.
1111111101000000011111111
Write Examples
A 16-bit write to any of the internal calibration registers
is performed as follows:
The first start bit 0 initiates the baud rate synchronization
sequence. The 8 data bits 01hex (LSB first) follow this
and then the stop bit, which is indicated above as a 1,
12 ______________________________________________________________________________________
Low-Cost Precision Sensor
Signal Conditioner
THREE-STATE
NEED WEAK
PULLUP
THREE-STATE
NEED WEAK
PULLUP
DRIVEN BY TESTER
DRIVEN BY MAX1452
DIO
0
1 1 1 1 1 0 1 0 0 1 1 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 1 0 0 0 1 1 1 1 1 1 1 1 1 1 1
Figure 5. DIO Output Data Format
1) Write the 16 data bits to DHR[15:0] using four byte
accesses into the interface register set.
register designated by IRSP[3:0] are sent out as a byte
framed by a start bit and a stop bit.
2) Write the address of the target internal calibration
register to ICRA[3:0].
Once the tester finishes sending the RdIRS command,
it must three-state its connection to DIO to allow the
MAX1452 to drive the DIO line. The MAX1452 will three-
state DIO high for 1 byte time and then drive with the
start bit in the next bit period followed by the data byte
and stop bit. The sequence is shown in Figure 5.
3) Write the load internal calibration register (LdICR)
command to CRIL[3:0].
When a LdICR command is issued to the CRIL register,
the calibration register loaded depends on the address
in the internal calibration register address (ICRA). Table
11 specifies which calibration register is decoded.
The data returned on a RdIRS command depends on
the address in IRSP. Table 12 defines what is returned
for the various addresses.
Erasing and Writing the EEPROM
The internal EEPROM needs to be erased (bytes set to
FFhex) prior to programming the desired contents.
Remember to save the 3 MSBs of byte 161hex (high-
byte of the configuration register) and restore it when
programming its contents to prevent modification of the
trimmed oscillator frequency.
Multiplexed Analog Output
When a RdAlg command is written to CRIL[3:0] the
analog signal designated by ALOC[3:0] is asserted on
the OUT pin. The duration of the analog signal is deter-
mined by ATIM[3:0] after which the pin reverts to three-
state. While the analog signal is asserted in the OUT
pin, DIO is simultaneously three-stated, enabling a par-
allel wiring of DIO and OUT. When DIO and OUT are
connected in parallel, the host computer or calibration
system must three-state its connection to DIO after
asserting the stop bit. Do not load the OUT line when
reading internal signals, such as BDR, FSOTC...etc.
The internal EEPROM can be entirely erased with the
ERASE command, or partially erased with the
PageErase command (see Table 10, CRIL command).
It is necessary to wait 6ms after issuing the ERASE or
PageErase command.
After the EEPROM bytes have been erased (value of
every byte = FFhex), the user can program its contents,
following the procedure below:
The analog output sequence with DIO and OUT is
shown in Figure 6.
The duration of the analog signal is controlled by
ATIM[3:0] as given in Table 13.
1) Write the 8 data bits to DHR[7:0] using two byte
accesses into the interface register set.
The analog signal driven onto the OUT pin is deter-
mined by the value in the ALOC register. The signals
are specified in Table 14.
2) Write the address of the target internal EEPROM
location to IEEA[9:0] using three byte accesses into
the interface register set.
Test System Configuration
The MAX1452 is designed to support an automated
production test system with integrated calibration and
temperature compensation. Figure 7 shows the imple-
mentation concept for a low-cost test system capable
of testing many transducer modules connected in par-
3) Write the EEPROM write command (EEPW) to
CRIL[3:0].
Serial Digital Output
When a RdIRS command is written to CRIL[3:0], DIO is
configured as a digital output and the contents of the
______________________________________________________________________________________ 13
Low-Cost Precision Sensor
Signal Conditioner
THREE-STATE
NEED WEAK
PULLUP
THREE-STATE
ATIM
THREE-STATE
NEED WEAK
PULLUP
2
+1 BYTE
DRIVEN BY TESTER
TIMES
DIO
0
1 1 1 1 1 0 1 0 0 1 1 0 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
HIGH IMPEDANCE
OUT
VALID OUT
Figure 6. Analog Output Timing
allel. The MAX1452 allows for a high degree of flexibili-
ty in system calibration design. This is achieved by use
of single-wire digital communication and three-state
output nodes. Depending upon specific calibration
requirements one may connect all the OUTs in parallel
or connect DIO and OUT on each individual module.
