DS2490Y Maxim Integrated Products, DS2490Y Datasheet - Page 5

• Manufacturer Part Number: DS2490Y
• Description: IC BRIDGE CLIP USB TO 1-W 24SOIC
• Manufacturer: Maxim Integrated Products

Specifications of DS2490Y

• Applications: USB
• Interface: 1-Wire
• Voltage - Supply: 3 V ~ 5.5 V
• Package / Case: 24-SOIC (7.5mm Width)
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

ACTIVE PULLUP Figure 3
The circuit operates as follows: At t
From this point on the 1-Wire bus is pulled high by the weak pullup current I
DS2490. The slope is determined by the load on the bus and the value of the pullup current. At t
voltage crosses the threshold voltage V
current I
As the voltage on the bus crosses the threshold V
(t
to the weak pullup current.
Falling Edges (DS2490-initiated)
Whenever the DS2490 begins pulling the 1-Wire bus low to initiate a time slot, for example, it first turns
off the weak pullup current I
a slew rate of typically 15 V/µs. This value is acceptable for short 1-Wire busses and adequate for
communication at overdrive speed. For 1-Wire networks of more than roughly 30m length, flexible speed
should always be used. One of the parameters that is adjustable at flexible speed is the slew rate of
DS2490-initiated falling edges. The effect of the slew rate control is shown in Figure 4.
SLEW RATE CONTROL Figure 4
Extensive tests have shown that 1-Wire networks with lengths of up to 300m will perform best if the fall
time t
is typically achieved by selecting a PULLDOWN SLEW RATE parameter code of 0 x 4 (see MODE
COMMANDS). If the actual measured fall time is longer than the target value, a parameter code of 0 x 3
APUOT
F
), the I
is in the range of 4 ± 0.5µs. This translates into a slew rate of approximately 1V/µs. This slew rate
WEAKPU
ACTPU
to the higher current I
current will continue to flow. After the timer is expired, the DS2490 will switch back
WEAKPU
5V
0.8 V
0V
1-Wire bus
5V
V
V
0V
high slew rate
is pulled up
. Then, at regular and overdrive speed it will generate a falling edge at
1-Wire bus
is discharged
1,
IAPTO
IAPO
the pulldown (induced by the DS2490 or a device on the bus) ends.
ACTPU
IAPO
. As a consequence, the voltage on the bus now rises faster.
. Now, the DS2490 switches over from the weak pullup
t
t
1
5 of 50
1
IAPTO
weak pull-up ends,
pull-down begins
t
F
at t
t
APUOT
t
3
2
, a timer is started. As long as this timer is on
low slew rate
Target for
long lines:
4 ± 0.5 µs
t
3
WEAKPU
provided by the
2,
the