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PDF MAX31850 Data sheet ( Hoja de datos )
| Número de pieza | MAX31850 | |
| Descripción | (MAX31850 / MAX31851) 1-Wire Thermocouple-to-Digital Converters | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de MAX31850 (archivo pdf) en la parte inferior de esta página. Total 25 Páginas | ||
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EVALUATION KIT AVAILABLE
MAX31850/MAX31851
Cold-Junction Compensated, 1-Wire
Thermocouple-to-Digital Converters
General Description
The MAX31850/MAX31851 cold-junction compensat-
ed, 1-WireM thermocouple-to-digital converters perform
cold-junction compensation and digitize the signal from
a K-, J-, N-, T-, S-, R-, or E-type thermocouple. The con-
verters resolve temperatures to 0.25NC, allow readings
as high as +1768NC and as low as -270NC, and exhibit
thermocouple accuracy of 8 LSBs (2NC) for temperatures
ranging from -200NC to +700NC.
Communication with the master microcontroller is over a
1-Wire bus that by definition requires only one data line
(and ground) for communication. Operating power can
be obtained directly from the data line (“parasite power”),
eliminating the need for an external power supply.
Each device has a unique 64-bit serial code, which
allows multiple units to function on the same 1-Wire bus.
Therefore, it is simple to use one microcontroller (the
master device) to monitor temperature from many ther-
mocouples distributed over a large area.
Four location address inputs simplify mapping of
individual units to specific locations.
Benefits and Features
S Integration Reduces Design Time and Lowers
System Cost
• 14-Bit, 0.25NC Resolution
• Integrated Cold-Junction Compensation
• Available for Multiple Thermocouples Types:
Supports K-, J-, N-, T-, and E-Type (MAX31850);
S- and R-Type (MAX31851)
• Detects Thermocouple Shorts to GND or VDD
• Detects Open Thermocouple
S 1-Wire Multiddrop Capability Simplifies
Multisensor Systems
• 1-Wire Interface (Read-Only); Power Can Be
Obtained from Interface (Parasite-Powered Mode)
Applications
Industrial
Appliances
HVAC
Medical
Ordering Information appears at end of data sheet.
Block Diagram
COLD-JUNCTION
COMPENSATION
S5
MAX31850
MAX31851
T+
T-
S1
S2
S3
S4
ADC
FAULT
DETECTION
REFERENCE
VOLTAGE
64-BIT ROM
AND
1-Wire PORT
MEMORY
CONTROL LOGIC
SCRATCHPAD
ADDRESS PIN INPUT
PARASITE-
POWER
CIRCUIT
CPP
POWER-
SUPPLY
SENSE
DQ
VDD
GND
AD0 AD1 AD2 AD3
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
For related parts and recommended products to use with this part, refer to: www.maximintegrated.com/MAX31850.related
For pricing, delivery, and ordering information, please contact Maxim Direct at
1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
19-6725; Rev 2; 1/15
1 page  
MAX31850/MAX31851
Cold-Junction Compensated, 1-Wire
Thermocouple-to-Digital Converters
1-Wire TIMING CHARACTERISTICS
(3.0V P VDD P 3.6V, TA = -40NC to +125NC, unless otherwise noted.) (Notes 2, 3)
PARAMETER
Time to Strong Pullup On
Time Slot
Recovery Time
Write-0 Low Time
Write-1 Low Time
Read Data Valid
Reset Time High
Reset Time Low
Presence Detect High
Presence Detect Low
Capacitance: DQ
Capacitance: AD0–AD3
SYMBOL
tSPON
tSLOT
tREC
tLOW0
tLOW1
tRDV
tRSTH
tRSTL
tPDHIGH
tPDLOW
CIN/OUT
CIN_ADD
CONDITIONS
Start Convert T command issued
(Note 15)
(Note 15)
(Note 15)
(Note 15)
(Note 15)
(Note 15)
(Notes 15, 16)
(Note 15)
(Note 15)
(Note 17)
(Note 17)
MIN TYP MAX UNITS
8 µs
60 120 µs
1 µs
60 120 µs
1 15 µs
15 µs
480 µs
480 µs
15 60 µs
60 240 µs
25 pF
50 pF
Note 2: Limits are 100% production tested at TA = +25NC. Limits over the operating temperature range and relevant supply volt-
age range are guaranteed by design and characterization.
Note 3: Limits are 100% production tested at TA = +25NC and +85NC. Limits over the operating temperature range and relevant sup-
ply voltage are guaranteed by design and characterization.