Set next test temperature:
•
Calibrate offset and FSO using the ODAC and FSO-
DAC, respectively.
•
Store calibration data in the test computer or
MAX1452 EEPROM user memory.
•
•
•
Calculate the correction coefficients.
Download correction coefficients to EEPROM.
Perform a final test.
Sensor Compensation Overview
Compensation requires an examination of the sensor
performance over the operating pressure and tempera-
ture range. Use a minimum of two test pressures (e.g.,
zero and full-span) and two temperatures. More test
pressures and temperatures will result in greater accu-
racy. A typical compensation procedure can be sum-
marized as follows:
Sensor Calibration and
Compensation Example
The MAX1452 temperature compensation design cor-
rects both sensor and IC temperature errors. This
enables the MAX1452 to provide temperature compen-
sation approaching the inherent repeatability of the
sensor. An example of the MAX1452’s capabilities is
shown in Figure 8.
Set reference temperature (e.g., 25°C):
•
Initialize each transducer by loading their respec-
tive registers with default coefficients (e.g., based
on mean values of offset, FSO and bridge resis-
tance) to prevent overload of the MAX1452.
A repeatable piezoresistive sensor with an initial offset
of 16.4mV and a span of 55.8mV was converted into a
compensated transducer (utilizing the piezoresistive
sensor with the MAX1452) with an offset of 0.5000V and
a span of 4.0000V. Nonlinear sensor offset and FSO
temperature errors, which were on the order of 20% to
30% FSO, were reduced to under 0.1% FSO. The fol-
lowing graphs show the output of the uncompensated
sensor and the output of the compensated transducer.
Six temperature points were used to obtain this result.
•
Set the initial bridge voltage (with the FSODAC) to
half of the supply voltage. Measure the bridge volt-
age using the BDR or OUT pins, or calculate based
on measurements.
•
•
Calibrate the output offset and FSO of the transduc-
er using the ODAC and FSODAC, respectively.
Store calibration data in the test computer or
MAX1452 EEPROM user memory.
MAX1452 Evaluation Kit
To expedite the development of MAX1452
based transducers and test systems, Maxim has pro-
duced the MAX1452 evaluation kit (EV kit). First-time
users of the MAX1452 are strongly encouraged to use
this kit.
14 ______________________________________________________________________________________
Low-Cost Precision Sensor
Signal Conditioner
DIO[1:N]
DIGITAL
DION
DIO2
DIO1
MULTIPLEXER
MODULE 1
MODULE 2
MODULE N
DATA
DATA
V
V
OUT
V
OUT
OUT
V
V
V
V
V
V
SS
DD
SS
DD
SS
DD
+5V
V
OUT
DVM
TEST OVEN
Figure 7. Automated Test System Concept
The EV kit is designed to facilitate manual program-
ming of the MAX1452 with a sensor. It includes the fol-
lowing:
3) MAX1452 Communication Software, which enables
programming of the MAX1452 from a computer
keyboard (IBM compatible), one module at a time.
1) Evaluation Board with or without a silicon pressure
4) Interface Adapter, which allows the connection of
sensor, ready for customer evaluation.
the evaluation board to a PC serial port.
2) Design/Applications Manual, which describes in
detail the architecture and functionality of the
MAX1452. This manual was developed for test
engineers familiar with data acquisition of sensor
data and provides sensor compensation algorithms
and test procedures.
______________________________________________________________________________________ 15
Low-Cost Precision Sensor
Signal Conditioner
UNCOMPENSATED SENSOR
TEMPERATURE ERROR
RAW SENSOR OUTPUT
T = +25°C
A
30.0
20.0
80
FSO
OFFSET
60
40
10.0
0.0
6
0
-10.0
-20.0
0
20
40
60
80
100
-50
0
50
TEMPERATURE (°C)
100
150
PRESSURE (kPs)
COMPENSATED TRANSDUCER
T = +25°C
A
COMPENSATED TRANSDUCER ERROR
5.0
4.0
3.0
2.0
1.0
0
0.15
0.1
0.05
0
-0.05
-0.1
-0.15
FSO
OFFSET
-50
0
50
TEMPERATURE (°C)
150
0
20
40
60
80
100
100
PRESSURE (kPs)
Figure 8. Comparison of an Uncalibrated Sensor and a Calibrated Transducer
Table 2. Registers
REGISTER
CONFIG
DESCRIPTION
Configuration Register
Offset DAC Register
ODAC
OTCDAC
FSODAC
FSOTCDAC
Offset Temperature Coefficient DAC Register
Full Span Output DAC Register
Full Span Output Temperature Coefficient DAC Register
16 ______________________________________________________________________________________
Low-Cost Precision Sensor
Signal Conditioner
Table 3. Configuration Register (CONFIG[15:0])
FIELD
15:13
12
NAME
DESCRIPTION
OSC[2:0]
Oscillator frequency setting. Factory preset, do not change.
