vides 9-bit to 12-bit Celsius temperature measurements
with ±0.5°C accuracy over a +10°C to +45°C temperature
range. Over its entire -55°C to +125°C operating range,
the device has ±2.0°C accuracy.
The device communicates over a 1-Wire
®
bus that, by
definition, requires only one data line (and ground) for
communication with a central microprocessor. In addi-
tion, the device derives power directly from the data line
(“parasite power”), eliminating the need for an external
power supply. Requiring so few pins enables the device
to be placed in a 3-pin TO-92 package. The form factor
of this package allows the device to be placed above
the board and thus measure the ambient temperature of
a system, as opposed to the board temperature that a
surface-mount package would measure.
Each MAX31820PAR has a unique 64-bit serial code, which
allows multiple MAX31820PAR devices to function on the
same 1-Wire bus. Therefore, it is simple to use one micropro-
cessor to control many devices distributed over a large area.
General Description
Benefits and Features
● Unique 1-Wire Interface Requires Only One Port Pin
for Communication
● Derives Power from Data Line (Parasite Power); No
Local Power Supply Needed
● Multidrop Capability Simplifies Distributed
Temperature-Sensing Applications
● Requires No External Components
● Measures Temperatures from -55°C to +125°C (-67°F
to +257°F)
● ±0.5°C Accuracy from +10°C to +45°C
● Thermometer Resolution is User-Selectable from
9 Bits to 12 Bits
● Converts Temperature to 12-Bit Digital Word in
750ms (Max)
● User-Definable Nonvolatile (NV) Alarm Settings
● Alarm Search Command Identifies and Addresses
Devices Whose Temperature is Outside Programmed
Limits (Temperature Alarm Condition)
● Available in 3-Pin TO-92 Package
● Software Compatible with the DS1822-PAR and
DS18B20-PAR
Ordering Information
appears at end of data sheet.
For related parts and recommended products to use with this part, refer
to
www.maximintegrated.com/MAX31820PAR.related.
Applications
● HVAC Environmental Controls
● Temperature Monitoring Systems Inside Buildings,
Equipment, or Machinery
● Process Monitoring and Control Systems
● Thermostatic Controls
● Industrial Systems
● Consumer Products
● Thermometers
● Any Thermally Sensitive System
Block Diagram
V
PU
4.7kΩ
DQ
64-BIT ROM
AND
1-Wire PORT
PARASITE-POWER
CIRCUIT
MEMORY
CONTROL LOGIC
MAX31820PAR
TEMPERATURE REGISTER
ALARM HIGH TRIGGER (T
H
)
REGISTER (EEPROM)
C
PP
GND
SCRATCHPAD
ALARM LOW TRIGGER (T
L
)
REGISTER (EEPROM)
CONFIGURATION REGISTER (EEPROM)
8-BIT CRC GENERATOR
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
19-6732; Rev 0; 6/13
MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
Absolute Maximum Ratings
Voltage Range on Any Pin Relative to Ground
....-0.5V to +6.0V
Operating Temperature Range ......................... -55°C to +100°C
Storage Temperature Range
............................ -55°C to +125°C
Soldering Temperature (reflow)
.......................................+260°C
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.
DC Electrical Characteristics
(V
PU
= 3.0V to 3.7V, T
A
= -55°C to +100°C, unless otherwise noted.) (Note 1)
PARAMETER
Pullup Supply Voltage
Thermometer Error
Input Logic-Low
Input Logic-High
Sink Current
Active Current
DQ Input Current
Drift
SYMBOL
V
PU
T
ERR
V
IL
V
IH
I
L
I
DQA
I
DQ
(Notes 2, 3)
+10°C to +45°C
-55°C to +100°C
(Notes 2, 4, 5)
(Notes 2, 6)
V
I/O
= 0.4V (Note 2)
(Note 7)
(Note 8)
(Note 9)
-0.3
3.0
4.0
1
5
±0.2
1.5
CONDITIONS
MIN
3.0
TYP
MAX
3.7
±0.5
±2
+0.8
3.7
UNITS
V
°C
V
V
mA
mA
µA
°C
www.maximintegrated.com
Maxim Integrated
│
2
MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
AC Electrical Characteristics
(V
PU
= 3.0V to 3.7V, T
A
= -55°C to +100°C, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
9-bit resolution
Temperature Conversion Time
t
CONV
10-bit resolution
11-bit resolution
12-bit resolution
Time to Strong Pullup On
Time Slot
Recovery Time
Write-Zero Low Time
Write-One Low Time
Read Data Valid
Reset Time High
Reset Time Low
Presence-Detect High
Presence-Detect Low
Capacitance
NONVOLATILE MEMORY
Nonvolatile Write Cycle Time
EEPROM Writes
EEPROM Data Retention
t
WR
N
EEWR
t
EEDR
-55°C to +55°C
-55°C to +55°C
50k
10
2
10
ms
Writes
Years
t
SPON
t
SLOT
t
REC
t
LOW0
t
LOW1
t
RDV
t
RSTH
t
RSTL
t
PDHIGH
t
PDLOW
C
IN/OUT
Start Convert T command or Copy
Scratchpad command issued
(Note 10)
(Note 10)
(Note 10)
(Note 10)
(Note 10)
(Note 10)
(Notes 10, 11)
(Note 10)
(Note 10)
480
480
15
60
960
60
240
25
60
1
60
1
120
15
15
CONDITIONS
MIN
TYP
MAX
93.75
187.5
375
750
10
120
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
pF
ms
UNITS
Note 1:
Limits are 100% tested at T
A
= +25°C and T
A
= +85°C. Limits over the operating temperature range and relevant supply
voltage are guaranteed by design and characterization.