Note 4: All voltages are referenced to GND. Currents entering the IC are specified positive and currents exiting the IC are negative.
Note 5: The pullup supply voltage specification assumes that the pullup device is ideal, and therefore the high level of the pullup
is equal to VPU. To meet the device’s VIH specification, the actual supply rail for the strong pullup transistor must include
margin for the voltage drop across the transistor when it is turned on. Thus: VPU_ACTUAL = VPU_IDEAL + VTRANSISTOR.
Note 6: To guarantee a presence pulse under low-voltage parasite power conditions, VILMAX, may have to be reduced to as low
as 0.5V.
Note 7: Standby current specified up to +70NC.
Note 8: To minimize IDDS, DQ should be within the following ranges: VGND P VDQ P VGND + 0.3V or VDD - 0.3V P VDQ P VDD.
Note 9: Active current refers to supply current during active temperature conversions.
Note 10: DQ is high (high-impedance state with external pullup).
Note 11: Not including cold-junction temperature error or thermocouple nonlinearity.
Note 12: Guaranteed by design. These limits represent six sigma distribution for TA = +25NC to +85NC. Outside this temperature
range, these limits are three sigma distribution.
Note 13: Guaranteed by design. These limits represent a three sigma distribution.
Note 14: After minimum VDD has been reached during power-up, wait 10ms before initiating temperature conversions.
Note 15: See the 1-Wire Timing Diagrams.
Note 16: Under parasite power, if tRSTL > 960Fs, a power-on reset (POR) may occur.
Note 17: Represents the maximum capacitive load that may be applied to the pins and still maintain timing and logic state.
Maxim Integrated
5
5 Page 
MAX31850/MAX31851
Cold-Junction Compensated, 1-Wire
Thermocouple-to-Digital Converters
VPU
VPU
MAX31850
MAX31851
GND DQ VDD
µP
4.7kΩ
1-Wire BUS
TO OTHER 1-Wire DEVICES
Figure 1. Supplying the Parasite-Powered MAX31850/MAX31851 During Temperature Conversions
MAX31850
MAX31851
VDD (EXTERNAL SUPPLY)
VPU GND DQ VDD
µP
4.7kΩ
1-Wire BUS
TO OTHER 1-Wire DEVICES
Figure 2. Powering the MAX31850/MAX31851 with an External Supply
Powering the MAX31850/MAX31851
The MAX31850/MAX31851 can be powered by an
external supply on the VDD pin, or they can operate
in “parasite power” mode, which allows the device to
function without a local external supply. Parasite power
is useful for applications that require remote tempera-
ture sensing or those that are very space-constrained.
Figure 1 shows the device’s parasite-power control cir-
cuitry, which “steals” power from the 1-Wire bus through
DQ when the bus is high. The stolen charge powers the
device while the bus is high, and some of the charge is
stored on the internal parasite-power capacitor (CPP) to
provide power when the bus is low. When the device is
used in parasite-power mode, VDD must be connected
to ground.
In parasite-power mode, the 1-Wire bus and CPP can
provide sufficient current to the device for most opera-
tions as long as the specified timing and voltage require-
ments are met (see the DC Electrical Characteristics
and the 1-Wire Timing Characteristics tables). However,
when the device is performing temperature conversions,
the operating current can be as high as 1.5mA. This
current can cause an unacceptable voltage drop across
the weak 1-Wire pullup resistor and is more current than
Maxim Integrated
can be supplied by CPP. To ensure that the device has
sufficient supply current, it is necessary to provide a
strong pullup on the 1-Wire bus whenever temperature
conversions are taking place. This can be accomplished
by using a MOSFET to pull the bus directly to the rail
as shown in Figure 1. The 1-Wire bus must be switched
to the strong pullup within 10Fs (max) after a Convert T
[44h] command is issued, and the bus must be held high
by the pullup for the duration of the conversion (tCONV).
No other activity can take place on the 1-Wire bus while
the pullup is enabled.
The device can also be powered by the conventional
method of connecting an external power supply to VDD,
as shown in Figure 2. The advantage of this method is
that the MOSFET pullup is not required, and the 1-Wire
bus is free to carry other traffic during the temperature
conversion period.
The use of parasite power is not recommended for tem-
peratures above 100NC because the device may not be
able to sustain communications due to the higher leak-
age currents that can exist at these temperatures. For
applications in which such temperatures are likely, it is
strongly recommended that the device be powered by
an external power supply.
11
11 Page | ||
| Páginas | Total 25 Páginas | |
| PDF Descargar | [ Datasheet MAX31850.PDF ] | |
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