R
Logic ‘1’ selects external R
and R
.
STC
EXT
ISRC
11
CLK1M EN
PGA Sign
IRO Sign
Logic ‘1’ enables CLK1M output driver.
Logic ‘1’ inverts INM and INP polarity.
10
9
Logic ‘1’ for positive input referred offset (IRO). Logic ‘0’ for negative input referred offset (IRO).
Input referred coarse offset adjustment.
8:6
5:2
1
IRO[2:0]
PGA[3:0]
ODAC Sign
Programmable gain amplifier setting.
Logic ‘1’ for positive offset DAC output. Logic ‘0’ for negative offset DAC output.
OTCDAC
Sign
0
Logic ‘1’ for positive offset TC DAC output. Logic ‘0’ for negative offset TC DAC output.
Table 4. Input Referred Offset (IRO[2:0])
INPUT REFERRED OFFSET
CORRECTION AS % OF VDD
INPUT REFERRED OFFSET, CORRECTION
AT VDD = 5VDC IN mV
IRO SIGN, IRO[2:0]
1,111
1,110
1,101
1,100
1,011
1,010
1,001
1,000
0,000
0,001
0,010
0,011
0,100
0,101
0,110
0,111
+1.25
+1.08
+0.90
+0.72
+0.54
+0.36
+0.18
0
+63
+54
+45
+36
+27
+18
+9
0
0
0
-0.18
-0.36
-0.54
-0.72
-0.90
-1.08
-1.25
-9
-18
-27
-36
-45
-54
-63
______________________________________________________________________________________ 17
Low-Cost Precision Sensor
Signal Conditioner
Table 5. PGA Gain Setting (PGA[3:0])
Table 6. Temp-Index Typical Values
TEMP-INDEX[7:0]
TEMPERATURE
PGA[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
PGA GAIN (V/V)
(°C)
DECIMAL
20
HEXADECIMAL
39
52
-40
25
14
41
6A
86
65
65
85
106
78
125
134
91
104
117
130
143
156
169
182
195
208
221
234
Table 7. EEPROM ODAC and FSODAC Lookup Table Memory Map
EEPROM ADDRESS ODAC
LOW BYTE AND HIGH BYTE
EEPROM ADDRESS FSODAC
LOW BYTE AND HIGH BYTE
TEMP-INDEX[7:0]
00hex
to
000hex and 001hex
to
200hex and 201hex
to
7Fhex
0FEhex and 0FFhex
2FEhex and 2FFhex
80hex
to
100hex and 101hex
to
1A0hex and 1A1hex
to
AFhex
15Ehex and 15Fhex
1FEhex and 1FFhex
18 ______________________________________________________________________________________
Low-Cost Precision Sensor
Signal Conditioner
Table 8. Control Location (CL[15:0])
FIELD
NAME
DESCRIPTION
15:8
CL[15:8]
Reserved
Control Location. Secure-Lock is activated by setting this to FFhex which disables DIO serial
communications and connects OUT to PGA output.
7:0
CL[7:0]
Table 9. IRSA Decoding
IRSA[3:0]
DESCRIPTION
Write IRSD[3:0] to DHR[3:0] (data hold register)
Write IRSD[3:0] to DHR[7:4] (data hold register)
0000
0001
0010
0011
0100
0101
Write IRSD[3:0] to DHR[11:8] (data hold register)
Write IRSD[3:0] to DHR[15:12] (data hold register)
Reserved
Reserved
Write IRSD[3:0] to ICRA[3:0] or IEEA[3:0], (internal calibration register address or internal EEPROM address
nibble 0)
0110
0111
1000
Write IRSD[3:0] to IEEA[7:4] (internal EEPROM address, nibble 1)
Write IRSD[3:0] to IRSP[3:0] or IEEA[9:8], (interface register set pointer where IRSP[1:0] is IEEA[9:8])
Write IRSD[3:0] to CRIL[3:0] (command register to internal logic)
Write IRSD[3:0] to ATIM[3:0] (analog timeout value on read)
Write IRSD[3:0] to ALOC[3:0] (analog location)
1001
1010
1011
1100 to 1110
1111
Reserved
Write IRSD[3:0] = 1111bin to relearn the baud rate
______________________________________________________________________________________ 19
Low-Cost Precision Sensor
Signal Conditioner
Table 10. CRIL Command Codes
CRIL[3:0]
NAME
LdICR
EEPW
ERASE
RdICR
RdEEP
RdIRS
DESCRIPTION
0000
Load internal calibration register at address given in ICRA with data from DHR[15:0].
