ds2482-101 Maxim Integrated Products, Inc., ds2482-101 Datasheet - Page 23

• Manufacturer Part Number: ds2482-101
• Description: Single-channel 1-wire Master With Sleep Mode
• Manufacturer: Maxim Integrated Products, Inc.

SDA is an open-drain output on the DS2482-101 that
requires a pullup resistor to realize high-logic levels.
Because the DS2482-101 uses SCL only as input (no
clock stretching), the master can drive SCL either
through an open-drain/-collector output with a pullup
resistor or a push-pull output.
According to the I
be able to sink at least 3mA at a V
condition determines the minimum value of the pullup
resistor as:
With an operating voltage of 5.5V, the minimum value
for the pullup resistor is 1.7kΩ. The “MINIMUM R
in Figure 12 shows how the minimum pullup resistor
changes with the operating voltage.
For I
sured from 30% to 70% of the pullup voltage. The maxi-
mum bus capacitance, C
time must not exceed 1000ns at standard speed and
300ns at fast speed. Assuming maximum rise time, the
Figure 12. I
Single-Channel 1-Wire Master with Sleep Mode
2
C systems, the rise time and fall time are mea-
2
C Fast Speed Pullup Resistor Selection Chart
2000
1600
1200
800
400
0
R
1
Applications Information
P(MIN)
SDA and SCL Pullup Resistors
2
______________________________________________________________________________________
C specification, a slave device must
= (V
Pullup Resistor R
B
CC
, is 400pF. The maximum rise
- 0.4V)/3mA
MINIMUM R
2
OL
of 0.4V. This DC
P
P
Sizing
P
” line
PULLUP VOLTAGE (V)
3
maximum resistor value at any given capacitance C
calculated as:
For a bus capacitance of 400pF, the maximum pullup
resistor values are 2.95kΩ at standard speed and 885Ω
at fast speed. A value between 1.7kΩ and 2.95kΩ
meets all requirements at standard speed.
Because an 885Ω pullup resistor, as would be required
to meet the rise time specification at fast speed and
400pF bus capacitance, is lower than R
different approach is necessary. The “MAX LOAD AT
MIN R
first calculating the minimum pullup resistor at any
given operating voltage (“MINIMUM R
calculating the respective bus capacitance that yields a
300ns rise time.
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 R
R
PMAXS
R
P
PMAXF
FAST MODE” line in Figure 12 is generated by
4
= 1000ns/[C
MAX LOAD AT MIN R
= 300ns/[C
B
P
x ln(7/3)] (standard speed)
B
FAST MODE
x ln(7/3)] (fast speed)
5
P
P(MIN)
” line) and then
500
400
300
200
100
0
P
at 5.5V, a
” line.
B
23
is