DS2480B+T&R Maxim Integrated Products, DS2480B+T&R Datasheet - Page 14

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

Specifications of DS2480B+T&R

• 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: Lead free / RoHS Compliant

DS2480B
CONTROLLED EDGES
One of the tasks of the DS2480B is to actively shape the edges of the 1-Wire communication waveforms.
This speeds up the recharging of the 1-Wire bus (rising edges) and reduces ringing of long lines (falling
edges). The circuitry for shaping rising edges is always on. The slew rate of falling edges is actively
controlled only at flexible speed and requires the parameter for slew rate control being different from its
power-on default value.
All Rising Edges
The active pullup of the rising edges reduces the rise time on the 1-Wire bus significantly compared to a
simple resistive pullup. Figure 4 shows how the DS2480B is involved in shaping a rising edge.
Figure 4. ACTIVE PULLUP
The circuit operates as follows: At t
the pulldown (induced by the DS2480B or a device on the bus) ends.
1
From this point on the 1-Wire bus is pulled high by the weak pullup current I
provided by the
WEAKPU
DS2480B. The slope is determined by the load on the bus and the value of the pullup current. At t
the
2
voltage crosses the threshold voltage V
. Now the DS2480B switches over from the weak pullup
IAPO
current I
to the higher current I
. As a consequence, the voltage on the bus now rises faster. As
WEAKPU
ACTPU
the voltage on the bus crosses the threshold V
at t
, a timer is started. As long as this timer is on
IAPTO
3
(t
), the I
current will continue to flow. After the timer is expired, the DS2480B will switch
APUOT
ACTPU
back to the weak pullup current. Excessive noise on the 1-Wire line at the V
level can cause an
IAPTO
undesirable trip of the active pullup. External R-C filtering as discussed in the HARDWARE
APPLICATION EXAMPLES section and Application Note 148 should be used to prevent false triggering.
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