Rainbow Electronics DS2482-800 - Manual (Page 22)

DS2482-800: Eight-Channel 1-Wire Master
22 of 22
capacitance of 400pF the maximum pullup resistor values are 2.95k W at standard speed and 885W at fast speed. A
value between of 1.7k W and 2.95kW meets all requirements at standard speed.
Since a 885
W pullup resistor, as would be required to meet the rise time specification at fast speed and 400pF bus
capacitance, is lower than Rpmin at 5.5V, a different approach is necessary. The "Max. Load…" line in Figure 12 is
generated by first calculating the minimum pullup resistor at any given operating voltage ("Minimum Rp" line) and
then calculating the respective bus capacitance that yields a rise time of 300ns.
Only for pullup voltages of 3V and lower can the maximum permissible bus capacitance of 400pF be maintained. A
reduced bus capacitance of 300pF is acceptable for pullup voltages of 4V and lower. For fast speed operation at
any pullup voltage, the bus capacitance must not exceed 200pF. The corresponding pullup resistor value at the
voltage is indicated by the "Minimum Rp" line.
Figure 12. I²C Fast Speed Pullup Resistor Selection Chart
0
400
800
1200
1600
2000
1 2 3 4 5
Pull-up Voltage
M
in
imu
m R
p
(
O
h
m
s)
0
100
200
300
400
500
Loa
d (
pF)
"Minimum Rp" Max. Load at Min. Rp fast mode
PACKAGE INFORMATION
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to
www.maxim-ic.com/DallasPackInfo .)