EEPROM write of 8 data bits from DHR[7:0] to address location pointed by IEEA [9:0].
Erase all of EEPROM (all bytes equal FFhex).
0001
0010
0011
Read internal calibration register as pointed to by ICRA and load data into DHR[15:0].
Read internal EEPROM location and load data into DHR[7:0] pointed by IEEA [9:0].
Read interface register set pointer IRSP[3:0]. See Table 12.
0100
0101
Output the multiplexed analog signal onto OUT. The analog location is specified in ALOC[3:0]
(Table 14) and the duration (in byte times) that the signal is asserted onto the pin is specified in
ATIM[3:0] (Table 13).
0110
0111
RdAlg
Erases the page of the EEPROM as pointed by IEEA[9:6]. There are 64 bytes per page and thus 12
pages in the EEPROM.
PageErase
Reserved
1000 to
1111
Reserved.
Table 11. IRCA Decode
ICRA[3:0]
NAME
CONFIG
ODAC
DESCRIPTION
0000
Configuration Register
Offset DAC Register
0001
0010
OTCDAC
FSODAC
FSOTCDAC
Offset Temperature Coefficient DAC Register
Full Scale Output DAC Register
0011
0100
Full Scale Output Temperature Coefficient DAC Register
Reserved. Do not write to this location (EEPROM test).
0101
0110 to
1111
Reserved. Do not write to this location.
20 ______________________________________________________________________________________
Low-Cost Precision Sensor
Signal Conditioner
Table 12. IRSP Decode
IRSP[3:0]
RETURNED VALUE
0000
0001
DHR[7:0]
DHR[15:8]
0010
IEEA[7:4], ICRA[3:0] concatenated
CRIL[3:0], IRSP[3:0] concatenated
ALOC[3:0], ATIM[3:0] concatenated
IEEA[7:0] EEPROM address byte
IEED[7:0] EEPROM data byte
TEMP-Index[7:0]
0011
0100
0101
0110
0111
1000
BitClock[7:0]
1001
Reserved. Internal flash test data.
1010-1111
11001010 (CAhex). This can be used to test communication.
Table 13. ATIM Definition
ATIM[3:0]
DURATION OF ANALOG SIGNAL SPECIFIED IN BYTE TIMES (8-BIT TIME)
0
✕
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
2 + 1 = 2 byte times i.e. (2 8) / baud rate
21 + 1 = 3 byte times
22 + 1 = 5 byte times
23 + 1 = 9 byte times
24 + 1 = 17 byte times
25 + 1 = 33 byte times
26 + 1 = 65 byte times
27 + 1 = 129 byte times
28 + 1 = 257 byte times
29 + 1 = 513 byte times
210 + 1 = 1025 byte times
211 + 1 = 2049 byte times
212 + 1 = 4097 byte times
213 + 1 = 8193 byte times
214 + 1 = 16,385 byte times
In this mode OUT is continuous, however DIO will accept commands after 32,769 byte times. Do not
parallel connect DIO to OUT.
1111
______________________________________________________________________________________ 21
Low-Cost Precision Sensor
Signal Conditioner
Table 14. ALOC Definition
ALOC[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
ANALOG SIGNAL
DESCRIPTION
OUT
PGA Output
BDR
Bridge Drive
ISRC
Bridge Drive Current Setting
Internal Positive Supply
Internal Ground
VDD
VSS
BIAS5U
AGND
Internal Test Node
Internal Analog Ground. Approximately half of VDD.
