i2c Pullup Resistor Online Calculator
V
cc
:
V
Supply rail voltage
3.3 V
5.0 V
t
r
:
ns
Maximal rise time of both SDA and SCL signals
Standard Mode
f
scl
= 100 kHz
Fast Mode
f
scl
= 400 kHz
Fast Mode Plus
f
scl
= 1000 kHz
1000 ns
300 ns
120 ns
C
b
:
pF
Maximal capacitive load for each bus line
Standard Mode
Fast Mode
Fast Mode Plus
400 pF
400 pF
550 pF
Some real world data:
FR4
C ~ 0.7 pF/cm
C ~ 1.3 pF/cm at 50 Ω
Coax
C ~ 1 pF/cm at 50 Ω
PCF8574
C < 7 pF/pin
ATTINY85
C = 14 pF/pin
ATMEGA328p
C = 10 pF/pin
ESP8266
C = 2 pF/pin
ESP32
C = 2 pF/pin
V
OL
:
V
The V
OL
level can be read as a valid logical
low by the input buffers of an IC.
Standard Mode
Fast Mode
Fast Mode Plus
0.4 V
0.4 V
0.4 V
0.2 * V
cc
0.2 * V
cc
I
OL
:
mA
I
OL
is defined as V
cc
> 2 V: 3 mA, V
cc
≤ 2 V: 2 mA
Results
Gra!!!
include existing Resistors
R:
Ω
Remove
Add another resistor
Results
Gra!!!
References
Texas Instruments
Application Report SLVA689 – February 2015
I2C Bus Pullup Resistor Calculation
NXP Semiconductors
UM10204
I2C-bus specification and user manual
Rev. 6 — 4 April 2014 User manual
Author
Holger Lembke