英语翻译

英语翻译
Circuit Description
The network driver (Figure 1) consists of a pulldown section (Q1,R1,C1,R5) and a pullup section (Q2,R2,C2,R6).
A third transistor and surrounding components (Q3,C4,R7) form a strong pullup section to supply extra power for
devices such as EEPROMs,or temperature sensors.This "strong-pullup" function is not discussed in this document.Of
the three transistors,a maximum of one is conducting at any time.When there is no 1-Wire communication ("idle"
state),all three transistors are nonconducting.
The series path of R4,R1 and R3 provides the standard 1-Wire pullup to VCC.With this circuit,the total pullup
resistance is approximately 1kΩ.This value applies when the 1-Wire line is idle.Since R4 is connected to the drain of
Q1,the current flowing through it when Q1 is conducting does not affect the lowlevel voltage on the 1-Wire line.R4
+R1+R3 together with the load or "weight" of the 1-Wire network determine the speed at which the voltage on the 1-
Wire rises to 5V.Lowering R4 is not recommended since it would raise the low-level voltage on the 1-Wire,which is
undesirable.The Schottky-diodes D1 and D2 eliminate spikes from ESD hits or cross coupling from other cabling
nearby by conducting them to GND and VCC,respectively.R3 limits the ESD current and protects D1 and D2.
A special characteristic of this driver is the proper line termination of the 1-Wire cable on the master end.The
category 5 unshielded twisted-pair data cable,which is recommended for 1-Wire applications,has a characteristic
impedance of approximately 100Ω.Line termination is accomplished through R1 or R2 in series with R3 when Q1 or
Q2 is conducting.C3 in series with R1 and R3 provide an AC-coupled termination for presence pulses.To adapt this
driver to a different impedance,R1 and R2 need to be changed accordingly.
All three sections of this driver are slew-rate controlled when the associated transistor is turned on.R5 and C1 limit
the slew rate when the driver pulls the 1-Wire line low,e.g.,at the beginning of a time slot or a reset pulse.R6 and
C2 limit the slew rate when the dynamic pullup becomes active.R7 and C4 limit the slew rate of the active pullup.
The time constant of all three sections is 0.5µs.This value results in a slew rate of approximately 4V/µs.For details
and scope traces see section Performance Examples.