DS2482-100 Dallas Semiconducotr, DS2482-100 Datasheet - Page 20

• Manufacturer Part Number: DS2482-100
• Description: Single-Channel 1-Wire Master
• Manufacturer: Dallas Semiconducotr

Figure 11. Application Schematic
Application Information
SDA and SCL Pullup Resistors
SDA is an open-drain output on the DS2482 that requires a pullup resistor to realize high logic levels. Because the
DS2482 uses SCL only as input (no clock stretching) the master may drive SCL either through an open-
drain/collector output with a pullup resistor or a push-pull output.
Pullup Resistor R
According to the I²C specification, a slave device must be able to sink at least 3mA at a V
condition determines the minimum value of the pullup resistor: Rpmin = (V
voltage of 5.5V, the minimum value for the pullup resistor is 1.7kW. The "Minimum RP" line in Figure 12 shows how
the minimum pullup resistor changes with the operating voltage.
For I²C systems, the rise time and fall time are measured from 30% to 70% of the pullup voltage. The maximum
bus capacitance C
fast speed. Assuming maximum rise time, the maximum resistor value at any given capacitance C
as: Rpmaxs = 1000ns/(C
capacitance of 400pF the maximum pullup resistor values are 2.95kW at standard speed and 885W at fast speed. A
value between of 1.7kW and 2.95kW meets all requirements at standard speed.
µC
(I²C port)
P
b
Sizing
is 400 pF. The maximum rise time at standard speed must not exceed 1000ns and 300ns at
b
*ln(7/3)) (standard speed) and Rpmaxf = 300ns/(C
V
CC
*R
P
SDA
SCL
AD0
AD1
SDA
SCL
AD0
AD1
DS2482-100
DS2482-100
PCTLZ
PCTLZ
V
CC
IO
IO
20 of 21
*R
*R
* R
t
t
R
Information for R
t
P
Line termination resistor, typically 100 W
I²C pull-up resistor, see Application
1-Wire line
Current Limiting
Resistor
1-Wire line
P
V
CC
sizing.
CC
b
*ln(7/3)) (fast speed). For a bus
- 0.4V)/3mA. With an operating
Device #2
1-Wire Device #1
(with special power
1-Wire
requirements)
OL
of 0.4V. This DC
b
is calculated