Full Scale Output DAC
FSODAC
FSOTCDAC
ODAC
Full Scale Output TC DAC
Offset DAC
OTCDAC
VREF
Offset TC DAC
Bandgap Reference Voltage (nominally 1.25V)
Internal Test Node
VPTATP
VPTATM
INP
Internal Test Node
Sensor’s Positive Input
INM
Sensor’s Negative Input
Table 15. Effects of Compensation
TYPICAL UNCOMPENSATED INPUT (SENSOR)
TYPICAL COMPENSATED TRANSDUCER OUTPUT
Offset…………………..…….…………………………..± 100%FSO
FSO…………………………….………………………..1 to 40mV/V
Offset TC…………………………………………………...20% FSO
Offset TC Nonlinearity…..………………………………….4% FSO
FSOTC…………………………..………………………..-20% FSO
FSOTC Nonlinearity…..……..…………………………….5% FSO
Temperature Range..….….……………………..-40°C to +125°C
OUT..…….……………………………..Ratiometric to VDD at 5.0V
Offset at +25°C……………………………………0.500V ± 200µV
FSO at +25°C……………………………………...4.000V ± 200µV
Offset accuracy over temp. range….………± 4mV (± 0.1% FSO)
FSO accuracy over temp. range……………± 4mV (± 0.1% FSO)
Chip Information
TRANSISTOR COUNT: 67,382
SUBSTRATE CONNECTED TO: V
SS
22 ______________________________________________________________________________________
Low-Cost Precision Sensor
Signal Conditioner
Detailed Block Diagram
EEPROM
(LOOKUP PLUS CONFIGURATION DATA)
V
DD
EEPROM ADDRESS USAGE
000H + 001H
OFFSET DAC LOOKUP TABLE
V
DD
✕
(176 16-BITS)
:
16-BIT
15EH + 15FH
160H + 161H
162H + 163H
164H + 165H
166H + 167H
168H + 169H
16AH + 16BH
16CH + 16DH
FSO
DAC
V
V
DD
CONFIGURATION REGISTER SHADOW
RESERVED
ISRC
V
SS
OFFSET TC REGISTER SHADOW
RESERVED
SS
FSOTC REGISTER SHADOW
CONTROL LOCATION REGISTER
USER STORAGE (52 BYTES)
TEST
V
DD
16-BIT
OFFSET
DAC
CLK1M
:
R
R
STC
75kΩ
ISRC
75kΩ
19EH + 19FH
1A0H + 1A1H
:
V
V
DDF
SS
FSO DAC LOOKUP TABLE
✕
(176 16-BITS)
V
SS
2FEH + 2FFH
V
DD
8-BIT
LOOKUP
ADDRESS
BANDGAP
TEMP
SENSOR
± 1
∑∆
16-BIT
FSOTC
INP
BDR
FSOTC
DAC
UNLOCK
DIO
DIGITAL
INTERFACE
V
SS
PHASE
REVERSAL
MUX
V
SS
FSOTC REGISTER
PGA BANDWIDTH ≈
3kHz ± 10%
✕
MUX
26
PGA
MUX
∑
∑
OUT
INM
INPUT REFERRED OFFSET
(COARSE OFFSET)
AMP-
PROGRAMMABLE GAIN STAGE
V
SS
± 1
PGA (3:0) PGA GAIN TOTAL GAIN
IRO (3, 2:0) OFFSET mV
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
39
52
1,111
1,110
1,101
1,100
1,011
1,010
1,001
1,000
0,000
0,001
0,010
0,011
0,100
0,101
0,110
0,111
63
54
45
36
27
18
9
AMPOUT
65
16-BIT
78
OFFSET
TC DAC
AMP+
91
104
117
130
143
156
169
182
195
208
221
234
V
SS
OTC REGISTER
0
UNCOMMITTED OP AMP
0
*INPUT REFERRED
OFFSET VALUE IS
PROPORTIONAL TO V
VALUES GIVEN ARE FOR
= 5V.
-9
PARAMETER
I/P RANGE
VALUE
TO V
-18
-27
-36
-45
-54
-63
V
SS
± 20mV
DD
.
DD
I/P OFFSET
V
DD
O/P RANGE
NO LOAD
1mA LOAD
V
V
, V ± 0.01V
SS DD
SS DD
, V ± 0.25V
UNITY GBW
10MHz TYPICAL
PGA BANDWIDTH ≈ 3kHz ± ±10%
______________________________________________________________________________________ 23
Low-Cost Precision Sensor
Signal Conditioner
Package Information
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
24 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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