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PDF MAX1459 Data sheet ( Hoja de datos )
| Número de pieza | MAX1459 | |
| Descripción | 2-Wire / 4-20mA Smart Signal Conditioner | |
| Fabricantes | Maxim Integrated | |
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19-1619; Rev 0; 1/00
EVAALVUAAILTAIOBNLEKIT
2-Wire, 4–20mA
Smart Signal Conditioner
General Description
The MAX1459 highly integrated analog-sensor signal
conditioner is optimized for piezoresistive sensor calibra-
tion and compensation with minimal external compo-
nents. It includes a programmable current source for
sensor excitation, a 3-bit programmable-gain amplifier
(PGA), a 128-bit internal EEPROM, and four 12-bit DACs.
Achieving a total error factor within 1% of the sensor’s
repeatability errors, the MAX1459 compensates offset,
offset temperature coefficient (offset TC), full-span output
(FSO), FSO temperature coefficient (FSOTC), and FSO
nonlinearity of silicon piezoresistive sensors.
The MAX1459 calibrates and compensates first-order
temperature errors by adjusting the offset and span of
the input signal through digital-to-analog converters
(DACs), thereby eliminating quantization noise.
The MAX1459 allows temperature compensation via the
external sensor, an internal temperature-dependent
resistor, or a dedicated external temperature transduc-
er. Accuracies better than 0.5% can be achieved with
low-cost external temperature sensors (i.e., silicon tran-
sistor), depending on sensor choice.
Built-in testability features on the MAX1459 result in the
integration of three traditional sensor-manufacturing
operations into one automated process:
• Pretest: Data acquisition of sensor performance
under the control of a host test computer.
• Calibration and compensation: Computation and
storage (in an internal EEPROM) of calibration and
compensation coefficients computed by the test
computer and downloaded to the MAX1459.
• Final test operation: Verification of transducer cali-
bration and compensation without removal from the
pretest socket.
Although optimized for use with piezoresistive sensors,
the MAX1459 may also be used with other resistive
sensors (i.e., accelerometers and strain gauges) with
some additional external components.
For custom versions of the MAX1459, see the Customization
section at end of data sheet.
________________________Applications
4–20mA Transmitters
Piezoresistive Pressure and Acceleration
Industrial Pressure Sensors
Load Cells/Wheatstone Bridges
Strain Gauges
Temperature Sensors
Features
o Highly Integrated Sensor Signal Conditioner for
2-Wire, 4–20mA Transmitters
o Sensor Errors Trimmed Using Correction
Coefficients Stored in Internal EEPROM—
Eliminates the Need for Laser Trimming and
Potentiometers
o Compensates Offset, Offset TC, FSO, FSOTC,
FSO Linearity
o Programmable Current Source (0.1mA to 2.0mA)
for Sensor Excitation
o Fast Signal-Path Settling Time (≈1ms)
o Accepts Sensor Outputs from +1mV/V to +40mV/V
o Fully Analog Signal Path
o Internal or External Temperature Reference
Compensation
o Automated Pilot Production (Calibration/
Compensation) System Available
o Write Protection for EEPROM Data Security
Ordering Information
PART
TEMP. RANGE PIN-PACKAGE
MAX1459CAP
0°C to +70°C
20 SSOP
MAX1459C/D
0°C to +70°C
Dice*
MAX1459AAP
-40°C to +125°C 20 SSOP
*Dice are tested at TA = +25°C, DC parameters only.
Functional Diagram appears at end of data sheet.
Pin Configuration
TOP VIEW
SCLK 1
CS 2
DIO 3
WE 4
FSOTC 5
AMP+ 6
AMP- 7
AMPOUT 8
TEMPIN 9
ISRC 10
MAX1459
20 VDD
19 NBIAS
18 CK50
17 TEMP2
16 TEMP1
15 INM
14 INP
13 BDRIVE
12 VSS
11 OUT
SSOP
________________________________________________________________ Maxim Integrated Products 1
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
1 page  
2-Wire, 4–20mA
Smart Signal Conditioner
Pin Description
PIN NAME
FUNCTION
1
SCLK
Data Clock Input. Used only during programming/testing. Internally pulled to VSS with a 1MΩ (typical) resistor.
Data is clocked in on the rising edge of the clock. Recommended SCLK frequency is below 50kHz.
2
CS
Chip-Select Input. The MAX1459 is selected when this pin is high. When low, OUT and DIO become high
impedance. Internally pulled to VDD with a 1MΩ (typical) resistor. Leave unconnected for normal operation.
3
DIO
Data Input/Output. Used only during programming/testing. Internally pulled to VSS with a 1MΩ (typical)
resistor. High impedance when CS is low.
Write Enable, Dual-Function Input Pin. Used to enable EEPROM erase/write operations. Also used to set
4 WE the DAC refresh-rate mode. Internally pulled to VDD with a 1MΩ (typ) resistor. See the Chip-Select (CS)
and Write-Enable (WE) section.
