Datasheet

DS1921G
Thermochron iButton
_______________________________________________________________________________________ 3
Note 1: System requirement.
Note 2: 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.
Note 3: 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.
Note 4: These values are derived from simulation across process, voltage, and temperature and are not production tested.
Note 5: Input load is to ground.
Note 6: All voltages are referenced to ground.
Note 7: 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
.
Note 8: Voltage below which, during a falling edge of IO, a logic 0 is detected.
Note 9: The voltage on IO must be less than or equal to V
ILMAX
whenever the master drives the line low.
Note 10: Voltage above which, during a rising edge on IO, a logic 1 is detected.
Note 11: The I-V characteristic is linear for voltages less than 1V.
Note 12: Numbers in bold are not in compliance with the published i
Button standards. See the Comparison Table .
Note 13: 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.
Note 14: 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
.
Note 15: 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
Note 16: Total accuracy is ∆ϑ plus 0.25°C quantization due to the 0.5°C digital resolution of the device.
ELECTRICAL CHARACTERISTICS (continued)
(V
PUP
= +2.8V to +5.25V, T
A
= -40°C to +85°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
IO PIN: 1-Wire WRITE
Standard speed 60 120
Overdrive speed, V
PUP
> 4.5V 6 15
Write-Zero Low Time
(Notes 1, 12, 13)
t
W0L
Overdrive speed 8.5 15
µs
Standard speed 5 15
Write-One Low Time
(Notes 1, 13)
t
W1L
Overdrive speed 1 2
µs
IO PIN: 1-Wire READ
Standard speed 5 15 - 
Read Low Time (Notes 1, 14) t
RL
Overdrive speed 1 2 - 
µs
Standard speed t
RL
+  15
Read Sample Time
(Notes 1, 14)
t
MSR
Overdrive speed t
RL
+  2
µs
REAL-TIME CLOCK
Frequency Deviation 
F
-5°C to +46°C -48 +46 ppm
TEMPERATURE CONVERTER
Tempcore Operating Range T
TC
-40 +85 °C
Conversion Time t
CONV
19 90 ms
Thermal Response Time
Constant

RESP
(Note 15) 130 s
-40°C to < -30°C -1.3 +1.3
-30°C to +70°C -1.0 +1.0
Conversion Error
(Notes 16, 17)

> +70°C to +85°C -1.3 +1.3
°C
Number of Conversions N
CONV
(Notes 4, 18) (See the lifetime graphs.) —