Note 2:
All voltages are referenced to ground.
Note 3:
The pullup supply voltage specification assumes that the pullup device (resistor or transistor) is ideal, and therefore the
high level of the pullup is equal to V
PU
. In order to meet the device’s V
IH
spec, 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: V
PU_ACTUAL
= V
PU_
IDEAL
+ V
TRANSISTOR
.
Note 4:
Logic-low voltages are specified at a sink current of 4mA.
Note 5:
To guarantee a presence pulse under low-voltage parasite-power conditions, V
ILMAX
may have to be reduced to as low as
0.5V.
Note 6:
Logic-high voltages are specified at a source current of 1mA.
Note 7:
Active current refers to supply current during active temperature conversions or EEPROM writes.
Note 8:
DQ line is high (high-Z state).
Note 9:
Drift data is based on a 1000-hour stress test at +125°C.
Note 10:
See the 1-Wire
Timing Diagrams.
Note 11:
If t
RSTL
> 960µs, a power-on reset may occur.
www.maximintegrated.com
Maxim Integrated
│
3
MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
1-Wire Timing Diagrams
1-Wire WRITE-ZERO TIME SLOT
t
SLOT
START OF NEXT CYCLE
t
REC
t
LOW0
1-Wire READ-ZERO TIME SLOT
t
SLOT
START OF NEXT CYCLE
t
REC
t
RDV
1-Wire RESET PULSE
RESET PULSE FROM HOST
t
RSTL
t
RSTH
1-Wire PRESENCE DETECT
t
PDHIGH
PRESENCE DETECT
t
PDLOW
www.maximintegrated.com
Maxim Integrated
│
4
MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
Pin Configuration
SIDE VIEW
GND
DQ
N.C.
1
2
3
FRONT VIEW
1
2
3
MAX31820PAR
TO-92
Pin Description
PIN
1
2
3
NAME
GND
DQ
N.C.
Ground
Data Input/Output. Open-drain, 1-Wire interface pin that provides power to the device when used in
parasite power mode (see the
Parasite Power
section).
Not Connected. Does not connect to internal circuit.
FUNCTION
Detailed Description
The MAX31820PAR ambient temperature sensor
provides 9-bit to 12-bit Celsius temperature measure-
ments with ±0.5°C accuracy over a +10°C to +45°C tem-
perature range. Over its entire -55°C to +125°C operating
range, the device has ±2.0°C accuracy. The device com-
municates over a 1-Wire bus that, by definition, requires
only one data line (and ground) for communication with
a central microprocessor. In addition, the device derives
power directly from the data line (“parasite power”),
eliminating the need for an external power supply.
Requiring so few pins enables the device to be placed
in a 3-pin TO-92 package. The form factor of this pack-
age allows the device to be placed above the board and
thus measure the ambient temperature of a system, as
opposed to the board temperature that a surface-mount
package would measure.
Each device has a unique 64-bit serial code, allowing
multiple MAX31820PAR devices to function on the same
1-Wire bus. Therefore, it is simple to use one micro-
processor to control many devices distributed over a
large area. The 64-bit ROM stores the device’s unique
serial code. The scratchpad memory contains the 2-byte
temperature register that stores the digital output from
the temperature sensor. In addition, the scratchpad pro-
vides access to the 1-byte upper and lower alarm trigger
registers (T
H
and T
L
) and the 1-byte configuration regis-
ter. The configuration register allows the user to set the
resolution of the temperature-to-digital conversion to 9,
10, 11, or 12 bits. The T
H
, T
L
, and configuration registers
are nonvolatile (EEPROM), so they retain data when the
device is powered down.
The device uses Maxim Integrated’s exclusive 1-Wire
bus protocol that implements bus communication using
one control signal. The control line requires a weak pullup
resistor since all devices are linked to the bus through a
three-state or open-drain port (i.e., the MAX31820PAR’s
DQ pin). In this bus system, the microprocessor (the
master device) identifies and addresses devices on the
bus using each device’s unique 64-bit code. Because
each device has a unique code, the number of devices
that can be addressed on one bus is virtually unlimited.
The 1-Wire bus protocol, including detailed explanations
of the commands and time slots, is covered in the
1-Wire
Bus System
section.
The device can also operate without an external power
supply. Power is instead supplied through the 1-Wire
pullup resistor through the DQ pin when the bus is high.
The high bus signal also charges an internal capacitor
(C
PP
), which then supplies power to the device when the
bus is low. This method of deriving power from the 1-Wire
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