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 addition,
the device can derive 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 MAX31820 has a unique 64-bit serial code, which
allows multiple MAX31820 devices to function on the same
1-Wire bus. Therefore, it is simple to use one microproces-
sor to control many devices distributed over a large area.
General Description
Benefits and Features
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
● Unique 1-Wire Interface Requires Only One Port Pin
for Communication
● Each Device has a Unique 64-Bit Serial Code Stored
in On-Board ROM
● Multidrop Capability Simplifies Distributed
Temperature-Sensing Applications
● Requires No External Components
● Can Be Powered from Data Line; 3.0V to 3.7V
Power-Supply Range
● 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
● TO-92 Package Allows Measurement of Ambient
Temperature
● Software Compatible with the DS1822 and DS18B20
Ordering Information
appears at end of data sheet.
For related parts and recommended products to use with this part, refer
to
www.maximintegrated.com/MAX31820.related.
Block Diagram
V
PU
4.7kΩ
DQ
MEMORY
CONTROL LOGIC
PARASITE-
POWER
CIRCUIT
C
PP
POWER-
SUPPLY
SENSE
MAX31820
TEMPERATURE REGISTER
ALARM HIGH TRIGGER
(T
H
) REGISTER (EEPROM)
GND
64-BIT ROM
AND
1-Wire PORT
SCRATCHPAD
ALARM LOW TRIGGER
(T
L
) REGISTER (EEPROM)
CONFIGURATION REGISTER (EEPROM)
8-BIT CRC GENERATOR
V
DD
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
19-6731; Rev 0; 6/13
MAX31820
1-Wire 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 +125°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
DD
= 3.0V to 3.7V, T
A
= -55°C to +125°C, unless otherwise noted.) (Note 1)
PARAMETER
Supply Voltage
Pullup Supply Voltage
(Notes 2, 3)
Thermometer Error (Note 4)
Input Logic-Low
SYMBOL
V
DD
V
PU
T
ERR
V
IL
CONDITIONS
Local power (Note 2)
Parasite power
Local power
+10°C to +45°C
-55°C to +125°C
(Notes 2, 5, 6)
-0.3
MIN
+3.0
+3.0
+3.0
TYP
MAX
+3.7
+3.7
V
DD
±0.5
±2
+0.8
lower
of 3.7
or
(V
DD
+
0.3)
lower
of 3.7
or
(V
DD
+
0.3)
750
1
5
±0.2
1000
1.5
UNITS
V
V
°C
V
Local power
Input Logic-High (Notes 2, 7)
V
IH
Parasite power
+2.2
V
+3.0
Sink Current
Standby Current
Active Current
DQ Input Current
Drift
I
L
I
DDS
I
DD
I
DQ
V
I/O
= 0.4V (Note 2)
(Notes 8, 9)
V
DD
= 5V (Note 10)
(Note 11)
(Note 12)
4.0
mA
nA
mA
µA
°C
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2
MAX31820
1-Wire Ambient Temperature Sensor
AC Electrical Characteristics
(V
DD
= 3.0V to 3.7V, T
A
= -55°C to +125°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 Write Cycle Time
EEPROM Writes
EEPROM Data Retention
t
SPON
t
SLOT
t
REC
t
LOW0
t
LOW1
t
RDV
t
RSTH
t
RSTL
t
PDHIGH
t
PDLOW
C
IN/OUT
t
WR
N
EEWR
t
EEDR
-55°C to +55°C
-55°C to +55°C
50k
10
2
Start Convert T command
(Note 13)
(Note 13)
(Note 13)
(Note 13)
(Note 13)
(Note 13)
(Notes 13, 14)
(Note 13)
(Note 13)
480
480
15
60
60
240
25
10
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
Writes
Years
ms
UNITS
NONVOLATILE MEMORY (T
A
= -55°C to +100°C)
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 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:
See typical performance curve.
Note 5:
Logic-low voltages are specified at a sink current of 4mA.
Note 6:
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 7:
Logic-high voltages are specified at a source current of 1mA.
Note 8:
Standby current specified up to +70°C. Standby current typically is 3µA at +125°C.
Note 9:
To minimize I
DDS
, DQ should be within the following ranges: V
GND
≤ V
DQ
≤ V
GND
+ 0.3V or V
DD
- 0.3V ≤ V
DQ
≤ V
DD
.
Note 10:
Active current refers to supply current during active temperature conversions or EEPROM writes.
Note 11:
DQ line is high (high-Z state).
Note 12:
Drift data is based on a 1000-hour stress test at +125°C.
Note 13:
See the 1-Wire
Timing Diagrams.
Note 14:
Under parasite power, if t
RSTL
> 960µs, a power-on reset may occur.
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Maxim Integrated
│
3
MAX31820
1-Wire 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
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4
MAX31820
1-Wire Ambient Temperature Sensor
Pin Configuration
SIDE VIEW
GND
DQ
V
DD
1
2
3
FRONT VIEW
1
2
3
MAX31820
TO-92
Pin Description
PIN
1
2
3
NAME
GND
DQ
V
DD
Ground
Data In/Out
Optional Power Supply
FUNCTION
Detailed Description
The MAX31820 ambient temperature sensor provides
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 commu-
nicates 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 can
derive 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 MAX31820 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 MAX31820’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
bus is referred to as “parasite power.” Alternatively, an
external supply on V
DD
can also power the device.
Operation
Measuring Ambient Temperature
A conventional surface-mount temperature sensor IC has
an excellent thermal connection to the circuit board on
which it is mounted. Heat travels from the board through
the leads to the sensor die. Air temperature can affect
