or operation above +50°C significantly reduces battery life.
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.
Operating Temperature Range ..........................-40°C to +85°C*
Storage Temperature Range..............................-40°C to +50°C*
ELECTRICAL CHARACTERISTICS
(V
PUP
= +2.8V to +5.25V, T
A
= -40°C to +85°C.)
PARAMETER
IO PIN: GENERAL DATA
1-Wire Pullup Resistance
Input Capacitance
Input Load Current
High-to-Low Switching Threshold
(Notes 4, 6, 7, 8)
Input Low Voltage
Low-to-High Switching Threshold
(Notes 4, 6, 7, 10)
Output Low Voltage at 4mA
R
PUP
C
IO
I
L
V
TL
V
IL
V
TH
V
OL
(Notes 1, 2)
(Notes 3, 4)
IO pin at V
PUP
(Note 5)
V
PUP
> 4.5V
(Notes 1, 6, 9)
V
PUP
> 4.5V
(Notes 6, 11)
Standard speed, R
PUP
= 2.2k
Recovery Time (Notes 1, 4)
t
REC
Overdrive speed, R
PUP
= 2.2k
Overdrive speed, directly prior to reset
pulse; R
PUP
= 2.2k
Standard speed
Overdrive speed
Standard speed, V
PUP
> 4.5V
Standard speed
Overdrive speed, V
PUP
> 4.5V
Overdrive speed
Presence-Detect High
Time (Note 12)
Presence-Detect Low
Time (Note 12)
Presence-Detect
Sample Time (Notes 1, 4)
t
PDH
Standard speed
Overdrive speed
Standard speed
t
PDL
Overdrive speed, V
PUP
> 4.5V
Overdrive speed
t
MSP
Standard speed
Overdrive speed
5
2
5
65
8
480
540
48
58
15
1.1
60
7.5
7.5
60
6
640
640
80
80
60
6
270
24
32
75
8.6
μs
μs
μs
μs
μs
μs
1.00
0.66
1.14
0.71
100
2.2
800
10
2.70
2.70
0.30
2.70
2.70
0.4
k
pF
μA
V
V
V
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Time-Slot Duration (Notes 1, 12)
t
SLOT
IO PIN: 1-Wire RESET, PRESENCE-DETECT CYCLE
Reset Low Time (Notes 1,12)
t
RSTL
2
Maxim Integrated
DS1921G
Thermochron iButton Device
ELECTRICAL CHARACTERISTICS (continued)
(V
PUP
= +2.8V to +5.25V, T
A
= -40°C to +85°C.)
PARAMETER
IO PIN: 1-Wire WRITE
Standard speed
Write-Zero Low Time
(Notes 1, 12, 13)
Write-One Low Time
(Notes 1, 13)
IO PIN: 1-Wire READ
Read Low Time (Notes 1, 14)
Read Sample Time
(Notes 1, 14)
REAL-TIME CLOCK
Frequency Deviation
TEMPERATURE CONVERTER
Tempcore Operating Range
Conversion Time
Thermal Response Time
Constant
Conversion Error
(Notes 16, 17)
Number of Conversions
N
CONV
T
TC
t
CONV
RESP
F
SYMBOL
CONDITIONS
MIN
60
6
8.5
5
1
5
1
t
RL
+
t
RL
+
-48
-40
19
TYP
MAX
120
15
15
15
2
15 -
2-
15
2
+46
+85
90
UNITS
t
W0L
Overdrive speed, V
PUP
> 4.5V
Overdrive speed
Standard speed
Overdrive speed
Standard speed
Overdrive speed
Standard speed
Overdrive speed
-5°C to +46°C
μs
t
W1L
μs
t
RL
t
MSR
μs
μs
ppm
°C
ms
s
(Note 15)
-40°C to < -30°C
-30°C to +70°C
> +70°C to +85°C
(Notes 4, 18)
-1.3
-1.0
-1.3
130
+1.3
+1.0
+1.3
°C
—
(See the lifetime graphs.)
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
Note 10:
Note 11:
Note 12:
Note 13:
Note 14:
Note 15:
Note 16:
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 found in the DS2480B may be required.
Capacitance on IO could be 800pF when power is first applied. If a 2.2kΩ resistor is used to pull up the data line, 2.5µs
after V
PUP
has been applied, the parasite capacitor does not affect normal communication.
These values are derived from simulation across process, voltage, and temperature and are not production tested.
Input load is to ground.
All voltages are referenced to ground.
V
TL
and V
TH
are functions 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
PUP
= 5.25V. In any case, V
TL
< V
TH
< V
PUP
.
Voltage below which, during a falling edge of IO, a logic 0 is detected.
The voltage on IO must be less than or equal to V
ILMAX
whenever the master drives the line low.
Voltage above which, during a rising edge on IO, a logic 1 is detected.
The I-V characteristic is linear for voltages less than 1V.
Numbers in
bold
are
not
in compliance with the published iButton device standards. See the
Comparison Table.
ε
in Figure 15 represents the time required for the pullup circuitry to pull the voltage on the IO pin 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 15 represents the time required for the pullup circuitry to pull the voltage on the IO pin 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
.
This number was derived from a test conducted by Cemagref in Antony, France, in July 2000.
http://www.cemagref.fr/English/index.htm Test Report No. E42
Total accuracy is
Δϑ
plus 0.25°C quantization due to the 0.5°C digital resolution of the device.
Maxim Integrated
3
DS1921G
Thermochron iButton Device
ELECTRICAL CHARACTERISTICS (continued)
(V
PUP
= +2.8V to +5.25V, T
A
= -40°C to +85°C.)
Note 17: 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 fail-
ure 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.
Note 18:
The number of temperature conversions (= samples) possible with the built-in energy source depends on the operating and
storage temperature of the device. When not in use for a mission, the RTC oscillator should be turned off and the device
should be stored at a temperature not exceeding +25°C. Under this condition the shelf life time is 10 years minimum.
COMPARISON TABLE
LEGACY VALUES
PARAMETER
STANDARD SPEED (μs)
MIN
t
SLOT
(including
t
REC
)
t
RSTL
t
PDH
t
PDL
t
W0L
61
480
15
60
60
MAX
(undefined)
(undefined)
60
240
120
OVERDRIVE SPEED (μs)
MIN
7
48
2
8
6
MAX
(undefined)
80
6
24
16
MIN
65*
540
15
60
60
DS1921G VALUES
STANDARD SPEED (μs)
MAX
(undefined)
640
60
270
120
OVERDRIVE SPEED (μs)
MIN
8*
58
1.1
7.5
8.5
MAX
(undefined)
80
6
32
15
*Intentional
change; longer recovery time between time slots.
Note:
Numbers in
bold
are
not
in compliance with the published iButton device standards.
iButton CAN PHYSICAL SPECIFICATION
SIZE
WEIGHT
See the
Package Information
section.
Ca. 3.3g
4
Maxim Integrated
DS1921G
Thermochron iButton Device
RTC Deviation vs. Temperature
4
UPPER LIMIT
2
RTC DEVIATION (MINUTES/MONTH)
0
LOWER LIMIT
-2
-4
-6
-8
-10
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
TEMPERATURE (°C)
Minimum Product Lifetime vs. Temperature at Different Sample Rates
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