DS2480B Maxim Integrated Products, DS2480B Datasheet - Page 15

• Manufacturer Part Number: DS2480B
• Description: IC LINE DRVR W/SENSOR 1-W 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Line Driver, Transmitterr

Specifications of DS2480B

• Number Of Drivers/receivers: 1/0
• Protocol: RS232
• Voltage - Supply: 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

DS2480B
Falling Edges (DS2480B-initiated)
Whenever the DS2480B begins pulling the 1-Wire bus low to initiate a time slot, for example, it first
turns off the weak pullup current I
. Then, at regular and Overdrive speeds it will generate a falling
WEAKPU
edge at a slew rate of typically 15V/ms. This value is acceptable for short 1-Wire busses and adequate for
communication at Overdrive speed. For MicroLAN networks of more than roughly 30m length one
should always use flexible speed. One of the parameters that is adjustable at flexible speed is the slew rate
of DS2480B-initiated falling edges. The effect of the slew rate control is shown in Figure 5.
Figure 5. SLEW RATE CONTROL
As extensive tests have shown, MicroLAN networks at a length of up to 300m will perform best if the fall
is in the range of 4 ± 0.5ms. This translates into a slew rate of approximately 1V/ms. This slew rate
time t
F
is typically achieved by setting the configuration parameter 001 (Pulldown Slew Rate Control) to a value
of 100 (see Table 4). If the actual measured fall time is longer than the target value, one should use a
value code of 011 or lower. If the fall time is shorter, one should use a value code of 101 or higher.
Once determined, the value code for the Pulldown Slew Rate Control parameter should be stored in the
host and always be loaded into the DS2480B after a power-on or master reset cycle.
TIMING DIAGRAMS
This section explains the waveforms generated by the DS2480B on the 1-Wire bus in detail. First the
communication waveforms such as the Reset/Presence Detect Sequence and the time slots are discussed.
After that follows a detailed description of the pulse function under various conditions. The waveforms as
generated by the DS2480B may deviate slightly from specifications found in the Book of DS19xx iButton
Standards or in data sheets of 1-Wire slave devices. However, at a closer look one will find that all of the
timing requirements are met.
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