Buffered Full-Span Output Temperature Coefficient DAC Output. An internal 100kΩ resistor (RFTC) con-
5 FSOTC nects FSOTC to ISRC (see Functional Diagram). Optionally, external resistors can be used in place of or in
parallel with RFTC and RISC.
6 AMP+ Auxiliary Op Amp Positive Input
7
AMP-
Auxiliary Op Amp Negative Input
8 AMPOUT Auxiliary Op Amp Output
Input pin for an External Temperature-Dependent Reference Voltage for FSOTC DAC and OTC DAC. In the
9 TEMPIN default mode, the MAX1459 uses the temperature-dependent bridge drive voltage as the FSOTC DAC and
OTC DAC reference.
10
ISRC
Current Source Reference. An internal 100kΩ resistor (RISRC) connects ISRC to VSS (see Functional
Diagram). Optionally, external resistors can be used in place of or in parallel with RFTC and RISRC.
11
OUT
Output Voltage. OUT is a Rail-to-Rail® output that can drive resistive loads down to 10kΩ and capacitive
loads up to 0.1µF.
12 VSS Negative Power Supply
13 BDRIVE Sensor Excitation Current Output. The current source that drives the bridge.
14 INP Positive Sensor Input. Input impedance is typically 1MΩ. Rail-to-rail input range.
15 INM Negative Sensor Input. Input impedance is typically 1MΩ. Rail-to-rail input range.
16 TEMP1 Temperature Sensor Terminal 1
17
TEMP2
Temperature Sensor Terminal 2. RTEMP is a 100kΩ temperature-dependent resistor with 4600ppm/°C
tempco.
18
CK50
Clock Output, nominally 50kHz
19 NBIAS Chip Current Bias Source. Connect an external 402kΩ ±1% resistor between VDD and NBIAS.
20 VDD Positive Power-Supply Input. Connect a 0.1µF capacitor from VDD to VSS.
Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
_______________________________________________________________________________________ 5
5 Page 
2-Wire, 4–20mA
Smart Signal Conditioner
Data Input/Output
The DIO line is an input/output pin used to issue com-
mands to the MAX1459 (input mode) or read the
EEPROM contents (output mode).
In input mode (the default mode), data on DIO is
latched on each rising edge of SCLK. Therefore, data
on DIO must be stable at the rising edge of SCLK and
should transition on the falling edge of SCLK.
DIO will switch to output mode after receiving either the
READ EEPROM command or the READ EEPROM
MATRIX command. See the Read EEPROM section for
detailed information.
Communication Protocol
To initiate communication, the first 8 bits on DIO after
CS transitions from low to high must be 101010U0 (AA
hex or A8 hex, defined as the INIT sequence). The
MAX1459 will then begin accepting 16-bit control
words (Figure 4).
If the INIT SEQUENCE is not detected, all subsequent
data on DIO is ignored until CS again transitions from
low to high and the correct INIT SEQUENCE is received.
The U bit of the INIT SEQUENCE controls the updating
of the DACs and configuration register from the internal
EEPROM. If this bit is low (U = 0, INIT SEQUENCE = A8
hex), all four internal DACs and the configuration regis-
ter will be updated from the EEPROM on the next rising
edge of CS (this is also the default on power-up). If the
U bit is high (INIT SEQUENCE = AA hex), the DACs
and configuration register will not be updated from the
internal EEPROM; they will retain their current value on
any subsequent CS rising edge. The MAX1459 contin-
ues to accept control words until CS is brought low.
Control Words
After receiving the INIT SEQUENCE on DIO, the
MAX1459 begins latching in 16-bit control words, MSB
first (Figure 5).
The first 4 bits of the control word (the MSBs,
CM3–CM0) are the command field. The last 12 bits
(D11–D0) represent the data field. The MAX1459 sup-
ports the commands listed in Table 5.
No-OP Command (0 hex)
The no-operation (No-OP) command must be issued
before and after the commands ERASE EEPROM and
WRITE EEPROM BIT. In the case of the ERASE EEP-
ROM command, the control word must be 0000 hex. In
the case of the WRITE EEPROM BIT command, the
command field must be 0h, and the data field must
have, in its lower bits, the EEPROM address to be writ-
ten (Figure 6). For example, to write location 1C hex of
CS
SCLK
DIO
tMIN = 1.5ms
8 CLK
CYCLES
16 CLK
CYCLES
16 CLK
CYCLES
n x 16 CLK
CYCLES
X 1 0 1 0 1 0 U 0 CM3 CM2 DO CM3 CM2 DO
INIT
SEQUENCE
CONTROL
WORD
CONTROL
WORD
CONTROL
WORDS
Figure 4. Communication Sequence
SCLK
COMMAND
MSB LSB MSB
DATA
LSB
DIO CM3 CM2 CM1 CM0 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
16-BIT CONTROL WORD
MSB
LSB
Figure 5. Control-Word Timing Diagram
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet MAX1459.PDF ] | |
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