DS1921G_12 datasheet(3/42 Pages) MAXIM

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Thermochron iButton

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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 2.2k

Ω resistor is used to pull up the data line, 2.5µs

after VPUP 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:

VTL and VTH are functions of the internal supply voltage, which is a function of VPUP and the 1-Wire recovery times. The

VTH and VTL maximum specifications are valid at VPUP = 5.25V. In any case, VTL < VTH < VPUP.

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 VILMAX 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 iButton 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 VIL to VTH. The

actual maximum duration for the master to pull the line low is tW1LMAX + tF -

ε and tW0LMAX + tF - 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 VIL to the input

high threshold of the bus master. The actual maximum duration for the master to pull the line low is tRLMAX + tF.

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)

(VPUP = +2.8V to +5.25V, TA = -40°C to +85°C.)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

IO PIN: 1-Wire WRITE

Standard speed

120

Overdrive speed, VPUP > 4.5V

Write-Zero Low Time

(Notes 1, 12, 13)

tW0L

Overdrive speed

8.5

µs

Standard speed

Write-One Low Time

(Notes 1, 13)

tW1L

Overdrive speed

µs

IO PIN: 1-Wire READ

Standard speed

15 -

Read Low Time (Notes 1, 14)

tRL

Overdrive speed

2 -

µs

Standard speed

tRL +

Read Sample Time

(Notes 1, 14)

tMSR

Overdrive speed

tRL +

µs

REAL-TIME CLOCK

Frequency Deviation

-5°C to +46°C

-48

+46

ppm

TEMPERATURE CONVERTER

Tempcore Operating Range

TTC

-40

+85

°C

Conversion Time

tCONV

Thermal Response Time

Constant

RESP

(Note 15)

130

-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

NCONV

(Notes 4, 18)

(See the lifetime graphs.)

—

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