DS1922E
iButton High-Temperature Logger with
8KB Data-Log Memory
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Operation above +125°C is restricted to mission operations only. Communication and 1-Wire pin specifications are not
specified for operation above +125°C.
System requirement.
Maximum allowable pullup resistance is a function of the number of 1-Wire devices in the system and 1-Wire recovery
times. The specified value here applies to systems with only one device and with the minimum 1-Wire recovery times. For
more heavily loaded systems, an active pullup such as that in the DS2480B can be required.
Capacitance on the data pin could be 800pF when V PUP is first applied. If a 2.2k Ω resistor is used to pull up the data line
2.5μs after V PUP has been applied, the parasite capacitance does not affect normal communications.
V TL and V TH are a function of the internal supply voltage, which is a function of V PUP and the 1-Wire recovery times. The
V TH and V TL maximum specifications are valid at V PUPMAX (5.25V). In any case, V TL < V TH < V PUP .
Voltage below which, during a falling edge on I/O, a logic 0 is detected.
The voltage on I/O must be less than or equal to V ILMAX whenever the master drives the line low.
Voltage above which, during a rising edge on I/O, a logic 1 is detected.
After V TH is crossed during a rising edge on I/O, the voltage on I/O must drop by V HY to be detected as logic 0.
The I-V characteristic is linear for voltages less than 1V.
The earliest recognition of a negative edge is possible at t REH after V TH has been previously reached.
Numbers in bold are not in compliance with the published iButton device standards. See the Comparison Table.
Interval during the negative edge on I/O at the beginning of a presence-detect pulse between the time at which the volt-
age is 90% of V PUP and the time at which the voltage is 10% of V PUP .
ε in Figure 13 represents the time required for the pullup circuitry to pull the voltage on I/O up from V IL to V TH . The actual
maximum duration for the master to pull the line low is t W1LMAX + t F - ε and t W0LMAX + t F - ε , respectively.
δ in Figure 13 represents the time required for the pullup circuitry to pull the voltage on I/O up from V IL to the input high
threshold of the bus master. The actual maximum duration for the master to pull the line low is t RLMAX + t F .
To conserve battery power, use 8-bit temperature logging whenever possible.
This number was derived from a test conducted by Cemagref in Antony, France, in July 2000:
www.cemagref.fr/English/index.htm Test Report No. E42.
Includes +0.1°C/-0.2°C calibration chamber measurement uncertainty.
Warning: Maxim data-logger products are 100% tested and calibrated at time of manufacture to ensure that they meet all
data sheet parameters, including temperature accuracy. As with any sensor-based product, user shall be responsible for
occasionally rechecking the temperature accuracy of the product to ensure it is still operating properly. Furthermore, as
with all products of this type, when deployed in the field and subjected to handling, harsh environments, or other hazards/
use conditions, there may be some extremely small but nonzero logger failure rate. In applications where the failure of any
logger is a concern, user shall assure that redundant (or other primary) methods of testing and determining the handling
methods, quality, and fitness of the articles and products are implemented to further mitigate any risk.
Devices leave the factory after having been run through a few cycles above +125°C. This is required for calibration of the
device but should not affect lifetime of the device as specified. However, this process results in a nonzero value in the
Device Samples Counter register (0223h–0225h), which provides evidence the device has been factory calibrated.
Maxim Integrated